We propose a unified framework that reconciles the stunning success of MOND on galactic scales with the triumph of the LambdaCDM model on cosmological scales. This is achieved through the physics of superfluidity. Dark matter consists of self-interacting axion-like particles that thermalize and condense to form a superfluid in galaxies, with ~mK critical temperature. The superfluid phonons mediate a MOND acceleration on baryonic matter. Our framework naturally distinguishes between galaxies (where MOND is successful) and galaxy clusters (where MOND is not): dark matter has a higher temperature in clusters, and hence is in a mixture of superfluid and normal phase. The rich and well-studied physics of superfluidity leads to a number of striking observational signatures.
We present the Kepler light curve of KIC 4552982, the first ZZ Ceti (hydrogen-atmosphere pulsating white dwarf star) discovered in the Kepler field of view. Our data span more than 1.5 years with a 86% duty cycle, making it the longest pseudo-continuous light curve ever recorded for a ZZ Ceti. This extensive data set provides the most complete coverage to-date of amplitude and frequency variations in a cool ZZ Ceti. We detect 20 independent frequencies of variability in the data that we compare with asteroseismic models to demonstrate that this star has a mass M$_*$ > 0.6 M$_{\rm Sun}$. We identify a rotationally split pulsation mode and derive a probable rotation period for this star of 17.47 $\pm$ 0.04 hr. In addition to pulsation signatures, the Kepler light curve exhibits sporadic, energetic outbursts that increase the star's relative flux by 2-17%, last 4-25 hours, and recur on an average timescale of 2.7 days. These are the first detections of a new dynamic white dwarf phenomenon that we believe may be related to the pulsations of this relatively cool (T$_{\rm eff}$ = 10,860 $\pm$ 120 K) ZZ Ceti star near the red edge of the instability strip.
We have observed two massive early-type galaxies with Keck/LRIS and measured radial gradients in the strengths of stellar absorption features from 4000-5500 \AA$\,$ and 8000-10,000 \AA. We present spatially resolved measurements of the dwarf-sensitive spectral indices NaI (8190 \AA) and Wing-Ford FeH (9915 \AA), as well as indices for species of H, C$_2$, CN, Mg, Ca, TiO, and Fe. Our measurements show a metallicity gradient in both objects, and Mg/Fe consistent with uniform $\alpha$-enhancement, matching widely observed trends for massive early-type galaxies. The NaI index and the CN$_1$ index at 4160 \AA$\,$ exhibit significantly steeper gradients, with a break at $r \sim 0.1 r_{\rm eff}$ ($r \sim 300$ pc). Inside this radius NaI and CN$_1$ increase sharply toward the galaxy center, relative to other indices. We interpret this trend as a rapid central rise in [Na/Fe] and [N/Fe]. In contrast, the FeH index exhibits a marginal decrease toward the galaxy center, relative to Fe. Our investigation is among the first to track FeH as a function of radius, and to demonstrate discrepant behavior between NaI and FeH. We suggest that a shallow gradient in FeH and steep, broken NaI profile reflect unique abundance patterns rather than a gradient in the stellar initial mass function.
Almost 50 years after radio pulsars were discovered in 1967, our understanding of these objects remains incomplete. On the one hand, within a few years it became clear that neutron star rotation gives rise to the extremely stable sequence of radio pulses, that the kinetic energy of rotation provides the reservoir of energy, and that electromagnetic fields are the braking mechanism. On the other hand, no consensus regarding the mechanism of coherent radio emission or the conversion of electromagnetic energy to particle energy yet exists. In this review, we report on three aspects of pulsar structure that have seen recent progress: the self-consistent theory of the magnetosphere of an oblique magnetic rotator; the location, geometry, and optics of radio emission; and evolution of the angle between spin and magnetic axes. These allow us to take the next step in understanding the physical nature of the pulsar activity.
NGC 4473 is a so--called double sigma (2$\sigma$) galaxy, i.e. a galaxy with rare, double peaks in its 2D stellar velocity dispersion. Here, we present the globular cluster (GC) kinematics in NGC 4473 out to $\sim10\,R_e$ (effective radii) using data from combined HST/ACS and Subaru/Suprime--Cam imaging and Keck/DEIMOS spectroscopy. We find that the 2$\sigma$ nature of NGC 4473 persists up to 3 $R_e$, though it becomes misaligned to the photometric major axis. We also observe a significant offset between the stellar and GC rotation amplitudes. This offset can be understood as a co--addition of counter--rotating stars producing little net stellar rotation. We identify a sharp radial transition in the GC kinematics at $\sim4\,R_e$ suggesting a well defined kinematically distinct halo. In the inner region ($<4\,R_e$), the blue GCs rotate along the photometric major axis, but in an opposite direction to the galaxy stars and red GCs. In the outer region ($>4\,R_e$), the red GCs rotate in an opposite direction compared to the inner region red GCs, along the photometric major axis, while the blue GCs rotate along an axis intermediate between the major and minor photometric axes. We also find a kinematically distinct population of very red GCs in the inner region with elevated rotation amplitude and velocity dispersion. The multiple kinematic components in NGC 4473 highlight the complex formation and evolutionary history of this 2$\sigma$ galaxy, as well as a distinct transition between the inner and outer components.
We explore the variability of quasars in the MgII and Hbeta broad emission lines and UV/optical continuum emission using the Sloan Digital Sky Survey Reverberation Mapping project (SDSