We compare the dynamics of satellite galaxies in the Sloan Digital Sky Survey to simple models in order to test the hypothesis that a large fraction of satellites co-rotate in coherent planes. We confirm the previously-reported excess of co-rotating satellite pairs located near diametric opposition with respect to the host, but show that this signal is unlikely to be due to rotating discs (or planes) of satellites. In particular, no overabundance of co-rotating satellites pairs is observed within $\sim 20^{\circ}-50^{\circ}$ of direct opposition, as would be expected for planar distributions inclined relative to the line-of-sight. Instead, the excess co-rotation for satellite pairs within $\sim 10^{\circ}$ of opposition is consistent with random noise associated with undersampling of an underlying isotropic velocity distribution. We conclude that at most $10\%$ of the hosts in our sample harbor co-rotating satellite planes (as traced by the luminous satellite population).
The importance of shocks in nova explosions has been highlighted by the recent discovery of \gamma-ray producing novae by Fermi. We use over three years of multi-band radio observations of nova V1723 Aql with the Karl G. Jansky Very Large Array (VLA) to show that shocks between fast and slow flows within the ejecta led to the acceleration of particles and the production of synchrotron radiation. Approximately one month after the start of V1723 Aql's eruption in 2010 September, shocks in the ejecta produced an unexpected radio flare, ultimately resulting in a radio light curve with a multi-peaked structure. More than a year after the start of the eruption, the radio emission became consistent with emanating from an expanding thermal remnant with a mass of $2\times10^{-4}$ M$_\odot$ and a temperature of $10^4$ K. However, the brightness temperature of greater than $10^6$ K at low frequencies during the first two months was too high to be due to thermal emission from the small amount of X-ray producing shock-heated gas. Radio images of the ejecta show dense structures with velocities of roughly 400 km/s (d/6 kpc) in the plane of the sky, perpendicular to a more elongated flow moving at 1500 km/s in the plane of the sky. The morpho-kinematic structure of the ejecta from V1723 Aql therefore appears to be similar to that of classical nova V959 Mon, in which collisions between a slow, dense torus and a faster flow both collimated the fast flow and gave rise to \gamma-ray producing shocks. Published optical spectroscopy and X-ray observations of V1723 Aql from the time of the radio flare are consistent with this picture. Our radio observations support the idea that shocks in novae occur when a fast flow collides with a dense, slow, collimating torus. Such shocks could be responsible for hard X-ray emission, \gamma-ray production, and double-peaked radio light curves from some classical novae.
We propose optimal estimators for bispectra from excited states. Two common properties of such bispectra are the enhancement in the collinear limit, and the prediction of oscillating features. We review the physics behind excited states and some of the choices made in the literature. We show that the enfolded template is a good template in the collinear limit, but does poorly elsewhere, establishing a strong case for an improved estimator. Although the detailed scale dependence of the bispectra differs depending on various assumptions, generally the predicted bispectra are either effectively 1 or 2-dimensional and a simple Fourier basis suffices for accurate reconstruction. For an optimal CMB data analysis, combining all n-point functions, the choice for the excited state needs to be the same when computing power spectrum, bispectrum and higher order correlation functions. This has not always been the case, which could lead to wrong conclusions. We calculate the bispectrum for different choices previously discussed for the power spectrum, setting up a consistent framework to search for evidence of excited states in the CMB data.
We present a multi-frequency far-field beam map for the 5m dish telescope at the Bleien Observatory measured using a commercially available drone. We describe the hexacopter drone used in this experiment, the design of the flight pattern, and the data analysis scheme. This is the first application of this calibration method to a single dish radio telescope in the far-field. The high signal-to-noise data allows us to characterise the beam pattern with high accuracy out to at least the 4th side-lobe. The resulting 2D beam pattern is compared with that derived from a more traditional calibration approach using an astronomical calibration source. We discuss the advantages of this method compared to other beam calibration methods. Our results show that this drone-based technique is very promising for ongoing and future radio experiments, where the knowledge of the beam pattern is key to obtaining high-accuracy cosmological and astronomical measurements.
We investigate the relation between star formation (SF) and black hole accretion luminosities, using a sample of 492 type-2 active galactic nuclei (AGNs) at z < 0.22, which are detected in the far-infrared (FIR) surveys with AKARI and Herschel. We adopt FIR luminosities at 90 and 100 um as SF luminosities, assuming the proposed linear proportionality of star formation rate with FIR luminosities. By estimating AGN luminosities from [OIII]5007 and [OI]6300 emission lines, we find a positive linear trend between FIR and AGN luminosities over a wide dynamical range. This result appears to be inconsistent with the recent reports that low-luminosity AGNs show essentially no correlation between FIR and X-ray luminosities, while the discrepancy is likely due to the Malmquist and sample selection biases. By analyzing the spectral energy distribution, we find that pure-AGN candidates, of which FIR radiation is thought to be AGN-dominated, show significantly low-SF activities. These AGNs hosted by low-SF galaxies are rare in our sample (~ 1%). However, the low fraction of low-SF AGN is possibly due to observational limitations since the recent FIR surveys are insufficient to examine the population of high-luminosity AGNs hosted by low-SF galaxies.
We examine the effect of Galactic diffractive interstellar scintillation as a means of explaining the reported deficit of Fast Radio Burst (FRB) detections at low Galactic latitude. We model the unknown underlying FRB flux density distribution as a power law with a rate scaling as $S_\nu^{-5/2+\delta}$ and account for the fact that the FRBs are detected at unknown positions within the telescope beam. We find that the event rate of FRBs located off the Galactic plane may be enhanced by a factor ~30-300% relative to objects near the Galactic plane without necessarily affecting the slope of the distribution. For FRBs whose flux densities are subject to relatively weak diffractive scintillation, as is typical for events detected at high Galactic latitudes, we demonstrate that an effect associated with Eddington bias is responsible for the enhancement. The magnitude of the enhancement increases with the steepness of the underlying flux density distribution, so that existing limits on the disparity in event rates between high and low Galactic latitudes suggest that the FRB population has a steep differential flux density distribution, scaling as $S_\nu^{-3.5}$ or steeper. Existing estimates of the event rate in the flux density range probed by the High Time Resolution Universe (HTRU) survey overestimate the true rate by a factor of ~3.
Linear cosmological perturbations of a large class of modified gravity and dark energy models can be unified in the effective field theory of cosmic acceleration, encompassing Horndeski scalar-tensor theories and beyond. The fully available model space inherent to this formalism cannot be constrained by measurements in the quasistatic small-scale regime alone. To facilitate the analysis of modifications from the concordance model beyond this limit, we introduce a semi-dynamical treatment extrapolated from the evolution of perturbations at a pivot scale of choice. At small scales, and for Horndeski theories, the resulting modifications recover a quasistatic approximation but account for corrections to it near the Hubble scale. For models beyond Horndeski gravity, we find that the velocity field and time derivative of the spatial metric potential can generally not be neglected, even in the small-scale limit. We test the semi-dynamical approximation against the linear perturbations of a range of dark energy and modified gravity models, finding good agreement between the two.
We explore the outcome of mass transfer via Roche lobe overflow (RLOF) of $M_{\rm He}\lesssim0.51 M_\odot$ pure helium burning stars in close binaries with white dwarfs (WDs). The evolution is driven by the loss of angular momentum through gravitational wave radiation (GWR), and both stars are modeled using Modules for Experiments in Stellar Astrophysics (MESA). The donors have masses of $M_{\rm He}=0.35, 0.4, \&\ 0.51M_\odot$ and accrete onto WDs of mass $M_{\rm WD}$ from $0.6M_\odot$ to $1.26M_\odot$. The initial orbital periods ($P_{\rm{orb}}$) span 20 to 80 minutes. For all cases, the accretion rate onto the WD is below the stable helium burning range, leading to accumulation of helium followed by unstable ignition. The mass of the convective core in the donors is small enough so that the WD accretes enough helium-rich matter to undergo a thermonuclear runaway in the helium shell before any carbon-oxygen enriched matter is transferred. The mass of the accumulated helium shell depends on $M_{\rm WD}$ and the accretion rate. We show that for $M_{\rm He}\gtrsim0.4 M_\odot$ and $M_{\rm WD}\gtrsim0.8 M_\odot$, the first flash is likely vigorous enough to trigger a detonation in the helium layer. These thermonuclear runaways may be observed as either faint and fast .Ia SNe, or, if the carbon in the core is also detonated, Type Ia SNe. Those that survive the first flash and eject mass will have a temporary increase in orbital separation, but GWR drives the donor back into contact, resuming mass transfer and triggering several subsequent weaker flashes.
To investigate the disk formation and jet launch in protostars is crucial to comprehend the earliest stages of star and planet formation. We aim to constrain the properties of the molecular jet and the disk of the HH 212 protostellar system at unprecedented angular scales through ALMA observations of sulfur-bearing molecules, SO 9(8)-8(7), SO 10(11)-10(10), SO2 8(2,6)-7(1,7). SO 9(8)-8(7) and SO2 8(2,6)-7(1,7) show broad velocity profiles. At systemic velocity they probe the circumstellar gas and the cavity walls. Going from low to high blue-/red-shifted velocities the emission traces the wide-angle outflow and the fast (~100-200 km/s) and collimated (~90 AU) molecular jet revealing the inner knots with timescales <50 years. The jet transports a mass loss rate >0.2-2e-6 Msun/yr, implying high ejection efficiency (>0.03-0.3). The SO and SO2 abundances in the jet are ~1e-7-1e-6. SO 10(11)-10(10) emission is compact and shows small-scale velocity gradients indicating that it originates partly from the rotating disk previously seen in HCO+ and C17O, and partly from the base of the jet. The disk mass is >0.002-0.013 Msun, and the SO abundance in the disk is ~1e-8-1e-7. SO and SO2 are effective tracers of the molecular jet in the inner few hundreds AU from the protostar. Their abundances indicate that 1% - 40% of sulfur is in SO and SO2 due to shocks in the jet/outflow and/or to ambipolar diffusion at the wind base. The SO abundance in the disk is 3-4 orders of magnitude larger than in evolved protoplanetary disks. This may be due to an SO enhancement in the accretion shock at the envelope-disk interface or in spiral shocks if the disk is partly gravitationally unstable.
We have analyzed the archival data of FUV observations for the region of GSH 006-15+7, a large shell-like structure discovered by Moss et al. (2012) from the H I velocity maps. FUV emission is seen to be enhanced in the lower supershell region. The FUV emission is considered to come mainly from the scattering of interstellar photons by dust grains. A corresponding Monte Carlo simulation indicates that the distance to the supershell is 1300 +- 800 pc, which is similar to the previous estimation of 1500 +- 500 pc based on kinematic considerations. The spectrum at lower Galactic latitudes of the supershell exhibits molecular hydrogen fluorescence lines; a simulation model for this candidate photodissociation region (PDR) yields an H_2 column density of N(H_2) = 10^{18.0-20.0} cm^{-2} with a rather high total hydrogen density of n_H ~ 30 cm^{-3}.
Pluto and its five known satellites form a complex dynamic system. Here we explore where additional satellites could exist exterior to Charon (the innermost moon) but interior of Hydra (the outermost). We also provide dynamical constraints for the masses of the known satellites. We show that there are significant stable regions interior of Styx and between Nix and Kerberos. In addition, we show that coorbitals of the known small satellites are stable, even at high inclinations, and discuss mass constraints on undiscovered satellites in such orbits.
In this study we present first results from multi-wavelength Hubble Space Telescope (HST) observations of the Galactic globular cluster GC NGC2808 as an extension of the Hubble Space Telescope UV Legacy Survey of Galactic GCs (GO-13297 and previous proprietary and HST archive data). Our analysis allowed us to disclose a multiple-stellar-population phenomenon in NGC2808 even more complex than previously thought. We have separated at least five different populations along the main sequence and the red giant branch (RGB), that we name A, B, C, D and E (though an even finer subdivision may be suggested by the data). We identified the RGB bump in four out of the five RGBs. To explore the origin of this complex CMD, we have combined our multi-wavelength HST photometry with synthetic spectra, generated by assuming different chemical compositions. The comparison of observed colors with synthetic spectra suggests that the five stellar populations have different contents of light elements and helium. Specifically, if we assume that NGC2808 is homogeneous in [Fe/H] (as suggested by spectroscopy for Populations B, C, D, E, but lacking for Population A) and that population A has a primordial helium abundance, we find that populations B, C, D, E are enhanced in helium by Delta Y~0.03, 0.03, 0.08, 0.13, respectively. We obtain similar results by comparing the magnitude of the RGB bumps with models. Planned spectroscopic observations will test whether also Population A has the same metallicity, or whether its photometric differences with Population B can be ascribed to small [Fe/H] and [O/H] differences rather than to helium.
In our previous works (Kataoka et al. 2013, Tahara et al. 2015), we found absorbed thermal X-ray plasma with kT ~ 0.3 keV observed ubiquitously near the edges of the Fermi bubbles and interpreted this emission as weakly shock-heated Galactic halo (GH) gas. Here we present a systematic and uniform analysis of archival Suzaku (29 pointings; 6 newly presented) and Swift (68 pointings; 49 newly presented) data within Galactic longitudes |l| < 20 deg and latitude 5 deg < |b| < 60 deg, covering the whole extent of the Fermi bubbles. We show that the plasma temperature is constant at kT = 0.30+-0.07 keV, while the emission measure (EM) varies by an order of magnitude, increasing toward the Galactic center (i.e., low |b|) with enhancements at the north polar spur (NPS), SE-claw and NW-clump features. Moreover, the EM distribution of kT ~ 0.30 keV plasma is highly asymmetric in the northern and southern bubbles. Although the association of the X-ray emission with the bubbles is not conclusive, we compare the observed EM properties with simple models assuming (i) a filled halo without bubbles, whose gas density follows a hydrostatic isothermal model (King profile) and (ii) a bubble-in-halo in which two identical bubbles expand into the halo forming thick shells of swept halo gas. We argue that the EM profile in the north (b > 0 deg) favors (ii), whereas that of the south (b < 0 deg) is rather close to (i), but weak excess signature is clearly detected also in the south like NPS (South Polar Spur; SPS). Such an asymmetry, if due to the bubbles, cannot be fully understood only by the inclination of bubbles' axis against the Galactic disk normal, thus suggesting asymmetric outflow due to different environmental/initial condition.
In this work, we select the high signal-to-noise ratio spectra of stars from the LAMOST data andmap theirMK classes to the spectral features. The equivalentwidths of the prominent spectral lines, playing the similar role as the multi-color photometry, form a clean stellar locus well ordered by MK classes. The advantage of the stellar locus in line indices is that it gives a natural and continuous classification of stars consistent with either the broadly used MK classes or the stellar astrophysical parameters. We also employ a SVM-based classification algorithm to assignMK classes to the LAMOST stellar spectra. We find that the completenesses of the classification are up to 90% for A and G type stars, while it is down to about 50% for OB and K type stars. About 40% of the OB and K type stars are mis-classified as A and G type stars, respectively. This is likely owe to the difference of the spectral features between the late B type and early A type stars or between the late G and early K type stars are very weak. The relative poor performance of the automatic MK classification with SVM suggests that the directly use of the line indices to classify stars is likely a more preferable choice.
How much electromagnetic energy crosses the photosphere in evolving solar active regions? With the advent of high-cadence vector magnetic field observations, addressing this fundamental question has become tractable. In this paper, we apply the "PTD-Doppler-FLCT-Ideal" (PDFI) electric field inversion technique of Kazachenko et al. (2014) to a 6-day HMI/SDO vector magnetogram and Doppler velocity sequence, to find the electric field and Poynting flux evolution in NOAA active region 11158, which produced an X2.2 flare early on 2011 February 15. We find photospheric electric fields ranging up to $1.5$ V/cm. The Poynting fluxes range up to $2\times10^{10}$ ergs$\cdot$cm$^{-2}$s$^{-1}$ with mean values around $10^8$-$10^9$ ergs$\cdot$cm$^{-2}$s$^{-1}$. Integrating the instantaneous energy flux over space and time, we find that the total magnetic energy accumulated above the photosphere from emergence to the moment before the X2.2 flare to be $E=10.6\times10^{32}$ ergs, which is partitioned as $2.0\times10^{32}$ ergs and $8.6\times10^{32}$ ergs, respectively, between free and potential energies. Those estimates are consistent with estimates from pre-flare non-linear force-free field (NLFFF) extrapolations and the Minimum Current Corona estimates (MCC), in spite of our very different approach. This study of photospheric electric fields demonstrates the potential of the PDFI approach for estimating Poynting fluxes and opens the door to more quantitative studies of the solar photosphere and more realistic data-driven simulations of coronal magnetic field evolution.
A comprehensive study of the mass sensitivity of the vibration-rotation-inversion transitions of $^{14}$NH$_3$, $^{15}$NH$_3$, $^{14}$ND$_3$, and $^{15}$ND$_3$ is carried out variationally using the TROVE approach. Variational calculations are robust and accurate, offering a new way to compute sensitivity coefficients. Particular attention is paid to the $\Delta k=\pm 3$ transitions between the accidentally coinciding rotation-inversion energy levels of the $\nu_2=0^+,0^-,1^+$ and $1^-$ states, and the inversion transitions in the $\nu_4=1$ state affected by the "giant" $l$-type doubling effect. These transitions exhibit highly anomalous sensitivities, thus appearing as promising probes of a possible cosmological variation of the proton-to-electron mass ratio $\mu$. Moreover, a simultaneous comparison of the calculated sensitivities reveals a sizeable isotopic dependence which could aid an exclusive ammonia detection.
The 340-year old supernova remnant Cassiopeia A at 3.4 kpc distance is the best-studied young core-collapse supernova remnant. Nucleosynthesis yields in radioactive isotopes have been studied with different methods, in particular for production and ejection of $^{44}$Ti and $^{56}$Ni which originate from the innermost regions of the supernova. $^{44}$Ti was first discovered in this remnant, but is not seen consistently in other core-collapse sources. We analyse the observations accumulated with the SPI spectrometer on INTEGRAL, together with an improved instrumental background method, to achieve high spectroscopic resolution which enables interpretation towards a velocity constraint on $^{44}$Ti ejecta from the 1.157 MeV $\gamma$-ray line of the $^{44}$Sc decay. We observe both the hard X-ray line at 78 keV and the $\gamma$-ray line at 1157 keV from the $^{44}$Ti decay chain, at a combined significance of 3.8 $\sigma$. Measured fluxes are $(2.1\pm0.4)~10^{-5}~\mathrm{ph~cm^{-2}~s^{-1}}$ and $(3.5\pm1.2)~10^{-5}~\mathrm{ph~cm^{-2}~s^{-1}}$, which corresponds to $(1.5\pm0.4)~10^{-4}$ and $(2.4\pm0.9)~10^{-4}~\mathrm{M}_{\odot}$ of $^{44}$Ti, respectively. The measured Doppler broadening of the lines implies expansion velocities of $4300$ and $2200~\mathrm{km~s^{-1}}$, respectively. Combining our results with previous studies, we determine a more precise estimate of ejected $^{44}$Ti of $(1.37\pm0.19)~10^{-4}~\mathrm{M}_{\odot}$. The measurements of both lines are consistent with previous studies. The flux in the line originating from excited $^{44}$Ca is significantly higher than the flux determined in the lines from $^{44}$Sc. Cosmic ray acceleration within the supernova remnant may be responsible for an additional contribution to this line from nuclear de-excitation following energetic particle collisions in the remnant and swept-up material.
We present results of the analysis of 70 RR Lyrae stars located in the bar of
the Large Magellanic Cloud (LMC). Combining spectroscopically determined
metallicity of these stars from the literature with precise periods from the
OGLE III catalogue and multi-epoch $K_{\rm s}$ photometry from the VISTA survey
of the Magellanic Clouds system (VMC), we derive a new near-infrared
period-luminosity-metallicity (${\rm PL_{K_{\rm s}}Z}$) relation for RR Lyrae
variables. In order to fit the relation we use a fitting method developed
specifically for this study. The zero-point of the relation is estimated in two
different ways: by assuming the value of the distance to the LMC and by using
Hubble Space Telescope (HST) parallaxes of five RR Lyrae stars in the Milky Way
(MW). The difference in distance moduli derived by applying these two
approaches is $\sim0.2$ mag. To investigate this point further we derive the
${\rm PL_{K_{\rm s}}Z}$ relation based on 23 MW RR Lyrae stars which had been
analysed in Baade-Wesselink studies. We compared the derived ${\rm PL_{K_{\rm
s}}Z}$ relations for RR Lyrae stars in the MW and LMC. Slopes and zero-points
are different, but still consistent within the errors. The shallow slope of the
metallicity term is confirmed by both LMC and MW variables.
The astrometric space mission Gaia is expected to provide a huge contribution
to the determination of the RR Lyrae ${\rm PL_{K_{\rm s}}Z}$ relation, however,
calculating an absolute magnitude from the trigonometric parallax of each star
and fitting a ${\rm PL_{K_{\rm s}}Z}$ relation directly to period and absolute
magnitude leads to biased results. We present a tool to achieve an unbiased
solution by modelling the data and inferring the slope and zero-point of the
relation via statistical methods.
The most violent space weather events (eruptive solar flares and coronal mass ejections) are driven by the release of free magnetic energy stored in the solar corona. Energy can build up on timescales of hours to days, and then may be suddenly released in the form of a magnetic eruption, which then propagates through interplanetary space, possibly impacting the Earth's space environment. Can we use the observed evolution of the magnetic and velocity fields in the solar photosphere to model the evolution of the overlying solar coronal field, including the storage and release of magnetic energy in such eruptions? The objective of CGEM, the Coronal Global Evolutionary Model, funded by the NASA/NSF Space Weather Modeling program, is to develop and evaluate such a model for the evolution of the coronal magnetic field. The evolving coronal magnetic field can then be used as a starting point for magnetohydrodynamic (MHD) models of the corona, which can then be used to drive models of heliospheric evolution and predictions of magnetic field and plasma density conditions at 1AU.
We consider the distortions of the CMB dipole anisotropy related to the primordial recombination radiation (PRR) and primordial $y$- and $\mu$-distortions. The signals arise due to our motion relative to the CMB restframe and appear as a frequency-dependent distortion of the CMB temperature dipole. To leading order, the expected relative distortion of CMB dipole does not depend on the particular observation directions and reaches the level of $10^{-6}$ for the PRR- and $\mu$-distortions and $10^{-5}$ for the $y$-distortion in the frequency range 1 $-$ 700 GHz. The temperature differences arising from the dipole anisotropy of the relic CMB distortions depend on observation directions. For mutually opposite directions, collinear to the CMB dipole axis, the temperature differences because of the PRR- and $\mu$-dipole anisotropy attain values $\Delta T\simeq 10\,$nK in the considered range. The temperature difference arising from the $y$-dipole anisotropy may reach values up to $1\,\mu$K. The key features of the considered effect are: (i) an observation of the effect does not require absolute calibration; (ii) patches of sky with minimal foreground contamination can be chosen. Future measurements of the CMB dipole distortion thus provide an alternative method for direct detection of the PRR-, $y$- and $\mu$-distortions.
He-like ions produce distinctive series of triplet lines under various astrophysical conditions. However, this emission can be affected by line-absorption from Li-like ions in the same medium. We investigate this absorption of He-like triplets and present the implications for diagnostics of plasmas in photoionisation equilibrium using the line ratios of the triplets. Our computations are carried out for the O VI and Fe XXIV absorption of the O VII and Fe XXV triplet emission lines, respectively. The fluorescent emission by the Li-like ions and continuum absorption of the He-like ion triplet lines are also investigated. We determine the absorption of the triplet lines as a function of Li-like ion column density and velocity dispersion of the emitting/absorbing medium. We find O VI line-absorption can significantly alter the O VII triplet line ratios in optically-thin plasmas, by primarily absorbing the intercombination lines and to lesser extent the forbidden line. Due to intrinsic line-absorption by O VI inside a photoionised plasma, the predicted ratio of forbidden to intercombination line intensity for the O VII triplet increases from 4 up to an upper-limit of 16. This process can explain the larger than expected triplet line ratios seen in some X-ray observations of photoionised plasmas. For the Fe XXV triplet, line-absorption by Fe XXIV becomes less apparent due to significant fluorescent emission by Fe XXIV. Without taking into account the associated Li-like ion line-absorption, the density diagnosis of photoionised plasmas using the observed line ratios of the He-like ion triplet emission lines can be unreliable, especially for low-Z ions.
We present the analysis of MOA-2007-BLG-197Lb, the first brown dwarf companion to a Sun-like star detected through gravitational microlensing. The event was alerted and followed-up photometrically by a network of telescopes from the PLANET, MOA, and uFUN collaborations, and observed at high angular resolution using the NaCo instrument at the VLT. From the modelling of the microlensing light curve, we derived the binary lens separation in Einstein radius units (s~1.13) and a mass ratio of (4.732+/-0.020)x10^{-2}. Annual parallax, lens orbital motion and finite source effects were included in the models. To recover the lens system's physical parameters, we combined the resulting light curve best-fit parameters with (J,H,Ks) magnitudes obtained with VLT NaCo and calibrated using IRSF and 2MASS data. We derived a lens total mass of 0.86+/-0.04 Msun and a lens distance of 4.2+/-0.3 kpc. We find that the companion of MOA-2007-BLG-197L is a brown dwarf of 41+/-2 Mjup observed at a projected separation of 4.3+/-0.1 AU, and orbits a 0.82+/-0.04 Msun G-K dwarf star. We study the statistical properties of this population of brown dwarfs detected by microlensing, transit, radial velocity, and direct imaging (most of these objects orbit solar-type stars), and we performed a two-dimensional, non-parametric probability density distribution fit to the data, which draws a structured brown dwarf landscape. We confirm the existence of a region that is strongly depleted in objects at short periods and intermediate masses (P<30 d, M~30-60 Mjup), but also find an accumulation of objects around P~500 d and M~20 Mjup, as well as another depletion region at long orbital periods (P>500 d) and high masses (M>50 Mjup). While these data provide important clues on mechanisms of brown dwarfs formation, more data are needed to establish their relative importance, in particular as a function of host star mass.
GLEAM, the GaLactic and Extragalactic All-sky MWA survey, is a survey of the entire radio sky south of declination +25 deg at frequencies between 72 and 231 MHz, made with the Murchison Widefield Array (MWA) using a drift scan method that makes efficient use of the MWA's very large field-of-view. We present the observation details, imaging strategies and theoretical sensitivity for GLEAM. The survey ran for two years, the first year using 40 kHz frequency resolution and 0.5 s time resolution; the second year using 10 kHz frequency resolution and 2 s time resolution. The resulting image resolution and sensitivity depends on observing frequency, sky pointing and image weighting scheme. At 154 MHz the image resolution is approximately 2.5 x 2.2/cos(DEC+26.7) arcmin with sensitivity to structures up to ~10 deg in angular size. We provide tables to calculate the expected thermal noise for GLEAM mosaics depending on pointing and frequency and discuss limitations to achieving theoretical noise in Stokes I images. We discuss challenges, and their solutions, that arise for GLEAM including ionospheric effects on source positions and linearly polarised emission, and the instrumental polarisation effects inherent to the MWA's primary beam.
Einstein Telescope (ET) is a planned third generation gravitational waves detector located in Europe. Its design will be different from currently build interferometers, because ET will consist of three interferometers rotated by a 60 deg with respect to each other in one plane. One of the biggest challenges for ET will be to determine sky position and distance to observed sources. If an object is observed in a few interferometers simultaneously one can estimate the position using traingulation from time delays, but so far there are no plans for a network of third generation detectors. Another possibility to deal with that problem is by using multimessenger approach, because redshift and sky position could be recovered from electromagnetic observations. In this paper we present a novel method of estimating distance and position in the sky of merging binaries. While our procedure is not as accurate as the multimessenger method, it can be applied to all observations, not just the ones with electromagnetic counterparts. We have shown that it is possible to significantly improve distance estimates using the measurements of the signal to noise ratio from all three interferometers .
We present the results of a search for nova shells around 101 cataclysmic variables (CVs), using Halpha images taken with the 4.2-m William Herschel Telescope (WHT) and the 2.5-m Isaac Newton Telescope Photometric Halpha Survey of the Northern Galactic Plane (IPHAS). Both telescopes are located on La Palma. We concentrated our WHT search on nova-like variables, whilst our IPHAS search covered all CVs in the IPHAS footprint. We found one shell out of the 24 nova-like variables we examined. The newly discovered shell is around V1315 Aql and has a radius of approx.2.5 arcmin, indicative of a nova eruption approximately 120 years ago. This result is consistent with the idea that the high mass-transfer rate exhibited by nova-like variables is due to enhanced irradiation of the secondary by the hot white dwarf following a recent nova eruption. The implications of our observations for the lifetime of the nova-like variable phase are discussed. We also examined 4 asynchronous polars, but found no new shells around any of them, so we are unable to confirm that a recent nova eruption is the cause of the asynchronicity in the white dwarf spin. We find tentative evidence of a faint shell around the dwarf nova V1363 Cyg. In addition, we find evidence for a light echo around the nova V2275 Cyg, which erupted in 2001, indicative of an earlier nova eruption approx.300 years ago, making V2275 Cyg a possible recurrent nova.
We report on the abundance analysis of Li in solar-type (G-type main
sequence) superflare stars which were found by the analysis of Kepler
photometric data. Li is a key element to understand the evolution of the
stellar convection zone which reflects the age of solar-type stars. We
performed the high dispersion spectroscopy of solar-type superflare stars with
Subaru/HDS, and confirmed that 34 stars show no evidence of binarity in our
previous study. In this study, we derived the Li abundances of these 34
objects.
We investigate correlations of Li abundance with stellar atmospheric
parameters, rotational velocity, and superflare activities to understand the
nature of superflare stars and the possibility of the nucleosynthesis of Li by
superflares. We confirm the large dispersion in the Li abundance, and the
correlation with stellar parameters is not seen. As compared with the Li
abundance in Hyades cluster which is younger than the Sun, it is suggested that
half of the observed stars are younger than Hyades cluster. The measured value
of $v \sin i$ (projected rotational velocity) supports those objects are
younger than the Sun. However, there are some objects which show the low Li
abundance and slowly rotate on the basis of the estimated $v \sin i$ and $P$
(period of brightness variation). This result indicates that the superflare
stars are not only young stars but also old stars like our Sun. In our
observations, we could not find any evidence of Li productions by superflares.
Further research on Li isotope abundances of superflare stars would clarify the
Li production by stellar flares.
During the last decades, increasingly precise astronomical observations of the Galactic Centre (GC) region at radio, infrared, and X-ray wavelengths laid the foundations to a detailed understanding of the high energy astroparticle physics of this most remarkable location in the Galaxy. Recently, observations of this region in high energy (HE, 10 MeV - 100GeV) and very high energy (VHE, > 100 GeV) gamma rays added important insights to the emerging picture of the Galactic nucleus as a most violent and active region where acceleration of particles to very high energies -- possibly up to a PeV -- and their transport can be studied in great detail. Moreover, the inner Galaxy is believed to host large concentrations of dark matter (DM), and is therefore one of the prime targets for the indirect search for gamma rays from annihilating or decaying dark matter particles. In this article, the current understanding of the gamma-ray emission emanating from the GC is summarised and the results of recent DM searches in HE and VHE gamma rays are reviewed.
Large-scale analyses of stellar samples comprised of cool, solar-like oscillators now commonly utilize the so-called asteroseismic scaling relations to estimate fundamental stellar properties. In this paper we present a test of the scaling relation for the global asteroseismic parameter $\nu_{\rm max}$, the frequency at which a solar-like oscillator presents its strongest observed pulsation amplitude. The classic relation assumes that this characteristic frequency scales with a particular combination of surface gravity and effective temperature that also describes the dependence of the cut-off frequency for acoustic waves in an isothermal atmosphere, i.e., $\nu_{\rm max} \propto gT_{\rm eff}^{-1/2}$. We test how well the oscillations of cool main-sequence and sub-giant stars adhere to this relation, using a sample of asteroseismic targets observed by the NASA \emph{Kepler} Mission. Our results, which come from a grid-based analysis, rule out departures from the classic $gT_{\rm eff}^{-1/2}$ scaling dependence at the level of $\simeq 1.5\,\rm per cent$ over the full $\simeq 1560\,\rm K$ range in $T_{\rm eff}$ that we tested. There is some uncertainty over the absolute calibration of the scaling. However, any variation with $T_{\rm eff}$ is evidently small, with limits similar to those above.
Using recent measurements of the spectrum and chemical composition of the highest energy cosmic rays, we consider the sources of these particles. We find that the data strongly prefers models in which the sources of the ultra-high energy cosmic rays inject predominantly intermediate mass nuclei, with comparatively few protons or heavy nuclei, such as iron or silicon. If the number density of sources per comoving volume does not evolve with redshift, the injected spectrum must be very hard ($\alpha\simeq 1$) in order to fit the spectrum observed at Earth. Such a hard spectral index would be surprising and difficult to accommodate theoretically. In contrast, much softer spectral indices, consistent with the predictions of Fermi acceleration ($\alpha\simeq 2$), are favored in models with negative source evolution. With this theoretical bias, these observations thus favor models in which the sources of the highest energy cosmic rays are preferentially located within the low-redshift universe.
By means of our own cosmological-hydrodynamical simulation and
semi-analytical model we studied galaxy population properties in clusters and
groups, spanning over 10 different bands from UV to NIR, and their evolution
since redshift z=2. We compare our results in terms of galaxy red/blue
fractions and luminous-to-faint ratio (LFR) on the Red Sequence (RS) with
recent observational data reaching beyond z=1.5. Different selection criteria
were tested in order to retrieve galaxies belonging to the RS: either by their
quiescence degree measured from their specific SFR ("Dead Sequence"), or by
their position in a colour-colour plane which is also a function of sSFR. In
both cases, the colour cut and the limiting magnitude threshold were let
evolving with redshift, in order to follow the natural shift of the
characteristic luminosity in the LF.
We find that the Butcher-Oemler effect is wavelength-dependent, with the
fraction of blue galaxies increasing steeper in optical colours than in NIR.
Besides, only when applying a lower limit in terms of fixed absolute magnitude,
a steep BO effect can be reproduced, while the blue fraction results less
evolving when selecting samples by stellar mass or an evolving magnitude limit.
We then find that also the RS-LFR behaviour, highly debated in the literature,
is strongly dependent on the galaxy selection function: in particular its very
mild evolution recovered when measured in terms of stellar mass, is in
agreement with values reported for some of the highest redshift confirmed
(proto)clusters. As to differences through environments, we find that normal
groups and (to a lesser extent) cluster outskirts present the highest values of
both star forming fraction and LFR at low z, while fossil groups and cluster
cores the lowest: this separation among groups begins after z~0.5, while
earlier all group star forming properties are undistinguishable.
In general relativity static gaseous atmospheres may be in hydrostatic balance in the absence of a supporting stellar surface, provided that the luminosity is close to the Eddington value. We construct analytic models of optically thin, spherically symmetric shells supported by the radiation pressure of a luminous central body in the Schwarzschild metric.
Swift J1734.5-3027 is a hard X-ray transient discovered by Swift while undergoing an outburst in September 2013. Archival observations showed that this source underwent a previous episode of enhanced X-ray activity in May-June 2013. In this paper we report on the analysis of all X-ray data collected during the outburst in September 2013, the first that could be intensively followed-up by several X-ray facilities. Our data-set includes INTEGRAL, Swift, and XMM-Newton observations. From the timing and spectral analysis of these observations, we show that a long type-I X-ray burst took place during the source outburst, making Swift J1734.5-3027 a new member of the class of bursting neutron star low-mass X-ray binaries. The burst lasted for about 1.9 ks and reached a peak flux of (6.0$\pm$1.8)$\times$10$^{-8}$ erg cm$^{-2}$ s$^{-1}$ in the 0.5-100 keV energy range. The estimated burst fluence in the same energy range is (1.10$\pm$0.10)$\times$10$^{-5}$ erg cm$^{-2}$. By assuming that a photospheric radius expansion took place during the first $\sim$200 s of the burst and that the accreted material was predominantly composed by He, we derived a distance to the source of 7.2$\pm$1.5 kpc.
Motivated by the possibility that different versions of the laws of physics could be realized within other universes, this paper delineates the galactic parameters that allow for habitable planets and revisits constraints on the amplitude $Q$ of the primordial density fluctuations. Previous work indicates that large values of $Q$ lead to galaxies so dense that planetary orbits cannot survive long enough for life to develop. Small values of $Q$ lead to delayed star formation, loosely bound galaxies, and compromised heavy element retention. This work generalizes previous treatments: [A] We consider models for the internal structure of galaxies and find the fraction of galactic real estate that allows stable, long-lived planetary orbits. [B] We perform a large ensemble of numerical simulations to estimate cross sections for the disruption of planetary orbits due to interactions with passing stars. [C] We consider disruption due to the background radiation fields produced by the galaxies. [D] One consequence of intense galactic background radiation fields is that some portion of the galaxy, denoted as the Galactic Habitable Zone, will provide the right flux levels to support habitable planets for essentially any planetary orbit. As $Q$ increases, the fraction of stars in a galaxy that allow for habitable planets decreases due to both orbital disruption and the intense background radiation. However, the outer parts of the galaxy always allow for habitable planets, so that the value of $Q$ does not have a well-defined upper limit. Moreover, some Galactic Habitable Zones are large enough to support more potentially habitable planets than the galaxies found in our universe. These results suggest that the possibilities for habitability in other universes are somewhat more favorable and far more diverse than previously imagined.
The dust cloud around $\lambda$ Orionis is observed to be circularly symmetric with a large angular extent ($\approx$ 8 degrees). However, whether the three-dimensional (3D) structure of the cloud is shell- or ring-like has not yet been fully resolved. We study the 3D structure using a new approach that combines a 3D Monte Carlo radiative transfer model for ultraviolet (UV) scattered light and an inverse Abel transform, which gives a detailed 3D radial density profile from a two-dimensional column density map of a spherically symmetric cloud. By comparing the radiative transfer models for a spherical shell cloud and that for a ring cloud, we find that only the shell model can reproduce the radial profile of the scattered UV light, observed using the S2/68 UV observation, suggesting a dust shell structure. However, the inverse Abel transform applied to the column density data from the Pan-STARRS1 dust reddening map results in negative values at a certain radius range of the density profile, indicating the existence of additional, non-spherical clouds near the nebular boundary. The additional cloud component is assumed to be of toroidal ring shape; we subtracted from the column density to obtain a positive, radial density profile using the inverse Abel transform. The resulting density structure, composed of a toroidal ring and a spherical shell, is also found to give a good fit to the UV scattered light profile. We therefore conclude that the cloud around $\lambda$ Ori is composed of both ring and shell structures.
In a new release, Iocco, Pato, and Bertone in arXiv:1505.05181 analyze the consistency of Modified Newtonian Dynamics (MOND) with their compiled Milky Way data and baryonic mass distribution models. We contribute to the discussion by feeding the mean of the seven baryonic mass distribution models that they considered in their original paper into the MOND formula assuming the so-called simple interpolation function, and directly plotting these results on top of the compiled observational rotation curve data from their original paper. Although there is no reason to assume that the mean of the seven baryonic mass distribution models is more correct than any of the individual models, it is a reasonable choice to feed into the equations and one that is less subject to bias inherent in choosing an arbitrary individual model for the MOND analysis to compare to the data. We find that the mean baryonic model using MOND with the simple interpolation function provides a striking fit to the rotation curve observational data with no parameter adjustments required, and we believe that this demonstration is visually transparent and contributes to the valuable discussion on the subject provided by Iocco, Pato, and Bertone. Our results are consistent with the findings of McGaugh (2008), but for an average of many baryonic models instead of just one.
Impulsive 30 THz continuum bursts have been recently observed in solar flares, utilizing small telescopes with a unique and relatively simple optical setup concept. The most intense burst was observed together with a GOES X2 class event on October 27, 2014, also detected at two sub-THz frequencies, RHESSI X-rays and SDO/HMI and EUV. It exhibits strikingly good correlation in time and in space with white light flare emission. It is likely that this association may prove to be very common. All three 30 THz events recently observed exhibited intense fluxes in the range of 104 solar flux units, considerably larger than those measured for the same events at microwave and sub-mm wavelengths. The 30 THz burst emission might be part of the same spectral burst component found at sub-THz frequencies. The 30 THz solar bursts open a promising new window for the study of flares at their origin
We investigate the cosmological dependence and the constraining power of large-scale galaxy correlations, including all redshift-distortions, wide-angle, lensing and gravitational potential effects on linear scales. We analyze the cosmological information present in the lensing convergence and in the gravitational potential terms describing the so-called "relativistic effects," and we find that, while smaller than the information contained in intrinsic galaxy clustering, it is not negligible. We investigate how neglecting them does bias cosmological measurements performed by future spectroscopic and photometric large-scale surveys such as SKA and Euclid. We perform a Fisher analysis using the CLASS code, modified to include scale-dependent galaxy bias and redshift-dependent magnification and evolution bias. Our results show that neglecting relativistic terms introduces an error in the forecasted precision in measuring cosmological parameters of the order of a few tens of percent, in particular when measuring the matter content of the Universe and primordial non-Gaussianity parameters. Therefore, we argue that radial correlations and integrated relativistic terms need to be taken into account when forecasting the constraining power of future large-scale number counts of galaxy surveys.
We report first results from an ongoing monitoring campaign to measure time delays between the six images of the quasar SDSS J2222+2745, gravitationally lensed by a galaxy cluster. The time delay between A and B, the two most highly magnified images, is measured to be $\tau_{AB} = 43.0 \pm 4.5$ days (95% confidence interval), consistent with previous model predictions for this lens system. The strong intrinsic variability of the quasar also allows us to derive a tentative time delay value of $\tau_{CA} = 694^{+23}_{-4}$ days between image C and A, in spite of modest overlap between their light curves in the current data set. Longer values of $\tau_{CA} \lesssim 830$ days cannot yet be firmly excluded, but further monitoring should be sufficient to confirm the tentative value during 2015. Image C, which is predicted to lead all the other lensed quasar images, has undergone a sharp, monotonic flux increase of 60-75% during 2014. The same brightening is predicted to occur in images A and B during 2016. The amplitude of this rise indicates that time delays involving all six known images in this system, including those of the demagnified central images D-F, will be obtainable from further ground-based monitoring of this system during the next few years.
We consider background dynamics of generalized Galileon theories in the context of inflation, where gravity and inflaton are non-minimally coupled to each other. In the inflaton oscillation regime, the Hubble parameter and energy density oscillate violently in many cases, in contrast to the Einstein gravity with minimally coupled inflaton. However, we find that there is an adiabatic invariant in the inflaton oscillation regime in any generalized Galileon theory. This adiabatic invariant is useful in estimating the expansion law of the universe and also the particle production rate due to the oscillation of the Hubble parameter.
In this article we have developed a formalism to obtain the Schr$\ddot{\rm{o}}$dinger equation for a particle in a frame undergoing an uniform acceleration in an otherwise flat Minkowski space-time geometry. We have presented an exact solution of the equation and obtained the eigenfunctions and the corresponding eigenvalues. It has been observed that the Schr$\ddot{\rm{o}}$dinger equation can be reduced to an one dimensional hydrogen atom problem. Whereas, the quantized energy levels are exactly identical with that of an one dimensional quantum harmonic oscillator. Hence considering transitions, we have predicted the existence of a new kind of quanta, which will either be emitted or absorbed if the particles get excited or de-excited respectively.
We analyse and compare the finite-temperature electroweak phase transition properties of classically (non)conformal extensions of the Standard Model. In the classically conformal scenarios the breaking of the electroweak symmetry is generated radiatively. The models feature new scalars coupled conformally to the Higgs sector as well as new fermions. We uncover the parameter space leading to a first order phase transition with(out) the Veltman conditions. We also discuss dark (matter) aspects of some of the models and compare with existing literature when appropriate. We observe that to accommodate both, a first order electroweak phase transition, and a phenomenologically viable dark matter candidate requires to go beyond the simplest extensions of the Standard Model. Furthermore these extensions must all feature new degrees of freedom that are naturally lighter than a TeV and therefore the associated models are testable at the upcoming Large Hadron Collider run two experiments.
The problem of scattering of CMB radiation on a wormhole is considered. It is shown that a static gas of wormholes does not perturb the spectrum of CMB. In the first order by $v/c$ the presence of peculiar velocities gives rise to the dipole contribution in $\Delta T/T$, which corresponds to the well-known kinetic Sunyaev-Zel'dovich effect. In next orders there appears a more complicated dependence of the perturbed CMB spectrum on peculiar velocities.
We reexamine inflation due to a constrained inflaton in the model of a complex scalar. Inflaton evolves along a spiral-like valley of special scalar potential in the scalar field space just like single field inflation. Sub-Planckian inflaton can induce sufficient $e$-foldings because of a long slow-roll path. In a special limit, the scalar spectral index and the tensor-to-scalar ratio has equivalent expressions to the inflation with monomial potential $\varphi^n$. The favorable values for them could be obtained by varying parameters in the potential. This model could be embedded in a certain radiative neutrino mass model.
There is an apparent power deficit relative to the $\Lambda$CDM prediction of the CMB spectrum at large scales, which, though not yet statistically significant, persists from WMAP to Planck data. Proposals that invoke some form of initial condition for the inflation have been made to address this apparent power suppression, albeit with conflicting conclusions. By studying the curvature perturbation spectrum of a scalar field in the FLRW Universe, we show that if the Universe begins in the era with positive or phantom pressure, the large-scale spectrum is suppressed, provided the Universe approaches to the adiabatic vacuum at small scales. It is noted that the large-scale spectrum could not be generated by causal mechanisms in the decelerating Universe since the super-horizon scales are initially across causally disconnected regions. On the other hand, as long as the Universe begins in the negative-pressure era, even if there is an intermediate era with positive-pressure, the large-scale spectrum would be enhanced rather than suppressed. The spectrum of the two-stage inflation model with a given two-field potential is further calculated, showing agreement with the conclusions obtained from the ad hoc single-field analysis.
We propose a new dynamical system formalism for the analysis of f(R) cosmologies. The new approach eliminates the need for cumbersome inversions to close the dynamical system and allows the analysis of the phase space of f(R)-gravity models which cannot be investigated using the standard technique. Differently form previously proposed similar techniques, the new method is constructed in such a way to associate to the fixed points scale factors, which contain four integration constants (i.e. solutions of fourth order differential equations). In this way a new light is shed on the physical meaning of the fixed points. We apply this technique to some f(R) Lagrangians relevant for inflationary and dark energy models.
Electron-scale surface waves are shown to be unstable in the transverse plane of a shear flow in an initially unmagnetized plasma, unlike in the (magneto)hydrodynamics case. It is found that these unstable modes have a higher growth rate than the closely related electron-scale Kelvin-Helmholtz instability in relativistic shears. Multidimensional particle-in-cell simulations verify the analytic results and further reveal the emergence of mushroom-like electron density structures in the nonlinear phase of the instability, similar to those observed in the Rayleigh Taylor instability despite the great disparity in scales and different underlying physics. Macroscopic ($\gg c/\omega_{pe}$) fields are shown to be generated by these microscopic shear instabilities, which are relevant for particle acceleration, radiation emission and to seed MHD processes at long time-scales.
We have measured the absorption of terahertz radiation in a BCS superconductor over a broad range of frequencies from 200 GHz to 1.1 THz, using a broadband antenna-lens system and a tantalum microwave resonator. From low frequencies, the response of the resonator rises rapidly to a maximum at the gap edge of the superconductor. From there on the response drops to half the maximum response at twice the pair-breaking energy. At higher frequencies, the response rises again due to trapping of pair-breaking phonons in the superconductor. In practice this is the first measurement of the frequency dependence of the quasiparticle creation efficiency due to pair-breaking in a superconductor. The efficiency, calculated from the different non-equilibrium quasiparticle distribution functions at each frequency, is in agreement with the measurements.
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Many astronomers now participate in large international collaborations, and it is important to examine whether these structures foster a scientific climate that is inclusive and diverse. The Committee on the Participation of Women in the Sloan Digital Sky Survey (CPWS) was formed to evaluate the demographics and gender climate within SDSS-IV, one of the largest and most geographically distributed astronomical collaborations. In April 2014, the CPWS administered a demographic survey to establish a baseline for the incipient SDSS-IV. We received responses from 250 participants (46% of the active membership). Half of the survey respondents were located in the US or Canada and 30% were based in Europe. Eleven percent of survey respondents considered themselves to be an ethnic minority at their current institution. Twenty-five percent of the SDSS-IV collaboration members are women, a fraction that is consistent with the US astronomical community, but substantially higher than the fraction of women in the IAU (16%). Approximately equal fractions of men and women report holding positions of leadership. When binned by academic age and career level, men and women also assume leadership roles at approximately equal rates, in a way that increases steadily for both genders with increasing seniority. In this sense, SDSS-IV has been successful in recruiting leaders that are representative of the collaboration. Yet, more progress needs to be made towards achieving gender balance and increasing diversity in the field of astronomy, and there is still room for improvement in the membership and leadership of SDSS-IV. For example, at the highest level of SDSS-IV leadership, women disproportionately assume roles related to education and public outreach. The CPWS plans to use these initial data to establish a baseline for tracking demographics over time as we work to assess and improve the climate of SDSS-IV.
We use the Sternberg et al. (2014) theory for interstellar atomic to molecular (HI-to-H$_2$) conversion to analyze HI-to-H$_2$ transitions in five (low-mass) star-forming and dark regions in the Perseus molecular cloud, B1, B1E, B5, IC348, and NGC1333. The observed HI mass surface densities of 6.3 to 9.2 M$_{\odot}$ pc$^{-2}$ are consistent with HI-to-H$_2$ transitions dominated by HI-dust shielding in predominantly atomic envelopes. For each source, we constrain the dimensionless parameter $\alpha G$, and the effective ratio, $I_{\rm UV}/n$, of the FUV intensity to hydrogen gas density. We find $\alpha G$ values from 5.0 to 47.0, implying characteristic atomic hydrogen densities 11.8 to 1.0 cm$^{-3}$, for $I_{\rm UV} \approx 1$ appropriate for Perseus. Our analysis implies that the dusty HI shielding layers are probably multiphased, with thermally unstable UNM gas in addition to cold CNM within the 21 cm kinematic radius.
We study how X-rays from stellar binary systems and the hot intracluster medium (ICM) affect the radiative cooling rates of gas in galaxies. Our study uses a novel implementation of gas cooling in the moving-mesh hydrodynamics code \textsc{arepo}. X-rays from stellar binaries do not affect cooling at all as their emission spectrum is too hard to effectively couple with galactic gas. In contrast, X-rays from the ICM couple well with gas in the temperature range $10^4 - 10^6$ K. Idealised simulations show that the hot halo radiation field has minimal impact on the dynamics of cooling flows in clusters because of the high virial temperature ($> 10^7$K), making the interaction between the gas and incident photons very ineffective. Satellite galaxies in cluster environments, on the other hand, experience a high radiation flux due to the emission from the host halo. Low mass satellites ($< 10^{12}\rm{M_\odot}$) in particular have virial temperatures that are exactly in the regime where the effect of the radiation field is maximal. Idealised simulations of satellite galaxies including only the effect of host halo radiation (no ram pressure stripping or tidal effects) fields show a drastic reduction in the amount of cool gas formed ($\sim 40\%$) on a short timescale of about $0.5$ Gyrs. A galaxy merger simulation including all the other environmental quenching mechanisms, shows about $20\%$ reduction in the stellar mass of the satellite and about $\sim 30\%$ reduction in star formation rate after $1$ Gyr due to the host hot halo radiation field. These results indicate that the hot halo radiation fields potentially play an important role in quenching galaxies in cluster environments.
During a galaxy merger, the supermassive black hole (SMBH) in each galaxy is thought to sink to the center of the potential and form a supermassive black hole binary; this binary can eject stars via 3-body scattering, bringing the SMBHs ever closer. In a static spherical galaxy model, the binary stalls at a separation of about a parsec after ejecting all the stars in its loss cone -- this is the well-known final parsec problem. However it has been shown that SMBH binaries in non-spherical galactic nuclei harden at a nearly constant rate until reaching the gravitational wave regime. Here we use a suite of direct N-body simulations to follow SMBH binary evolution in both corotating and counterrotating flattened galaxy models. For N larger than 500K, we find that the evolution of the SMBH binary is convergent, and is independent of the particle number. Rotation in general increases the hardening rate of SMBH binaries even more effectively than galaxy geometry alone. SMBH binary hardening rates are similar for co- and counterrotating galaxies. In the corotating case, the center of mass of SMBH binary settles into an orbit that is in a corotation resonance with the background rotating model, and the coalescence time is roughly few hundred Myr faster than a non-rotating flattened model. We find that counterrotation drives SMBHs to coalesce on a nearly radial orbit promptly after forming a hard binary. We discuss the implications for gravitational wave astronomy, hypervelocity star production, and the effect on the structure of the host galaxy.
The formation channel of the tens of compact debris discs which orbit white dwarfs (WDs) at a distance of one Solar radius remains unknown. Asteroids that survive the giant branch stellar phases beyond a few au are assumed to be dynamically thrust towards the WD and tidally disrupted within its Roche radius, generating extremely eccentric (e>0.98) rings. Here, we establish that WD radiation compresses and circularizes the orbits of super-micron to cm-sized ring constituents to entirely within the WD's Roche radius. We derive a closed algebraic formula which well-approximates the shrinking time as a function of WD cooling age, the physical properties of the star and the physical and orbital properties of the ring particles. The shrinking timescale increases with both particle size and cooling age, yielding age-dependent WD debris disc size distributions.
New observations indicate that ultrafaint dwarf galaxies (UFD) -- the least luminous systems bound by dark matter halos (<10^5 Lsun) -- may have formed before reionization. The extrapolated virial masses today are uncertain with estimates ranging from 10^8 Msun to 10^9 Msun. We show that the progenitor halo masses of UFDs can be as low as Mvir = 10^7 Msun. Under the right conditions, such a halo can survive the energy input of a supernova and its radiative progenitor. A clumpy medium is much less susceptible to both internal and external injections of energy. It is less prone to SN sweeping because the coupling efficiency of the explosive energy is much lower than for a diffuse ISM. With the aid of the 3D hydro/ionization code Fyris, we show that sufficient baryons are retained to form stars following a single supernova event in dark matter halos down to Mvir ~ 10^7 Msun with radiative cooling. The gas survives the SN explosion, is enriched with the abundance yields of the discrete events, and reaches surface densities where low mass stars can form. Our highest resolution simulations reveal why cooling is so effective in retaining gas compared to any other factor. In the early stages, the super-hot metal-enriched SN ejecta exhibit strong cooling, leading to much of the explosive energy being lost. Consistent with earlier work, the baryons do *not* survive in smooth or adiabatic models in the event of a supernova. The smallest galaxies carry signatures of the earliest epochs of star formation, which may distinguish a small primordial galaxy from one that was stripped down to its present size through tidal interaction. We discuss these results in the context of local UFDs and damped Ly-alpha systems (z~2) at very low metallicity ([Fe/H] ~ -3). We show that both classes of objects are consistent with primordial low-mass systems that have experienced only a few enrichment events.
Cold accretion is a primary growth mechanism of simulated galaxies, yet observational evidence of "cold flows" at redshifts where they should be most efficient ($z=2$-4) is scarce. In simulations, cold streams manifest as Lyman-limit absorption systems (LLSs) with low heavy-element abundances similar to those of the diffuse IGM. Here we report on an abundance survey of 17 H I-selected LLSs at $z=3.2$-4.4 which exhibit no metal absorption in SDSS spectra. Using medium-resolution spectra obtained at Magellan, we derive ionization-corrected metallicities (or limits) with a Markov-Chain Monte Carlo sampling that accounts for the large uncertainty in $N_{\rm HI}$ measurements typical of LLSs. The metal-poor LLS sample overlaps with the IGM in metallicity and is best described by a model where $71^{+13}_{-11}\%$ are drawn from the IGM chemical abundance distribution. These represent roughly half of all LLSs at these redshifts, suggesting that 28-40$\%$ of the general LLS population at $z\sim3.7$ could trace unprocessed gas. An ancillary sample of ten LLSs without any a priori metal-line selection is best fit with $48^{+14}_{-12}\%$ of metallicities drawn from the IGM. We compare these results with regions of a moving-mesh simulation; the simulation finds only half as many baryons in IGM-metallicity LLSs, and most of these lie beyond the virial radius of the nearest galaxy halo. A statistically significant fraction of all LLSs have low metallicity and therefore represent candidates for accreting gas; large-volume simulations can establish what fraction of these candidates actually lie near galaxies and the observational prospects for detecting the presumed hosts in emission.
SN HFF14Tom is a Type Ia Supernova (SN) discovered at z = 1.3457 +- 0.0001 behind the galaxy cluster Abell 2744 (z = 0.308). In a cosmology-independent analysis, we find that HFF14Tom is 0.77 +- 0.15 magnitudes brighter than unlensed Type Ia SNe at similar redshift, implying a lensing magnification of mu_obs = 2.03 +- 0.29. This observed magnification provides a rare opportunity for a direct empirical test of galaxy cluster lens models. Here we test 17 lens models, 13 of which were generated before the SN magnification was known, qualifying as pure "blind tests". The models are collectively fairly accurate: 8 of the models deliver median magnifications that are consistent with the measured mu to within 1-sigma. However, there is a subtle systematic bias: the significant disagreements all involve models overpredicting the magnification. We evaluate possible causes for this mild bias, and find no single physical or methodological explanation to account for it. We do find that model accuracy can be improved to some extent with stringent quality cuts on multiply-imaged systems, such as requiring that a large fraction have spectroscopic redshifts. In addition to testing model accuracies as we have done here, Type Ia SN magnifications could also be used as inputs for future lens models of Abell 2744 and other clusters, providing valuable constraints in regions where traditional strong- and weak-lensing information is unavailable.
(abridged) Methods: We derive maps of submillimeter dust optical depth and effective dust temperature from Herschel data that were calibrated against Planck. After calibration, we then fit a modified blackbody to the long-wavelength Herschel data, using the Planck-derived dust opacity spectral index beta, derived on scales of 30' (or ~1 pc). We use this model to make predictions of the submillimeter flux density at 850 micron, and we compare these in turn with APEX-Laboca observations. Results: A comparison of the submillimeter dust optical depth and near-infrared extinction data reveals evidence for an increased submillimeter dust opacity at high column densities, interpreted as an indication of grain growth in the inner parts of the core. Additionally, a comparison of the Herschel dust model and the Laboca data reveals that the frequency dependence of the submillimeter opacity, described by the spectral index beta, does not change. A single beta that is only slightly different from the Planck-derived value is sufficient to describe the data, beta=1.53+/-0.07. We apply a similar analysis to Barnard 68, a core with significantly lower column densities than FeSt 1-457, and we do not find evidence for grain growth but also a single beta. Conclusions: While we find evidence for grain growth from the dust opacity in FeSt 1-457, we find no evidence for significant variations in the dust opacity spectral index beta on scales 0.02<x<1 pc (or 36"<x<30'). The correction to the Planck-derived dust beta that we find in both cases is on the order of the measurement error, not including any systematic errors, and it would thus be reasonable to directly apply the dust beta from the Planck all-sky dust model. As a corollary, reliable effective temperature maps can be derived which would be otherwise affected by beta variations.
We present the open-source Python code pyMCZ that determines oxygen abundance and its distribution from strong emission lines in the standard metallicity scales, based on the original IDL code of Kewley & Dopita (2002) with updates from Kewley & Ellison (2008), and expanded to include more recently developed scales. The standard strong-line diagnostics have been used to estimate the oxygen abundance in the interstellar medium through various emission line ratios in many areas of astrophysics, including galaxy evolution and supernova host galaxy studies. We introduce a Python implementation of these methods that, through Monte Carlo (MC) sampling, better characterizes the statistical reddening-corrected oxygen abundance confidence region. Given line flux measurements and their uncertainties, our code produces synthetic distributions for the oxygen abundance in up to 13 metallicity scales simultaneously, as well as for E(B-V), and estimates their median values and their 66% confidence regions. In addition, we provide the option of outputting the full MC distributions, and their kernel density estimates. We test our code on emission line measurements from a sample of nearby supernova host galaxies ($z<0.15$) and compare our metallicity results with those from previous methods. We show that our metallicity estimates are consistent with previous methods but yield smaller uncertainties. We also offer visualization tools to assess the spread of the oxygen abundance in the different scales, as well as the shape of the estimated oxygen abundance distribution in each scale, and develop robust metrics for determining the appropriate MC sample size. The code is open access and open source and can be found at https://github.com/nyusngroup/pyMCZ
The widths, dispersion measures, dispersion indices and fluences of Fast Radio Bursts (FRB) impose coupled constraints that all models must satisfy. Observation of dispersion indices close to their low density limit of $-2$ sets a model-independent upper bound on the electron density and a lower bound on the size of any dispersive plasma cloud. The non-monotonic dependence of burst widths (after deconvolution of instrumental effects) on dispersion measure excludes the intergalactic medium as the location of scattering that broadens the FRB in time. Temporal broadening far greater than that of pulsars at similar high Galactic latitudes implies that scattering occurs close to the sources, where high densities and strong turbulence are plausible. FRB energetics are consistent with supergiant pulses from young, fast, high-field pulsars at cosmological distances. The distribution of FRB dispersion measures is inconsistent with expanding clouds (such as SNR). It excludes space-limited distributions (such as the local supercluster), but agrees with a homogeneous cosmological distribution with intergalactic dispersion. The FRB $\log{N}$--$\log{S}$ relation also indicates a cosmological distribution, aside from the anomalously bright Lorimer burst.
MUSE observations of NGC5813 reveal a complex structure in the velocity dispersion map, previously hinted by SAURON observations. The structure is reminiscent of velocity dispersion maps of galaxies comprising two counter-rotating discs, and may explain the existence of the kinematically distinct core (KDC). Further evidence for two counter-rotating components comes from the analysis of the higher moments of the stellar line-of-sight velocity distributions and fitting MUSE spectra with two separate Gaussian line-of-sight velocity distributions. The emission-line kinematics show evidence of being linked to the present cooling flows and the buoyant cavities seen in X-rays. We detect ionised gas in a nuclear disc-like structure, oriented like the KDC, which is, however, not directly related to the KDC. We build an axisymmetric Schwarzschild dynamical model, which shows that the MUSE kinematics can be reproduced well with two counter-rotating orbit families, characterised by relatively low angular momentum components, but clearly separated in integral phase space and with radially varying contributions. The model indicates that the counter-rotating components in NGC5813 are not thin discs, but dynamically hot structures. Our findings give further evidence that KDCs in massive galaxies should not necessarily be considered as structurally or dynamically decoupled regions, but as the outcomes of the mixing of different orbital families, where the balance in the distribution of mass of the orbital families is crucial. We discuss the formation of the KDC in NGC5813 within the framework of gas accretion, binary mergers and formation of turbulent thick discs from cold streams at high redshift.
We report contributions to cosmic infrared background (CIB) intensities originating from known galaxies, and their companions, at submillimeter wavelengths. Using the publicly-available UltraVISTA catalog, and maps at 250, 350, and 500 {\mu}m from Herschel/SPIRE, we perform a novel measurement that exploits the fact that correlated sources will bias stacked flux densities if the resolution of the image is poor; i.e., we intentionally smooth the image - in effect degrading the angular resolution - before stacking and summing intensities. By smoothing the maps we are capturing the contribution of faint (undetected in K_S ~ 23.4) sources that are physically associated with the detected sources. We find that the cumulative CIB increases with increased smoothing, reaching 9.82 +- 0.78, 5.77 +- 0.43, and 2.32 +- 0.19 nWm^-2/sr at 250, 350, and 500 {\mu}m at 300 arcsec full width half maximum. This corresponds to a fraction of the fiducial CIB of 0.94 +- 0.23, 1.07 +- 0.31, and 0.97 +- 0.26 at 250, 350, and 500 {\mu}m, where the uncertainties are dominated by those of the absolute CIB. We then propose, with a simple model combining parametric descriptions for stacked flux densities and stellar mass functions, that emission from galaxies with log(M/Msun) > 8.5 can account for the entire measured total intensities, and argue against contributions from extended, diffuse emission. Finally, we discuss prospects for future survey instruments to improve the estimates of the absolute CIB levels, and observe any potentially remaining emission at z > 4.
The numbers and types of evolved massive stars found in nearby galaxies provide an exacting test of stellar evolution models. Because of their proximity and rich massive star populations, the Magellanic Clouds have long served as the linchpins for such studies. Yet the continued accidental discoveries of Wolf-Rayet (WR) stars in these systems demonstrate that our knowledge is not as complete as usually assumed. Therefore, we undertook a multi-year survey for WRs in the Magellanic Clouds. Our results from our first year (reported previously) confirmed nine new LMC WRs. Of these, six were of a type never before recognized, with WN3-type emission combined with O3-type absorption features. Yet these stars are 2-3 magnitudes too faint to be WN3+O3 V binaries. Here we report on the second year of our survey, including the discovery of four more WRs, two of which are also WN3/O3s, plus two "slash" WRs. This brings the total of LMC WRs known to 152, 13 (8.2%) of which were found by our survey, which is now 60% complete. We find that the spatial distribution of the WN3/O3s are similar to that of other WRs in the LMC, suggesting that they are descended from the same progenitors. We call attention to the fact that five of the 12 known SMC WRs may in fact be similar WN3/O3s rather than the binaries they have often assumed to be. We also discuss our other discoveries: a newly found Onfp-type star, and a peculiar emission-line object. Finally, we consider the completeness limits of our survey.
We present the first cosmological galaxy evolved using the modern smoothed particle hydrodynamics (SPH) code GASOLINE2 with superbubble feedback. We show that superbubble-driven galactic outflows powered by Type II supernovae alone can produce $\rm{L^*}$ galaxies with flat rotation curves with circular velocities $\sim 200\; \rm{km/s}$, low bulge-to-disc ratios, and stellar mass fractions that match observed values from high redshift to the present. These features are made possible by the high mass loadings generated by the evaporative growth of superbubbles. Outflows are driven extremely effectively at high redshift, expelling gas at early times and preventing overproduction of stars before $z=2$. Centrally concentrated gas in previous simulations has often lead to unrealistically high bulge to total ratios and strongly peaked rotation curves. We show that supernova-powered superbubbles alone can produce galaxies that agree well with observed properties without the need for additional feedback mechanisms or increased feedback energy. We present additional results arising from properly modelled hot feedback.
In this paper we show a plausible mechanism that could lead to the formation
of the Dark Lanes in Lunar Swirls, and the electromagnetic shielding of the
lunar surface that results in the preservation of the white colour of the lunar
regolith.
We present the results of a fully self-consistent 2 and 3 dimensional
particle-in-cell simulations of mini-magnetospheres that form above the lunar
surface and show that they are consistent with the formation of `lunar swirls'
such as the archetypal formation Reiner Gamma. The simulations show how the
microphysics of the deflection/shielding of plasma operates from a
kinetic-scale cavity, and show that this interaction leads to a footprint with
sharp features that could be the mechanism behind the generation of `dark
lanes'. The physics of mini-magnetospheres is described and shown to be
controlled by space-charge fields arising due to the magnetized electrons and
unmagnetized ions. A comparison between model and observation is shown for a
number of key plasma parameters.
We investigate how galaxies in VIPERS (the VIMOS Public Extragalactic Redshift Survey) inhabit the cosmological density field by examining the correlations across the observable parameter space of galaxy properties and clustering strength. The high-dimensional analysis is made manageable by the use of group-finding and regression tools. We find that the major trends in galaxy properties can be explained by a single parameter related to stellar mass. After subtracting this trend, residual correlations remain between galaxy properties and the local environment pointing to complex formation dependencies. As a specific application of this work we build subsamples of galaxies with specific clustering properties for use in cosmological tests.
Aims. Using the VIMOS Public Extragalactic Redshift Survey (VIPERS) we aim to jointly estimate the key parameters that describe the galaxy density field and its spatial correlations in redshift space. Methods. We use the Bayesian formalism to jointly reconstruct the redshift-space galaxy density field, power spectrum, galaxy bias and galaxy luminosity function given the observations and survey selection function. The high-dimensional posterior distribution is explored using the Wiener filter within a Gibbs sampler. We validate the analysis using simulated catalogues and apply it to VIPERS data taking into consideration the inhomogeneous selection function. Results. We present joint constraints on the anisotropic power spectrum as well as the bias and number density of red and blue galaxy classes in luminosity and redshift bins as well as the measurement covariances of these quantities. We find that the inferred galaxy bias and number density parameters are strongly correlated although these are only weakly correlated with the galaxy power spectrum. The power spectrum and redshift-space distortion parameters are in agreement with previous VIPERS results with the value of the growth rate $f\sigma_8 = 0.38$ with 18% uncertainty at redshift 0.7.
The influence of the transient thermal effects on the partition of the energy of selfrecoils in germanium and silicon into energy eventually given to electrons and to atomic recoils respectively is studied. The transient effects are treated in the frame of the thermal spike model, which considers the electronic and atomic subsystems coupled through the electron-phonon interaction. For low energies of selfrecoils, we show that the corrections to the energy partition curves due to the energy exchange during the transient processes modify the Lindhard predictions. These effects depend on the initial temperature of the target material, as the energies exchanged between electronic and lattice subsystems have different signs for temperatures lower and higher than about 15 K. More of the experimental data reported in the literature support the model.
Observations of comets and asteroids show that the Solar Nebula that spawned our planetary system was rich in water and organic molecules. Bombardment brought these organics to the young Earth's surface, seeding its early chemistry. Unlike asteroids, comets preserve a nearly pristine record of the Solar Nebula composition. The presence of cyanides in comets, including 0.01% of methyl cyanide (CH3CN) with respect to water, is of special interest because of the importance of C-N bonds for abiotic amino acid synthesis. Comet-like compositions of simple and complex volatiles are found in protostars, and can be readily explained by a combination of gas-phase chemistry to form e.g. HCN and an active ice-phase chemistry on grain surfaces that advances complexity[3]. Simple volatiles, including water and HCN, have been detected previously in Solar Nebula analogues - protoplanetary disks around young stars - indicating that they survive disk formation or are reformed in situ. It has been hitherto unclear whether the same holds for more complex organic molecules outside of the Solar Nebula, since recent observations show a dramatic change in the chemistry at the boundary between nascent envelopes and young disks due to accretion shocks[8]. Here we report the detection of CH3CN (and HCN and HC3N) in the protoplanetary disk around the young star MWC 480. We find abundance ratios of these N-bearing organics in the gas-phase similar to comets, which suggests an even higher relative abundance of complex cyanides in the disk ice. This implies that complex organics accompany simpler volatiles in protoplanetary disks, and that the rich organic chemistry of the Solar Nebula was not unique.
Recently, Planck measured a value of the cosmic microwave background (CMB) optical depth due to electron scattering of $\tau=0.066 \pm 0.016$. This is lower than previous measurements from WMAP and is consistent with a modest extrapolation of the ionising emissivity of known galaxies to fainter sources. Here we show that this leaves essentially no room for an early partial reionisation of the intergalactic medium (IGM) by high-redshift Population III (Pop III) stars, expected to have formed in low-mass minihaloes. We perform semi-analytic calculations of reionisation to quantify the resulting constraints. Our model includes the contribution from Pop II stars in atomic cooling haloes, calibrated with high-redshift galaxy observations, as well as the contribution from minihaloes with a self-consistent treatment of Lyman-Werner (LW) feedback. We find that without LW feedback (and assuming a minihalo escape fraction of 0.5) the star formation efficiency of Pop III stars cannot be greater than $\sim{\rm a~few}\times 10^{-4}$, without violating the constraints set by Planck data. This excludes massive Pop III star formation in typical $10^6 M_\odot$ minihaloes. Including LW feedback alleviates this tension, allowing Pop III stars to form early on before they are quenched by feedback. We also perform a simple estimate of the possible impact on reionisation of X-rays produced by accretion onto black hole remnants of Pop III stars. We find that unless the accretion duty cycle is very low ($\lesssim 0.01$), this could lead to an optical depth inconsistent with Planck.
We present an open-source Thermochemical Equilibrium Abundances (TEA) code that calculates the abundances of gaseous molecular species. The code is based on the methodology of White et al. (1958) and Eriksson (1971). It applies Gibbs free-energy minimization using an iterative, Lagrangian optimization scheme. Given elemental abundances, TEA calculates molecular abundances for a particular temperature and pressure or a list of temperature-pressure pairs. We tested the code against the method of Burrows & Sharp (1999), the free thermochemical equilibrium code CEA (Chemical Equilibrium with Applications), and the example given by White et al. (1958). Using their thermodynamic data, TEA reproduces their final abundances, but with higher precision. We also applied the TEA abundance calculations to models of several hot-Jupiter exoplanets, producing expected results. TEA is written in Python in a modular format. There is a start guide, a user manual, and a code document in addition to this theory paper. TEA is available under a reproducible-research, open-source license via https://github.com/dzesmin/TEA.
The highest brightness temperature ever observed are from "nanoshots" from the Crab pulsar which we argue could be the signature of bursts of vacuum $e^{\pm}$ pair production. If so this would be the first time the astronomical Schwinger effect has been observed. These "Schwinger sparks" would be an intermittent but extremely powerful, $\sim 10^3 L_{\astrosun}$, 10 PeV $e^{\pm}$ accelerator in the heart of the Crab. These nanosecond duration sparks are generated in a volume less than $1 m^3$ and the existence of such sparks has implications for the small scale structure of the magnetic field of young pulsars such as the Crab. This mechanism may also play a role in producing other enigmatic bright short radio transients such as fast radio bursts.
We investigate the performance of grid-based techniques in estimating the age of stars in detached eclipsing binary systems. We evaluate the precision of the estimates due to the uncertainty in the observational constraints, and the systematic bias caused by the uncertainty in convective core overshooting, element diffusion, mixing-length value, and initial helium content. We adopted the SCEPtER grid, which includes stars with mass in the range [0.8; 1.6] Msun and evolutionary stages from the ZAMS to the central hydrogen depletion. Age estimates have been obtained by a generalisation of the technique described in our previous work. We showed that the typical 1 sigma random error in age estimates - due to the uncertainty on the observational constraints - is about +- 7%, which is nearly independent of the masses of the two stars. However, such an error strongly depends on the evolutionary phase and becomes larger and asymmetric for stars near the ZAMS where it ranges from about +90% to -25%. The systematic bias due to the including mild and strong convective core overshooting is about 50% and 120% of the error due to observational uncertainties. A variation of +- 1 in the helium-to-metal enrichment ratio accounts for about +- 150% of the random error. The neglect of microscopic diffusion accounts for a bias of about 60% of the random error. We also introduced a statistical test of the expected difference in the recovered age of two coeval stars in a binary system. We find that random fluctuations within the current observational uncertainties can lead genuine coeval binary components to appear to be non-coeval with a difference in age as high as 60%.
The FITS (Flexible Image Transport System) data format has been the de facto data format for astronomy-related data products since its inception in the late 1970s. While the FITS file format is widely supported, it lacks many of the features of more modern data serialization, such as the Hierarchical Data Format (HDF5). The HDF5 file format offers considerable advantages over FITS, such as improved I/O speed and compression, but has yet to gain widespread adoption within astronomy. One of the major holdbacks is that HDF5 is not well supported by data reduction software packages and image viewers. Here, we present a comparison of FITS and HDF5 as a format for storage of astronomy datasets. We show that the underlying data model of FITS can be ported to HDF5 in a straightforward manner, and that by doing so the advantages of the HDF5 file format can be leveraged immediately. In addition, we present a software tool, fits2hdf, for converting between FITS and a new `HDFITS' format, where data are stored in HDF5 in a FITS-like manner. We show that HDFITS allows faster reading of data (up to 100x of FITS in some use cases), and improved compression (higher compression ratios and higher throughput). Finally, we show that by only changing the import lines in Python-based FITS utilities, HDFITS formatted data can be presented transparently as an in-memory FITS equivalent.
Source position time series produced by International VLBI Service for Geodesy and astrometry (IVS) Analysis Centers were analyzed. These series was computed using different software and analysis strategy. Comparison of this series showed that they have considerably different scatter and systematic behavior. Based on the inspection of all the series, new sources were identified as sources with irregular (non-random) position variations. Two statistics used to estimate the noise level in the time series, namely RMS and ADEV were compared.
We introduce Copernicus Complexio (COCO), a high-resolution cosmological N-body simulation of structure formation in the $\Lambda$cdm model. COCO follows an approximately spherical region of radius $\sim 17.4h^{-1}$Mpc, in which the particle mass is $1.1 \times 10^5h^{-1}M_{\odot}$, embedded in a much larger periodic cube followed at lower resolution. Thus, the resolution in the inner volume is 60 times better than in the Millennium-II simulation. COCO gives the dark matter halo mass function over eight orders of magnitude in halo mass; it forms $\sim 60$ halos of galactic size, each resolved with about 10 million particles. The concentration-mass relation of COCO halos deviates from a single power law for masses $M_{200}<$a few$\times 10^{8}h^{-1}M_{\odot}$, where it flattens in agreement with results by Sanchez-Conde et al. We confirm the power-law character of the subhalo mass function, $\overline N(>\mu)\propto\mu^{-s}$, down to a reduced subhalo mass $M_{sub}/M_{200}\equiv\mu=10^{-6}$, with a best-fit power-law index, $s=0.94$, for hosts of mass $\langle M_{200}\rangle=10^12h^{-1}M_{\odot}$, increasing very slowly with host mass. The host-mass invariance of the reduced maximum circular velocity function of subhaloes, $\nu\equiv V_{max}/V_{200}$, hinted at in previous simulations, is clearly demonstrated over five orders of magnitude in host mass. Similarly, we find that the average, normalized radial distribution of subhaloes is approximately universal (i.e. independent of subhalo mass), as previously suggested by the Aquarius simulations of individual halos. Finally, we find that at fixed physical subhalo size, subhaloes in lower mass hosts typically have lower central densities than those in higher mass hosts.
Aims. We present an X-ray study of the supernova remnant SNR J0533-7202 in the Large Magellanic Cloud (LMC) and determine its physical characteristics based on its X-ray emission. Methods. We observed SNR J0533-7202 with XMM-Newton (flare-filtered exposure times of 18 ks EPIC-pn and 31 ks EPIC-MOS1/MOS2). We produced X-ray images of the SNR, performed an X-ray spectral analysis, and compared the results to multi-wavelength studies. Results. The distribution of X-ray emission is highly non-uniform, with the south-west region brighter than the north-east. The X-ray emission is correlated with the radio emission from the remnant. We determine that this morphology is likely due to the SNR expanding into a non-uniform ambient medium and not an absorption effect. We estimate the size to be 53.9 (\pm 3.4) x 43.6 (\pm 3.4) pc, with the major axis rotated ~64 degrees east of north. We find no spectral signatures of ejecta and infer that the X-ray plasma is dominated by swept-up interstellar medium. Using the spectral fit results and the Sedov self-similar solution, we estimate an age of ~17-27 kyr, with an initial explosion energy of (0.09-0.83) x 10^51 erg. We detected an X-ray source located near the centre of the remnant, namely XMMU J053348.2-720233. The source type could not be conclusively determined due to the lack of a multi-wavelength counterpart and low X-ray counts. We find that it is likely either a background active galactic nucleus or a low-mass X-ray binary in the LMC. Conclusions. We detected bright thermal X-ray emission from SNR J0533-7202 and determined that the remnant is in the Sedov phase of its evolution. The lack of ejecta emission prohibits us from typing the remnant with the X-ray data. Therefore, the likely Type Ia classification based on the local stellar population and star formation history reported in the literature cannot be improved upon.
The diagram of indices of coronal and chromospheric activity allowed us to reveal stars where solar-type activity appears and regular cycles are forming. Using new consideration of a relation between coronal activity and the rotation rate, together with new data on the ages of open clusters, we estimate the age of the young Sun corresponding to the epoch of formation of its cycle. The properties of the activity of this young Sun, with an age slightly older than one billion years, are briefly discussed. An analysis of available data on the long-term regular variability of late-type stars leads to the conclusion that duration of a cycle associated with solar-type activity increases with the deceleration of the stellar rotation; i.e., with age. New data on the magnetic fields of comparatively young G stars and changes in the role of the large-scale and the local magnetic fields in the formation of the activity of the young Sun are discussed. Studies in this area aim to provide observational tests aimed at identifying the conditions for the formation of cyclic activity on stars in the lower part of the main sequence, and test some results of dynamo theory.
We report the discovery of a new totally-eclipsing binary (RA=06:40:29.11; Dec=+38:56:52.2; J=2000.0; Rmax=17.2 mag) with an sdO primary and a strongly irradiated red dwarf companion. It has an orbital period of Porb=0.187284394(11) d and an optical eclipse depth in excess of 5 magnitudes. We obtained two low-resolution classification spectra with GTC/OSIRIS and ten medium-resolution spectra with WHT/ISIS to constrain the properties of the binary members. The spectra are dominated by H Balmer and He II absorption lines from the sdO star, and phase-dependent emission lines from the irradiated companion. A combined spectroscopic and light curve analysis implies a hot subdwarf temperature of Teff(spec) = 55 000 +/- 3000K, surface gravity of log g(phot) = 6.2 +/- 0.04 (cgs) and a He abundance of log(nHe/nH) = -2.24 +/- 0.40. The hot sdO star irradiates the red-dwarf companion, heating its substellar point to about 22 500K. Surface parameters for the companion are difficult to constrain from the currently available data: the most remarkable features are the strong H Balmer and C II-III lines in emission. Radial velocity estimates are consistent with the sdO+dM classification. The photometric data do not show any indication of sdO pulsations with amplitudes greater than 7mmag, and Halpha-filter images do not provide evidence of the presence of a planetary nebula associated with the sdO star.
PEPSI is the bench-mounted, two-arm, fibre-fed and stabilized Potsdam Echelle Polarimetric and Spectroscopic Instrument for the 2x8.4 m Large Binocular Telescope (LBT). Three spectral resolutions of either 43 000, 120 000 or 270 000 can cover the entire optical/red wavelength range from 383 to 907 nm in three exposures. Two 10.3kx10.3k CCDs with 9-{\mu}m pixels and peak quantum efficiencies of 96 % record a total of 92 echelle orders. We introduce a new variant of a wave-guide image slicer with 3, 5, and 7 slices and peak efficiencies between 96 %. A total of six cross dispersers cover the six wavelength settings of the spectrograph, two of them always simultaneously. These are made of a VPH-grating sandwiched by two prisms. The peak efficiency of the system, including the telescope, is 15% at 650 nm, and still 11% and 10% at 390 nm and 900 nm, respectively. In combination with the 110 m2 light-collecting capability of the LBT, we expect a limiting magnitude of 20th mag in V in the low-resolution mode. The R=120 000 mode can also be used with two, dual-beam Stokes IQUV polarimeters. The 270 000-mode is made possible with the 7-slice image slicer and a 100- {\mu}m fibre through a projected sky aperture of 0.74", comparable to the median seeing of the LBT site. The 43000-mode with 12-pixel sampling per resolution element is our bad seeing or faint-object mode. Any of the three resolution modes can either be used with sky fibers for simultaneous sky exposures or with light from a stabilized Fabry-Perot etalon for ultra-precise radial velocities. CCD-image processing is performed with the dedicated data-reduction and analysis package PEPSI-S4S. A solar feed makes use of PEPSI during day time and a 500-m feed from the 1.8 m VATT can be used when the LBT is busy otherwise. In this paper, we present the basic instrument design, its realization, and its characteristics.
We have developed a new technique called Direct Shear Mapping (DSM) to measure gravitational lensing shear directly from observations of a single background source. The technique assumes the velocity map of an un-lensed, stably-rotating galaxy will be rotationally symmetric. Lensing distorts the velocity map making it asymmetric. The degree of lensing can be inferred by determining the transformation required to restore axisymmetry. This technique is in contrast to traditional weak lensing methods, which require averaging an ensemble of background galaxy ellipticity measurements, to obtain a single shear measurement. We have tested the efficacy of our fitting algorithm with a suite of systematic tests on simulated data. We demonstrate that we are in principle able to measure shears as small as 0.01. In practice, we have fitted for the shear in very low redshift (and hence un-lensed) velocity maps, and have obtained null result with an error of $\pm 0.01$. This high sensitivity results from analysing spatially resolved spectroscopic images (i.e. 3D data cubes), including not just shape information (as in traditional weak lensing measurements) but velocity information as well. Spirals and rotating ellipticals are ideal targets for this new technique. Data from any large IFU or radio telescope is suitable, or indeed any instrument with spatially resolved spectroscopy such as SAMI, ALMA, HETDEX and SKA.
Absolute ages of young stars are important for many issues in pre-main sequence stellar and circumstellar evolution but are long recognized as difficult to derive and calibrate. In this paper, we use literature spectral types and photometry to construct empirical isochrones in HR diagrams for low-mass stars and brown dwarfs in the eta Cha, epsilon Cha, and TW Hya Associations and the beta Pic and Tuc-Hor Moving Groups. A successful theory of pre-main sequence evolution should match the shapes of the stellar loci for these groups of young stars. However, when comparing the combined empirical isochrones to isochrones predicted from evolutionary models, discrepancies lead to a spectral type (mass) dependence in stellar age estimates. Improved prescriptions for convection and boundary conditions in the latest models of pre-main sequence models lead to a significantly improved correspondence between empirical and model isochrones, with small offsets at low temperatures that may be explained by observational uncertainties or by model limitations. Independent of model predictions, linear fits to combined stellar loci of these regions provide a simple empirical method to order clusters by luminosity with a reduced dependence on spectral type. Age estimates calculated from various sets of modern models that reproduce Li depletion boundary ages of the beta Pic Moving Group also imply a ~4 Myr age for the low mass members of the Upper Sco OB Association, which is younger than the 11 Myr age that has been recently estimated for intermediate mass members.
The ubiquitousness of solar inter-network horizontal magnetic field has been revealed by the space-borne observations with high spatial resolution and polarization sensitivity. However, no consensus has been achieved on the origin of the horizontal field among solar physicists. For a better understanding, in this study we analyze the cyclic variation of inter-network horizontal field by using the spectro-polarimeter observations provided by Solar Optical Telescope on board Hinode, covering the interval from 2008 April to 2015 February. The method of wavelength integration is adopted to achieve a high signal-to-noise ratio. It is found that from 2008 to 2015 the inter-network horizontal field does not vary when solar activity increases, and the average flux density of inter-network horizontal field is 87$\pm$1 G, In addition, the imbalance between horizontal and vertical field also keeps invariant within the scope of deviation, i.e., 8.7$\pm$0.5, from the solar minimum to maximum of solar cycle 24. This result confirms that the inter-network horizontal field is independent of sunspot cycle. The revelation favors the idea that a local dynamo is creating and maintaining the solar inter-network horizontal field.
Solar inter-network magnetic field is the weakest component of solar magnetism, but contributes most of the solar surface magnetic flux. The study on its origin has been constrained by the inadequate tempo-spatial resolution and sensitivity of polarization observations. With dramatic advances in spatial resolution and detective sensitivity, solar spectro-polarimetry provided by the Solar Optical Telescope aboard Hinode in an interval from solar minimum to maximum of cycle 24 opens an unprecedented opportunity to study the cyclic behavior of solar inter-network magnetic field. More than 1000 Hinode magnetograms observed from 2007 January to 2014 August are selected in the study. It has been found that there is a very slight correlation between sunspot number and magnetic field at the inter-network flux spectrum. From solar minimum to maximum of cycle 24, the flux density of solar inter-network field is invariant, which is 10$\pm1$ G. The observations suggest that the inter-network magnetic field does not arise from the flux diffusion or flux recycling of solar active regions, thereby indicating the existence of a locally small-scale dynamo. Combining the full-disk magnetograms observed by SOHO/MDI and SDO/HMI in the same period, we find that the area ratio of the inter-network region to the full-disk of the Sun apparently decreases from solar minimum to maximum but always exceeds 60\% even though in the phase of solar maximum.
Induced Compton scattering (ICS) is an interaction between intense electro-magnetic radiations and plasmas, where ICS transfers the energy from photons to plasmas. Although ICS is important for laser plasma interactions in laboratory experiments and for radio emission from pulsars propagating in pulsar wind plasmas, the detail of photon cooling process has not been understood. The problem is that, when ICS dominates, evolution of photon spectra is described as a nonlinear convection equation, which makes photon spectra to be multi-valued. Here, we propose a new approach to treat evolution of photon spectra affected by ICS. Starting from the higher-order Kompaneets equation, we find a new equation that resolves the unphysical behavior of photon spectra. In addition, we find the steady-state analytic solution, which is linearly stable. We also successfully simulate the evolution of photon spectra without artificial viscosity. We find that photons rapidly lose their energy by ICS with continuously forming solitary structures in frequency-space. The solitary structures have the logarithmically same width characterized by an electron temperature. The energy transfer from photons to plasma is more effective for broader spectrum of photons such as expected in astrophysical situations.
We explore the degeneracy and discreteness problems in the standard cosmological model ({\Lambda}CDM). We use the Observational Hubble Data (OHD) and the type Ia supernova (SNe Ia) data to study this issue. In order to describe the discreteness in fitting of data, we define a factor G to test the influence from each single data point and analyze the goodness of G. Our results indicate that a higher absolute value of G shows a better capability of distinguishing models, which means the parameters are restricted into smaller confidence intervals with a larger figure of merit evaluation. Consequently, we claim that the factor G is an effective way in model differentiation when using different models to fit the observational data.
In quantum theory of gravity, we expect the Lorentz Invariance Violation (LIV) and the modification of the dispersion relation between energy and momentum for photons. The effect of the energy-dependent velocity due to the modified dispersion relation for photons was studied in the standard cosmological context by using a sample of Gamma Ray Bursts (GRBs). In this paper we mainly discuss the possible LIV effect by using different cosmological models for the accelerating universe. Due to the degeneracies among model parameters, the GRBs' time delay data are combined with the cosmic microwave background data from the Planck first year release, the baryon acoustic oscillation data at six different redshifts, as well as Union2 type Ia supernovae data, to constrain both the model parameters and the LIV effect. We find no evidence of LIV.
Symbiotic stars are interacting binary systems with the longest orbital periods. They are typically formed by a white dwarf, a red giant and a nebula. These objects are natural astrophysical laboratories for studying the evolution of binaries. Current estimates of the population of Milky Way symbiotic stars vary from 3000 up to 400000. However, the current census is less than 300. The Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) survey can obtain hundreds of thousands of stellar spectra per year, providing a good opportunity to search for new symbiotic stars. In this work we detect 4 of such binaries among 4,147,802 spectra released by the LAMOST, of which two are new identifications. The first is LAMOST J12280490-014825.7, considered to be an S-type halo symbiotic star. The second is LAMOST J202629.80+423652.0, a D-type symbiotic star.
A review of the Annual Review of Astronomy and Astrophysics Volume 52, 2014 (Ed. S.M. Faber, Ewine van Dishoeck, and John Kormendy) is given, with a perspective of understanding the current trends in Astronomy and Astrophysics. The impact of high volume data, high connectivity, and fast computations is clearly seen in the various research areas discussed in this volume. This has provided unprecedented development in the understanding of various astrophysical phenomena. At the same time, some negative trends like commodification of science, ignoring dissenting views are also evident.
Context. Observations suggest that exoplanets such as HD 189733b form clouds in their atmospheres which have a strong feedback onto their thermodynamical and chemical structure, and overall appearance. Aims. Inspired by mineral cloud modelling efforts for Brown Dwarf atmospheres, we present the first spatially varying kinetic cloud model structures for HD 189733b. Methods. We apply a 2-model approach using results from a 3D global radiation-hydrodynamic simulation of the atmosphere as input for a detailed, kinetic cloud formation model. Sampling the 3D global atmosphere structure with 1D trajectories allows us to model the spatially varying cloud structure on HD 189733b. The resulting cloud properties enable the calculation of the scattering and absorption properties of the clouds. Results. We present local and global cloud structure and property maps for HD 189733b. The calculated cloud properties show variations in composition, size and number density of cloud particles which are strongest between the dayside and nightside. Cloud particles are mainly composed of a mix of materials with silicates being the main component. Cloud properties, and hence the local gas composition, change dramatically where temperature inversions occur locally. The cloud opacity is dominated by absorption in the upper atmosphere and scattering at higher pressures in the model. The calculated 8{\mu}m single scattering Albedo of the cloud particles are consistent with Spitzer bright regions. The cloud particles scattering properties suggest that they would sparkle/reflect a midnight blue colour at optical wavelengths.
We have performed a new abundance analysis of Carina Red Giant (RG) stars from spectroscopic data collected with UVES (high resolution) and FLAMES/GIRAFFE (high and medium resolution) at ESO/VLT. The former sample includes 44 RGs, while the latter consists of 65 (high) and ~800 (medium resolution) RGs, covering a significant fraction of the galaxy's RG branch (RGB), and red clump stars. To improve the abundance analysis at the faint magnitude limit, the FLAMES/GIRAFFE data were divided into ten surface gravity and effective temperature bins. The spectra of the stars belonging to the same gravity/temperature bin were stacked. This approach allowed us to increase by at least a factor of five the signal-to-noise ratio in the faint limit (V>20.5mag). We took advantage of the new photometry index cU,B,I introduced by Monelli et al. (2014), as an age and probably a metallicity indicator, to split stars along the RGB. These two stellar populations display distinct [Fe/H] and [Mg/H] distributions: their mean Fe abundances are -2.15$\pm$0.06dex (sig=0.28), and -1.75$\pm$0.03dex (sig=0.21), respectively. The two iron distributions differ at the 75% level. This supports preliminary results by Lemasle et al. (2012) and by Monelli et al. (2014). Moreover, we found that the old and intermediate-age stellar populations have mean [Mg/H] abundances of -1.91$\pm$0.05dex (sig=0.22) and -1.35$\pm$0.03dex (sig=0.22); these differ at the 83% level. Carina's {\alpha}-element abundances agree, within 1sigma, with similar abundances for field Halo stars and for cluster (Galactic, Magellanic) stars. The same outcome applies to nearby dwarf spheroidals and ultra-faint dwarf galaxies, in the iron range covered by Carina stars. Finally, we found evidence of a clear correlation between Na and O abundances, thus suggesting that Carina's chemical enrichment history is quite different than in the globular clusters.
We present the analytical solutions for the evolution of matter density perturbations, for a model with a constant dark energy equation of state $w$ but when the effects of the dark energy perturbations are properly taken into account. We consider two cases, the first when the sound speed of the perturbations is zero $c_s^2=0$ and the general case $0<c_s^2 \leq 1$. In the first case our solution is exact, while in the second case we found an approximate solution which works to better than $0.3\%$ accuracy for $k>10 H_0$ or equivalently $k/h>0.0033 \textrm{Mpc}^{-1}$. We also estimate the corrections to the growth index $\gamma(z)$, commonly used to parametrize the growth-rate. We find that these corrections due to the DE perturbations affect the growth index $\gamma$ at the $3\%$ level. We also compare our new expressions for the growth index with other expressions already present in the literature and we find that the latter are less accurate than the ones we propose here. Therefore, our analytical calculations are necessary as the theoretical predictions for the fundamental parameters to be constrained by the upcoming surveys need to be as accurate as possible, especially since we are entering in the precise cosmology era where parameters will be measured to the percent level.
The Mid-IR colors ($F_{8}/F_{24}$) of galaxies together with their IR-UV luminosity correlations can be used to get some insight into the relative abundance of the different dust grain populations present in them. The ELAIS-N1 field contains thousands of galaxies which do not have optical spectra but have been observed in the Mid-IR by {\it Spitzer} and UV by {\it GALEX} making it ideal for these studies. As part of this work we have selected a sample of galaxies from the ELAIS-N1 field which have photometric observations in the MIR and UV as well as photometric redshifts from the SDSS database. We put the constraint that the redshifts are $\le$ 0.1, thereby giving us a total of 309 galaxies. We find that the majority of the galaxies in the sample are PAH dominated due to their high MIR flux ratio. We also find a reasonable correlation between the Mid-IR and the UV luminosities out of which the Mid-IR emission from PAHs at 8 $\mu$m is marginally better correlated than the 24 $\mu$m VSG emission with the UV luminosities. However, if we divide the sample based on their $F_{8}/F_{24}$ ratios which is also an indicator of metallicity, the MIR-UV correlation seems to increase with the $F_{8}/F_{24}$ ratio. But the MIR-UV correlations are not very different for the PAHs and the VSG population within the individual metallicity groups.
Thanks to their thermal emission, Tidal Disruption Events (TDEs) were detected regularly in the soft X-rays and sometimes in the optical. Only few of them have been detected at hard X-rays: two are high redshift beamed events, one occurred at the core of a nearby galaxy and the last one is of a different nature, involving a compact object in the Milky Way. The aims of this work are to obtain a first sample of hard X-ray selected un-beamed TDEs, to determine their frequency and to probe if TDEs are usually or exceptionally emitting at hard X-rays. We performed extensive search for hard X-ray flares at the positions of over 53000 galaxies up to a distance of 100 Mpc in the Swift BAT archive. Light curves were extracted and parametrized. The quiescent hard X-ray emission was used to exclude persistently active galactic nuclei. Significant flares from non-active galaxies were derived and checked for possible contamination. We found a sample of nine TDE candidates, which translates in a rate of $2 \times 10^{-5}$ galaxy$^{-1}$ yr$^{-1}$ above the BAT detection limit. This rate is consistent with these observed by XMM-Newton at soft X-rays and in the optical from SDSS observations, and expected from simulations. We conclude that hard X-ray emission should be ubiquitous in un-beamed TDEs and that electrons should be accelerated in their accretion flow.
Gamma-ray burst sources are distributed with a high level of isotropy, which is compatible with either a cosmological origin or an extended Galactic halo origin. The brightness distribution is another indicator used to characterize the spatial distribution in distance. In this paper the author discusses detailed fits of the BATSE gamma-ray burst peak-flux distributions with Friedmann models taking into account possible density evolution and standard candle luminosity functions. A chi-square analysis is used to estimate the goodness of the fits and the author derives the significance level of limits on the density evolution and luminosity function parameters. Cosmological models provide a good fit over a range of parameter space which is physically reasonable
We present an innovative method called FilExSeC (Filaments Extraction, Selection and Classification), a data mining tool developed to investigate the possibility to refine and optimize the shape reconstruction of filamentary structures detected with a consolidated method based on the flux derivative analysis, through the column-density maps computed from Herschel infrared Galactic Plane Survey (Hi-GAL) observations of the Galactic plane. The present methodology is based on a feature extraction module followed by a machine learning model (Random Forest) dedicated to select features and to classify the pixels of the input images. From tests on both simulations and real observations the method appears reliable and robust with respect to the variability of shape and distribution of filaments. In the cases of highly defined filament structures, the presented method is able to bridge the gaps among the detected fragments, thus improving their shape reconstruction. From a preliminary "a posteriori" analysis of derived filament physical parameters, the method appears potentially able to add a sufficient contribution to complete and refine the filament reconstruction.
The protoMIRAX hard X-ray imaging telescope is a balloon-borne experiment developed as a pathfinder for the MIRAX satellite mission. The experiment consists essentially in a coded-aperture hard X-ray (30-200 keV) imager with a square array (13$\times$13) of 2mm-thick planar CZT detectors with a total area of 169 cm$^2$. The total, fully-coded field-of-view is $21^{\circ}\times 21^{\circ}$ and the angular resolution is 1$^{\circ}$43'. In this paper we describe the protoMIRAX instrument and all the subsystems of its balloon gondola, and we show simulated results of the instrument performance. The main objective of protoMIRAX is to carry out imaging spectroscopy of selected bright sources to demonstrate the performance of a prototype of the MIRAX hard X-ray imager. Detailed background and imaging simulations have been performed for protoMIRAX balloon flights. The 3$\sigma$ sensitivity for the 30-200 keV range is ~1.9 $\times$ 10$^{-5}$ photons cm$^{-2}$ s$^{-1}$ for an integration time of 8 hs at an atmospheric depth of 2.7 g cm$^{-2}$ and an average zenith angle of 30$^{\circ}$. We have developed an attitude control system for the balloon gondola and new data handling and ground systems that also include prototypes for the MIRAX satellite. We present the results of Monte Carlo simulations of the camera response at balloon altitudes, showing the expected background level and the detailed sensitivity of protoMIRAX. We also present the results of imaging simulations of the Crab region. The results show that protoMIRAX is capable of making spectral and imaging observations of bright hard X-ray source fields. Furthermore, the balloon observations will carry out very important tests and demonstrations of MIRAX hardware and software in a near space environment.
The small-scale magnetic field is ubiquitous at the solar surface---even at high latitudes. From observations we know that this field is uncorrelated (or perhaps even weakly anticorrelated) with the global sunspot cycle. Our aim is to explore the origin, and particularly the cycle dependence of this field using three-dimensional dynamo simulations. We use a simple model of a turbulent dynamo in a shearing box driven by helically forced turbulence. Depending on the dynamo parameters, large-scale (global) and small-scale (local) dynamos can be excited independently in this model. Based on simulations in different parameter regimes, we find that, when only the large-scale dynamo is operating in the system, the small-scale magnetic field generated through shredding and tangling of the large-scale magnetic field is positively correlated with the global magnetic cycle. However, when both dynamos are operating, the small-scale field is produced from both the small-scale dynamo and the tangling of the large-scale field. In this situation, when the large-scale field is weaker than the equipartition value of the turbulence, the small-scale field is almost uncorrelated with the large-scale magnetic cycle. On the other hand, when the large-scale field is stronger than the equipartition value, we observe a clear anticorrelation between the small-scale field and the large-scale magnetic cycle. This anticorrelation can be interpreted as a suppression of both the small-scale dynamo and the tangling of the large-scale field. Based on our studies we conclude that the observed small-scale magnetic field in the Sun is generated by the combined mechanisms of small-scale dynamo and tangling of the large-scale field. The observed cyclic variation of the small-scale field is produced by the interaction between the large-scale field and the flow.
The spectrum of a supernova results from a complex array of overlapping atomic signatures that are sensitive to the composition and state of unburned and freshly synthesized material. Most theoretical models indicate that observed features near 6000-6300 Angstroms in type I spectra are due to more than a single component of Si II l6355, if at all for poorly matched Ib, Ic, and super-luminous supernovae; an interpretation of Si II l6355 works for nominal 6150 Angstrom absorption features of all type Ia supernovae during the first month of free expansion while the same interpretation has not been successful for a majority of type Ib and Ic. Instead, canonical 6250 Angstrom absorption features of type Ib and Ic spectra are likely shaped primarily by faint signatures of Halpha. Meanwhile, we also find the identification of Si II l6355 in the spectra of broad-lined Ic and super-luminous events of type I/R is less convincing in spite of numerous model spectra used to show otherwise. Here we argue a more likely explanation for these 6000-6300 Angstrom features is that they are conspicuous signatures of blue-shifted absorption and emission in Halpha, which is observed for type II supernovae. Such a solution has yet to be investigated in detail for classically defined type I supernovae on account of historical mix-ups in supernova nomenclatures; type I means no hydrogen [sic]. Here we revisit line identifications of type I supernovae and briefly discuss implications for progenitor systems.
We demonstrate observational evidence for the occurrence of convectively driven internal gravity waves (IGW) in young massive O-type stars observed with high-precision CoRoT space photometry. This evidence results from a comparison between velocity spectra based on 2D hydrodynamical simulations of IGW in a differentially-rotating massive star and the observed spectra.We also show that the velocity spectra caused by IGW may lead to detectable line-profile variability and explain the occurrence of macroturbulence in the observed line profiles of OB stars. Our findings provide predictions that can readily be tested by including a sample of bright slowly and rapidly rotating OB-type stars in the scientific programme of the K2 mission accompanied by high-precision spectroscopy and their confrontation with multi-dimensional hydrodynamic simulations of IGW for various masses and ages.
We develop the effective theory of large-scale structure for non-Gaussian initial conditions. The effective stress tensor in the dark matter equations of motion contains new operators, which originate from the squeezed limit of the primordial bispectrum. Parameterizing the squeezed limit by a scaling and an angular dependence, captures large classes of primordial non-Gaussianity. Within this parameterization, we classify the possible contributions to the effective theory. We show explicitly how all terms consistent with the symmetries arise from coarse graining the dark matter equations of motion and its initial conditions. We also demonstrate that the system is closed under renormalization and that the basis of correction terms is therefore complete. The relevant corrections to the matter power spectrum and bispectrum are computed numerically and their relative importance is discussed.
We present imaging and spectroscopic observations with HST and VLT of the ring of SN 1987A from 1994 to 2014. After an almost exponential increase of the shocked emission from the hotspots up to day ~8,000 (~2009), both this and the unshocked emission are now fading. From the radial positions of the hotspots we see an acceleration of these up to 500-1000 km/s, consistent with the highest spectroscopic shock velocities from the radiative shocks. In the most recent observations (2013 and 2014), we find several new hotspots outside the inner ring, excited by either X-rays from the shocks or by direct shock interaction. All of these observations indicate that the interaction with the supernova ejecta is now gradually dissolving the hotspots. We predict, based on the observed decay, that the inner ring will be destroyed by ~2025.
High frequency (millisecond) quasi-periodic oscillations (HF QPOs) are observed in the X-ray power-density spectra of several microquasars and low mass X-ray binaries. Two distinct QPO peaks, so-called twin peak QPOs, are often detected simultaneously exhibiting their frequency ratio close or equal to 3/2. Following the analytic theory and previous studies of observable spectral signatures, we aim to model the twin peak QPOs as a spectral imprint of specific dual oscillation regime defined by a combination of the lowest radial and vertical oscillation mode of optically thick slender tori with constant specific angular momentum. We examined power spectra and fluorescent K$\alpha$ iron line profiles for two different simulation setups with the mode frequency relations corresponding to the epicyclic resonance HF QPOs model and modified relativistic precession QPOs model. We use relativistic ray-tracing implemented in parallel simulation code LSDplus. In the background of the Kerr spacetime geometry, we analyze the influence of the distant observer inclination and the spin of the central compact object. Relativistic optical projection of the oscillating slender torus is illustrated by images in false colours related to the frequency shift. We show that performed simulations yield power spectra with the pair of dominant peaks corresponding to the frequencies of radial and vertical oscillation modes with the proper ratio equal to 3/2 on a wide range of inclinations and spin values. We also discuss exceptional cases of a very small and very high inclination as well as unstable high spin relativistic precession-like configuration predicting constant frequency ratio equal to 1/2. We demonstrate signifiant dependency of broadened K$\alpha$ iron line profiles on the inclination of the distant observer.
The post-helium burning evolution of stars from 7 to 11 solar masses is complicated by the lingering effects of degeneracy and off-center ignition. Here stars in this mass range are studied using a standard set of stellar physics. Two important aspects of the study are the direct coupling of a reaction network of roughly 220 nuclei to the structure calculation at all stages and the use of a sub grid model to describe the convective bounded flame that develops during neon and oxygen burning. Below 9.0 solar masses, degenerate oxygen-neon cores form that may become either white dwarfs or electron-capture supernovae. Above 10.3 solar masses the evolution proceeds "normally" to iron-core collapse, without composition inversions or degenerate flashes. Emphasis here is upon the stars in between which typically ignite oxygen burning off center. After oxygen burns in a convectively bounded flame, silicon burning ignites in a degenerate flash that commences closer to the stellar center and with increasing violence for stars of larger mass. In some cases the silicon flash is so violent that it could lead to the early ejection of the hydrogen envelope. This might have interesting observable consequences. For example, the death of a 10.0 solar mass star could produce two supernova-like displays, a faint low energy event due to the silicon flash, and an unusually bright supernova many months later as the low energy ejecta from core collapse collides with the previously ejected envelope. The potential relation to the Crab supernova is discussed.
Precision radial velocities are required to discover and characterize planets orbiting nearby stars. Optical and near infrared spectra that exhibit many hundreds of absorption lines can allow the m/s precision levels required for such work. However, this means that studies have generally focused on solar-type dwarf stars. After the main-sequence, intermediate-mass stars (former A-F stars) expand and rotate slower than their progenitors, thus thousands of narrow absorption lines appear in the optical region, permitting the search for planetary Doppler signals in the data for these types of stars. We present the discovery of two giant planets around the intermediate-mass evolved star HIP65891 and HIP107773. The best Keplerian fit to the HIP65891 and HIP107773 radial velocities leads to the following orbital parameters: P=1084.5 d; m$_b$sin$i$ = 6.0 M$_{jup}$; $e$=0.13 and P=144.3 d; m$_b$sin$i$ = 2.0 M$_{jup}$; $e$=0.09, respectively. In addition, we confirm the planetary nature of the outer object orbiting the giant star HIP67851. The orbital parameters of HIP67851c are: P=2131.8 d, m$_c$sin$i$ = 6.0 M$_{jup}$ and $e$=0.17. With masses of 2.5 M$_\odot$ and 2.4 M$_\odot$ HIP65891 and HIP107773 are two of the most massive stars known to host planets. Additionally, HIP67851 is one of five giant stars that are known to host a planetary system having a close-in planet ($a <$ 0.7 AU). Based on the evolutionary states of those five stars, we conclude that close-in planets do exist in multiple systems around subgiants and slightly evolved giants stars, but probably they are subsequently destroyed by the stellar envelope during the ascent of the red giant branch phase. As a consequence, planetary systems with close-in objects are not found around horizontal branch stars.
The Horndeski theory is known as the most general scalar-tensor theory with second-order field equations. In this paper, we explore the bi-scalar extension of the Horndeski theory. Following Horndeski's approach, we determine all the possible terms appearing in the second-order field equations of the bi-scalar-tensor theory. We compare the field equations with those of the generalized multi-Galileons, and confirm that our theory contains new terms that are not included in the latter theory. We also discuss the construction of the Lagrangian leading to our most general field equations.
We reconsider a gauge theory of gravity in which the gauge group is the conformal group SO(4,2) and the action is of the Yang-Mills form, quadratic in the curvature. The resulting gravitational theory exhibits local conformal symmetry and reduces to Weyl-squared gravity under certain conditions. When the theory is linearized about flat spacetime, we find that matter which couples to the generators of special conformal transformations reproduces Newton's inverse square law. Conversely, matter which couples to generators of translations induces a constant and possibly repulsive force far from the source, which may be relevant for explaining the late time acceleration of the universe. The coupling constant of theory is dimensionless, which means that it is potentially renormalizable.
The couplings between supermassive black-hole binaries and their environments within galactic nuclei have been well studied as part of the search for solutions to the final parsec problem. The scattering of stars by the binary or the interaction with a circumbinary disk may efficiently drive the system to sub-parsec separations, allowing the binary to enter a regime where the emission of gravitational-waves can drive it to merger within a Hubble time. However, these interactions can also affect the orbital parameters of the binary. In particular, they may drive an increase in binary eccentricity which survives until the system's gravitational-wave signal enters the pulsar-timing array band. Therefore, if we can measure the eccentricity from observed signals, we can potentially deduce some of the properties of the binary environment. To this end, we build on previous techniques to present a general Bayesian pipeline with which we can detect and estimate the parameters of an eccentric supermassive black-hole binary system with pulsar-timing arrays. Additionally, we generalize the pulsar-timing array $\mathcal{F}_e$-statistic to eccentric systems, and show that both this statistic and the Bayesian pipeline are robust when studying circular or arbitrarily eccentric systems. We explore how eccentricity influences the detection prospects of single gravitational-wave sources, as well as the detection penalty incurred by employing a circular waveform template to search for eccentric signals, and conclude by identifying important avenues for future study.
A spherically symmetric wormhole in Newtonian gravitation in curved space, enhanced with a connection between the mass density and the Ricci scalar, is presented. The wormhole, consisting of two connected asymptotically flat regions, inhabits a spherically symmetric curved space. The gravitational potential, gravitational field and the pressure that supports the fluid that permeates the Newtonian wormhole are computed. Particle dynamics and tidal effects in this geometry are studied. The possibility of having Newtonian black holes in this theory is sketched.
The reconstruction procedure, which has proven quite useful to obtain viable models of the universe evolution, is here employed in order to construct inflation models. It has the advantages that it ensures full consistency with astronomical observations and that it allows to evaluate the stability of the resulting cosmological model quite easily. The reconstruction for two different types of Lagrangian, included in the frame of G-inflation, is carried out in detail and explicit models for each Lagrangian are constructed. As a bonus for having used this reconstruction formalism, the final models are easily adjusted to satisfy the observational constraints---imposed by the most recent data releases of the Planck mission---on the spectral index, the tensor to scalar ratio, and the running of the spectral index. Further, it turns also to be not difficult to make the models stable. Thus, the method here developed provides a general and very efficient tool, a quite natural procedure to construct models consistent with very precise observations. It can also be applied to other models, besides the ones here considered.
We extend the formalism of dark matter directional detection to arbitrary one-body dark matter-nucleon interactions. The new theoretical framework generalizes the one currently used, which is based on 2 types of dark matter-nucleon interaction only. It includes 14 dark matter-nucleon interaction operators, 8 isotope-dependent nuclear response functions, and the Radon transform of the first 2 moments of the dark matter velocity distribution. We calculate the recoil energy spectra at dark matter directional detectors made of CF$_4$, CS$_2$ and $^{3}$He for the 14 dark matter-nucleon interactions, using nuclear response functions recently obtained through numerical nuclear structure calculations. We highlight the new features of the proposed theoretical framework, and present our results for a spherical dark matter halo and for a stream of dark matter particles. This study lays the foundations for model independent analyses of dark matter directional detection experiments.
Deflection angles of massive test particles moving along an unbound trajectory in the Schwarzschild metric are considered for the case of large deflection. We analytically consider the strong deflection limit, which is opposite to the commonly applied small deflection approximation and corresponds to the situation when a massive particle moves from infinity, makes several revolutions around a central object and goes to infinity. For this purpose we rewrite an integral expression for the deflection angle as an explicit function of the parameters determining the trajectory and expand it. Remarkably, in the limiting case of strong deflection, we succeed in deriving for the first time the analytical formulas for deflection angles as explicit functions of parameters at infinity. In particular, we show that in this case the deflection angle can be calculated as an explicit function of the impact parameter and velocity at infinity beyond the usual assumption of small deflection.
The very high energy Galactic gamma-ray sky is partially opaque in the (0.1-10) PeV energy range. In the light of the recently detected high energy neutrino flux by IceCube, a comparable very high energy gamma-ray flux is expected in any scenario with a sizable Galactic contribution to the neutrino flux. Here we elaborate on the peculiar energy and anisotropy features imposed upon these very high energy gamma-rays by the absorption on the cosmic microwave background photons and Galactic interstellar light. As a notable application of our considerations, we study the prospects of probing the PeV-scale decaying DM scenario, proposed as a possible source of IceCube neutrinos, by extensive air shower (EAS) cosmic ray experiments.
Combining feebly interacting massive particle (FIMP) dark matter (DM) with scale invariance (SI) leads to extremely light FIMP (thus the FImP) with FImP miracle, i.e., the mass and relic generations of FImP DM share the same dynamics. In this paper we show that due to the lightness of FImP, it, especially for a scalar FImP, can easily accommodate large DM self-interaction. For a fermionic FImP, such as the sterile neutrino, self-interaction additionally requires a mediator which is another FImP, a scalar boson with mass either much lighter or heavier than the FImP DM. DM self-interaction opens a new window to observe FImP (miracle), which does not leave traces in the conventional DM searches. As an example, FImP can account for the offsets between the centroid of DM halo and stars of galaxies recently observed in the galaxy cluster Abel 3827.
In this essay we propose that the theory of gravity's vacuum is described by a de Sitter geometry. Under this assumption we consider an adjustment mechanism able to screen any value of the vacuum energy of the matter fields. We discuss the most general scalar-tensor cosmological models with second order equations of motion that have a fixed de Sitter critical point for any kind of material content. These models give rise to interesting cosmological evolutions that we shall discuss.
We revisit three of the mathematical formalisms used to describe magnetized quark matter in compact objects within the MIT and the Nambu-Jona-Lasinio models and then compare their results. The tree formalisms are based on 1) isotropic equations of state, 2) anisotropic equations of state with different parallel and perpendicular pressures and 3) the assumption of a chaotic field approximation that results in a truly isotropic equation of state. We have seen that the magnetization obtained with both models is very different: while the MIT model produces well-behaved curves that are always positive for large magnetic fields, the NJL model yields a magnetization with lots of spikes and negative values. This fact has strong consequences on the results based on the existence of anisotropic equations of state. We have also seen that, while the isotropic formalism results in maximum stellar masses that increase considerably when the magnetic fields increase, maximum masses obtained with the chaotic field approximation never vary more than 5.5$\%$. The effect of the magnetic field on the radii is opposed in the MIT and NJL models: with both formalisms, isotropic and chaotic field approximation, for a fixed mass, the radii increase with the increase of the magnetic field in the MIT bag model and decrease in the NJL, the radii of quark stars described by the NJL model being smaller than the ones described by the MIT model.
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The formation of planetesimals requires that primordial dust grains grow from micron- to km-sized bodies. Dust traps caused by gas pressure maxima have been proposed as regions where grains can concentrate and grow fast enough to form planetesimals, before radially migrating onto the star. We report new VLA Ka & Ku observations of the protoplanetary disk around the Herbig Ae/Be star MWC 758. The Ka image shows a compact emission region in the outer disk indicating a strong concentration of big dust grains. Tracing smaller grains, archival ALMA data in band 7 continuum shows extended disk emission with an intensity maximum to the north-west of the central star, which matches the VLA clump position. This segregation of grains sizes is expected in the context of dust trapping, where big grains are trapped more easily than smaller grains in gas pressure maxima. We develop a non-axisymmetric parametric model inspired by a steady state vortex solution which reproduces the observations, including the spectral energy distribution. Finally, we compare the radio continuum with SPHERE scattered light data. The ALMA continuum spatially coincides with a region devoid of scattered polarised emission and the VLA clump is offset to the north of the north-western spiral-like feature, indicating moderate or no flaring in the outer disk.
We present an observational constraint for the typical active galactic nucleus (AGN) phase lifetime. The argument is based on the time lag between an AGN central engine switching on and becoming visible in X-rays, and the time the AGN then requires to photoionize a large fraction of the host galaxy. Based on the typical light travel time across massive galaxies, and the observed fraction of X-ray selected AGN without AGN-photoionized narrow lines, we estimate that the AGN phase typically lasts $\sim10^{5}$ years. This lifetime is short compared to the total growth time of $10^{7}-10^{9}$ years estimated from e.g. the Soltan argument and implies that black holes grow via many such short bursts and that AGN therefore "flicker" on and off. We discuss some consequences of this flickering behavior for AGN feedback and the analogy of X-ray binaries and AGN lifecycles.
We describe the discovery of a bright, young Kuiper belt-like debris disk around HD 115600, a $\sim$ 1.4--1.5 M$_\mathrm{\odot}$, $\sim$ 15 Myr old member of the Sco-Cen OB Association. Our H-band coronagraphy/integral field spectroscopy from the \textit{Gemini Planet Imager} shows the ring has a (luminosity scaled) semi major axis of ($\sim$ 22 AU) $\sim$ 48 AU, similar to the current Kuiper belt. The disk appears to have neutral scattering dust, is eccentric (e $\sim$ 0.1--0.2), and could be sculpted by analogues to the outer solar system planets. Spectroscopy of the disk ansae reveal a slightly blue to gray disk color, consistent with major Kuiper belt chemical constituents, where water-ice is a very plausible dominant constituent. Besides being the first object discovered with the next generation of extreme adaptive optics systems (i.e. SCExAO, GPI, SPHERE), HD 115600's debris ring and planetary system provides a key reference point for the early evolution of the solar system, the structure and composition of the Kuiper belt, and the interaction between debris disks and planets.
We use present cosmological observations and forecasts of future experiments to illustrate the power of large-scale structure (LSS) surveys in probing dark matter (DM) microphysics and unveiling potential deviations from the standard $\Lambda$CDM scenario. To quantify this statement, we focus on an extension of $\Lambda$CDM with DM-neutrino scattering, which leaves a distinctive imprint on the angular and matter power spectra. After finding that future CMB experiments (such as COrE+) will not significantly improve the constraints set by the Planck satellite, we show that the next generation of galaxy clustering surveys (such as DESI) could play a leading role in constraining alternative cosmologies and even have the potential to make a discovery. Typically, we find that DESI would be an order of magnitude more sensitive to DM interactions than Planck (if s-wave) and two orders of magnitude (if p-wave), thus probing effects that until now have only been accessible via N-body simulations.
We have expanded the sample of observed white dwarfs in the rich open cluster NGC 2099 (M37) with the Keck Low-Resolution Imaging Spectrometer. Of 20 white dwarf candidates, the spectroscopy shows 19 to be true white dwarfs with 14 of these having high S/N. We find 11 of these 14 to be consistent with singly evolved cluster members. They span a mass range of $\sim$0.7 to 0.95 M$_\odot$, excluding a low-mass outlier, corresponding to progenitor masses of $\sim$3 to 4 M$_\odot$. This region of the initial final mass relation (IFMR) has large scatter and a slope that remains to be precisely determined. With this large sample of white dwarfs that belong to a single age and metallicity population, we find an initial-final mass relation of (0.171$\pm$0.057)M$_{\rm initial}$+0.219$\pm$0.187 M$_\odot$, significantly steeper than the linear relation adopted over the full observed white dwarf mass range in many previous studies. Comparison of this new relation from the solar metallicity NGC 2099 to 18 white dwarfs in the metal-rich Hyades and Praesepe shows that their IFMR also has a consistently steep slope. This strong consistency also suggests that there is no significant metallicity dependence of the IFMR at this mass and metallicity range. As a result, the IFMR can be more reliably determined with this broad sample of 29 total white dwarfs giving M$_{\rm final}$=(0.163$\pm$0.022)M$_{\rm initial}$+0.238$\pm$0.071 M$_\odot$ from M$_{\rm initial}$ of 3 to 4 M$_\odot$. A steep IFMR in this mass range indicates that the full IFMR is nonlinear.
We announce the discovery of a highly inflated transiting hot Jupiter discovered by the KELT-North survey. A global analysis including constraints from isochrones indicates that the V = 10.8 host star (HD 343246) is a mildly evolved, G dwarf with $T_{\rm eff} = 5754_{-55}^{+54}$ K, $\log{g} = 4.078_{-0.054}^{+0.049}$, $[Fe/H] = 0.272\pm0.038$, an inferred mass $M_{*}=1.211_{-0.066}^{+0.078}$ M$_{\odot}$, and radius $R_{*}=1.67_{-0.12}^{+0.14}$ R$_{\odot}$. The planetary companion has mass $M_P = 0.867_{-0.061}^{+0.065}$ $M_{J}$, radius $R_P = 1.86_{-0.16}^{+0.18}$ $R_{J}$, surface gravity $\log{g_{P}} = 2.793_{-0.075}^{+0.072}$, and density $\rho_P = 0.167_{-0.038}^{+0.047}$ g cm$^{-3}$. The planet is on a roughly circular orbit with semimajor axis $a = 0.04571_{-0.00084}^{+0.00096}$ AU and eccentricity $e = 0.035_{-0.025}^{+0.050}$. The best-fit linear ephemeris is $T_0 = 2456883.4803 \pm 0.0007$ BJD$_{\rm TDB}$ and $P = 3.24406 \pm 0.00016$ days. This planet is one of the most inflated of all known transiting exoplanets, making it one of the few members of a class of extremely low density, highly-irradiated gas giants. The low stellar $\log{g}$ and large implied radius are supported by stellar density constraints from follow-up light curves, plus an evolutionary and space motion analysis. We also develop a new technique to extract high precision radial velocities from noisy spectra that reduces the observing time needed to confirm transiting planet candidates. This planet boasts deep transits of a bright star, a large inferred atmospheric scale height, and a high equilibrium temperature of $T_{eq}=1675^{+61}_{-55}$ K, assuming zero albedo and perfect heat redistribution, making it one of the best targets for future atmospheric characterization studies.
We propose that ultra-high-energy (UHE) cosmic rays (CRs) above $10^{18}$eV are produced in relativistic jets of powerful active galactic nuclei via an original mechanism, which we dub "espresso" acceleration: "seed" galactic CRs with energies $\lesssim 10^{17}$eV that penetrate the jet sideways receive a "one-shot" boost of a factor of $\sim\Gamma^2$ in energy, where $\Gamma$ is the Lorentz factor of the relativistic flow. For typical jet parameters, a few per cent of the CRs in the host galaxy can undergo this process, and powerful blazars with $\Gamma\gtrsim 30$ may accelerate UHECRs up to more than $10^{20}$eV. The chemical composition of espresso-accelerated UHECRs is determined by the one at the Galactic CR knee, and is expected to be proton-dominated at $10^{18}$eV and increasingly heavy at higher energies, in agreement with recent observations of the Pierre Auger Observatory.
Extensive N-body simulations are among the key means for the study of numerous astrophysical and cosmological phenomena, so various schemes are developed for possibly higher accuracy computations. We demonstrate the principal possibility for revealing the evolution of a perturbed Hamiltonian system with an accuracy independent on time. The method is based on the Laplace transform and the derivation and analytical solution of an evolution equation in the phase space for the resolvent and using computer algebra.
We present data and initial results from VLT/X-shooter emission-line spectroscopy of 96 GRB-selected galaxies at 0.1<z<3.6, the largest sample of GRB host spectroscopy available to date. The majority of our GRBs was detected by Swift and 76% are at 0.5<z<2.5 with a median z~1.6. Based on Balmer and/or forbidden lines of oxygen, nitrogen and neon, we measure systemic redshifts, star-formation rates, visual attenuations (A_V), oxygen abundances and emission-line widths (sigma). We find a strong change of the typical physical properties of GRB hosts with redshift. The median SFR, for example, increases from ~0.6 M_sun/yr at z~0.6 up to ~15 M_sun/yr at z~2. A higher ratio of [OIII]/[OII] at higher redshifts leads to an increasing distance of GRB-selected galaxies to the locus of local galaxies in the BPT diagram. Oxygen abundances of the galaxies are distributed between 12+log(O/H)=7.9 and 12+log(O/H)=9.0 with a median of 12+log(O/H)~8.5. The fraction of GRB-selected galaxies with super-solar metallicities is around 20% at z<1 in the adopted metallicity scale. This is significantly less than the fraction of star-formation in similar galaxies, illustrating that GRBs are scarce in high-metallicity environments. At z~3, sensitivity limits us to probing only the most luminous GRB hosts for which we derive metallicities of Z ~< 0.5 Z_sun. Together with a high incidence of galaxies with similar metallicity in our sample at z~1.5, this indicates that the metallicity dependence observed at low redshift will not be dominant at z~3.
We present the SuperNova Explosion Code SNEC, an open-source Lagrangian code for the hydrodynamics and equilibrium-diffusion radiation transport in the expanding envelopes of supernovae. Given a model of a progenitor star, an explosion energy, and an amount and distribution of radioactive nickel, SNEC generates the bolometric light curve, as well as the light curves in different wavelength bands assuming black body emission. As a first application of SNEC, we consider the explosions of a grid of 15 Msun (at zero-age main sequence) stars whose hydrogen envelopes are stripped to different extents and at different points in their evolution. The resulting light curves exhibit plateaus with durations of ~20-100 days if >~1.5-2 Msun of hydrogen-rich material is left and no plateau if less hydrogen-rich material is left. The shorter plateau lengths are unlike the Type IIP supernova light curves typically observed in nature. This suggests that, at least for zero-age main sequence masses <~ 20 Msun, hydrogen mass loss occurs as an all or nothing process, perhaps pointing to the important role binary interactions play in observed mass-stripped supernovae (i.e., Type Ib/c events). These light curves are also unlike what is typically seen for Type IIL supernovae, arguing that simply varying the amount of mass loss cannot explain these events. The most stripped models begin to show double-peaked light curves similar to what is often seen for Type IIb supernovae, confirming previous work that these supernovae can come from progenitors that have a small amount of hydrogen and a radius of ~500 Rsun.
In this paper we study the effects of letting the dark matter and the gas in the Universe couple to the scalar field of the symmetron model, a modified gravity theory, with varying coupling strength. We also search for a way to distinguish between universal and non-universal couplings in observations. The research is done utilising a series of hydrodynamic, cosmological N-Body simulations, studying the resulting power spectra and galaxy halo properties such as the density and temperature profiles. Results show that in the cases of universal coupling the deviations in the bias from $\Lambda$CDM is smaller than in the cases of non-universal couplings throughout the halos. Density profile deviations can differ significantly between dark matter and gas, with the dark matter having deviations of several factors higher than the deviations in the gas. Large halos and small halos show vastly different effects from the symmetron scalar field, a direct demonstration of the screening mechanism.
Using high-cadence extreme-ultraviolet (EUV) images obtained by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, we investigate the solar sources of 26 $^{3}$He-rich solar energetic particle (SEP) events at $\lesssim$1 MeV nucleon$^{-1}$ that were well-observed by the Advanced Composition Explorer during solar cycle 24. Identification of the solar sources is based on the association of $^{3}$He-rich events with type III radio bursts and electron events as observed by Wind. The source locations are further verified in EUV images from the Solar and Terrestrial Relations Observatory, which provides information on solar activities in the regions not visible from the Earth. Based on AIA observations, $^{3}$He-rich events are not only associated with coronal jets as emphasized in solar cycle 23 studies, but also with more spatially extended eruptions. The properties of the $^{3}$He-rich events do not appear to be strongly correlated with those of the source regions. As in the previous studies, the magnetic connection between the source region and the observer is not always reproduced adequately by the simple potential field source surface model combined with the Parker spiral. Instead, we find a broad longitudinal distribution of the source regions extending well beyond the west limb, with the longitude deviating significantly from that expected from the observed solar wind speed.
The identification of on-going planet formation requires the finest angular resolutions and deepest sensitivities in observations inspired by state-of-the-art numerical simulations. Hydrodynamic simulations of planet-disk interactions predict the formation of circumplanetary disks (CPDs) around accreting planetary cores. These CPDs have eluded unequivocal detection -their identification requires predictions in CPD tracers. In this work, we aim to assess the observability of embedded CPDs with ALMA as features imprinted in the gas kinematics. We use 3D Smooth Particle Hydrodynamic (SPH) simulations of CPDs around 1 and 5 M_Jup planets at large stellocentric radii, in locally isothermal and adiabatic disks. The simulations are then connected with 3D radiative transfer for predictions in CO isotopologues. Observability is assessed by corrupting with realistic long baseline phase noise extracted from the recent HL Tau ALMA data. We find that the presence of a CPD produces distinct signposts: 1) compact emission separated in velocity from the overall circumstellar disk's Keplerian pattern, 2) a strong impact on the velocity pattern when the Doppler shifted line emission sweeps across the CPD location, and 3) a local increase in the velocity dispersion. We test our predictions with a simulation tailored for HD 100546 -which has a reported protoplanet candidate. We find that the CPDs are detectable in all 3 signposts with ALMA Cycle 3 capabilities for both 1 and 5 M_Jup protoplanets, when embedded in an isothermal disk.
We study the angular clustering of $\sim 6\times 10^5$ NVSS sources on scales $\gtrsim 50 h^{-1}$ Mpc in the context of the $\Lambda$CDM scenario. The analysis partially relies on the redshift distribution of 131 radio galaxies, inferred from the Hercules and CENSORS survey, and an empirical fit to the stellar to halo mass (SHM) relation. For redshifts $z\lesssim 0.7$, the fraction of radio activity versus stellar mass evolves as $f_{_{\rm RL}}\sim M_*^{\alpha_0+\alpha_1 z}$ where $\alpha_0=2.529{\pm0.184}$ and $\alpha_1=1.854^{+0.708}_{-0.761}$. The estimate on $\alpha_0$ is largely driven by the results of Best et al. (2005), while the constraint on $\alpha_1$ is new. We derive a biasing factor $b(z=0.5)=2.093^{+0.164}_{-0.109}$ between radio galaxies and the underlying mass.The function $b(z)=0.33z^2+0.85 z +1.6$ fits well the redshift dependence. We also provide convenient parametric forms for the redshift dependent radio luminosity function, which are consistent with the redshift distribution and the NVSS source count versus flux.
We present an investigation of the polar crown prominence that erupted on 2012 March 12. This prominence is observed at the southeast limb by SDO/AIA (end-on view) and displays a quasi vertical-thread structure. Bright U-shape/horn-like structure is observed surrounding the upper portion of the prominence at 171 angstrom before the eruption and becomes more prominent during the eruption. The disk view of STEREO-B shows that this long prominence is composed of a series of vertical threads and displays a half loop-like structure during the eruption. We focus on the magnetic support of the prominence vertical threads by studying the structure and dynamics of the prominence before and during the eruption using observations from SDO and STEREO-B. We also construct a series of magnetic field models (sheared arcade model, twisted flux rope model, and unstable model with hyperbolic flux tube (HFT)). Various observational characteristics appear to be in favor of the twisted flux rope model. We find that the flux rope supporting the prominence enters the regime of torus instability at the onset of the fast rise phase, and signatures of reconnection (post-eruption arcade, new U-shape structure, rising blobs) appear about one hour later. During the eruption, AIA observes dark ribbons seen in absorption at 171 angstrom corresponding to the bright ribbons shown at 304 angstrom, which might be caused by the erupting filament material falling back along the newly reconfigured magnetic fields. Brightenings at the inner edge of the erupting prominence arcade are also observed in all AIA EUV channels, which might be caused by the heating due to energy released from reconnection below the rising prominence.
[abridge] Volume-weighted statistics of large scale peculiar velocity is preferred by peculiar velocity cosmology, since it is free of uncertainties of galaxy density bias entangled in mass-weighted statistics. However, measuring the volume-weighted velocity statistics from galaxy (halo/simulation particle) velocity data is challenging. For the first time, we apply the Kriging interpolation to obtain the volume-weighted velocity field. Kriging is a minimum variance estimator. It predicts the most likely velocity for each place based on the velocity at other places. We test the performance of Kriging quantified by the E-mode velocity power spectrum from simulations. Dependences on the variogram prior used in Kriging, the number $n_k$ of the nearby particles to interpolate and the density $n_P$ of the observed sample are investigated. (1) We find that Kriging induces $1\%$ and $3\%$ systematics at $k\sim 0.1h{\rm Mpc}^{-1}$ when $n_P\sim 6\times 10^{-2} ({\rm Mpc}/h)^{-3}$ and $n_P\sim 6\times 10^{-3} ({\rm Mpc}/h)^{-3}$, respectively. The deviation increases for decreasing $n_P$ and increasing $k$. When $n_P\lesssim 6\times 10^{-4} ({\rm Mpc}/h)^{-3}$, a smoothing effect dominates small scales, causing significant underestimation of the velocity power spectrum. (2) Increasing $n_k$ helps to recover small scale power. However, for $n_P\lesssim 6\times 10^{-4} ({\rm Mpc}/h)^{-3}$ cases, the recovery is limited. (3) Kriging is more sensitive to the variogram prior for lower sample density. We conclude that for $n_P\sim 6\times 10^{-4} ({\rm Mpc}/h)^{-3}$ which corresponds to the density of $\sim 10^{13} M_\odot/h$ haloes, systematic error in the measured volume-weighted velocity power spectrum often exceeds $1\%$, for the most straightforward application of Kriging. We discuss potential improvements that may be achieved by more delicate versions of Kriging.
This remark describes efficiency improvements to Algorithm 916 [Zaghloul and Ali 2011]. It is shown that the execution time required by the algorithm, when run at its highest accuracy, may be improved by more than a factor of two. A better accuracy vs efficiency trade off scheme is also implemented; this requires the user to supply the number of significant figures desired in the computed values as an extra input argument to the function. Using this trade-off, it is shown that the efficiency of the algorithm may be further improved significantly while maintaining reasonably accurate and safe results that are free of the pitfalls and complete loss of accuracy seen in other competitive techniques. The current version of the code is provided in Matlab and Scilab in addition to a Fortran translation prepared to meet the needs of real-world problems where very large numbers of function evaluations would require the use of a compiled language. To fulfill this last requirement, a recently proposed reformed version of Humlicek's w4 routine, shown to maintain the claimed accuracy of the algorithm over a wide and fine grid is implemented in the present Fortran translation for the case of 4 significant figures. This latter modification assures the reliability of the code to be employed in the solution of practical problems requiring numerous evaluation of the function for applications tolerating low accuracy computations (<10-4).
The aim of the project is to search for lithium in absorption at 6707.8
Angstroms to constrain the nature and the mass of the brightest low-metallicity
L-type dwarfs (refered to as L subdwarfs) identified in large-scale surveys.
We obtained low- to intermediate-resolution (R~2500-9000) optical (~560-770
nm) spectra of two mid-L subdwarfs, SDSSJ125637.13-022452.4 (SDSS1256; sdL3.5)
and 2MASSJ162620.14+392519.5 (2MASS1626; sdL4) with spectrographs on the
European Southern Observatory Very Large Telescope and the Gran Telescopio de
Canarias.
We report the presence of a feature at the nominal position of the lithium
absorption doublet at 6707.8 Angstroms in the spectrum of SDSS1256, with an
equivalent width of 66+/-27 Angstroms at 2.4 sigma, which we identify as
arising from a CaH molecular transition based on atmosphere models. We do not
see any feature at the position of the lithium feature in the spectrum of
2MASS1626. The existence of overlapping molecular absorption sets a confusion
detection limit of [Li/H]=-3 for equivalently-typed L subdwarfs. We provided
improved radial velocity measurements of -126+/-10 km/s and -239+/-12 km/s for
SDSS1256 and 2MASS1626, respectively, as well as revised Galactic orbits. We
implemented adjusting factors for the CaH molecule in combination with the
NextGen atmosphere models to fit the optical spectrum of SDSS1256 in the
6200-7300 Angstroms range. We also estimate the expected Li abundance from
interstellar accretion ([Li/H]=-5), place limits on circumstellar accretion
(10^9 g/yr), and discuss the prospects of Li searches in cooler L and T
subdwarfs.
Young terrestrial planets, when they are still embedded in a circumstellar disk, accumulate an atmosphere of nebula gas. The evolution and eventual evaporation of the protoplanetary disk affect the structure and dynamics of the planetary atmosphere. These processes, combined with other mass loss mechanisms, such as thermal escape driven by extreme ultraviolet and soft X-ray radiation (XUV) from the young host star, determine how much of the primary atmosphere, if anything at all, survives into later stages of planetary evolution. Our aim is to explore the structure and the dynamic outflow processes of nebula-accreted atmospheres in dependency on changes in the planetary environment. We integrate stationary hydrostatic models and perform time-dependent dynamical simulations to investigate the effect of a changing nebula environment on the atmospheric structure and the timescales on which the protoatmosphere reacts to these changes. We find that the behavior of the atmospheres strongly depends on the mass of the planetary core. For planets of about Mars-mass the atmospheric structure, and in particular the atmospheric mass, changes drastically and on very short timescales whereas atmospheres around higher mass planets are much more robust and inert.
We are still in the early days of exoplanet discovery. Astronomers are beginning to model the atmospheres and interiors of exoplanets and have developed a deeper understanding of processes of planet formation and evolution. However, we have yet to map out the full complexity of multi-planet architectures or to detect Earth analogues around nearby stars. Reaching these ambitious goals will require further improvements in instrumentation and new analysis tools. In this chapter, we provide an overview of five observational techniques that are currently employed in the detection of exoplanets: optical and IR Doppler measurements, transit photometry, direct imaging, microlensing, and astrometry. We provide a basic description of how each of these techniques works and discuss forefront developments that will result in new discoveries. We also highlight the observational limitations and synergies of each method and their connections to future space missions.
Signs of damping wing absorption attenuating the Lyman-$\alpha$ emission line of the first known $z \sim 7$ quasar, ULAS J1120+0641, recently provided exciting evidence of a significantly neutral IGM. This long-awaited signature of reionization was inferred, in part, from a deficit of flux in the quasar's Lyman-$\alpha$ emission line based on predictions from a composite of lower-redshift quasars. The composite sample was chosen based on its C IV emission line properties; however, as the original study by Mortlock et al. noted, the composite contained a slight velocity offset in C IV compared to ULAS J1120+0641. Here we test whether this offset may be related to the predicted strength of the Lyman-$\alpha$ emission line. We confirm the significant ($\sim 10$ per cent at r.m.s.) scatter in Lyman-$\alpha$ flux for quasars of a given C IV velocity and equivalent width found by Mortlock et al. We further find that among lower-redshift objects chosen to more closely match the C IV properties of ULAS J1120+0641, its Lyman-$\alpha$ emission falls within the observed distribution of fluxes. Among lower-redshift quasars chosen to more closely match in C IV velocity and equivalent width, we find that ULAS J1120+0641 falls within the observed distribution of Lyman-$\alpha$ emission line strengths. This suggests that damping wing absorption may not be present, potentially weakening the case for neutral gas around this object. Larger samples of z$>$7 quasars may therefore be needed to establish a clearer picture of the IGM neutral fraction at these redshifts.
The Rosetta mission of the European Space Agency has been orbiting the comet 67P/Churyumov-Gerasimenko (67P) since August 2014 and is now in its escort phase. A large complement of scientific experiments designed to complete the most detailed study of a comet ever attempted are onboard Rosetta. We present results for the photometric and spectrophotometric properties of the nucleus of 67P derived from the OSIRIS imaging system, which consists of a Wide Angle Camera (WAC) and a Narrow Angle Camera (NAC). The disk-averaged phase function of the nucleus of 67P shows a strong opposition surge with a G parameter value of -0.13$\pm$0.01 in the HG system formalism and an absolute magnitude $H_v(1,1,0)$ = 15.74$\pm$0.02 mag. The integrated spectrophotometry in 20 filters covering the 250-1000 nm wavelength range shows a red spectral behavior, without clear absorption bands except for a potential absorption centered at $\sim$ 290 nm that is possibly due to SO$_2$ ice. The nucleus shows strong phase reddening, with disk-averaged spectral slopes increasing from 11\%/(100 nm) to 16\%/(100 nm) in the 1.3$^{\circ}$--54$^{\circ}$ phase angle range. The geometric albedo of the comet is 6.5$\pm$0.2\% at 649 nm, with local variations of up to $\sim$ 16\% in the Hapi region. From the disk-resolved images we computed the spectral slope together with local spectrophotometry and identified three distinct groups of regions (blue, moderately red, and red). The Hapi region is the brightest, the bluest in term of spectral slope, and the most active surface on the comet. Local spectrophotometry shows an enhancement of the flux in the 700-750 nm that is associated with coma emissions.
KIC 10526294 is a very slowly rotating and slowly pulsating late B-type star. Its 19 consecutive dipole gravity modes constitute a series with almost constant period spacing. This unique collection of identified modes probes the near-core environment of this star and holds the potential to reveal the size and structure of the overshooting zone on top of the convective core, as well as the mixing properties of the star. We pursue forward seismic modelling based on adiabatic eigenfrequencies of equilibrium models for eight extensive evolutionary grids tuned to KIC 10526294, by varying the initial mass, metallicity, chemical mixture, and the extent of the overshooting layer on top of the convective core. We examine models for both OP and OPAL opacities and test the occurrence of extra diffusive mixing. We find a tight mass, metallicity relation within the ranges $M$ ~ 3.13 to 3.25 Msun and $Z$ ~ 0.014 to 0.028. We deduce that an exponentially decaying diffusive core overshooting prescription describes the seismic data better than a step function formulation and derive a value of $f_{ov}$ between 0.017 and 0.018. Moreover, the inclusion of extra diffusive mixing with a value of $\log D_{\rm mix}$ between 1.75 and 2.00 dex (with $D_{\rm mix}$ in cm^2/sec) improves the goodness-of-fit based on the observed and modelled frequencies with a factor 11 compared to the case where no extra mixing is considered, irrespective of the $(M,Z)$ combination within the allowed seismic range. The inclusion of diffusive mixing in addition to core overshooting is essential to explain the structure in the observed period spacing pattern of this star. Moreover, we deduce that an exponentially decaying prescription for the core overshooting is to be preferred over a step function. Our best models for KIC 10526294 approach the seismic data to a level that they can serve future inversion of its stellar structure.
(Abridged) We present a spectral analysis of a deep (220 ks) XMM-Newton observation of the Phoenix cluster (SPT-CL J2344-4243), which we also combine with Chandra archival ACIS-I data. We extract CCD and RGS X-ray spectra from the core region to search for the signature of cold gas, and constrain the mass deposition rate in the cooling flow which is thought to be responsible of the massive star formation episode observed in the BCG. We find an average mass deposition rate of $\dot M = 620 (-190 +200)_{stat} (-50 +150)_{syst} M_\odot$/yr in the temperature range 0.3-3.0 keV from MOS data. A temperature-resolved analysis shows that a significant amount of gas is deposited only above 1.8 keV, while upper limits of the order of hundreds of $M_\odot$/yr can be put in the 0.3-1.8 keV temperature range. From pn data we obtain $\dot M = 210 (-80 +85)_{stat} ( -35 +60)_{syst} M_\odot$/yr, and the upper limits from the temperature-resolved analysis are typically a factor of 3 lower than MOS data. In the RGS spectrum, no line emission from ionization states below Fe XXIII is seen above $12 \AA$, and the amount of gas cooling below $\sim 3$ keV has a best-fit value $\dot M = 122_{-122}^{+343}$ $M_{\odot}$/yr. In addition, our analysis of the FIR SED of the BCG based on Herschel data provides $SFR = (530 \pm 50) M_\odot$/yr, significantly lower than previous estimates by a factor 1.5. Current data are able to firmly identify substantial amount of cooling gas only above 1.8 keV in the core of the Phoenix cluster. While MOS data analysis is consistent with values as high as $\dot M \sim 1000$ within $1 \sigma$, pn data provide $\dot M < 500 M_\odot$ yr$^{-1}$ at $3\sigma$ c.l. at temperature below 1.8 keV. At present, this discrepancy cannot be explained on the basis of known calibration uncertainties or other sources of statistical noise.
Context. The LIRG Zw 049.057 contains a compact obscured nucleus where a considerable amount of the galaxy's luminosity is generated. This nucleus contains a dusty environment that is rich in molecular gas. One approach to probing this kind of environment and to revealing what is hidden behind the dust is to study the rotational lines of molecules that couple well with the IR radiation emitted by the dust. Methods. We observed Zw 049.057 with PACS and SPIRE onboard the Herschel Space Observatory in rotational lines of H2O, H218O, OH, 18OH, and [O I]. We modeled the unresolved core of the galaxy using a spherically symmetric radiative transfer code. Results. We present the full SPIRE FTS spectrum of Zw 049.057, along with relevant spectral scans in the PACS range. We find that a minimum of two different components (nuclear and extended) are required in order to account for the rich molecular line spectrum. The nuclear component has a radius of 10-30 pc, a very high infrared surface brightness (1e14 Lsun/kpc2), warm dust (Td > 100 K), and a very large H2 column density (NH2 = 1e24-1e25 cm-2). The modeling also indicates high nuclear H2O (5e-6) and OH (4e-6) abundances relative to H2 as well as a low 16O/18O-ratio of 50-100. We also find a prominent infall signature in the [O I] line. We tentatively detect a 500 km/s outflow in the H2O 313->202 line. Conclusions. The high surface brightness of the core indicates the presence of either a buried active galactic nucleus or a very dense nuclear starburst.nThe H2O abundance is comparable to that of other compact (ultra-)luminous infrared galaxies such as NGC 4418 and Arp 220 - and also to hot cores in the Milky Way. The enhancement of 18O is a possible indicator that the nucleus of Zw 049.057 is in a similar evolutionary stage as the nuclei of Arp 220 - and more advanced than NGC 4418.
The Herschel Space Observatory has had a tremendous impact on the study of extragalactic dust. Specifically, early-type galaxies (ETG) have been the focus of several studies. In this paper we combine results from two Herschel studies - a Virgo cluster study HeViCS and a broader, low-redshift H-ATLAS/GAMA study - and contrast the dust and associated properties for similar mass galaxies. This comparison is motivated by differences in results exhibited between multiple Herschel studies of early-type galaxies. A comparison between consistent modified blackbody derived dust mass is carried out, revealing strong differences between the two samples in both dust mass and dust-to-stellar mass ratio. In particular, the HeViCS sample lacks massive ETG with as high a specific dust content as found in H-ATLAS. This is most likely connected with the difference in environment for the two samples. We calculate nearest neighbour environment densities in a consistent way, showing that H-ATLAS ETG occupy sparser regions of the local Universe, whereas HeViCS ETG occupy dense regions. This is also true for ETG that are not Herschel-detected but are in the Virgo and GAMA parent samples. Spectral energy distributions are fit to the panchromatic data. From these we find that in H-ATLAS the specific star formation rate anticorrelates with stellar mass and reaches values as high as in our Galaxy. On the other hand HeViCS ETG appear to have little star formation. Based on the trends found here, H-ATLAS ETG are thought to have more extended star formation histories and a younger stellar population than HeViCS ETG.
Numerical simulations of self-gravitating systems are generally based on N-body codes, which solve the equations of motion of a large number of interacting particles. This approach suffers from poor statistical sampling in regions of low density. In contrast, Vlasov codes, by meshing the entire phase space, can reach higher accuracy irrespective of the density. Here, we performed one-dimensional Vlasov simulations of a long-standing cosmological problem, namely the fractal properties of an expanding Einstein-De Sitter universe in Newtonian gravity. The N-body results were confirmed for high-density regions and extended to regions of low matter density, where the N-body approach usually fails.
Radio-loud AGN typically manifest powerful relativistic jets extending up to millions of light years and often showing superluminal motions organised in a complex kinematic pattern. A number of physical models are still competing to explain the jet structure and kinematics revealed by radio images using the VLBI technique. Robust measurements of longitudinal and transverse velocity field in the jets would provide crucial information for these models. This is a difficult task, particularly for transversely resolved jets in objects like 3C 273 and M87. To address this task, we have developed a new technique for identifying significant structural patterns (SSP) of smooth, transversely resolved flows and obtaining a velocity field from cross-correlation of these regions in multi-epoch observations. Detection of individual SSP is performed using the wavelet decomposition and multiscale segmentation of the observed structure. The cross-correlation algorithm combines structural information on different scales of the wavelet decomposition, providing a robust and reliable identification of related SSP in multi -epoch images. The algorithm enables recovering structural evolution on scales down to 0.25 full width at half maximum (FWHM) of the image point spread function (PSF). We present here examples of applying this algorithm to obtain the first detailed transverse velocity fields and to study the kinematic evolution in the parsec-scale jets in 3C 273 and M87.
Using our population synthesis code, we found that the typical chirp mass defined by $(m_1m_2)^{3/5}/(m_1+m_2)^{1/5}$ of Pop III binary black holes (BH-BHs) is $\sim30~\rm M_{\odot}$ with the total mass of $\sim60~\rm M_{\odot}$ so that the inspiral chirp signal as well as quasi normal mode (QNM) of the merged black hole (BH) are interesting targets of KAGRA, Adv. LIGO, Adv. Virgo and GEO network. The detection rate of the coalescing Pop III BH-BHs is 262 $\rm events~yr^{-1}$$(\rm SFR_P/(10^{-2.5}~\rm M_{\odot} \rm~yr^{-1}~Mpc^{-3}))\cdot Err_{sys}$ in our standard model where $\rm SFR_{p}$ and $\rm Err_{sys}$ are the peak value of the Pop III star formation rate and the systematic error with $\rm Err_{sys}=1$ for our standard model, respectively. To evaluate the robustness of chirp mass distribution and the range of $\rm Err_{sys}$, we examine the dependence of the results on the unknown parameters and the distribution functions in the population synthesis code. We found that the chirp mass has a peak at $\sim 30 ~\rm M_{\odot}$ in most of parameters and distribution functions as well as $\rm Err_{sys}$ ranges from 0.05577 to 2.289. Therefore, the detection rate of the coalescing Pop III BH-BHs ranges $14.6-599.3\ {\rm events~yr^{-1} ~(SFR_p/(10^{-2.5}~M_{\odot}~yr^{-1}~Mpc^{-3}))}$. The minimum rate corresponds to the worst model which we think unlikely so that unless $ {\rm ~(SFR_p/(10^{-2.5}~M_{\odot}~yr^{-1}~Mpc^{-3})) \ll 0.1}$, we expect the Pop III BH-BHs merger rate of at least one event per year by KAGRA, Adv. LIGO, Adv. Virgo and GEO network. Since the expected frequency of the QNM of the merged BH of mass $\sim60~\rm M_{\odot}$ is $\sim 200~{\rm Hz}$ where the interferometers have good sensitivity, there is a good chance to check if the Einstein theory is correct or not in the strong gravity region.
Upcoming HI surveys will deliver large datasets, and automated processing using the full 3-D information (two positional dimensions and one spectral dimension) to find and characterize HI objects is imperative. In this context, visualization is an essential tool for enabling qualitative and quantitative human control on an automated source finding and analysis pipeline. We discuss how Visual Analytics, the combination of automated data processing and human reasoning, creativity and intuition, supported by interactive visualization, enables flexible and fast interaction with the 3-D data, helping the astronomer to deal with the analysis of complex sources. 3-D visualization, coupled to modeling, provides additional capabilities helping the discovery and analysis of subtle structures in the 3-D domain. The requirements for a fully interactive visualization tool are: coupled 1-D/2-D/3-D visualization, quantitative and comparative capabilities, combined with supervised semi-automated analysis. Moreover, the source code must have the following characteristics for enabling collaborative work: open, modular, well documented, and well maintained. We review four state of-the-art, 3-D visualization packages assessing their capabilities and feasibility for use in the case of 3-D astronomical data.
We have completed a Chandra snapshot survey of 54 radio jets that are extended on arcsec scales. These are associated with flat spectrum radio quasars spanning a redshift range z=0.3 to 2.1. X-ray emission is detected from the jet of approximately 60% of the sample objects. We assume minimum energy and apply conditions consistent with the original Felten-Morrison calculations in order to estimate the Lorentz factors and the apparent Doppler factors. This allows estimates of the enthalpy fluxes, which turn out to be comparable to the radiative luminosities.
Due to the lack of long term pulsed emission in quiescence and the strong timing noise, it is impossible to directly measure the braking index $n$ of a magnetar. Based on the estimated ages of their potentially associated supernova remnants (SNRs), we estimate the values of $n$ of nine magnetars with SNRs, and find that they cluster in a range of $1\sim$41. Six magnetars have smaller braking indices of $1<n<3$, and we interpret them within a combination of magneto-dipole radiation and wind aided braking, while the larger braking indices of $n>3$ for other three magnetars are attributed to the decay of external braking torque, which might be caused by magnetic field decay. We estimate the possible wind luminosities for the magnetars with $1<n<3$, and the dipolar magnetic field decay rates for the magnetars with $n>3$ within the updated magneto-thermal evolution models. We point out that there could be some connections between the magnetar's anti-glitch event and its braking index, and the magnitude of $n$ should be taken into account when explaining the event. Although the constrained range of the magnetars' braking indices is tentative, our method provides an effective way to constrain the magnetars' braking indices if the measurements of the SNRs' ages are reliable, which can be improved by future observations.
The Gaia-ESO Survey (GES) is a large public spectroscopic survey at the European Southern Observatory Very Large Telescope. A key aim is to provide precise radial velocities (RVs) and projected equatorial velocities (v sin i) for representative samples of Galactic stars, that will complement information obtained by the Gaia astrometry satellite. We present an analysis to empirically quantify the size and distribution of uncertainties in RV and v sin i using spectra from repeated exposures of the same stars. We show that the uncertainties vary as simple scaling functions of signal-to-noise ratio (S/N) and v sin i, that the uncertainties become larger with increasing photospheric temperature, but that the dependence on stellar gravity, metallicity and age is weak. The underlying uncertainty distributions have extended tails that are better represented by Student's t-distributions than by normal distributions. Parametrised results are provided, that enable estimates of the RV precision for almost all GES measurements, and estimates of the v sin i precision for stars in young clusters, as a function of S/N, v sin i and stellar temperature. The precision of individual high S/N GES RV measurements is 0.22-0.26 km/s, dependent on instrumental configuration.
One of the main aims of the ESA Rosetta mission is to study the origin of the solar system by exploring comet 67P/Churyumov-Gerasimenko at close range. In this paper we discuss the origin and evolution of comet 67P/Churyumov-Gerasimenko in relation to that of comets in general and in the framework of current solar system formation models. We use data from the OSIRIS scientific cameras as basic constraints. In particular, we discuss the overall bi-lobate shape and the presence of key geological features, such as layers and fractures. We also treat the problem of collisional evolution of comet nuclei by a particle-in-a-box calculation for an estimate of the probability of survival for 67P/Churyumov-Gerasimenko during the early epochs of the solar system. We argue that the two lobes of the 67P/Churyumov-Gerasimenko nucleus are derived from two distinct objects that have formed a contact binary via a gentle merger. The lobes are separate bodies, though sufficiently similar to have formed in the same environment. An estimate of the collisional rate in the primordial, trans-planetary disk shows that most comets of similar size to 67P/Churyumov-Gerasimenko are likely collisional fragments, although survival of primordial planetesimals cannot be excluded. A collisional origin of the contact binary is suggested, and the low bulk density of the aggregate and abundance of volatile species show that a very gentle merger must have occurred. We thus consider two main scenarios: the primordial accretion of planetesimals, and the re-accretion of fragments after an energetic impact onto a larger parent body. We point to the primordial signatures exhibited by 67P/Churyumov-Gerasimenko and other comet nuclei as critical tests of the collisional evolution.
We describe a low-cost, open-access, CubeSat-based calibration instrument that is designed to support ground-based and sub-orbital experiments searching for various polarization signals in the cosmic microwave background (CMB). All modern CMB polarization experiments require a robust calibration program that will allow the effects of instrument-induced signals to be mitigated during data analysis. A bright, compact, and linearly polarized astrophysical source with polarization properties known to adequate precision does not exist. Therefore, we designed a space-based millimeter-wave calibration instrument, called CalSat, to serve as an open-access calibrator, and this paper describes the results of our design study. The calibration source on board CalSat is composed of five "tones" with one each at 47.1, 80.0, 140, 249 and 309 GHz. The five tones we chose are well matched to (i) the observation windows in the atmospheric transmittance spectra, (ii) the spectral bands commonly used in polarimeters by the CMB community, and (iii) The Amateur Satellite Service bands in the Table of Frequency Allocations used by the Federal Communications Commission. CalSat would be placed in a polar orbit allowing visibility from observatories in the Northern Hemisphere, such as Mauna Kea in Hawaii and Summit Station in Greenland, and the Southern Hemisphere, such as the Atacama Desert in Chile and the South Pole. CalSat also would be observable by balloon-borne instruments launched from a range of locations around the world. This global visibility makes CalSat the only source that can be observed by all terrestrial and sub-orbital observatories, thereby providing a universal standard that permits comparison between experiments using appreciably different measurement approaches.
From the numerous detected planets outside the Solar system, no terrestrial planet comparable to our Earth has been discovered so far. The search for an Exo-Earth is certainly a big challenge which may require the detections of planetary systems resembling our Solar system in order to find life like on Earth. However, even if we find Solar system analogues, it is not certain that a planet in Earth position will have similar circumstances as those of Earth. Small changes in the architecture of the giant planets can lead to orbital perturbations which may change the conditions of habitability for a terrestrial planet in the habitable zone (HZ). We present a numerical investigation where we first study the motion of test-planets in a particular Jupiter-Saturn configuration for which we can expect strong gravitational perturbations on the motion at Earth position according to a previous work. In this study, we show that these strong perturbations can be reduced significantly by the neighboring planets of Earth. In the second part of our study we investigate the motion of test-planets in inclined Jupiter-Saturn systems where we analyze changes in the dynamical behavior of the inner planetary system. Moderate values of inclination seem to counteract the perturbations in the HZ while high inclinations induce more chaos in this region. Finally, we carry out a stability study of the actual orbits of Venus, Earth and Mars moving in the inclined Jupiter-Saturn systems for which we used the Solar system parameters. This study shows that the three terrestrial planets will only move in low-eccentric orbits if Saturn's inclination is <=10{\deg}. Therefore, it seems that it is advantageous for the habitability of Earth when all planets move nearly in the same plane.
The existence of a classical bulge in disk galaxies holds important clue to
the assembly history of galaxies. Finding observational evidence of very low
mass classical bulges particularly in barred galaxies including our Milky Way,
is a challenging task as the bar driven secular evolution might bring
significant dynamical change to these bulges alongside the stellar disk.
Using high-resolution N-body simulation, we show that if a cool stellar disk
is assembled around a non-rotating low-mass classical bulge, the disk rapidly
grows a strong bar within a few rotation time scales. Later, the bar driven
secular process transform the initial classical bulge into a flattened rotating
stellar system whose central part also have grown a bar-like component rotating
in sync with the disk bar. During this time, a boxy/peanut (hereafter, B/P)
bulge is formed via the buckling instability of the disk bar and the vertical
extent of this B/P bulge being slightly higher than that of the classical
bulge, it encompasses the whole classical bulge. The resulting composite bulge
appears to be both photometrically and kinematically identical to a B/P bulge
without any obvious signature of the classical component. Our analysis suggest
that many barred galaxies in the local universe might be hiding such low-mass
classical bulges. We suggest that stellar population and chemodynamical
analysis might be required in establishing the evidence for such low-mass
classical bulges.
Locating planets in HabitableZones (HZs) around other stars is a growing field in contemporary astronomy. Since a large percentage of all G-M stars in the solar neighbourhood are expected to be part of binary or multiple stellar systems, investigations of whether habitable planets are likely to be discovered in such environments are of prime interest to the scientific community. As current exoplanet statistics predicts that the chances are higher to find new worlds in systems that are already known to have planets, we examine four known extrasolar planetary systems in tight binaries in order to determine their capacity to host additional habitable terrestrial planets. Those systems are Gliese 86, gamma Cephei, HD 41004 and HD 196885. In the case of gamma Cephei, our results suggest that only the M dwarf companion could host additional potentially habitable worlds. Neither could we identify stable, potentially habitable regions around HD 196885 A. HD 196885 B can be considered a slightly more promising target in the search for Earth-twins. Gliese 86 A turned out to be a very good candidate, assuming that the systems history has not been excessively violent. For HD 41004, we have identified admissible stable orbits for habitable planets, but those strongly depend on the parameters of the system. A more detailed investigation shows that for some initial conditions stable planetary motion is possible in the HZ of HD 41004 A. In spite of the massive companion HD 41004 Bb, we found that HD 41004 B, too, could host additional habitable worlds.
We study Lagrangian Perturbation Theory (LPT) and its regularization in the Effective Field Theory (EFT) approach. We evaluate the LPT displacement with the same phases as a corresponding $N$-body simulation, which allows us to compare perturbation theory to the non-linear simulation with significantly reduced cosmic variance, and provides a more stringent test than simply comparing power spectra. We reliably detect a non-vanishing leading order EFT coefficient and a stochastic displacement term, uncorrelated with the LPT terms. This stochastic term is expected in the EFT framework, and, to the best of our understanding, is not an artifact of numerical errors or transients in our simulations. This term constitutes a limit to the accuracy of perturbative descriptions of the displacement field and its phases, corresponding to a $1\%$ error on the non-linear power spectrum at $k=0.2 h$/Mpc at $z=0$. Predicting the displacement power spectrum to higher accuracy or larger wavenumbers thus requires a model for the stochastic displacement.
Classical radiation power from an accelerated massive charge diverges in the zero-mass limit, while some general arguments suggest that strictly massless charge does not not radiate at all. On the other hand, the regularized classical radiation reaction force, though looking odd, is non-zero and finite. To clarify this controversy, we consider radiation problem in massless scalar quantum electrodynamics in the external magnetic field. In this framework, synchrotron radiation is found to be non-zero, finite, and essentially quantum. Its spectral distribution is calculated using Schwinger's proper time technique for {\em ab initio} massless particle of zero spin. Provided $E^2\gg eH$, the maximum in the spectrum is shown to be at $\hbar \omega=E/3$, and the average photon energy is $4E/9$. The normalized spectrum is universal, depending neither on $E$ nor on $H$. Quantum nature of radiation makes classical radiation reaction equation meaningless for massless charge. Our results are consistent with the view (supported by the renormalization group argument) that the correct classical limit of massless quantum electrodynamics is free theory.
The behavior and properties of neutrinos in non-uniform nuclear matter, surrounded by electrons and other neutrinos are studied. The nuclear matter itself is modeled by the non-linear Walecka model, where the so-called nuclear pasta phase is described using the Thomas-Fermi approximation, solved in a Wigner-Seitz cell. We obtain the total cross-section and mean-free path for the neutrinos, taking into account scattering and neutrino absorption, and compare the final results for two known kind of model parametrizations: one in which non-linear effects in the strong sector are explicitly written in the model Lagrangian and another one in which the coupling constants are density dependent. The solution for this problem is important for the understanding of neutrino diffusion in a newly born neutron star after a supernova explosion.
The interaction between refraction from a distribution of inhomogeneous plasma and gravitational lensing introduces novel effects to the paths of light rays passing by a massive object. The plasma contributes additional terms to the equations of motion, and the resulting ray trajectories are frequency-dependent. Lensing phenomena and circular orbits are investigated for plasma density distributions $N \propto 1/r^h$ with $h \geq 0$ in the Schwarzschild space-time. For rays passing by the mass near the plasma frequency refractive effects can dominate, effectively turning the gravitational lens into a mirror. We obtain the turning points, circular orbit radii, and angular momentum for general $h$. Previous results have shown that light rays behave like massive particles with an effective mass given by the plasma frequency for a constant density $h=0$. We study the behaviour for general $h$ and show that when $h=2$ the plasma term acts like an additional contribution to the angular momentum of the passing ray. When $h=3$ the potential and radii of circular orbits are analogous to those found in studies of massless scalar fields on the Schwarzschild background. As a physically motivated example we study the pulse profiles of a compact object with antipodal hotspots sheathed in a dense plasma, which shows dramatic frequency-dependent shifts from the behaviour in vacuum. Finally, we consider the potential observability and applications of such frequency-dependent plasma effects in general relativity for several types of neutron star.
This paper treats non-relativistic matter and a scalar field $\phi$ minimally coupled to gravity in flat Friedmann-Lema\^itre-Robertson-Walker cosmology. The field equations are reformulated as a three-dimensional dynamical system on an extended compact state space, complemented with cosmographic diagrams. Revisiting a select set of familiar potentials, but in a generic global dynamical systems setting, suggests that one should impose global and asymptotic bounds on $\lambda=-V^{-1}\,dV/d\phi$ in order to obtain an attracting separatrix surface that describes the evolution of all solutions with $\Omega_m$ initially close to one, set by, e.g., inflation. Furthermore, letting $\lambda \rightarrow 0$ for all $\phi$ and $\Omega_m\rightarrow 1$ initially yields $\Lambda$CDM cosmology and thus it is possible to continuously modify $\Lambda$CDM dynamics by choosing potentials that continuously deform the $\Lambda$CDM attracting separatrix surface, thereby also providing a useful testbed for $\Lambda$CDM cosmology; specific examples of potentials and the associated global dynamics are given.
Tribrid inflation is a variant of supersymmetric hybrid inflation in which the inflaton is a matter field (which can be charged under gauge symmetries) and inflation ends by a GUT-scale phase transition of a waterfall field. These features make tribrid inflation a promising framework for realising inflation with particularly close connections to particle physics. Superpotentials of tribrid inflation involve effective operators suppressed by some cutoff scale, which is often taken as the Planck scale. However, these operators may also be generated by integrating out messenger superfields with masses below the Planck scale, which is in fact quite common in GUT and/or flavour models. The values of the inflaton field during inflation can then lie above this mass scale, which means that for reliably calculating the model predictions one has to go beyond the effective theory description. We therefore discuss realisations of effective theories of tribrid inflation and specify in which cases effects from the messenger fields are expected, and under which conditions they can safely be neglected. In particular, we point out how to construct realisations where, despite the fact that the inflaton field values are above the messenger mass scale, the predictions for the observables are (to a good approximation) identical to the ones calculated in the effective theory treatment where the messenger mass scale is identified with the (apparent) cutoff scale.
In this work, we investigate inflationary cosmology using a deformed scalar field theory. This scalar field theory will be deformed by the generalized uncertainty principle containing a linear momentum term. Apart from being consistent with the existence of a minimum measurable length scale, this generalized uncertainty principle is also consistent with doubly special relativity and hence with the existence of maximum measurable momentum. We use this deformed scalar field theory to analyze the tensor and scalar mode equations in a de Sitter background, in addition to calculating modifications to the tensor-to-scalar ratio. We demonstrate that our calculations fit the Planck's data better than the ones motivated from the usual generalized uncertainty principle which only contains quadratic powers of momentum.
The importance of contact discontinuities in 2D isothermal flows has rarely been discussed, since most Riemann solvers are derived for 1D Euler equations. We present a new contact resolving approximate Riemann solver for the isothermal Euler equations and show its performance for several one- and two-dimensional test problems. The new solver extends the well-known HLL solver, while retaining its computational simplicity. The significant gain in resolution of vortices is displayed by a simulation of the K\'arm\'an vortex street. We discuss the loss of Galilean invariance and its implications for the resolution of contact discontinuities, which is experienced by all modern numerical schemes for hydrodynamics in non-moving grids.
We discuss inflaton decays and reheating in no-scale Starobinsky-like models of inflation, calculating the effective equation-of-state parameter, $w$, during the epoch of inflaton decay, the reheating temperature, $T_{\rm reh}$, and the number of inflationary e-folds, $N_*$, comparing analytical approximations with numerical calculations. We then illustrate these results with applications to models based on no-scale supergravity and motivated by generic string compactifications, including scenarios where the inflaton is identified as an untwisted-sector matter field with direct Yukawa couplings to MSSM fields, and where the inflaton decays via gravitational-strength interactions. Finally, we use our results to discuss the constraints on these models imposed by present measurements of the scalar spectral index $n_s$ and the tensor-to-scalar perturbation ratio $r$, converting them into constraints on $N_*$, the inflaton decay rate and other parameters of specific no-scale inflationary models.
In the framework of $f(T)$ theories of gravity, we solve the field equations for $f(T)=T+\alpha T^{n}$, in the weak-field approximation and for spherical symmetry spacetime. Since $f(T)=T$ corresponds to Teleparallel Gravity, which is equivalent to General Relativity, the non linearity of the Lagrangian are expected to produce perturbations of the general relativistic solutions, parameterized by $\alpha$. Hence, we use the $f(T)$ solutions to model the gravitational field of the Sun, and exploit data from accurate tracking of spacecrafts orbiting Mercury and Saturn to infer preliminary insights on what could be obtained about the model parameter $\alpha$ and the cosmological constant $\Lambda$. It turns out that improvements of about one-three orders with respect to the present-day constraints in the literature of magnitude seem possible.
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Extended material at large radii surrounding a supernova can result in a double-peaked light curve when the material is sufficiently massive that the supernova shock continues to propagate into it and sufficiently extended that it produces a bright first peak. Such material can be the leftover, low-mass envelope of a star that has been highly stripped, the mass associated with a wind, or perhaps mass surrounding the progenitor due to some type of pre-explosion activity. I summarize the conditions necessary for such a light curve to occur, describe what can be learned about the extended material from the light curve shape, and provide a semi-analytic model for fitting the first peak in these double-peaked supernovae. This is applied to the specific case of a Type Ic super-luminous supernova, LSQ14bdq. The mass in the extended material around this explosion's progenitor is measured to be small, ~0.2-0.5 Msun. The radius of this material must be >500 Rsun, but it is difficult to constrain due to a degeneracy between radius and the supernova's energy. In the future, spectra taken during the first peak will be important for measuring the velocity and composition of the extended material so that this degeneracy can be overcome.
Estimating the number of microlensing events observed in different parts of the Galactic bulge is a crucial point in planning microlensing experiments. Reliable estimates are especially important if observing resources are scarce, as is the case for space missions: K2, WFIRST, and Euclid. Here we show that the number of detected events can be reliably estimated based on statistics of stars observed in targeted fields. The statistics can be estimated relatively easily, which makes presented method suitable for planning future microlensing experiments.
From pulsating stars to transiting exoplanets, the search for periodic signals in K2 data, Kepler's 2-wheeled extension, is relevant to a long list of scientific goals. Systematics affecting K2 light curves due to the decreased spacecraft pointing precision inhibit the easy extraction of periodic signals from the data. We here develop a method for producing periodograms of K2 light curves that are insensitive to pointing-induced systematics; the Systematics-Insensitive Periodogram (SIP). Traditional sine-fitting periodograms use a generative model to find the frequency of a sinusoid that best describes the data. We extend this principle by including systematic trends, based on a set of 'Eigen light curves', following Foreman-Mackey et al. (2015), in our generative model as well as a sum of sine and cosine functions over a grid of frequencies. Using this method we are able to produce periodograms with vastly reduced systematic features. The quality of the resulting periodograms are such that we can recover acoustic oscillations in giant stars and measure stellar rotation periods without the need for any detrending. The algorithm is also applicable to the detection of other periodic phenomena such as variable stars, eclipsing binaries and short-period exoplanet candidates. The SIP code is available at https://github.com/RuthAngus/SIPK2.
This paper considers the impact of Lyman-$\alpha$ (WF) coupling and X-ray heating on the evolution of the 21-cm brightness-temperature 1-point statistics (as predicted by semi-numerical simulations). The X-ray production efficiency is varied over four orders of magnitude and the hardness of the X-ray spectrum is also varied (from that predicted for high mass X-ray binaries to the softer spectrum expected from the hot inter-stellar medium). We find peaks in the redshift evolution of both the variance and skewness associated (in amplitude and redshift) to the efficiency of X-ray production. The amplitude of the variance is also sensitive to the hardness of the X-ray SED. It is possible to break this degeneracy as the skewness is not sensitive to the X-ray spectral hardness. There is an earlier peak in the variance's evolution associated with fluctuations in WF-coupling followed by a plateau connecting it to the heating peak; the redshift extent of this provides insight into the relative timing of the coupling and heating phases. Importantly, we note that a late X-ray heating scenario would seriously hamper our ability to constrain reionization with the variance. Late X-ray heating also qualitatively alters the evolution of the skewness, providing a clean way to constrain such models. We find that, if foregrounds can be removed, first generation instruments (such as LOFAR, MWA and PAPER) could constrain reionization and late X-ray heating models with the variance. We find that HERA and SKA (phase 1) will be able to constrain both reionization and heating by measuring the variance using foreground avoidance techniques. If foregrounds can be removed these instruments will also be able to tightly constrain the nature of WF coupling.
We develop a simple dynamical model for the evolution of gas in the centres of barred spiral galaxies, using the Milky Way's Central Molecular Zone (CMZ, i.e., the central few hundred pc) as a case study. We show that, in the presence of a galactic bar, gas in a disc in the central regions of a galaxy will be driven inwards by angular momentum transport induced by acoustic instabilities within the bar's inner Lindblad resonance. This transport process drives turbulence within the gas that temporarily keeps it strongly gravitationally stable and prevents the onset of rapid star formation. However, at some point the rotation curve must transition from approximately flat to approximately solid body, and the resulting reduction in shear reduces the transport rates and causes gas to build up, eventually producing a gravitationally-unstable region that is subject to rapid and violent star formation. For the observed rotation curve of the Milky Way, the accumulation happens $\sim 100$ pc from the centre of the Galaxy, in good agreement with the observed location of gas clouds and young star clusters in the CMZ. The characteristic timescale for gas accumulation and star formation is of order $10-20$ Myr. We argue that similar phenomena should be ubiquitous in other barred spiral galaxies.
Studying the reflection of X-rays off the inner edge of the accretion disk in a neutron star low-mass X-ray binary, allows us to investigate the accretion geometry and to constrain the radius of the neutron star. We report on a NuSTAR observation of 4U 1608-52 obtained during a faint outburst in 2014 when the neutron star, which has a known spin frequency of 620 Hz, was accreting at ~1-2% of the Eddington limit. The 3-79 keV continuum emission was dominated by a Gamma~2 power law, with a ~1-2% contribution from a kTbb~0.3-0.6 keV black body component. The high-quality NuSTAR spectrum reveals the hallmarks of disk reflection; a broad iron line peaking near 7~keV and a Compton back-scattering hump around ~20-30 keV. Modeling the disk reflection spectrum points to a binary inclination of i~30-40 degrees and a small `coronal' height of h<8.5 GM/c2. Furthermore, our spectral analysis suggests that the inner disk radius extended to Rin~7-10 GM/c2, close to the innermost stable circular obit. This constrains the neutron star radius to R<21 km and the redshift from the stellar surface to z>0.12, for a mass of M=1.5 Msun and a spin parameter of a=0.29.
Detection of the fluctuations in 21 cm line emission from neutral hydrogen during the Epoch of Reionization in thousand hour integrations poses stringent requirements on calibration and image quality, both of which necessitate accurate primary beam models. The Murchison Widefield Array (MWA) uses phased array antenna elements which maximize collecting area at the cost of complexity. To quantify their performance, we have developed a novel beam measurement system using the 137 MHz ORBCOMM satellite constellation and a reference dipole antenna. Using power ratio measurements, we measure the {\it in situ} beampattern of the MWA antenna tile relative to that of the reference antenna, canceling the variation of satellite flux or polarization with time. We employ angular averaging to mitigate multipath effects (ground scattering), and assess environmental systematics with a null experiment in which the MWA tile is replaced with a second reference dipole. We achieve beam measurements over 30 dB dynamic range in beam sensitivity over a large field of view (65\% of the visible sky), far wider and deeper than drift scans through astronomical sources allow. We verify an analytic model of the MWA tile at this frequency within a few percent statistical scatter within the full width at half maximum. Towards the edges of the main lobe and in the sidelobes, we measure tens of percent systematic deviations. We compare these errors with those expected from known beamforming errors.
We present the main steps that will be taken to extract H$\alpha$ emission flux from Javalambre Photometric Local Universe Survey (J-PLUS) photometric data. For galaxies with $z\lesssim0.015$, the H$\alpha$+[NII] emission is covered by the J-PLUS narrow-band filter $F660$. We explore three different methods to extract the H$\alpha$ + [NII] flux from J-PLUS photometric data: a combination of a broad-band and a narrow-band filter ($r'$ and $F660$), two broad-band and a narrow-band one ($r'$, $i'$ and $F660$), and a SED-fitting based method using 8 photometric points. To test these methodologies, we simulated J-PLUS data from a sample of 7511 SDSS spectra with measured H$\alpha$ flux. Based on the same sample, we derive two empirical relations to correct the derived H$\alpha$+[NII] flux from dust extinction and [NII] contamination. We find that the only unbiased method is the SED fitting based one. The combination of two filters underestimates the measurements of the H$\alpha$ + [NII] flux by a 28%, while the three filters method by a 9%. We study the error budget of the SED-fitting based method and find that, in addition to the photometric error, our measurements have a systematic uncertainty of a 4.3%. Several sources contribute to this uncertainty: differences between our measurement procedure and the one used to derive the spectroscopic values, the use of simple stellar populations as templates, and the intrinsic errors of the spectra, which were not taken into account. Apart from that, the empirical corrections for dust extinction and [NII] contamination add an extra uncertainty of 14%. Given the J-PLUS photometric system, the best methodology to extract H$\alpha$ + [NII] flux is the SED-fitting based one. Using this method, we are able to recover reliable H$\alpha$ fluxes for thousands of nearby galaxies in a robust and homogeneous way.
We present near-simultaneous Chandra/HST observations of the very faint ($L_{x} < 10^{36}$ erg s$^{-1}$) X-ray transient source M15 X-3, as well as unpublished archival Chandra observations of M15 X-3. The Chandra observations constrain the luminosity of M15 X-3 to be $< 10^{34}$ erg s$^{-1}$ in all observed epochs. The X-ray spectrum shows evidence of curvature, and prefers a fit to a broken power-law with break energy $E_{\rm break} = 2.7^{+0.4}_{-0.6}$ keV, and power law indices of $\Gamma_{1} = 1.3^{+0.1}_{-0.2}$ and $\Gamma_{2} = 1.9^{+0.2}_{-0.2}$ over a single power law. We fit our new F438W ($B$), F606W (broad $V$), and F814W ($I$) HST data on the blue optical counterpart with a model for an accretion disk and a metal-poor main sequence star. From this fit, we determine the companion to be consistent with a main sequence star of mass $0.440^{+0.035}_{-0.060}$ $M_{\odot}$ in a $\sim$4-hour orbit. X-ray irradiation of the companion is likely to be a factor in the optical emission from the system, which permits the companion to be smaller than calculated above, but larger than $0.15$ $M_{\odot}$ at the $3\sigma$ confidence level. M15 X-3 seems to be inconsistent with all suggested hypotheses explaining very faint transient behavior, except for magnetospherically inhibited accretion.
We present a new method to test the cosmological model, and to estimate the cosmological parameters, based on the non-linear relation between ultraviolet and X-ray luminosity of quasars. We built a data set of ~1,250 quasars by merging several literature samples with X-ray measurements at 2 keV and SDSS photometry, which was used to estimate the extinction-corrected 2500~\AA\ flux. We obtained three main results: (1) we checked the non-linear relation between X-ray and UV luminosities in small redshift bins up to z~6, confirming that it holds at all redshifts with the same slope; (2) we built a Hubble diagram for quasars up to z~6, which is well matched to that of supernovae in the common z=0-1.4 redshift interval, and extends the test of the cosmological model up to z~6; (3) we showed that this non-linear relation is a powerful tool to estimate cosmological parameters. With present data, assuming a $\Lambda$CDM model, we obtain $\Omega_M$=0.21$^{+0.08}_{-0.10}$ and $\Omega_\Lambda$=0.95$^{+0.30}_{-0.20}$ ($\Omega_M$=0.28$\pm$0.04 and $\Omega_\Lambda$=0.74$\pm0.08$ from a joint quasar-SNe fit). However, much more precise measurements will be achieved in the future. A few thousands SDSS quasars already have serendipitous X-ray observations with Chandra or XMM-Newton, and at least 100,000 quasars with UV and X-ray data will be available from the eROSITA all-sky survey in a few years. Euclid, LSST, and Athena surveys will further increase the sample size to at least several hundred thousands. Our simulations show that these samples will provide tight constraints on the cosmological parameters, and will allow to test possible deviations from the standard model with higher precisions than available today.
We study the connection between the chromospheric and photospheric behaviour of the active late-type star FK Comae. We use spot temperature modelling, light curve inversion based on narrow- and wide-band photometric measurements, Halpha observations from 1997-2010, and Doppler maps from 2004-2010 to compare the behaviour of chromospheric and photospheric features. Investigating low-resolution Halpha spectra we find that the changes in the chromosphere seem to happen mainly on a time scale longer than a few hours, but shorter variations were also observed. According to the Halpha measurements prominences are often found in the chromosphere that reach to more than a stellar radius and are stable for weeks, and which seem to be often, but not every time connected with dark photospheric spots. The rotational modulation of the Halpha emission seems to typically be anticorrelated with the light curve, but we did not find convincing evidence of a clear connection in the long-term trends of the Halpha emission and the brightness of the star. In addition, FK Com seems to be in an unusually quiet state in 2009-2010 with very little chromospheric activity and low spot contrast, that might indicate the long-term decrease of activity.
We investigate the multiplicity properties of 408 B-type stars observed in the 30 Doradus region of the Large Magellanic Cloud with multi-epoch spectroscopy from the VLT-FLAMES Tarantula Survey (VFTS). We use a cross-correlation method to estimate relative radial velocities from the helium and metal absorption lines for each of our targets. Objects with significant radial-velocity variations (and with an amplitude larger than 16 km/s) are classified as spectroscopic binaries. We find an observed spectroscopic binary fraction (defined by periods of <10^3.5 d and mass ratios >0.1) for the B-type stars, f_B(obs) = 0.25 +/- 0.02, which appears constant across the field of view, except for the two older clusters (Hodge 301 and SL 639). These two clusters have significantly lower fractions of 0.08 +/- 0.08 and 0.10 +/- 0.09, respectively. Using synthetic populations and a model of our observed epochs and their potential biases, we constrain the intrinsic multiplicity properties of the dwarf and giant (i.e. relatively unevolved) B-type stars in 30 Dor. We obtain a present-day binary fraction f_B(true) = 0.58 +/- 0.11, with a flat period distribution. Within the uncertainties, the multiplicity properties of the B-type stars agree with those for the O stars in 30 Dor from the VFTS.
We present a simulation of the long-term evolution of a Population III supernova remnant in a cosmological minihalo. Employing passive Lagrangian tracer particles, we investigate how chemical stratification and anisotropy in the explosion can affect the abundances of the first low-mass, metal-enriched stars. We find that reverse shock heating can leave the inner mass shells at entropies too high to cool, leading to carbon-enhancement in the re-collapsing gas. This hydrodynamic selection effect could explain the observed incidence of carbon-enhanced metal-poor (CEMP) stars at low metallicity. We further explore how anisotropic ejecta distributions, recently seen in direct numerical simulations of core-collapse explosions, may translate to abundances in metal-poor stars. We find that some of the observed scatter in the Population II abundance ratios can be explained by an incomplete mixing of supernova ejecta, even in the case of only one contributing enrichment event. We demonstrate that the customary hypothesis of fully-mixed ejecta clearly fails if post-explosion hydrodynamics prefers the recycling of some nucleosynthetic products over others. Furthermore, to fully exploit the stellar-archaeological program of constraining the Pop III initial mass function from the observed Pop II abundances, considering these hydrodynamical transport effects is crucial. We discuss applications to the rich chemical structure of ultra-faint dwarf satellite galaxies, to be probed in unprecedented detail with upcoming spectroscopic surveys.
We have derived the Galactic bulge initial mass function of the SWEEPS field down to 0.15 $M_{\odot}$, using deep photometry collected with the Advanced Camera for Surveys on the Hubble Space Telescope. Observations at several epochs, spread over 9 years, allowed us to separate the disk and bulge stars down to very faint magnitudes, $F814W \approx$ 26 mag, with a proper-motion accuracy better than 0.5 mas/yr (20 km/s). This allowed us to determine the initial mass function of the pure bulge component uncontaminated by disk stars for this low-reddening field in the Sagittarius window. In deriving the mass function, we took into account the presence of unresolved binaries, errors in photometry, distance modulus and reddening, as well as the metallicity dispersion and the uncertainties caused by adopting different theoretical color-temperature relations. We found that the Galactic bulge initial mass function can be fitted with two power laws with a break at $M \sim$ 0.56 $M_{\odot}$, the slope being steeper ($\alpha = -2.41\pm$0.50) for the higher masses, and shallower ($\alpha = -1.25\pm$0.20) for the lower masses. In the high-mass range, our derived mass function agrees well with the mass function derived for other regions of the bulge. In the low-mass range however, our mass function is slightly shallower, which suggests that separating the disk and bulge components is particularly important in the low-mass range. The slope of the bulge mass function is also similar to the slope of the mass function derived for the disk in the high-mass regime, but the bulge mass function is slightly steeper in the low-mass regime. We used our new mass function to derive stellar mass--to--light values for the Galactic bulge and we found $M/L_{F814W} =$ 2.2$\pm$0.3 and $M/L_{F606W} =$ 3.2$\pm$0.5.
Modified gravity models require a screening mechanism to be able to evade the stringent constraints from local gravity experiments, and, at the same time give rise to observable astrophysical and cosmological signatures. Such screened modified gravity models necessarily have dynamics determined by complex non-linear equations that usually needs to be solved on a model-by-model basis to produce predictions. This makes testing them a cumbersome process. In this paper, we investigate if there is a common signature of all the different models that is suitable to test them on cluster scales. To do this we propose an observable related to the fifth-force -- which observationally can be related to the ratio of dynamical to lensing mass of a halo - and then show that the predictions for this observable can be rescaled to a near universal form for a large class of modified gravity models. We demonstrate this using the Hu-Sawicky $f(R)$, the Symmetron, the nDGP and the Dilaton model - as well as unifying parametrizations. The universal form is determined by only three quantities: a strength, a mass and a width-parameter. We also show how these parameters can be derived from a specific theory. This self-similarity in the predictions can hopefully be used to search for signatures of modified gravity on cluster scales in a model-independent way.
Context. The elliptical galaxy NGC 3923 is known to be surrounded by a number
of stellar shells, a probable remnant of an accreted galaxy. Despite its
uniqueness, the deepest images of its outskirts come from the 80s. B\'{i}lek et
al. (2014) predicted a new shell to lie in this region on the basis of the MOND
theory of modified dynamics.
Aims. To obtain the deepest image ever of the galaxy and to map the tidal
features in it.
Methods. The image of the galaxy was taken by the MegaCam camera at the
Canada-France-Hawaii Telescope in the $g'$ band. It reached the
surface-brightness limit of 29 mag arcsec$^{-2}$. Moreover, we reanalyze an
archival HST image of the galaxy.
Results. We detected up to 42 shells in NGC 3923. This is by far most of all
galaxies. We present the description of the shells and other tidal features in
the galaxy. A probable progenitor of some of these features was discovered. The
shell system likely originates from two or more progenitors. The predicted
shell was not detected, but we found that the prediction was based on incorrect
assumptions and poor data.
(abridged) We analyse the clustering features of Large Scale Structures (LSS) in the presence of massive neutrinos, employing a set of large-volume, high-resolution cosmological N-body simulations, where neutrinos are treated as a separate collisionless fluid. The volume of 8$\cGpc$, combined with a resolution of about $8\times 10^{10}\Ms$ for the cold dark matter (CDM) component, represents a significant improvement over previous N-body simulations in massive neutrino cosmologies. We show that most of the nonlinear evolution is generated exclusively by the CDM component. We find that accounting only for the nonlinear evolution of the CDM power spectrum allows to recover the total matter power spectrum with the same accuracy as the massless case. Indeed, we show that, the most recent version of the \halofit\ formula calibrated on $\Lambda$CDM simulations can be applied directly to the linear CDM power spectrum without requiring additional fitting parameters in the massive case. As a second step, we study the abundance and clustering properties of CDM halos, confirming that, in massive neutrino cosmologies, the proper definition of the halo bias should be made with respect to the {\em cold} rather than the {\em total} matter distribution, as recently shown in the literature. Here we extend these results to the redshift space, finding that, when accounting for massive neutrinos, an improper definition of the linear bias can lead to a systematic error of about 1-$2 \%$ in the determination of the linear growth rate from anisotropic clustering. This result is quite important if we consider that future spectroscopic galaxy surveys, as \eg\ Euclid, are expected to measure the linear growth-rate with statistical errors less than about $3 \%$ at $z\lesssim1$.
We recover spiral and barred spiral patterns in disk galaxy simulations with a Wave Dark Matter (WDM) background (also known as Scalar Field Dark Matter (SFDM), Ultra-Light Axion (ULA) dark matter, and Bose-Einstein Condensate (BEC) dark matter). Here we show how the interaction between a baryonic disk and its Dark Matter Halo triggers the formation of spiral structures when the halo is allowed to have a triaxial shape and angular momentum. This is a more realistic picture within the WDM model since a non-spherical rotating halo seems to be more natural. By performing hydrodynamic simulations, along with earlier test particles simulations, we demonstrate another important way in which wave dark matter is consistent with observations. The common existence of bars in these simulations is particularly noteworthy. This may have consequences when trying to obtain information about the dark matter distribution in a galaxy, the mere presence of spiral arms or a bar usually indicates that baryonic matter dominates the central region and therefore observations, like rotation curves, may not tell us what the DM distribution is at the halo center. But here we show that spiral arms and bars can develop in DM dominated galaxies with a central density core without supposing its origin on mechanisms intrinsic to the baryonic matter.
We present the analysis of the Chandra X-ray Observatory observations of the eccentric gamma-ray binary PSR B1259-63/LS 2883. The analysis shows that the extended X-ray feature seen in previous observations is still moving away from the binary with an average projected velocity of about 0.07c and shows a hint of acceleration. The spectrum of the feature appears to be hard (photon index of 0.8) with no sign of softening compared to previously measured values. We interpret it as a clump of plasma ejected from the binary through the interaction of the pulsar with the decretion disk of the O-star around periastron passage. We suggest that the clump is moving in the unshocked relativistic pulsar wind (PW), which can accelerate the clump. Its X-ray emission can be interpreted as synchrotron radiation of the PW shocked by the collision with the clump.
We investigate the dependence of gas kinematics and column densities in the MgII-absorbing circumgalactic medium on galaxy color, azimuthal angle, and inclination to trace baryon cycle processes. Our sample of 30 foreground isolated galaxies at $0.3<z_{\rm gal}<1.0$, imaged with the Hubble Space Telescope, are probed by background quasars within a projected distance of $20<D<110$ kpc. From the high-resolution ($\Delta v\simeq 6.6$ km s$^{-1}$) quasar spectra, we quantify the extent of the absorber velocity structure with pixel-velocity two-point correlation functions. Absorbers with the largest velocity dispersions are associated with blue, face-on ($i<57^{\circ}$) galaxies probed along the projected minor axis ($\Phi \geq 45^{\circ}$), while those with the smallest velocity dispersions belong to red, face-on galaxies along the minor axis. The velocity structure is similar for edge-on ($i \geq 57^{\circ}$) galaxies regardless of galaxy color or azimuthal angle, for red galaxies with azimuthal angle, and for blue and red galaxies probed along the projected major axis ($\Phi<45^{\circ}$). The cloud column densities for face-on galaxies and red galaxies are smaller than for edge-on galaxies and blue galaxies, respectively. These results are consistent with biconical outflows along the minor axis for star-forming galaxies and accreting and/or rotating gas, which is most easily observed in edge-on galaxies probed along the major axis. Gas entrained in outflows may be fragmented with large velocity dispersions, while gas accreting onto or rotating around galaxies may be more coherent due to large path lengths and smaller velocity dispersions. Quiescent galaxies may exhibit little-to-no outflows along the minor axis, while accretion/rotation may exist along the major axis.
We present an analysis of the diffuse soft X-ray emission from the nuclear region of M51 combining both XMM-Newton RGS and Chandra data. Most of the RGS spectrum of M51 can be fitted with a thermal model with a temperature of $\sim0.5$ keV except for the OVII triplet, which is forbidden-line dominated. The Fe L-shell lines peak around the southern cloud, where the OVIII and NVII Lya lines also peak. In contrast, the peak of the OVII forbidden line is about 10$"$ offset from that of the other lines, indicating that it is from a spatially distinct component. The spatial distribution of the OVII triplet mapped by the Chandra data shows that most of the OVII triplet flux is located at faint regions near edges, instead of the southern cloud where other lines peak. This distribution of the OVII triplet is inconsistent with the photoionization model. Other mechanisms that could produce the anomalous OVII triplet, including a recombining plasma and charge exchange X-ray emission, are discussed.
We use high-resolution (0.5 arcsec) CO(2-1) observations performed with ALMA to trace the kinematics of the molecular gas in the Seyfert 2 galaxy IC5063. A fast outflow of molecular gas extends along the entire radio jet, with the highest outflow velocities about 0.5kpc from the nucleus, at the location of the brighter hot-spot in the W lobe. The data show that a massive, fast outflow with velocities up to 650 km/s of cold molecular gas is present, in addition to one detected earlier in warm H2, HI and ionised gas. Both the central AGN and the radio jet could energetically drive the outflow. However, the characteristics of the outflowing gas point to the radio jet being the main driver. This is important, because IC5063, although one of the most powerful Seyfert galaxies, is a relatively weak radio source (P = 3x10^23 W/Hz). All the observed characteristics can be described by a scenario of a radio plasma jet expanding into a clumpy medium, interacting directly with the clouds and inflating a cocoon that drives a lateral outflow into the interstellar medium. This model is consistent with results obtained by recent simulations such as those of Wagner et al.. A stronger, direct interaction between the jet and a gas cloud is present at the location of the brighter W lobe. Even assuming the most conservative values for the conversion factor CO-to-H2, the mass of the outflowing gas is between 1.9 and 4.8x10^7 Msun. These amounts are much larger than those of the outflow of warm gas (molecular and ionized) and somewhat larger than of the HI outflow. This suggests that most of the observed cold molecular outflow is due to fast cooling after being shocked. This gas is the end product of the cooling process. Our CO observations demonstrate that fast outflows of molecular gas can be driven by relativistic jets.
The target of this work is to investigate the physical nature of polar jets
in the solar corona and their possible contribution to coronal heating and
solar wind flow based on the analysis of X-ray images acquired by the Hinode
XRT telescope. We estimate the di?erent forms of energy associated with many of
these small-scale eruptions, in particular the kinetic energy and enthalpy. Two
Hinode XRT campaign datasets focusing on the two polar coronal holes were
selected to analyze the physical properties of coronal jets; the analyzed data
were acquired using a series of three XRT filters. Typical kinematical
properties (e.g., length, thickness, lifetime, ejection rate, and velocity) of
18 jets are evaluated from the observed sequences, thus providing information
on their possible contribution to the fast solar wind flux escaping from
coronal holes. Electron temperatures and densities of polar-jet plasmas are
also estimated using ratios of the intensities observed in di?erent filters.
We find that the largest amount of energy eventually provided to the corona
is thermal. The energy due to waves may also be significant, but its value is
comparatively uncertain. The kinetic energy is lower than thermal energy, while
other forms of energy are comparatively low. Lesser and fainter events seem to
be hotter, thus the total contribution by polar jets to the coronal heating
could have been underestimated so far. The kinetic energy flux is usually
around three times smaller than the enthalpy counterpart, implying that this
energy is converted into plasma heating more than in plasma acceleration. This
result suggests that the majority of polar jets are most likely not escaping
from the Sun and that only cooler ejections could possibly have enough kinetic
energy to contribute to the total solar wind flow.
We study the frequency distributions of Delta Scuti stars observed by the Kepler satellite in short-cadence mode. To minimize errors in the estimated stellar parameters, we divided the instability strip into ten regions and determined the mean frequency distribution in each region. We confirm that the presence of low frequencies is a property of all Delta Scuti stars, rendering meaningless the concept of Delta Sct/Gamma Dor hybrids. We obtained the true distribution of equatorial rotational velocities in each region and calculated the frequency distributions predicted by pulsation models, taking into account rotational splitting of the frequencies. We confirm that rotation cannot account for the presence of low frequencies. We calculated a large variety of standard pulsation models with different metal and helium abundances, but were unable to obtain unstable low-frequency modes driven by the kappa mechanism in any model. We also constructed models with modified opacities in the envelope. Increasing the opacity at a temperature log T = 5.06 by a factor of two does lead to instability of low-degree modes at low frequencies, but also decreases the frequency range of Delta Sct-type pulsations to some extent. We also re-affirm the fact that less than half of the stars in the Delta Sct instability strip have pulsations detectable by Kepler. We also point out the huge variety of frequency patterns in stars with roughly similar parameters, suggesting that nonlinearity is an important factor in Delta Sct pulsations.
The study of the Cosmic Near-Infrared Background (CIB) light after subtraction of resolved sources can push the limits of current observations and infer the level of galaxy and black hole activity in the early universe. However, disentangling the relative contribution from low- and high-redshift sources is not trivial. Spatial fluctuations of the CIB exhibit a clustering excess at angular scales $\sim 1^\circ$ whose origin has not been conclusively identified. We explore the likelihood that this signal is dominated by emission from galaxies and accreting black holes in the early Universe. We find that, if the first small mass galaxies have a normal IMF, the light of their ageing stars (fossils) integrated over cosmic time contributes a comparable amount to the CIB as their pre-reionization progenitors. However, the measured fluctuation signal is too large to be produced by galaxies at redshifts $z>8$ unless their star formation efficiencies are much larger than those inferred from the observed Lyman-dropout population. In order to produce the observed level of CIB fluctuation without violating constraints from galaxy counts and the electron optical depth of the IGM, minihalos at $z>12$ must form stars with efficiency $f_\star \gtrsim 0.1$ and, although a top-heavy IMF is preferred, have a very low escape fraction of ionizing radiation, $f_{\rm esc}<0.01$. If instead the CIB fluctuations are produced by high-$z$ black holes, one requires vigorous accretion in the early universe reaching $\rho_{\rm acc} \gtrsim 10^5M_\odot{\rm Mpc^{-3}}$ by $z\simeq 10$. This growth must stop by $z \sim 6$ and be significantly obscured not to overproduce the soft cosmic X-ray background (CXB) and its observed coherence with the CIB. We therefore find the range of suitable possibilities at high-$z$ to be narrow, but could possibly be widened by including additional physics and evolution at those epochs.
We study the distribution, masses, and dynamical properties of galaxy groups in the A2142 supercluster. We analyse the global luminosity density distribution in the supercluster and divide the supercluster into the high-density core and the low-density outskirts regions. We find galaxy groups and filaments in the regions of different global density, calculate their masses and mass-to-light ratios and analyse their dynamical state with several 1D and 3D statistics. We use the spherical collapse model to study the dynamical state of the supercluster. We show that in A2142 supercluster groups and clusters with at least ten member galaxies lie along an almost straight line forming a 50 Mpc/h long main body of the supercluster. The A2142 supercluster has a very high density core surrounded by lower-density outskirt regions. The total estimated mass of the supercluster is M_est = 6.2 10^{15}M_sun. More than a half of groups with at least ten member galaxies in the supercluster lie in the high-density core of the supercluster, centered at the rich X-ray cluster A2142. Most of the galaxy groups in the core region are multimodal. In the outskirts of the supercluster, the number of groups is larger than in the core, and groups are poorer. The orientation of the cluster A2142 axis follows the orientations of its X-ray substructures and radio halo, and is aligned along the supercluster axis. The high-density core of the supercluster with the global density D8 > 17 and perhaps with D8 > 13 may have reached the turnaround radius and started to collapse. A2142 supercluster with luminous, collapsing core and straight body is an unusual object among galaxy superclusters. In the course of the future evolution the supercluster may be split into several separate systems.
We present a model that explains the observed deviation of the spectra of some pulsars and magnetars from the power-law spectra which are seen in the bulk of the pulsar population. Our model is based on the assumption that the observed variety of pulsar spectra can be naturally explained by the thermal free-free absorption that takes place in the surroundings of the pulsars. In this context, the variety of the pulsar spectra can be explained according to the shape, density and temperature of the absorbing media and the optical path of the line-of-sight across that. We have put specific emphasis on the case of the radio magnetar SGR J1745-2900 (also known as Sgr A* magnetar), modeling the rapid variations of the pulsar spectrum after the outburst of Apr 2013 as due to the free-free absorption of the radio emission in the electron material ejected during the magnetar outburst. The ejecta expands with time and consequently the absorption rate decreases and the shape of the spectrum changes in such a way that the peak frequency shifts towards the lower radio frequencies. In the hypothesis of an absorbing medium, we also discuss the similarity between the spectral behaviour of the binary pulsar B1259-63 and the spectral peculiarities of isolated pulsars.
In a Universe where AGN feedback regulates star formation in massive galaxies, a strong correlation between these two quantities is expected. If the gas causing star formation is also responsible for feeding the central black hole, then a positive correlation is expected. If powerful AGNs are responsible for the star formation quenching, then a negative correlation is expected. Observations so far have mainly found a mild correlation or no correlation at all (i.e. a flat relation between star formation rate (SFR) and AGN luminosity), raising questions about the whole paradigm of "AGN feedback". In this paper, we report the predictions of the GALFORM semi-analytical model, which has a very strong coupling between AGN activity and quenching of star formation. The predicted SFR-AGN luminosity correlation appears negative in the low AGN luminosity regime, where AGN feedback acts, but becomes strongly positive in the regime of the brightest AGN. Our predictions reproduce reasonably well recent observations by Rosario et al., yet there is some discrepancy in the normalisation of the correlation at low luminosities and high redshifts. Though this regime could be strongly influenced by observational biases, we argue that the disagreement could be ascribed to the fact that GALFORM neglects AGN variability effects. Interestingly, the galaxies that dominate the regime where the observations imply a weak correlation are massive early-type galaxies that are subject to AGN feedback. Nevertheless, these galaxies retain high enough molecular hydrogen contents to maintain relatively high star formation rates and strong infrared emission.
The Milky Way is expected to be embedded in a halo of dark matter particles, with the highest density in the central region, and decreasing density with the halo-centric radius. Dark matter might be indirectly detectable at Earth through a flux of stable particles generated in dark matter annihilations and peaked in the direction of the Galactic Center. We present a search for an excess flux of muon (anti-) neutrinos from dark matter annihilation in the Galactic Center using the cubic-kilometer-sized IceCube neutrino detector at the South Pole. There, the Galactic Center is always seen above the horizon. Thus, new and dedicated veto techniques against atmospheric muons are required to make the southern hemisphere accessible for IceCube. We used 319.7 live-days of data from IceCube operating in its 79-string configuration during 2010 and 2011. No neutrino excess was found and the final result is compatible with the background. We present upper limits on the self-annihilation cross-section, $\left<\sigma_\mathrm{A} v\right>$, for WIMP masses ranging from 30 GeV up to 10 TeV, assuming cuspy (NFW) and flat-cored (Burkert) dark matter halo profiles, reaching down to $\simeq 4 \cdot 10^{-24}$ cm$^3$ s$^{-1}$, and $\simeq 2.6 \cdot 10^{-23}$ cm$^3$ s$^{-1}$ for the $\nu\overline{\nu}$ channel, respectively.
We present preliminary results of terrestrial planet formation using on the one hand classical numerical integration of hundreds of small bodies on CPUs and on the other hand -- for comparison reasons -- the results of our GPU code with thousands of small bodies which then merge to larger ones. To be able to determine the outcome of collision events we use our smooth particle hydrodynamics (SPH) code which tracks how water is lost during such events.
Information about stellar magnetic field topologies is obtained primarily from high-resolution circular polarisation (Stokes $V$) observations. Due to their generally complex morphologies, the stellar Stokes $V$ profiles are usually interpreted with elaborate inversion techniques such as Zeeman Doppler imaging (ZDI). Here we further develop a new method of interpretation of circular polarisation signatures in spectral lines using cumulative Stokes $V$ profiles (anti-derivative of Stokes $V$). This method is complimentary to ZDI and can be applied for validation of the inversion results or when the available observational data are insufficient for an inversion. Based on the rigorous treatment of polarised line formation in the weak-field regime, we show that, for rapidly rotating stars, the cumulative Stokes $V$ profiles contain information about the spatially resolved longitudinal magnetic field density. Rotational modulation of these profiles can be employed for a simple, qualitative characterisation of the stellar magnetic field topologies. We apply this diagnostic method to the archival observations of the weak-line T Tauri star V410 Tau and Bp He-strong star HD 37776. We show that the magnetic field in V410 Tau is dominated by an azimuthal component, in agreement with the ZDI map that we recover from the same data set. For HD 37776 the cumulative Stokes $V$ profile variation indicates the presence of multiple regions of positive and negative field polarity. This behaviour agrees with the ZDI results but contradicts the popular hypothesis that the magnetic field of this star is dominated by an axisymmetric quadrupolar component.
The space-borne missions CoRoT and Kepler have provided a large amount of precise photometric data. Among the stars observed, red giants show a rich oscillation pattern that allows their precise characterization. Long-duration observations allow for investigating the fine structure of this oscillation pattern. A common pattern of oscillation frequency was observed in red giant stars, which corresponds to the second-order development of the asymptotic theory. This pattern, called the universal red giant oscillation pattern, describes the frequencies of stellar acoustic modes. We aim to investigate the deviations observed from this universal pattern, thereby characterizing them in terms of the location of the second ionization zone of helium. We also show how this seismic signature depends on stellar evolution. We measured the frequencies of radial modes with a maximum likelihood estimator method, then we identified a modulation corresponding to the departure from the universal oscillation pattern. We identify the modulation component of the radial mode frequency spacings in more than five hundred red giants. The variation in the modulation that we observe at different evolutionary states brings new constraints on the interior models for these stars. We also derive an updated form of the universal pattern that accounts for the modulation and provides highly precise radial frequencies.
We combine Herschel observations of a total of 12 sources to construct the most uniform survey of HF and H2O in our Galactic disk. Both molecules are detected in absorption along all sight lines. The high spectral resolution of the Heterodyne Instrument for the Far-Infrared (HIFI) allows us to compare the HF and H2O distributions in 47 diffuse cloud components sampling the disk. We find that the HF and H2O velocity distributions follow each other almost perfectly and establish that HF and H2O probe the same gas-phase volume. Our observations corroborate theoretical predictions that HF is a sensitive tracer of H2 in diffuse clouds, down to molecular fractions of only a few percent. Using HF to trace H2 in our sample, we find that the N(H2O)-to-N(HF) ratio shows a narrow distribution with a median value of 1.51. Our results further suggest that H2O might be used as a tracer of H2 -within a factor 2.5- in the diffuse interstellar medium. We show that the measured factor of ~2.5 variation around the median is driven by true local variations in the H2O abundance relative to H2 throughout the disk. The latter variability allows us to test our theoretical understanding of the chemistry of oxygen-bearing molecules in the diffuse gas. We show that both gas-phase and grain-surface chemistry are required to reproduce our H2O observations. This survey thus confirms that grain surface reactions can play a significant role in the chemistry occurring in the diffuse interstellar medium n_H < 1000 cm^-3.
We report on searching for Classical B-type emission-line (CBe) stars from the first data release (DR1) of the Large Sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST; also named the Guoshoujing Telescope). A total of 192 (12 known CBes) objects were identified as CBe candidates with prominent He~I~$\lambda4387$, He~I~$\lambda4471$, and Mg~II~$\lambda4481$ absorption lines, as well as H$\beta$~$\lambda4861$ and H$\alpha$~$\lambda6563$ emission lines. These candidates significantly increases current CBe sample of about 8\%. Most of the CBe candidates are distributed at the Galactic Anti-Center due to the LAMOST observing strategy. Only two of CBes are in the star clusters with ages of 15.8 and 398~Myr, respectively.
We examine a small prominence eruption that occurred on 2014 May 1 at 01:35 UT and was observed by the Interface Region Imaging Spectrometer (IRIS) and the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO). Pre- and post-eruption images were taken by the X-Ray Telescope (XRT) on Hinode. Pre-eruption, a dome-like structure exists above the prominence, as demarcated by coronal rain. As the eruption progresses, we find evidence for reconnection between the prominence magnetic field and the overlying field. Fast flows are seen in AIA and IRIS, indicating reconnection outflows. Plane-of-sky flows of ~300 km s$^{-1}$ are observed in the AIA 171 A channel along a potentially reconnected field line. IRIS detects intermittent fast line-of-sight flows of ~200 km s$^{-1}$ coincident with the AIA flows. Differential emission measure calculations show heating at the origin of the fast flows. Post-eruption XRT images show hot loops probably due to reconfiguration of magnetic fields during the eruption and subsequent heating of plasma in these loops. Although there is evidence for reconnection above the prominence during the eruption, high spatial resolution images from IRIS reveal potential reconnection sites below the prominence. A height-time analysis of the erupting prominence shows a slow initial rise with a velocity of ~0.4 km s$^{-1}$ followed by a rapid acceleration with a final velocity of ~250 km s$^{-1}$. Brightenings in IRIS during the transition between these two phases indicate the eruption trigger for the fast part of the eruption is likely a tether-cutting mechanism rather than a break-out mechanism.
Next year, 2015, the New Horizons spacecraft will have a close encounter with Pluto. In the present study we discuss some possibilities regarding what the spacecraft may encounter during its approach to Pluto. Among them we should include: the presence of geological activity due to heat generated by tides; the unlikely presence of an intrinsic magnetic field; the possibility of a plasmasphere and a plasmapause; the position of an ionopause; the existence of an ionospheric trans-terminator flow similar to that at Venus and Mars; and the presence of a Magnus force that produces a deflection of Pluto plasma wake. This deflection oscillates up and down in its orbit around the sun.
Asteroseismology can be used to constrain some properties of dark-matter (DM) particles (Casanellas & Lopes, 2013). In this work, we performed an asteroseismic modelling of the main-sequence solar-like pulsator KIC 2009505 (also known as Dushera) in order to test the existence of DM particles with the characteristics that explain the recent results found in some of the DM direct detection experiments. We found that the presence of a convective core in KIC 2009504 is incompatible with the existence of some particular models of DM particles.
We have performed multivariate statistical analyses of photometric and chemical abundance parameters of three large samples of stars in the globular cluster $\omega$ Centauri. The statistical analysis of a sample of 735 stars based on seven chemical abundances with the method of Maximum Parsimony (cladistics) yields the most promising results: seven groups are found, distributed along three branches with distinct chemical, spatial and kinematical properties. A progressive chemical evolution can be traced from one group to the next, but also within groups, suggestive of an inhomogeneous chemical enrichment of the initial interstellar matter. The adjustment of stellar evolution models shows that the groups with metallicities [Fe/H]\textgreater{}-1.5 are Helium-enriched, thus presumably of second generation. The spatial concentration of the groups increases with chemical evolution, except for two groups, which stand out in their other properties as well. The amplitude of rotation decreases with chemical evolution, except for two of the three metal-rich groups, which rotate fastest, as predicted by recent hydrodynamical simulations. The properties of the groups are interpreted in terms of star formation in gas clouds of different origins. In conclusion, our multivariate analysis has shown that metallicity alone cannot segregate the different populations of $\omega$ Centauri.
So far the highly unstable phase of luminous blue variables (LBVs) has not been understood well. It is still uncertain why and which massive stars enter this phase. Investigating the variabilities by looking for a possible regular or even (semi-)periodic behaviour could give a hint at the underlying mechanism for these variations and might answer the question of where these variabilities originate. Finding out more about the LBV phase also means understanding massive stars better in general, which have (e.g. by enriching the ISM with heavy elements, providing ionising radiation and kinetic energy) a strong and significant influence on the ISM, hence also on their host galaxy. Photometric and spectroscopic data were taken for the LBV Var C in M33 to investigate its recent status. In addition, scanned historic plates, archival data, and data from the literature were gathered to trace Var C's behaviour in the past. Its long-term variability and periodicity was investigated. Our investigation of the variability indicates possible (semi-)periodic behaviour with a period of 42.3 years for Var C. That Var C's light curve covers a time span of more than 100 years means that more than two full periods of the cycle are visible. The critical historic maximum around 1905 is less strong but discernible even with the currently rare historic data. The semi-periodic and secular structure of the light curve is similar to the one of LMC R71. Both light curves hint at a new aspect in the evolution of LBVs.
A growing number of close binary stars are being discovered among central stars of planetary nebulae. Recent and ongoing surveys are finding new systems and contributing to our knowledge of the evolution of close binary systems. The push to find more systems was largely based on early discoveries which suggested that 10 to 15% of all central stars are close binaries. One goal of this series of papers is confirmation and classification of these systems as close binaries and determination of binary system parameters. Here we provide time-resolved multi-wavelength photometry of the central star of Abell 65 as well as further analysis of the nebula and discussion of possible binary--nebula connections. Our results for Abell 65 confirm recent work showing that it has a close, cool binary companion, though several of our model parameters disagree with the recently published values. With our longer time baseline of photometric observations from 1989--2009 we also provide a more precise orbital period of 1.0037577 days.
Aqueye+ is a new ultrafast optical single photon counter, based on single photon avalanche photodiodes (SPAD) and a 4-fold split-pupil concept. It is a completely revisited version of its predecessor, Aqueye, successfully mounted at the 182 cm Copernicus telescope in Asiago. Here we will present the new technological features implemented on Aqueye+, namely a state of the art timing system, a dedicated and optimized optical train, a high sensitivity and high frame rate field camera and remote control, which will give Aqueye plus much superior performances with respect to its predecessor, unparalleled by any other existing fast photometer. The instrument will host also an optical vorticity module to achieve high performance astronomical coronography and a real time acquisition of atmospheric seeing unit. The present paper describes the instrument and its first performances.
Two photon correlations are studied for a binary star system. It is investigated how the differential Hanbury Brown and Twiss (HBT) approach can be used in order to determine orbital parameters of a binary star.
By now, observations of exoplanets have found more than 50 binary star systems hosting 71 planets. We expect these numbers to increase as more than 70% of the main sequence stars in the solar neighborhood are members of binary or multiple systems. The planetary motion in such systems depends strongly on both the parameters of the stellar system (stellar separation and eccentricity) and the architecture of the planetary system (number of planets and their orbital behaviour). In case a terrestrial planet moves in the so-called habitable zone (HZ) of its host star, the habitability of this planet depends on many parameters. A crucial factor is certainly the amount of water. We investigate in this work the transport of water from beyond the snow-line to the HZ in a binary star system and compare it to a single star system.
Stellar activity induced by active structures (eg, spots, faculae) is known to strongly impact the radial velocity time series. It then limits the detection of small planetary RV signals (eg, an Earth-mass planet in the habitable zone of a solar-like star). In previous papers, we studied the detectability of such planets around the Sun seen as an edge-on star. For that purpose, we computed the RV and photometric variations induced by solar magnetic activity, using all active structures observed over one entire cycle. Our goal is to perform similar studies on stars with different physical and geometrical properties. As a first step, we focus on Sun-like stars seen with various inclinations, and on estimating detection capabilities with forthcoming instruments. To do so, we first parameterize the solar active structures with the most realistic pattern so as to obtain results consistent with the observed ones. We simulate the growth, evolution and decay of solar spots, faculae and network, using parameters and empiric laws derived from solar observations and literature. We generate the corresponding structure lists over a full solar cycle. We then build the resulting spectra and deduce the RV and photometric variations for a `Sun' seen with various inclinations. The produced RV signal takes into account the photometric contribution of structures as well as the attenuation of the convective blueshift. The comparison between our simulated activity pattern and the observed one validates our model. We show that the inclination of the stellar rotation axis has a significant impact on the time series. RV long-term amplitudes as well as short-term jitters are significantly reduced when going from edge-on to pole-on configurations. Assuming spin-orbit alignment, the optimal configuration for planet detection is an inclined star (i~45{\deg}).
We analyze potential effects of an extraterrestrial civilization's use of orbiting mirrors to illuminate the dark side of a synchronously rotating planet on planetary transit light curves. Previous efforts to detect civilizations based on side effects of planetary-scale engineering have focused on structures affecting the host star output (e.g. Dyson spheres). However, younger civilizations are likely to be less advanced in their engineering efforts, yet still capable of sending small spacecraft into orbit. Since M dwarfs are the most common type of star in the solar neighborhood, it seems plausible that many of the nearest habitable planets orbit dim, low-mass M stars, and will be in synchronous rotation. Logically, a civilization evolving on such a planet may be inspired to illuminate their planet's dark side by placing a single large mirror at the L2 Lagrangian point, or launching a fleet of small thin mirrors into planetary orbit. We briefly examine the requirements and engineering challenges of such a collection of orbiting mirrors, then explore their impact on transit light curves. We incorporate stellar limb darkening and model a simplistic mirror fleet's effects for transits of Earth-like (R = 0.5 to 2 R_Earth) planets which would be synchronously rotating for orbits within the habitable zone of their host star. Although such an installation is undetectable in Kepler data, JWST will provide the sensitivity necessary to detect a fleet of mirrors orbiting Earth-like habitable planets around nearby stars.
We measure the merger fraction of Type 2 radio-loud and radio-quiet active galactic nuclei at z>1 using new samples. The objects have HST images taken with WFC3 in the IR channel. These samples are compared to the 3CR sample of radio galaxies at z>1 and to a sample of non-active galaxies. We also consider lower redshift radio galaxies with HST observations and previous generation instruments (NICMOS and WFPC2). The full sample spans an unprecedented range in both redshift and AGN luminosity. We perform statistical tests to determine whether the different samples are differently associated with mergers. We find that all (92%) radio-loud galaxies at z>1 are associated with recent or ongoing merger events. Among the radio-loud population there is no evidence for any dependence of the merger fraction on either redshift or AGN power. For the matched radio-quiet samples, only 38% are merging systems. The merger fraction for the sample of non-active galaxies at z>1 is indistinguishable from radio-quiet objects. This is strong evidence that mergers are the triggering mechanism for the radio-loud AGN phenomenon and the launching of relativistic jets from supermassive black holes. We speculate that major BH-BH mergers play a major role in spinning up the central supermassive black holes in these objects.
Neutral hydrogen represents the major observable baryonic constituent of galaxies that fuels the formation of stars through the transformation in molecular hydrogen. The emission of the hydrogen recombination line Halpha is the most direct tracer of the process that transforms gas (fuel) into stars. We continue to present Halpha3 (acronym for Halpha-alpha-alpha), an extensive Halpha+[NII] narrow-band imaging campaign of galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA), using the instrumentation available at the San Pedro Martir observatory (Mexico). In only four years since 2011 we were able to complete in 48 nights the Halpha imaging observations of 724 galaxies in the region of the Coma supercluster 10^h < R.A. <16^h; 24^o < Dec. <28^o and 3900<cz<9000 kms^{-1}. Of these, 603 are selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) and constitute a 97% complete sample. They provide for the first time a complete census of the massive star formation properties of local gas-rich galaxies belonging to different environments (cluster vs filaments), morphological type (spirals vs dwarf Irr), over a wide range of stellar mass (10^{8}-10^{11.5} Modot) in the Coma Supercluster. The present Paper V provides the Halpha data and the derived star formation rates for the observed galaxies.
The winds of cool luminous AGB stars are commonly assumed to be driven by radiative acceleration of dust grains which form in the extended atmospheres produced by pulsation-induced shock waves. The dust particles gain momentum by absorption or scattering of stellar photons, and they drag along the surrounding gas particles through collisions, triggering an outflow. This scenario, here referred to as Pulsation-Enhanced Dust-DRiven Outflow (PEDDRO), has passed a range of critical observational tests as models have developed from empirical and qualitative to increasingly self-consistent and quantitative. A reliable theory of mass loss is an essential piece in the bigger picture of stellar and galactic chemical evolution, and central for determining the contribution of AGB stars to the dust budget of galaxies. In this review, I discuss the current understanding of wind acceleration and indicate areas where further efforts by theorists and observers are needed.
We conduct a detailed lensing, dynamics and stellar population analysis of nine massive lens early-type galaxies (ETGs) from the X-Shooter Lens Survey (XLENS). Combining gravitational lensing constraints from HST imaging with spatially-resolved kinematics and line-indices constraints from VLT X-Shooter (XSH) spectra, we infer the low-mass slope and the low cut-off mass of the stellar Initial Mass Function (IMF): $x_{250}=2.37^{+0.12}_{-0.12}$ and $M_{{\rm low}, 250}= 0.131^{+0.023}_{-0.026}\, M_{\odot}$, respectively, for a reference point with $\sigma \equiv 250\, {{\rm kms}}^{-1}$ and R$_{{\rm eff}} \equiv 10$ kpc. All the XLENS systems are consistent with an IMF slope steeper than Milky Way-like. We find no significant correlations between IMF slope and any other quantity, except for an anti-correlation between total dynamical mass density and low-mass IMF slope at the 87% CL [$dx/d\log(\rho)$ = $ -0.19^{+0.15}_{-0.15}$]. This anti-correlation is consistent with the low redshift lenses found by Smith et al. (2015) that have high velocity dispersions and high stellar mass densities but surprisingly shallow IMF slopes.
We identify and analyze thermal dark matter candidates in the fraternal twin Higgs model and its generalizations. The relic abundance of fraternal twin dark matter is set by twin weak interactions, with a scale tightly tied to the weak scale of the Standard Model by naturalness considerations. As such, the dark matter candidates benefit from a "fraternal WIMP miracle," reproducing the observed dark matter abundance for dark matter masses between 10 and 100 GeV. However, the couplings dominantly responsible for dark matter annihilation do not lead to interactions with the visible sector. The direct detection rate is instead set via fermionic Higgs portal interactions, which are likewise constrained by naturalness considerations but parametrically weaker than those leading to dark matter annihilation. The predicted direct detection cross section is close to current LUX bounds and presents an opportunity for the next generation of direct detection experiments.
Two-point functions, the mean field squared and the vacuum expectation value (VEV) of the energy-momentum tensor are investigated for the electromagnetic field in the geometry of parallel plates on background of $(D+1)$% -dimensional dS spacetime. We assume that the field is prepared in the Bunch-Davies vacuum state and on the plates a boundary condition is imposed that is a generalization of the perfectly conducting boundary condition for an arbitrary number of spatial dimensions. It is shown that for $D\geq 4$ the background gravitational field essentially changes the behavior of the VEVs at separations between the plates larger than the curvature radius of dS spacetime. At large separations, the Casimir forces are proportional to the inverse fourth power of the distance for all values of spatial dimension $D\geq 3$. For $D\geq 4$ this behavior is in sharp contrast with the case of plates in Minkowski bulk where the force decays as the inverse $(D+1)$th power of the distance.
A single field inflation based on a supergravity model with a shift symmetry and $U(1)$ extension of the MSSM is analyzed. We show that one of the real components of the two $U(1)$ charged scalar fields plays the role of inflaton {with} an effective scalar potential similar to the "new chaotic inflation" scenario. Both non-anomalous and anomalous (with Fayet-Iliopoulos term) $U(1)$ are studied. We show that the non-anomalous $U(1)$ scenario is consistent with data of the cosmic microwave background and recent astrophysical measurements. A possible kinetic mixing between $U(1)$ {and} $U(1)_{B-L}$ is considered in order to allow for natural decay channels of the inflaton, leading to a reheating epoch. Upper limits on the reheating temperature thus turn out to favour an intermediate ($\sim {\cal O}(10^{13})$ GeV) scale $B-L$ symmetry breaking.
The framework of non-relativistic effective field theory (NREFT) aims to generalise the standard analysis of direct detection experiments in terms of spin-dependent (SD) and spin-independent (SI) interactions. We show that a number of NREFT operators lead to distinctive new directional signatures, such as prominent ring-like features in the directional recoil rate, even for relatively low mass WIMPs. We discuss these signatures and how they could affect the interpretation of future results from directional detectors. We demonstrate that considering a range of possible operators introduces a factor of 2 uncertainty in the number of events required to confirm the median recoil direction of the signal. Furthermore, using directional detection, it is possible to distinguish the more general NREFT interactions from the standard SI/SD interactions at the $2\sigma$ level with $\mathcal{O}(100-500)$ events. In particular, we demonstrate that for certain NREFT operators, directional sensitivity provides the only method of distinguishing them from these standard operators, highlighting the importance of directional detectors in probing the particle physics of dark matter.
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The cosmic web that characterizes the large-scale structure of the Universe can be quantified by a variety of methods. For example, large redshift surveys can be used in combination with point process algorithms to extract long curvilinear filaments in the galaxy distribution. Alternatively, given a full 3D reconstruction of the velocity field, kinematic techniques can be used to decompose the web into voids, sheets, filaments and knots. In this paper we look at how two such algorithms - the Bisous model and the velocity shear web - compare with each other in the local Universe (within 100 Mpc), finding good agreement. This is both remarkable and comforting, given that the two methods are radically different in ideology and applied to completely independent and different data sets. Unsurprisingly, the methods are in better agreement when applied to unbiased and complete data sets, like cosmological simulations, than when applied to observational samples. We conclude that more observational data is needed to improve on these methods, but that both methods are most likely properly tracing the underlying distribution of matter in the Universe.
Evidence for non-zero mean stellar velocities in the direction perpendicular to the Galactic plane has been accumulating from various recent large spectroscopic surveys. Previous analytical and numerical work has shown that a "breathing mode" of the Galactic disc, similar to what is observed in the Solar vicinity, can be the natural consequence of a non-axisymmetric internal perturbation of the disc. Here we provide a general analytical framework, in the context of perturbation theory, allowing us to compute the vertical bulk motions generated by a single internal perturber (bar or spiral pattern). In the case of the Galactic bar, we show that these analytically predicted bulk motions are well in line with the outcome of a numerical simulation. The mean vertical motions induced by the Milky Way bar are small (mean velocity of less than 1 km/sec) and cannot be responsible alone for the observed breathing mode, but they are existing. Our analytical treatment is valid close to the plane for all the non-axisymmetric perturbations of the disc that can be described by small-amplitude Fourier modes. Further work should study how the coupling of multiple internal perturbers and external perturbers is affecting the present analytical results.
Knowledge of the chemical composition and absolute masses of Capella are key to understanding the evolutionary state of this benchmark binary system comprising two giant stars. Previous efforts, including our own 2009 study, have largely failed to reach an acceptable agreement between the observations and current stellar evolution models, preventing us from assessing the status of the primary. Here we report a revision of the physical properties of the components incorporating recently published high-precision radial velocity measurements, and a new detailed chemical analysis providing abundances for more than 20 elements in both stars. We obtain highly precise (to about 0.3%) masses of 2.5687 +/- 0.0074 and 2.4828 +/- 0.0067 solar masses, radii of 11.98 +/- 0.57 and 8.83 +/- 0.33 solar radii, effective temperatures of 4970 +/- 50 K and 5730 +/- 60 K, and independently measured luminosities based on the orbital parallax (78.7 +/- 4.2 and 72.7 +/- 3.6 solar luminosities). We find an excellent match to stellar evolution models at the measured composition of [Fe/H] = -0.04 +/- 0.06. Three different sets of models place the primary star firmly at the end of the core helium-burning phase (clump), while the secondary is known to be evolving rapidly across the Hertzprung gap. The measured lithium abundance, the C/N ratio, and the 12C/13C isotopic carbon abundance ratio, which change rapidly in the giant phase, are broadly in agreement with expectations from models. Predictions from tidal theory for the spin rates, spin-orbit alignment, and other properties do not fare as well, requiring a 40-fold increase in the efficiency of the dissipation mechanisms in order to match the observations.
We present the design and test results of a compact optical fiber double-scrambler for high-resolution Doppler radial velocity instruments. This device consists of a single optic: a high-index $n$$\sim$2 ball lens that exchanges the near and far fields between two fibers. When used in conjunction with octagonal fibers, this device yields very high scrambling gains and greatly desensitizes the fiber output from any input illumination variations, thereby stabilizing the instrument profile of the spectrograph and improving the Doppler measurement precision. The system is also highly insensitive to input pupil variations, isolating the spectrograph from telescope illumination variations and seeing changes. By selecting the appropriate glass and lens diameter the highest efficiency is achieved when the fibers are practically in contact with the lens surface, greatly simplifying the alignment process when compared to classical double-scrambler systems. This prototype double-scrambler has demonstrated significant performance gains over previous systems, achieving scrambling gains in excess of 10,000 with a throughput of $\sim$87% using uncoated Polymicro octagonal fibers. Adding a circular fiber to the fiber train further increases the scrambling gain to $>$20,000, limited by laboratory measurement error. While this fiber system is designed for the Habitable-zone Planet Finder spectrograph, it is more generally applicable to other instruments in the visible and near-infrared. Given the simplicity and low cost, this fiber scrambler could also easily be multiplexed for large multi-object instruments.
The evidence that stellar systems surrounding the Milky Way (MW) are distributed in a Vast Polar Structure (VPOS) may be observationally biased by satellites detected in surveys of the northern sky. The recent discoveries of more than a dozen new systems in the southern hemisphere thus constitute a critical test of the VPOS phenomenon. We report that the new objects are located close to the original VPOS, with half of the sample having offsets less than 20 kpc. The positions of the new satellite galaxy candidates are so well aligned that the orientation of the revised best-fitting VPOS structure is preserved to within 9 degrees and the VPOS flattening is almost unchanged (31 kpc height). Interestingly, the shortest distance of the VPOS plane from the MW center is now only 2.5 kpc, indicating that the new discoveries balance out the VPOS at the Galactic center. The vast majority of the MW satellites are thus consistent with sharing a similar orbital plane as the Magellanic Clouds, confirming a hypothesis proposed by Kunkel & Demers and Lynden-Bell almost 40 years ago. We predict the absolute proper motions of the new objects assuming they orbit within the VPOS. Independent of the VPOS results we also predict the velocity dispersions of the new systems under three distinct assumptions: that they (i) are dark-matter-free star clusters obeying Newtonian dynamics, (ii) are dwarf satellites lying on empirical scaling relations of galaxies in dark matter halos, and (iii) obey MOND.
We present a detailed study of the metal-polluted DB white dwarf SDSS J0845+2257 (Ton 345). Using high-resolution HST/COS and VLT spectroscopy, we have detected hydrogen and eleven metals in the atmosphere of the white dwarf. The origin of these metals is almost certainly the circumstellar disc of dusty and gaseous debris from a tidally-disrupted planetesimal, accreting at a rate of 1.6E10 gs^-1. Studying the chemical abundances of the accreted material demonstrates that the planetesimal had a composition similar to the Earth, dominated by rocky silicates and metallic iron, with a low water content. The mass of metals within the convection zone of the white dwarf corresponds to an asteroid of at least ~130-170 km in diameter, although the presence of ongoing accretion from the debris disc implies that the planetesimal was probably larger than this. While a previous abundance study of the accreted material has shown an anomalously high mass fraction of carbon (15 percent) compared to the bulk Earth, our independent analysis results in a carbon abundance of just 2.5 percent. Enhanced abundances of core material (Fe, Ni) suggest that the accreted object may have lost a portion of its mantle, possibly due to stellar wind stripping in the asymptotic giant branch. Time-series spectroscopy reveals variable emission from the orbiting gaseous disc, demonstrating that the evolved planetary system at SDSS J0845+2257 is dynamically active.
We present first results on polarization swings in optical emission of blazars obtained by RoboPol, a monitoring program of an unbiased sample of gamma-ray bright blazars specially designed for effective detection of such events. A possible connection of polarization swing events with periods of high activity in gamma rays is investigated using the dataset obtained during the first season of operation. It was found that the brightest gamma-ray flares tend to be located closer in time to rotation events, which may be an indication of two separate mechanisms responsible for the rotations. Blazars with detected rotations have significantly larger amplitude and faster variations of polarization angle in optical than blazars without rotations. Our simulations show that the full set of observed rotations is not a likely outcome (probability $\le 1.5 \times 10^{-2}$) of a random walk of the polarization vector simulated by a multicell model. Furthermore, it is highly unlikely ($\sim 5 \times 10^{-5}$) that none of our rotations is physically connected with an increase in gamma-ray activity.
We examine changes in the molecular abundances resulting from increased heating due to a self-luminous planetary companion embedded within a narrow circumstellar disk gap. Using 3D models that include stellar and planetary irradiation, we find that luminous young planets locally heat up the parent circumstellar disk by many tens of Kelvin, resulting in efficient thermal desorption of molecular species that are otherwise locally frozen out. Furthermore, the heating is deposited over large regions of the disk, $\pm5$ AU radially and spanning $\lesssim60^\circ$ azimuthally. From the 3D chemical models, we compute rotational line emission models and full ALMA simulations, and find that the chemical signatures of the young planet are detectable as chemical asymmetries in $\sim10h$ observations. HCN and its isotopologues are particularly clear tracers of planetary heating for the models considered here, and emission from multiple transitions of the same species is detectable, which encodes temperature information in addition to possible velocity information from the spectra itself. We find submillimeter molecular emission will be a useful tool to study gas giant planet formation in situ, especially beyond $R\gtrsim10$ AU.
We present results from a sample of XMM-Newton and Suzaku observations of interstellar clouds that cast shadows in the soft X-ray background (SXRB) - the first uniform analysis of such a sample from these missions. By fitting to the on- and off-shadow spectra, we separated the foreground and Galactic halo components of the SXRB. We tested different foreground models - two solar wind charge exchange (SWCX) models and a Local Bubble (LB) model. We also examined different abundance tables. We found that Anders & Grevesse (1989) abundances, commonly used in previous SXRB studies, may result in overestimated foreground brightnesses and halo temperatures. We also found that assuming a single solar wind ionization temperature for a SWCX model can lead to unreliable results. We compared our measurements of the foreground emission with predictions of the SWCX emission from a smooth solar wind, finding only partial agreement. Using available observation-specific SWCX predictions and various plausible assumptions, we placed an upper limit on the LB's OVII intensity of ~0.8 photons/cm^2/s/sr (90% confidence). Comparing the halo results obtained with SWCX and LB foreground models implies that, if the foreground is dominated by SWCX and is brighter than ~1.5e-12 erg/cm^2/s/deg^2 (0.4-1.0 keV), then using an LB foreground model may bias the halo temperature upward and the 0.5-2.0 keV surface brightness downward by ~(0.2-0.3)e6 K and ~(1-2)e-12 erg/cm^2/s/deg^2, respectively. Similarly, comparing results from different observatories implies that there may be uncertainties in the halo temperature and surface brightness of up to ~0.2e6 K and ~25%, respectively, in addition to the statistical uncertainties. These uncertainties or biases may limit the ability of X-ray measurements to discriminate between Galactic halo models.
The Encircled Energy Fraction and its quantiles, notably the Half Energy Width, are routinely used to characterize the quality of X-ray optical systems. They are however always quoted without a statistical error. We show how non-parametric statistical methods can be used to redress this situation, and we discuss how the knowledge of the statistical error can be used to speed up the characterization efforts for future X-ray observatories.
We present a study of the M83 cluster population, covering the disc of the galaxy between radii of 0.45 and 4.5 kpc. We aim to probe the properties of the cluster population as a function of distance from the galactic centre. We observe a net decline in cluster formation efficiency ($\Gamma$, i.e. the amount of star formation happening in bound clusters) from about 19 % in the inner region to 7 % in the outer part of the galaxy. The recovered $\Gamma$ values within different regions of M83 follow the same $\Gamma$ versus star formation rate density relation observed for entire galaxies. We also probe the initial cluster mass function (ICMF) as a function of galactocentric distance. We observe a significant steepening of the ICMF in the outer regions (from $-1.90\pm0.11$ to $-2.70\pm0.14$) and for the whole galactic cluster population (slope of $-2.18\pm0.07$) of M83. We show that this change of slope reflects a more fundamental change of the 'truncation mass' at the high-mass end of the distribution. This can be modelled as a Schechter function of slope $-2$ with an exponential cut-off mass ($M_{\rm c}$) that decreases significantly from the inner to the outer regions (from 4.00 to $0.25\times 10^5$ M$_\odot$) while the galactic $M_{\rm c}$ is $\approx1.60\times10^5$ M$_\odot$. The trends in \Gamma and ICMF are consistent with the observed radial decrease of the $\Sigma({\rm H}_2)$, hence in gas pressure. As gas pressure declines cluster formation becomes less efficient. We conclude that the host galaxy environment appears to regulate 1) the fraction of stars locked in clusters; 2) the upper mass limit of the ICMF, consistently described by a near-universal slope $-2$ truncated at the high-mass end.
We study the impact of neutrino masses on the shape and height of the BAO peak of the matter correlation function, both in real and redshift space. In order to describe the nonlinear evolution of the BAO peak we run N-body simulations and compare them with simple analytic formulae. We show that the evolution with redshift of the correlation function and its dependence on the neutrino masses is well reproduced in a simplified version of the Zel'dovich approximation, in which the mode-coupling contribution to the power spectrum is neglected. While in linear theory the BAO peak decreases for increasing neutrino masses, the effect of nonlinear structure formation goes in the opposite direction, since the peak broadening by large scale flows is less effective. As a result of this combined effect, the peak decreases by $\sim 0.6 \%$ for $ \sum m_\nu = 0.15$ eV and increases by $\sim1.2 \%$ for $ \sum m_\nu = 0.3$ eV, with respect to a massless neutrino cosmology with equal value of the other cosmological parameters. We extend our analysis to redshift space and to halos, and confirm the agreement between simulations and the analytic formulae. We argue that all analytical approaches having the Zel'dovich propagator in their lowest order approximation should give comparable performances, irrespectively to their formulation in Lagrangian or in Eulerian space.
The Lya emission line of HI is intrinsically the brightest feature in the spectrum of astrophysical nebulae, making it a very attractive observational tool with which to survey galaxies. Moreover as a UV resonance line, Lya possesses several unique characteristics that make it useful to study the ISM and ionizing stellar population at all cosmic epochs. In this review I present a summary of Lya observations of galaxies in the nearby universe. At UV magnitudes reachable with current facilities, only ~5% of the local galaxy population shows a Lya equivalent width (EW_Lya) that exceeds 20\AA. This fraction increases dramatically at higher z, but only in the local universe can we study galaxies in detail and assemble unprecedented multi-wavelength datasets. I discuss many local Lya observations, showing that when galaxies show net Lya emission, they ubiquitously produce large halos of scattered Lya, that dominate the integrated luminosity. We discuss how global EW_Lya and the Lya escape fraction (fescLya) are higher (EW_Lya >~ 20\AA\ and fescLya> 10%) in galaxies that represent the less massive and younger end of the distributions for local objects. This is connected with various properties, such that Lya-emitters have lower metallicities (median value of 12+log(O/H) ~ 8.1) and dust reddening. However, the presence of galactic outflows is also vital to Doppler shift the Lya line out of resonance with the HI, as high EW_Lya is found only among galaxies with winds faster than ~50km/s. The evidence is then assembled into a coherent picture, and the requirement for star formation driven feedback is discussed in the context of an evolutionary sequence where the ISM is accelerated and/or subject to fluid instabilities, which reduce the scattering of Lya. Concluding remarks take the form of perspectives upon the most pressing questions that can be answered by observation.
Most field stars will have encountered the highest stellar density and hence the largest number of interactions in their birth environment. Yet the stellar dynamics during this crucial phase are poorly understood. Here we analyze the radial velocities measured for 152 out of 380 observed stars in the 2-6 Myr old star cluster IC 348 as part of the SDSS-III APOGEE. The radial velocity distribution of these stars is fitted with one or two Gaussians, convolved with the measurement uncertainties including binary orbital motions. Including a second Gaussian improves the fit; the high-velocity outliers that are best fit by this second component may either (1) be contaminants from the nearby Perseus OB2 association, (2) be a halo of ejected or dispersing stars from IC 348, or (3) reflect that IC 348 has not relaxed to a Gaussian velocity distribution. We measure a velocity dispersion for IC 348 of $0.72 \pm 0.07$ km s$^{-1}$ (or $0.64 \pm 0.08$ km s$^{-1}$ if two Gaussians are fitted), which implies a supervirial state, unless the gas contributes more to the gravitational potential than expected. No evidence is found for a dependence of this velocity dispersion on distance from the cluster center or stellar mass. We also find that stars with lower extinction (in the front of the cloud) tend to be redshifted compared with stars with somewhat higher extinction (towards the back of the cloud). This data suggests that the stars in IC 348 are converging along the line of sight. We show that this correlation between radial velocity and extinction is unlikely to be spuriously caused by the small cluster rotation of $0.024 \pm 0.013$ km s$^{-1}$ arcmin$^{-1}$ or by correlations between the radial velocities of neighboring stars. This signature, if confirmed, will be the first detection of line-of-sight convergence in a star cluster(...)
An algorithm is described for evolving the phase-space density of stars or compact objects around a massive black hole at the center of a galaxy. The technique is based on numerical integration of the Fokker-Planck equation in energy-angular momentum space, f(E,L,t), and includes, for the first time, diffusion coefficients that describe the effects of both random and correlated encounters (resonant relaxation), as well as energy loss due to emission of gravitational waves. Destruction or loss of stars into the black hole are treated by means of a detailed boundary-layer analysis. Performance of the algorithm is illustrated by calculating two-dimensional, time-dependent and steady-state distribution functions and their corresponding loss rates.
We present high-precision timing observations spanning up to nine years for 37 millisecond pulsars monitored with the Green Bank and Arecibo radio telescopes as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project. We describe the observational and instrumental setups used to collect the data, and methodology applied for calculating pulse times of arrival; these include novel methods for measuring instrumental offsets and characterizing low signal-to-noise ratio timing results. The time of arrival data are fit to a physical timing model for each source, including terms that characterize time-variable dispersion measure and frequency-dependent pulse shape evolution. In conjunction with the timing model fit, we have performed a Bayesian analysis of a parameterized timing noise model for each source, and detect evidence for time-correlated "red" signals in 10 of the pulsars. Subsequent papers in this series will present further analysis of this data set aimed at detecting or limiting the presence of nanohertz-frequency gravitational wave signals.
We investigate the chemistry of ion molecules in protoplanetary disks, motivated by the detection of N$_2$H$^+$ ring around TW Hya. While the ring inner radius coincides with the CO snow line, it is not apparent why N$_2$H$^+$ is abundant outside the CO snow line in spite of the similar sublimation temperatures of CO and N$_2$. Using the full gas-grain network model, we reproduced the N$_2$H$^+$ ring in a disk model with millimeter grains. The chemical conversion of CO and N$_2$ to less volatile species (sink effect hereinafter) is found to affect the N$_2$H$^+$ distribution. Since the efficiency of the sink depends on various parameters such as activation barriers of grain surface reactions, which are not well constrained, we also constructed the no-sink model; the total (gas and ice) CO and N$_2$ abundances are set constant, and their gaseous abundances are given by the balance between adsorption and desorption. Abundances of molecular ions in the no-sink model are calculated by analytical formulas, which are derived by analyzing the full-network model. The N$_2$H$^+$ ring is reproduced by the no-sink model, as well. The 2D (R-Z) distribution of N$_2$H$^+$, however, is different among the full-network model and no-sink model. The column density of N$_2$H$^+$ in the no-sink model depends sensitively on the desorption rate of CO and N$_2$, and the flux of cosmic ray. We also found that N$_2$H$^+$ abundance can peak at the temperature slightly below the CO sublimation, even if the desorption energies of CO and N$_2$ are the same.
We present Australia Telescope Compact Array radio data of the dwarf irregular galaxy ESO 324-G024 which is seen in projection against the giant, northern lobe of the radio galaxy Centaurus A (Cen A, NGC 5128). The distorted morphology and kinematics of ESO 324-G024, as observed in the 21 cm spectral line emission of neutral hydrogen, indicate disruptions by external forces. We investigate whether tidal interactions and/or ram pressure stripping are responsible for the formation of the HI tail stretching to the northeast of ESO 324-G024 with the latter being most probable. Furthermore, we closely analyze the sub-structure of Cen A's polarized radio lobes to ascertain whether ESO 324-G024 is located in front, within or behind the northern lobe. Our multi-wavelength, multi-component approach allows us to determine that ESO 324-G024 is most likely behind the northern radio lobe of Cen A. This result helps to constrain the orientation of the lobe, which is likely inclined to our line of sight by approximately 60 degrees if NGC 5128 and ESO 324-G024 are at the same distance.
We present MUFFIT, a new generic code optimized to retrieve the main stellar population parameters of galaxies in photometric multi-filter surveys, and we check its reliability and feasibility with real galaxy data from the ALHAMBRA survey. Making use of an error-weighted $\chi^2$-test, we compare the multi-filter fluxes of galaxies with the synthetic photometry of mixtures of two single stellar populations at different redshifts and extinctions, to provide through a Monte Carlo method the most likely range of stellar population parameters (mainly ages and metallicities), extinctions, redshifts, and stellar masses. To improve the diagnostic reliability, MUFFIT identifies and removes from the analysis those bands that are significantly affected by emission lines. We highlight that the retrieved age-metallicity locus for a sample of $z \le 0.22$ early-type galaxies in ALHAMBRA at different stellar mass bins are in very good agreement with the ones from SDSS spectroscopic diagnostics. Moreover, a one-to-one comparison between the redshifts, ages, metallicities, and stellar masses derived spectroscopically for SDSS and by MUFFIT for ALHAMBRA reveals good qualitative agreements in all the parameters. In addition, and using as input the results from photometric-redshift codes, MUFFIT improves the photometric-redshift accuracy by $\sim 10$-$20\%$, and it also detects nebular emissions in galaxies, providing physical information about their strengths. Our results show the potential of multi-filter galaxy data to conduct reliable stellar population studies with the appropiate analysis techniques, as MUFFIT.
Recently a new Lagrangian framework was introduced to describe interactions between scalar fields and relativistic perfect fluids. This allows two consistent generalizations of coupled quintessence models: non-vanishing pressures and a new type of derivative interaction. Here the implications of these to the formation of cosmological large-scale structure are uncovered at the linear order. The full perturbation equations in the two cases are derived in a unified formalism and their Newtonian, quasi-static limit is studied analytically. Requiring the absence of an effective sound speed for the coupled dark matter fluid restricts the Lagrangian to be a linear function of the matter number density. This still leaves new potentially viable classes of both algebraically and derivatively interacting models wherein the coupling may impact the background expansion dynamics and imprint signatures into the large-scale structure.
We carry out three-dimensional hydrodynamic simulations of the supernova remnants (SNRs) produced inside molecular clouds (MCs) near their surface using the HLL code (Harten et al. 1983). We explore the dynamical evolution and the X-ray morphology of SNRs after breaking through the MC surface for ranges of the explosion depths below the surface and the density ratios of the clouds to the intercloud media (ICM). We find that if an SNR breaks out through an MC surface in its Sedov stage, the outermost dense shell of the remnant is divided into several layers. The divided layers are subject to the Rayleigh-Taylor instability and fragmented. On the other hand, if an SNR breaks through an MC after the remnant enters the snowplow phase, the radiative shell is not divided to layers. We also compare the predictions of previous analytic solutions for the expansion of SNRs in stratified media with our onedimensional simulations. Moreover, we produce synthetic X-ray surface brightness in order to research the center-bright X-ray morphology shown in thermal composite SNRs. In the late stages, a breakout SNR shows the center-bright X-ray morphology inside an MC in our results. We apply our model to the observational results of the X-ray morphology of the thermal composite SNR 3C 391.
We investigate effects of a global magnetic field on the dynamics of an ensemble of clumps within a magnetized advection-dominated accretion flow by neglecting interactions between the clumps and then solving the collisionless Boltzman equation. In the strong-coupling limit, in which the averaged radial and the rotational velocities of the clumps follow the ADAF dynamics, the averaged radial velocity square of the clumps is calculated analytically for different magnetic field configurations. The value of the averaged radial velocity square of the clumps increases with increasing the strength of the radial or vertical components of the magnetic field. But a purely toroidal magnetic field geometry leads to a reduction of the value of the averaged radial velocity square of the clumps at the inner parts with increasing the strength of this component. Moreover, dynamics of the clumps strongly depends on the amount of the advected energy so that the value of the averaged radial velocity square of the clumps increases in the presence of a global magnetic field as the flow becomes more advective.
Concerted effort is currently ongoing to open up the Epoch of Reionization (EoR) ($z\sim$15-6) for studies with IR and radio telescopes. Whereas IR detections have been made of sources (Lyman-$\alpha$ emitters, quasars and drop-outs) in this redshift regime in relatively small fields of view, no direct detection of neutral hydrogen, via the redshifted 21-cm line, has yet been established. Such a direct detection is expected in the coming years, with ongoing surveys, and could open up the entire universe from $z\sim$6-200 for astrophysical and cosmological studies, opening not only the EoR, but also its preceding Cosmic Dawn ($z\sim$30-15) and possibly even the later phases of the Dark Ages ($z\sim$200-30). All currently ongoing experiments attempt statistical detections of the 21-cm signal during the EoR, with limited signal-to-noise. Direct imaging, except maybe on the largest (degree) scales at lower redshifts, as well as higher redshifts will remain out of reach. The Square Kilometre Array(SKA) will revolutionize the field, allowing direct imaging of neutral hydrogen from scales of arc-minutes to degrees over most of the redshift range $z\sim$6-28 with SKA1-LOW, and possibly even higher redshifts with the SKA2-LOW. In this SKA will be unique, and in parallel provide enormous potential of synergy with other upcoming facilities (e.g. JWST). In this chapter we summarize the physics of 21-cm emission, the different phases the universe is thought to go through, and the observables that the SKA can probe, referring where needed to detailed chapters in this volume (Abridged).
The induced gravitational collapse (IGC) paradigm explains a class of energetic, $E_{\rm iso}\gtrsim 10^{52}$~erg, long-duration gamma-ray bursts (GRBs) associated with Ic supernovae, recently named binary-driven hypernovae (BdHNe). The progenitor is a tight binary system formed of a carbon-oxygen (CO) core and a neutron star companion. The supernova ejecta of the exploding CO core triggers a hypercritical accretion process onto the neutron star, which reaches in a few seconds the critical mass, and gravitationally collapses to a black hole emitting a GRB. In our previous simulations of this process we adopted a spherically symmetric approximation to compute the features of the hypercritical accretion process. We here present the first estimates of the angular momentum transported by the supernova ejecta, $L_{\rm acc}$, and perform numerical simulations of the angular momentum transfer to the neutron star during the hyperaccretion process in full general relativity. We show that the neutron star: i) reaches in a few seconds either mass-shedding limit or the secular axisymmetric instability depending on its initial mass; ii) reaches a maximum dimensionless angular momentum value, $[c J/(G M^2)]_{\rm max}\approx 0.7$; iii) can support less angular momentum than the one transported by supernova ejecta, $L_{\rm acc} > J_{\rm NS,max}$, hence there is an angular momentum excess which necessarily leads to jetted emission.
We observed with the JVLA at 3.6 and 1.3 cm a sample of 11 proto-brown dwarf candidates in Taurus in a search for thermal radio jets driven by the most embedded brown dwarfs. We detected for the first time four thermal radio jets in proto-brown dwarf candidates. We compiled data from UKIDSS, 2MASS, Spitzer, WISE and Herschel to build the Spectral Energy Distribution (SED) of the objects in our sample, which are similar to typical Class~I SEDs of Young Stellar Objects (YSOs). The four proto-brown dwarf candidates driving thermal radio jets also roughly follow the well-known trend of centimeter luminosity against bolometric luminosity determined for YSOs, assuming they belong to Taurus, although they present some excess of radio emission compared to the known relation for YSOs. Nonetheless, we are able to reproduce the flux densities of the radio jets modeling the centimeter emission of the thermal radio jets using the same type of models applied to YSOs, but with corresponding smaller stellar wind velocities and mass-loss rates, and exploring different possible geometries of the wind or outflow from the star. Moreover, we also find that the modeled mass outflow rates for the bolometric luminosities of our objects agree reasonably well with the trends found between the mass outflow rates and bolometric luminosities of YSOs, which indicates that, despite the "excess" centimeter emission, the intrinsic properties of proto-brown dwarfs are consistent with a continuation of those of very low mass stars to a lower mass range. Overall, our study favors the formation of brown dwarfs as a scaled-down version of low-mass stars.
Future surveys of large-scale structure will be able to measure perturbations on the scale of the cosmological horizon, and so could potentially probe a number of novel relativistic effects that are negligibly small on sub-horizon scales. These effects leave distinctive signatures in the power spectra of clustering observables and, if measurable, would open a new window on relativistic cosmology. We quantify the size and detectability of the effects for a range of future large-scale structure surveys: spectroscopic and photometric galaxy redshift surveys, intensity mapping surveys of neutral hydrogen, and continuum surveys of radio galaxies. Our forecasts show that next-generation experiments, reaching out to redshifts z ~ 4, will not be able to detect previously-undetected general-relativistic effects from the single-tracer power spectra alone, although they may be able to measure the lensing magnification in the auto-correlation. We also perform a rigorous joint forecast for the detection of primordial non-Gaussianity through the excess power it produces in the clustering of biased tracers on large scales, finding that uncertainties of sigma(f_NL) ~ 1-2 should be achievable. We discuss the systematic effects that must be mitigated to achieve this level of sensitivity, and some alternative approaches that should help to improve the constraints.
The slope of the locally measured spectrum of cosmic rays varies from 2.8 for protons with energies below 200 GeV down to 2.5 for heavy nuclei with energies in the TeV-PeV range. It is not clear if the locally measured slope values are representative for those of the overall population of Galactic cosmic rays and if the slope of the cosmic ray spectrum varies across the Galaxy. We use the data of Fermi Space gamma-ray Telescope to derive a measurement of the slope of the cosmic ray spectrum across the Galactic Disk and to compare it with that of the Large Magellanic Cloud cosmic rays. A special choice of the background estimation regions allows us to single out the neutral pion decay component of the gamma-ray flux in the energy range above 10 GeV and to separate it from (a) emission from the local interstellar medium around the Solar system and (b) from the inverse Compton emission produced by cosmic ray electrons. Results. The spectrum of the pion decay gamma-ray emission from the Galactic disk in the energy band 10 GeV - 1 TeV has the slope 2.4. There is no evidence for the variation of the slope with Galactic longitude / distance from the Galactic Centre. The slope of the spectrum of cosmic rays derived from the gamma-ray data, 2.45, is harder than the slope of the locally observed cosmic ray proton spectrum. Pion decay emission from a powerlaw distribution of cosmic rays with the same hard slope also provides a fit to the gamma-ray spectrum of the Large Magellanic Cloud. Identical and hard slopes of the spectra of cosmic rays in the Milky Way and in the Large Magellanic Cloud are consistent with a straightforward theoretical model in which cosmic rays are injected by shock acceleration with the spectrum with the slope 2...2.1 which is subsequently modified by 1/3...1/2 by the energy-dependent escape of cosmic rays through the turbulent Galactic magnetic field.
The focussing optics of NuSTAR have enabled high signal-to-noise spectra to be obtained from many X-ray bright Active Galactic Nuclei (AGN) and Galactic Black Hole Binaries (BHB). Spectral modelling then allows robust characterization of the spectral index and upper energy cutoff of the coronal power-law continuum, after accounting for reflection and absorption effects. Spectral-timing studies, such as reverberation and broad iron line fitting, of these sources yield coronal sizes, often showing them to be small and in the range of 3 to 10 gravitational radii in size. Our results indicate that coronae are hot and radiatively compact, lying close to the boundary of the region in the compactness - temperature diagram which is forbidden due to runaway pair production. The coincidence suggests that pair production and annihilation are essential ingredients in the coronae of AGN and BHB and that they control the shape of the observed spectra.
We check how the Fermi/LAT data constrain physics of hot accretion flows, most likely present in low-luminosity AGNs. Using a precise model of emission from hot flows, we examine the dependence of their gamma-ray emission, resulting from proton-proton interactions, on accretion rate, black hole spin, magnetic field strength, electron heating efficiency and particle distribution. Then, we compare the hadronic gamma-ray luminosities predicted by the model for several nearby Seyfert 1 galaxies with the results of our analysis of 6.4 years of the Fermi/LAT observations of these AGNs. In agreement with previous studies, we find a significant gamma-ray detection in NGC 6814 and we could only derive upper limits for the remaining objects, although we note marginally significant (~3 sigma) signals at the positions of NGC 4151 and NGC 4258. The derived upper limits for the flux above 1 GeV allow us to constrain the proton acceleration efficiency in flows with heating of electrons dominated by Coulomb interactions, which case is favored by X-ray spectral properties. In such flows, at most ~10% of the accretion power can be used for a relativistic acceleration of protons. Upper limits for the flux below 1 GeV can constrain the magnetic field strength and black hole spin value, we find such constraints for NGC 7213 and NGC 4151. We also note that the spectral component above ~4 GeV found in the Fermi/LAT data of Centaurus A by Sahakyan et al. may be due to hadronic emission from a flow within the above constraint. We rule out such an origin of the gamma-ray emission from NGC 6814. Finally, we note that the three Seyfert 2/starburst galaxies, NGC 4595, NGC 1068 and Circinus, show an interesting correlation of their gamma-ray luminosities with properties of their active nuclei, and we discuss it in the context of the hot flow model.
The 3He({\alpha},{\gamma})7Be reaction affects not only the production of 7Li in Big Bang nucleosynthesis, but also the fluxes of 7Be and 8B neutrinos from the Sun. This double role is exploited here to constrain the former by the latter. A number of recent experiments on 3He({\alpha},{\gamma})7Be provide precise cross section data at E = 0.5-1.0 MeV center-of-mass energy. However, there is a scarcity of precise data at Big Bang energies, 0.1-0.5 MeV, and below. This problem can be alleviated, based on precisely calibrated 7Be and 8B neutrino fluxes from the Sun that are now available, assuming the neutrino flavour oscillation framework to be correct. These fluxes and the standard solar model are used here to determine the 3He(alpha,gamma)7Be astrophysical S-factor at the solar Gamow peak, S(23+6-5 keV) = 0.548+/-0.054 keVb. This new data point is then included in a re-evaluation of the 3He({\alpha},{\gamma})7Be S-factor at Big Bang energies, following an approach recently developed for this reaction in the context of solar fusion studies. The re-evaluated S-factor curve is then used to re-determine the 3He({\alpha},{\gamma})7Be thermonuclear reaction rate at Big Bang energies. The predicted primordial lithium abundance is 7Li/H = 5.0e-10, far higher than the Spite plateau.
Selection effects can bedevil the inference of the properties of a population of astronomical catalogues, unavoidably biasing the observed catalogue. This is particularly true when mapping interstellar extinction in three dimensions: more extinguished stars are fainter and so generally less likely to appear in any magnitude limited catalogue of observations. This paper demonstrates how to account for this selection effect when mapping extinction, so that accurate and unbiased estimates of the true extinction are obtained. We advocate couching the description of the problem explicitly as a Poisson point process, which allows the likelihoods employed to be easily and correctly normalised in such a way that accounts for the selection functions applied to construct the catalogue of observations.
We investigate the variations of the radial O/H abundance gradients from planetary nebulae (PN) located at different distances from the galactic plane. In particular, we determine the abundance gradients at different heights from the plane in order to investigate a possible gradient inversion for the objects at larger distances from the plane. We consider a large sample of PN with known distances, so that the height relative to the galactic plane can be derived, and accurate abundances, so that the gradients can be determined.
Context. Astrophysical jets are ubiquitous in the Universe on all scales, but
their large-scale dynamics and evolution in time are hard to observe since they
usually develop at a very slow pace.
Aims. We aim to obtain the first observational proof of the expected
large-scale evolution and interaction with the environment in an astrophysical
jet. Only jets from microquasars offer a chance to witness the real-time,
full-jet evolution within a human lifetime, since they combine a 'short', few
parsec length with relativistic velocities.
Methods. The methodology of this work is based on a systematic recalibraton
of interferometric radio observations of microquasars available in public
archives. In particular, radio observations of the microquasar GRS 1758-258
over less than two decades have provided the most striking results.
Results. Significant morphological variations in the extended jet structure
of GRS 1758-258 are reported here that were previously missed. Its northern
radio lobe underwent a major morphological variation that rendered the hotspot
undetectable in 2001 and reappeared again in the following years. The reported
changes confirm the Galactic nature of the source. We tentatively interpret
them in terms of the growth of instabilities in the jet flow. There is also
evidence of surrounding cocoon. These results can provide a testbed for models
accounting for the evolution of jets and their interaction with the
environment.
We present Karl G. Jansky Very Large Array (VLA) observations of the CO ($J = 2 \rightarrow 1$) line emission towards the $z = 6.419$ quasar SDSS J$114816.64+525150.3$ (J$1148+5251$). The molecular gas is found to be marginally resolved with a major axis of $0.9"$ (consistent with previous size measurements of the CO ($J = 7 \rightarrow 6$) emission). We observe tentative evidence for extended line emission towards the south west on a scale of ~$1.4"$, but this is only detected at $3.3\sigma$ significance and should be confirmed. The position of the molecular emission region is in excellent agreement with previous detections of low frequency radio continuum emission as well as [C ii] line and thermal dust continuum emission. These CO ($J = 2 \rightarrow 1$) observations provide an anchor for the low excitation part of the molecular line SED. We find no evidence for extended low excitation component, neither in the spectral line energy distribution nor the image. We fit a single kinetic gas temperature model of 50 K. We revisit the gas and dynamical masses in light of this new detection of a low order transition of CO, and confirm previous findings that there is no extended reservoir of cold molecular gas in J$1148+5251$, and that the source departs substantially from the low $z$ relationship between black hole mass and bulge mass. Hence, the characteristics of J$1148+5251$ at $z = 6.419$ are very similar to $z$~$2$ quasars, in the lack of a diffuse cold gas reservoir and kpc-size compactness of the star forming region.
We use 32 age measurements of passively evolving galaxies as a function of redshift to test and compare the standard model ($\Lambda$CDM) with the $R_{\rm h}=ct$ Universe. We show that the latter fits the data with a reduced $\chi^2_{\rm dof}=0.435$ for a Hubble constant $H_{0}= 67.2_{-4.0}^{+4.5}$ km $\rm s^{-1}$ $\rm Mpc^{-1}$. By comparison, the optimal flat $\Lambda$CDM model, with two free parameters (including $\Omega_{\rm m}=0.12_{-0.11}^{+0.54}$ and $H_{0}=94.3_{-35.8}^{+32.7}$ km $\rm s^{-1}$ $\rm Mpc^{-1}$), fits the age-\emph{z} data with a reduced $\chi^2_{\rm dof}=0.428$. Based solely on their $\chi^2_{\rm dof}$ values, both models appear to account for the data very well, though the optimized $\Lambda$CDM parameters are only marginally consistent with those of the concordance model ($\Omega_{\rm m}=0.27$ and $H_{0}= 70$ km $\rm s^{-1}$ $\rm Mpc^{-1}$). Fitting the age-$z$ data with the latter results in a reduced $\chi^2_{\rm dof}=0.523$. However, because of the different number of free parameters in these models, selection tools, such as the Akaike, Kullback and Bayes Information Criteria, favour $R_{\rm h}=ct$ over $\Lambda$CDM with a likelihood of $\sim 66.5\%-80.5\%$ versus $\sim 19.5\%-33.5\%$. These results are suggestive, though not yet compelling, given the current limited galaxy age-$z$ sample. We carry out Monte Carlo simulations based on these current age measurements to estimate how large the sample would have to be in order to rule out either model at a $\sim 99.7\%$ confidence level. We find that if the real cosmology is $\Lambda$CDM, a sample of $\sim 45$ galaxy ages would be sufficient to rule out $R_{\rm h}=ct$ at this level of accuracy, while $\sim 350$ galaxy ages would be required to rule out $\Lambda$CDM if the real Universe were instead $R_{\rm h}=ct$.
Robust modelling of strong lensing systems is fundamental to exploit the information they contain about the distribution of matter in galaxies and clusters. In this work, we present Lensed, a new code which performs forward parametric modelling of strong lenses. Lensed takes advantage of a massively parallel ray-tracing kernel to perform the necessary calculations on a modern graphics processing unit (GPU). This makes the precise rendering of the background lensed sources much faster, and allows the simultaneous optimisation of tens of parameters for the selected model. With a single run, the code is able to obtain the full posterior probability distribution for the lens light, the mass distribution and the background source at the same time. Lensed is first tested on mock images which reproduce realistic space-based observations of lensing systems. In this way, we show that it is able to recover unbiased estimates of the lens parameters, even when the sources do not follow exactly the assumed model. Then, we apply it to a subsample of the SLACS lenses, in order to demonstrate its use on real data. The results generally agree with the literature, and highlight the flexibility and robustness of the algorithm.
Context: AGB stars lose a large percentage of their mass in a dust-driven wind. This creates a circumstellar envelope, which can be studied through thermal dust emission and molecular emission lines. In the case of high mass-loss rates, this study is complicated by the high optical depths and the intricate coupling between gas and dust radiative transfer characteristics. An important aspect of the physics of gas-dust interactions is the strong influence of dust on the excitation of several molecules, including H2O. Aims: The dust and gas content of the envelope surrounding the high mass-loss rate OH/IR star OH 127.8+0.0, as traced by Herschel observations, is studied, with a focus on the H2O content and the dust-to-gas ratio. We report detecting a large number of H2O vapor emission lines up to J = 9 in the Herschel data, for which we present the measured line strengths. Methods: The treatments of both gas and dust species are combined using two numerical radiative transfer codes. The method is illustrated for both low and high mass-loss-rate sources. Specifically, we discuss different ways of assessing the dust-to-gas ratio: 1) from the dust thermal emission spectrum and the CO molecular gas line strengths; 2) from the momentum transfer from dust to gas and the measured gas terminal velocity; and 3) from the determination of the required amount of dust to reproduce H2O lines for a given H2O vapor abundance. These three diagnostics probe different zones of the outflow, for the first time allowing an investigation of a possible radial dependence of the dust-to-gas ratio. Results: ... Continued in article.
We main goal of this paper is to test whether the NIR peak magnitudes of SNe
Ia could be accurately estimated with only a single observation obtained close
to maximum light, provided the time of B band maximum and the optical stretch
parameter are known. We obtained multi-epoch UBVRI and single-epoch J and H
photometric observations of 16 SNe Ia in the redshift range z=0.037-0.183,
doubling the leverage of the current SN Ia NIR Hubble diagram and the number of
SNe beyond redshift 0.04. This sample was analyzed together with 102 NIR and
458 optical light curves (LCs) of normal SNe Ia from the literature.
The analysis of 45 well-sampled NIR LCs shows that a single template
accurately describes them if its time axis is stretched with the optical
stretch parameter. This allows us to estimate the NIR peak magnitudes even with
one observation obtained within 10 days from B-band maximum. We find that the
NIR Hubble residuals show weak correlation with DM_15 and E(B-V), and for the
first time we report a possible dependence on the J_max-H_max color. The
intrinsic NIR luminosity scatter of SNe Ia is estimated to be less than
0.08-0.10 mag, which is smaller than what can be derived for a similarly
heterogeneous sample at optical wavelengths. In conclusion, we find that SNe Ia
are at least as good standard candles in the NIR as in the optical. We showed
that it is feasible to extended the NIR SN Ia Hubble diagram to z=0.2 with very
modest sampling of the NIR LCs, if complemented by well-sampled optical LCs.
Our results suggest that the most efficient way to extend the NIR Hubble
diagram to high redshift would be to obtain a single observation close to the
NIR maximum. (abridged)
The Monte Carlo method is the most popular technique to perform radiative transfer simulations in a general 3D geometry. The algorithms behind and acceleration techniques for Monte Carlo radiative transfer are discussed extensively in the literature, and many different Monte Carlo codes are publicly available. On the contrary, the design of a suite of components that can be used for the distribution of sources and sinks in radiative transfer codes has received very little attention. The availability of such models, with different degrees of complexity, has many benefits. For example, they can serve as toy models to test new physical ingredients, or as parameterised models for inverse radiative transfer fitting. For 3D Monte Carlo codes, this requires algorithms to efficiently generate random positions from 3D density distributions. We describe the design of a flexible suite of components for the Monte Carlo radiative transfer code SKIRT. The design is based on a combination of basic building blocks (which can be either analytical toy models or numerical models defined on grids or a set of particles) and the extensive use of decorators that combine and alter these building blocks to more complex structures. For a number of decorators, e.g. those that add spiral structure or clumpiness, we provide a detailed description of the algorithms that can be used to generate random positions. Advantages of this decorator-based design include code transparency, the avoidance of code duplication, and an increase in code maintainability. Moreover, since decorators can be chained without problems, very complex models can easily be constructed out of simple building blocks. Finally, based on a number of test simulations, we demonstrate that our design using customised random position generators is superior to a simpler design based on a generic black-box random position generator.
A monitoring programme of CSS 121005:212625+201948 covering nearly two observing seasons has shown that it is a typical SU UMa dwarf nova, but it has one of the shortest supercycles of its class, at 66.9(6) d. The superoutbursts are interspersed with 3 to 7 short duration (~2 days) normal outbursts each of which are separated by a mean interval of 11 days, but can be as short as 2 days. The most intensively studied superoutburst was that of 2014 November, which lasted 14 days and had an outburst amplitude of >4.8 magnitudes, reaching magnitude 15.7 at its brightest. Time resolved photometry revealed superhumps with a peak-to-peak amplitude of 0.2 magnitudes, later declining to 0.1 magnitude. The superhump period was Psh = 0.08838(18) d. Time resolved photometry was conducted during several other superoutbursts, which gave broadly similar results.
Ozone is an important radiative trace gas in the Earth's atmosphere. The presence of ozone can significantly influence the thermal structure of an atmosphere, and by this e.g. cloud formation. Photochemical studies suggest that ozone can form in carbon dioxide-rich atmospheres. We investigate the effect of ozone on the temperature structure of simulated early Martian atmospheres. With a 1D radiative-convective model, we calculate temperature-pressure profiles for a 1 bar carbon dioxide atmosphere. Ozone profiles are fixed, parameterized profiles. We vary the location of the ozone layer maximum and the concentration at this maximum. The maximum is placed at different pressure levels in the upper and middle atmosphere (1-10 mbar). Results suggest that the impact of ozone on surface temperatures is relatively small. However, the planetary albedo significantly decreases at large ozone concentrations. Throughout the middle and upper atmospheres, temperatures increase upon introducing ozone due to strong UV absorption. This heating of the middle atmosphere strongly reduces the zone of carbon dioxide condensation, hence the potential formation of carbon dioxide clouds. For high ozone concentrations, the formation of carbon dioxide clouds is inhibited in the entire atmosphere. In addition, due to the heating of the middle atmosphere, the cold trap is located at increasingly higher pressures when increasing ozone. This leads to wetter stratospheres hence might increase water loss rates on early Mars. However, increased stratospheric H2O would lead to more HOx, which could efficiently destroy ozone. This result emphasizes the need for consistent climate-chemistry calculations to assess the feedback between temperature structure, water content and ozone chemistry. Furthermore, convection is inhibited at high ozone amounts, leading to a stably stratified atmosphere.
Probing the structures of stellar winds is of prime importance for the understanding of massive stars. Based on their optical spectral morphology and variability, the stars of the Oef class have been suggested to feature large-scale structures in their wind. High-resolution X-ray spectroscopy and time-series of X-ray observations of presumably-single O-type stars can help us understand the physics of their stellar winds. We have collected XMM-Newton observations and coordinated optical spectroscopy of the O6Ief star lambda Cep to study its X-ray and optical variability and to analyse its high-resolution X-ray spectrum. We investigate the line profile variability of the He II 4686 and H-alpha emission lines in our time series of optical spectra, including a search for periodicities. We further discuss the variability of the broadband X-ray flux and analyse the high-resolution spectrum of lambda Cep using line-by-line fits as well as a code designed to fit the full high-resolution X-ray spectrum consistently. During our observing campaign, the He II 4686 line varies on a timescale of ~18 hours. On the contrary, the H-alpha line profile displays a modulation on a timescale of 4.1 days which is likely the rotation period of the star. The X-ray flux varies on time-scales of days and could in fact be modulated by the same 4.1 days period as H-alpha, although both variations are shifted in phase. The high-resolution X-ray spectrum reveals broad and skewed emission lines as expected for the X-ray emission from a distribution of wind-embedded shocks. Most of the X-ray emission arises within less than 2R* above the photosphere.
The finding of residual gas in the large central cavity of the HD142527 disk motivates questions on the origin of its non-Keplerian kinematics, and possible connections with planet formation. We aim to understand the physical structure that underlies the intra-cavity gaseous flows, guided by new molecular-line data in CO(6-5) with unprecedented angular resolutions. Given the warped structure inferred from the identification of scattered-light shadows cast on the outer disk, the kinematics are consistent, to first order, with axisymmetric accretion onto the inner disk occurring at all azimuth. A steady-state accretion profile, fixed at the stellar accretion rate, explains the depth of the cavity as traced in CO isotopologues. The abrupt warp and evidence for near free-fall radial flows in HD 142527 resemble theoretical models for disk tearing, which could be driven by the reported low mass companion, whose orbit may be contained in the plane of the inner disk. The companion's high inclination with respect to the massive outer disk could drive Kozai oscillations over long time-scales; high-eccentricity periods may perhaps account for the large cavity. While shadowing by the tilted disk could imprint an azimuthal modulation in the molecular-line maps, further observations are required to ascertain the significance of azimuthal structure in the density field inside the cavity of HD142527.
We present an analysis of multi-epoch low-resolution spectrophotometry, complemented by the light curves provided by massive photometric surveys spanning over 100 years, of the symbiotic binary LMC S63. We showed that it is an eclipsing binary with the orbital period of 1050d. We also found evidence of outbursts in history of the white dwarf. If it was a Z-And type outburst, as is most likely, it would be a second such outburst recorded in the Magellanic Cloud symbiotic system. We confirmed that the red giant is enhanced in carbon, and estimated C/O~1.2 by fitting a model atmosphere to the SALT spectrum. We also found bi-periodic pulsations of the red giant, and demonstrated that it is similar to other carbon variables with confirmed bi-periodicity.
A pathway to the formation of planetesimals, and eventually giant planets, may occur in concentrations of dust grains trapped in pressure maxima. Dramatic crescent-shaped dust concentrations have been seen in recent radio images at sub-mm wavelengths. These disk asymmetries could represent the initial phases of planet formation in the dust trap scenario, provided that grain sizes are spatially segregated. A testable prediction of azimuthal dust trapping is that progressively larger grains should be more sharply confined and furthermore the trapped grains should follow a distribution that is markedly different from the gas. However, gas tracers such as CO and the infrared emission from small grains are both very optically thick where the submm continuum originates, so observations have been unable to test the trapping predictions or to identify compact concentrations of larger grains required for planet formation by core-accretion. Here we report multifrequency observations of HD142527, from 34GHz to 700GHz, that reveal a compact concentration of ~cm-sized grains, with a few Earth masses, embedded in a large-scale crescent of ~mm-sized particles. The emission peaks at wavelengths shorter than ~1mm are optically thick and trace the temperature structure resulting from shadows cast by the inner regions. Given this temperature structure, we infer that the largest dust grains are concentrated in the 34 GHz clump. We conclude that dust trapping is efficient for approximately cm-sized grains and leads to enhanced concentrations, while the smaller grains largely reflect the gas distribution.
Fingering convection (or thermohaline convection) is a weak yet important kind of mixing that occurs in stably-stratified stellar radiation zones in the presence of an inverse mean-molecular-weight gradient. Brown et al. (2013) recently proposed a new model for mixing by fingering convection, which contains no free parameter, and was found to fit the results of direct numerical simulations in almost all cases. Notably, however, they found that mixing was substantially enhanced above their predicted values in the few cases where large-scale gravity waves, followed by thermo-compositional layering, grew spontaneously from the fingering convection. This effect is well-known in the oceanographic context, and is attributed to the excitation of the so-called "collective instability". In this work, we build on the results of Brown et al. (2013) and of Traxler et al. (2011b) to determine the conditions under which the collective instability may be expected. We find that it is only relevant in stellar regions which have a relatively large Prandtl number (the ratio of the kinematic viscosity to the thermal diffusivity), $O(10^{-3})$ or larger. This implies that the collective instability cannot occur in main sequence stars, where the Prandtl number is always much smaller than this (except in the outer layers of surface convection zones where fingering is irrelevant anyway). It could in principle be excited in regions of high electron degeneracy, during He core flash, or in the interiors of white dwarfs. We discuss the implications of our findings for these objects, both from a theoretical and from an observational point of view.
Due to instrumental limitations and a lack of disk detections, the structure between the envelope and the rotationally supported disk has been poorly studied. This is now possible with ALMA through observations of CO isotopologs and tracers of freezeout. Class 0 sources are ideal for such studies given their almost intact envelope and young disk. The structure of the disk-envelope interface of the prototypical Class 0 source, VLA1623A which has a confirmed Keplerian disk, is constrained from ALMA observations of DCO+ 3-2 and C18O 2-1. The physical structure of VLA1623 is obtained from the large-scale SED and continuum radiative transfer. An analytic model using a simple network coupled with radial density and temperature profiles is used as input for a 2D line radiative transfer calculation for comparison with the ALMA Cycle 0 12m array and Cycle 2 ACA observations of VLA1623. DCO+ emission shows a clumpy structure bordering VLA1623A's Keplerian disk, suggesting a cold ring-like structure at the disk-envelope interface. The radial position of the observed DCO+ peak is reproduced in our model only if the region's temperature is between 11-16K, lower than expected from models constrained by continuum and SED. Altering the density has little effect on the DCO+ position, but increased density is needed to reproduce the disk traced in C18O. The DCO+ emission around VLA1623A is the product of shadowing of the envelope by the disk. Disk-shadowing causes a drop in the gas temperature outside of the disk on >200AU scales, encouraging deuterated molecule production. This indicates that the physical structure of the disk-envelope interface differs from the rest of the envelope, highlighting the drastic impact that the disk has on the envelope and temperature structure. The results presented here show that DCO+ is an excellent cold temperature tracer.
Distances to stars are key to revealing a three-dimensional view of the Milky Way, yet their determination is a major challenge in astronomy. Whilst the brightest nearby stars benefit from direct parallax measurements, fainter stars are subject of indirect determinations with uncertainties exceeding 30%. We present an alternative approach to measuring distances using spectroscopically-identified twin stars. Given a star with known parallax, the distance to its twin is assumed to be directly related to the difference in their apparent magnitudes. We found 175 twin pairs from the ESO public HARPS archives and report excellent agreement with Hipparcos parallaxes within 7.5%. Most importantly, the accuracy of our results does not degrade with increasing stellar distance. With the ongoing collection of high-resolution stellar spectra, our method is well-suited to complement Gaia.
M31N 2015-01a (or M31LRN 2015) is a red nova that erupted in January 2015 -- the first event of this kind observed in M31 since 1988. Very few similar events have been confirmed as of 2015. Most of them are considered to be products of stellar mergers. Results of an extensive optical monitoring of the transient in the period January-March 2015 are presented. Eight optical telescopes were used for imaging. Spectra were obtained on BTA, GTC and the Rozhen 2m telescope. We present a highly accurate 70 d lightcurve and astrometry with a 0.05" uncertainty. The color indices reached a minimum 2-3 d before peak brightness and rapidly increased afterwards. The spectral type changed from F5I to F0I in 6 d before the maximum and then to K3I in the next 30 d. The luminosity of the transient was estimated to $8.7^{+3.3}_{-2.2}\times10^{5}L_{\odot}$ during the optical maximum. Both the photometric and the spectroscopic results confirm that the object is a red nova, similar to V838 Monocerotis.
We present thermal model fits for 11 Jovian and 3 Saturnian irregular satellites based on measurements from the WISE/NEOWISE dataset. Our fits confirm spacecraft-measured diameters for the objects with in situ observations (Himalia and Phoebe) and provide diameters and albedo for 12 previously unmeasured objects, 10 Jovian and 2 Saturnian irregular satellites. The best-fit thermal model beaming parameters are comparable to what is observed for other small bodies in the outer Solar System, while the visible, W1, and W2 albedos trace the taxonomic classifications previously established in the literature. Reflectance properties for the irregular satellites measured are similar to the Jovian Trojan and Hilda Populations, implying common origins.
It is shown here that in neutral ion gases the thermal energy transport can occur in the form of new types of thermal soliton waves. The solitons can form under a vanishing net heating function, and for a quadratic net heating. It is predicted that these solitons play an important role in a diversity of terrestrial and astrophysical phenomena. We claim that the reported soliton waves can be observed under ordinary laboratory conditions.
Recent progress in the determination of both masses and radii of neutron stars are starting to place stringent constraints on the dense matter equation of state. In particular, new theoretical developments together with improved statistical tools seem to favor stellar radii that are significantly smaller than those predicted by models using purely nucleonic equations of state. Given that the underlying equation of state must also account for the observation of $2M_{\odot}$ neutron stars, theoretical approaches to the study of the dense matter equation of state are facing serious challenges. In response to this challenge, we compute in a model-independent way the underlying equation of state associated with an assumed mass-radius template similar to the "common radius" assumption used in recent studies. Once such a mass-radius template is adopted, the equation of state follows directly from the implementation of Lindblom's algorithm; assumptions on the nature or composition of the dense stellar core are not required. By analyzing mass-radius profiles with a maximum mass consistent with observation and common radii in the 8 to 11 km range, a lower limit on the stellar radius of $R_{\rm NS}\!\gtrsim\!10.7$ km is obtained in order to prevent the equation of state from violating causality.
One intriguing BSM particle is the QCD axion, which could simultaneously provide a solution to the Strong CP problem and account for some, if not all, of the dark matter density in the universe. This particle is a pNGB of the conjectured Peccei-Quinn (PQ) symmetry of the Standard Model. Its mass and interactions are suppressed by a heavy symmetry breaking scale, $f_a$, whose value is roughly greater than $10^{9}$ GeV (or, conversely, the axion mass, $m_a$, is roughly less than $10^4\ \mu \text{eV}$). The density of axions in the universe, which cannot exceed the relic dark matter density and is a quantity of great interest in axion experiments like ADMX, is a result of the early-universe interplay between cosmological evolution and the axion mass as a function of temperature. The latter quantity is proportional to the second derivative of the QCD free energy with respect to the CP-violating phase, $\theta$. However, this quantity is generically non-perturbative and previous calculations have only employed instanton models at the high temperatures of interest (roughly 1 GeV). In this and future works, we aim to calculate the temperature-dependent axion mass at small $\theta$ from first-principle lattice calculations, with controlled statistical and systematic errors. Once calculated, this temperature-dependent axion mass is input for the classical evolution equations of the axion density of the universe. Due to a variety of lattice systematic effects at the very high temperatures required, we perform a calculation of the leading small-$\theta$ cumulant of the theta vacua on large volume lattices for SU(3) Yang-Mills with high statistics as a first proof of concept, before attempting a full QCD calculation in the future. From these pure glue results, the misalignment mechanism yields the axion mass bound $m_a \geq (14.6\pm0.1) \ \mu \text{eV}$ when PQ-breaking occurs after inflation.
Gravitational theories with multiple scalar fields coupled to the metric and each other - a natural extension of the well studied single-scalar-tensor theories - are interesting phenomenological frameworks to describe deviations from general relativity in the strong-field regime. In these theories, the N-tuple of scalar fields takes values in a coordinate patch of an N-dimensional Riemannian target-space manifold whose properties are poorly constrained by weak-field observations. Here we introduce for simplicity a non-trivial model with two scalar fields and a maximally symmetric target-space manifold. Within this model we present a preliminary investigation of spontaneous scalarization for relativistic, perfect fluid stellar models in spherical symmetry. We find that the scalarization threshold is determined by the eigenvalues of a symmetric scalar-matter coupling matrix, and that the properties of strongly scalarized stellar configurations additionally depend on the target-space curvature radius. In preparation for numerical relativity simulations, we also write down the 3+1 decomposition of the field equations for generic tensor-multi-scalar theories in vacuum.
Recent studies of low redshift type Ia supernovae (SNIa) indicate that half explode from less than Chandrasekhar mass white dwarfs, implying ignition must proceed from something besides the canonical criticality of Chandrasekhar mass SNIa progenitors. We show that $0.1-10$ PeV mass asymmetric dark matter, with imminently detectable nucleon scattering interactions, can accumulate to the point of self-gravitation in a white dwarf and collapse, shedding gravitational potential energy by scattering off nuclei, thereby heating the white dwarf and igniting the flame front that precedes SNIa. We combine data on SNIa masses with data on the ages of SNIa-adjacent stars. This combination reveals a $ 3 \sigma$ inverse correlation between SNIa masses and ignition ages, which could result from increased capture of dark matter in 1.4 versus 1.1 solar mass white dwarfs. Future studies of SNIa in galactic centers will provide additional tests of dark-matter-induced type Ia ignition. Remarkably, both bosonic and fermionic SNIa-igniting dark matter also resolve the missing pulsar problem by forming black holes in $\gtrsim 10$ Myr old pulsars at the center of the Milky Way.
We study the viability of regions of large $\tan \beta$ within the framework of Fat Higgs/$\lambda$-SUSY Models. We compute the one-loop effective potential to find the corrections to the Higgs boson mass due to the heavy non-standard Higgs bosons. As the tree level contribution to the Higgs boson mass is suppressed at large $\tan \beta$, these one-loop corrections are crucial to raising the Higgs boson mass to the measured LHC value. By raising the Higgsino and singlino mass parameters, typical electroweak precision constraints can also be avoided. We illustrate these new regions of Fat Higgs/$\lambda$-SUSY parameter space by finding regions of large $\tan \beta$ that are consistent with all experimental constraints including direct dark matter detection experiments, relic density limits and the invisible decay width of the $Z$ boson. We find that there exist regions around $\lambda = 1.25, \tan \beta = 50$ and a uniform psuedo-scalar $4~{\rm TeV} \lsim M_A \lsim 8$~TeV which are consistent will all present phenomenological constraints. In this region the dark matter relic abundance and direct detection limits are satisfied by a lightest neutralino that is mostly bino or singlino. As an interesting aside we also find a region of low $\tan \beta$ and small singlino mass parameter where a well-tempered neutralino avoids all cosmological and direct detection constraints.
If the top quark is heavy enough, the Standard Model potential is unstable at large Higgs values. This is particularly problematic during inflation, which sources large perturbations of the Higgs. The instability could be cured by a threshold effect induced by a scalar with a large vacuum expectation value and directly connected to the Standard Model through a Higgs portal coupling. However, we find that in a minimal model in which the scalar generates inflation, this mechanism does not stabilize the potential because the mass required for inflation is beyond the instability scale. On the other hand, if the potential is absolutely stable, successful inflation in agreement with current CMB data can occur along a valley of the potential with a Mexican hat profile. We revisit the stability conditions, independently of inflation, and clarify that the threshold effect cannot work if the Higgs portal coupling is too small. We also show that inflation in a false Higgs vacuum appearing radiatively for a tuned ratio of the Higgs and top masses leads to an amplitude of primordial gravitational waves that is far too high, ruling out this possibility.
One proposal for deriving effective cosmological models from theories of quantum gravity is to view the former as a mean-field (hydrodynamic) description of the latter, which describes a universe formed by a 'condensate' of quanta of geometry. This idea has been successfully applied within the setting of group field theory (GFT), a quantum field theory of 'atoms of space' which can form such a condensate. We further clarify the interpretation of this mean-field approximation, and show how it can be used to obtain a semiclassical description of the GFT, in which the mean field encodes a classical statistical distribution of geometric data. In this sense, GFT condensates are quantum homogeneous geometries that also contain statistical information about cosmological inhomogeneities. We show in the isotropic case how this information can be extracted from geometric GFT observables and mapped to quantities of observational interest. Basic uncertainty relations of (non-commutative) Fourier transforms imply that this statistical description can only be compatible with the observed near-homogeneity of the Universe if the typical length scale associated to the distribution is much larger than the fundamental 'Planck' scale. As an example of effective cosmological equations derived from the GFT dynamics, we then use a simple approximation in one class of GFT models to derive the 'improved dynamics' prescription of holonomy corrections in loop quantum cosmology.
Relativistic energy density functionals have become a standard framework for nuclear structure studies of ground-state properties and collective excitations over the entire nuclide chart. We review recent developments in modeling nuclear weak-interaction processes: charge-exchange excitations and the role of isoscalar proton-neutron pairing, charged-current neutrino-nucleus reactions relevant for supernova evolution and neutrino detectors, and calculation of beta-decay rates for r-process nucleosynthesis.
We study how gravitational focusing (GF) of dark matter by the Sun affects the annual and biannual modulation of the expected signal in non-directional direct dark matter searches, in the presence of dark matter substructure in the local dark halo. We consider the Sagittarius stream and a possible dark disk, and show that GF suppresses some, but not all, of the distinguishing features that would characterize substructure of the dark halo were GF neglected.
In this work, we consider Hojman symmetry in $f(T)$ theory. Unlike Noether conservation theorem, the symmetry vectors and the corresponding conserved quantities in Hojman conservation theorem can be obtained by using directly the equations of motion, rather than Lagrangian or Hamiltonian. We find that Hojman symmetry can exist in $f(T)$ theory, and the corresponding exact cosmological solutions are obtained. We find that the functional form of $f(T)$ is restricted to be the power-law or hypergeometric type, while the universe experiences a power-law or hyperbolic expansion. These results are different from the ones obtained by using Noether symmetry in $f(T)$ theory.
The time evolution of cosmological parameters in early Universe at the deconfinement transition is studied by an equation of state (EoS) which takes into account the finite baryon density and the background magnetic field. The non perturbative dynamics is described by the Field Correlator Method (FCM) which gives, with a small number of free parameters, a good fit of lattice data. The entire system has two components, i.e. the quark-gluon plasma and the electroweak sector, and the solutions of the Friedmann equation show that the scale factor, $a(t)$, and $H(t)= (1/a)da/dt$ are weakly dependent on the EoS, but the deceleration parameter, $q(t)$, and the jerk, $j(t)$, are strongly modified above the critical temperature $T_c$, corresponding to a critical time $t_c \simeq 20-25 \mu s$. The time evolution of the cosmological parameters suggest that above and around $T_c$ there is a transient state of acceleration typical of a matter dominated Universe; this is entailed by the QCD strong interaction driven by the presence of massive colored objects.
We point out that domain wall formation is a more common phenomenon in the Axiverse than previously thought. Level crossing could take place if there is a mixing between axions, and if some of the axions acquire a non-zero mass through non-perturbative effects as the corresponding gauge interactions become strong. The axion potential changes significantly during the level crossing, which affects the axion dynamics in various ways. We find that, if there is a mild hierarchy in the decay constants, the axion starts to run along the valley of the potential, passing through many crests and troughs, until it gets trapped in one of the minima; the {\it axion roulette}. The axion dynamics exhibits a chaotic behavior during the oscillations, and which minimum the axion is finally stabilized is highly sensitive to the initial misalignment angle. Therefore, the axion roulette is considered to be accompanied by domain wall formation. The cosmological domain wall problem can be avoided by introducing a small bias between the vacua. We discuss cosmological implications of the domain wall annihilation for baryogenesis and future gravitational wave experiments.
In a wide variety of natural and laboratory magnetized plasmas, filaments appear as a result of interchange instability. These convective structures substantially enhance transport in the direction perpendicular to the magnetic field. According to filament models, their propagation may follow different regimes depending on the parallel closure of charge conservation. This is of paramount importance in magnetic fusion plasmas, as high collisionality in the scrape-off layer may trigger a regime transition leading to strongly enhanced perpendicular particle fluxes. This work reports for the first time on an experimental verification of this process, linking enhanced transport with a regime transition as predicted by models. Based on these results, a novel scaling for global perpendicular particle transport in reactor relevant tokamaks such as ASDEX-Upgrade and JET is found, leading to important implications for next generation fusion devices.
In this paper, we examine a flat FLRW spacetime with a scalar field potential and show by applying Osgood's criterion to the Einstein field equations that all such models, irrespective of the particular choice of potential develop finite-time singularities. That is, we show that solutions to the field equations rapidly diverge in finite time. This can have important implications for the role of inflation in cosmological models, since one of the implications of this is that within the inflationary epoch, a singularity develops in finite time, which would call into question the role of inflation in the dynamic evolution of our universe. We further point out that a possible reason for this behaviour is that the solutions to the field equations in such inflationary scenarios do not obey global existence and uniqueness properties, which is a typical characteristic of solutions that diverge in finite time.
Recent years have seen increased theoretical and experimental effort towards the first-ever detection of cosmic-ray antideuterons, in particular as an indirect signature of dark matter annihilation or decay. In contrast to indirect dark matter searches using positrons, antiprotons, or gamma-rays, which suffer from relatively high and uncertain astrophysical backgrounds, searches with antideuterons benefit from very suppressed conventional backgrounds, offering a potential breakthrough in unexplored phase space for dark matter. This article is based on the first dedicated cosmic-ray antideuteron workshop, which was held at UCLA in June 2014. It reviews broad classes of dark matter candidates that result in detectable cosmic-ray antideuteron fluxes, as well as the status and prospects of current experimental searches. The coalescence model of antideuteron production and the influence of antideuteron measurements at particle colliders are discussed. This is followed by a review of the modeling of antideuteron propagation through the magnetic fields, plasma currents, and molecular material of our Galaxy, the solar system, the Earth's geomagnetic field, and the atmosphere. Finally, the three ongoing or planned experiments that are sensitive to cosmic-ray antideuterons, BESS, AMS-02, and GAPS, are detailed. As cosmic-ray antideuteron detection is a rare event search, multiple experiments with orthogonal techniques and backgrounds are essential. Many theoretical and experimental groups have contributed to these studies over the last decade, this review aims to provide the first coherent discussion of the relevant dark matter theories that antideuterons probe, the challenges to predictions and interpretations of antideuteron signals, and the experimental efforts toward cosmic antideuteron detection.
We have performed for the first time a comprehensive study of the sensitivity of $r$-process nucleosynthesis to individual nuclear masses across the chart of nuclides. Using the latest version (2012) of the Finite-Range Droplet Model, we consider mass variations of $\pm0.5$ MeV and propagate each mass change to all affected quantities, including $Q$-values, reaction rates, and branching ratios. We find such mass variations can result in up to an order of magnitude local change in the final abundance pattern produced in an $r$-process simulation. We identify key nuclei whose masses have a substantial impact on abundance predictions for hot, cold, and neutron star merger $r$-process scenarios and could be measured at future radioactive beam facilities.
No. In a number of papers Green and Wald argue that the standard FLRW model approximates our Universe extremely well on all scales, except in the immediate vicinity of very strong field astrophysical objects. In particular, they argue that the effect of inhomogeneities on average properties of the Universe (backreaction) is irrelevant. We show that their claims are not valid. Specifically, we demonstrate, referring to their recent review paper, that (i) their two-dimensional example used to illustrate the fitting problem differs from the actual problem in important respects, and it assumes what is to be proven; (ii) the proof of the trace-free property of backreaction is unphysical and the theorem about it is mathematically flawed; (iii) the scheme that underlies the trace-free theorem does not involve averaging and therefore does not capture crucial non-local effects; (iv) their arguments are to a large extent coordinate-dependent, and (v) many of their criticisms of backreaction frameworks do not apply to the published definitions of these frameworks.
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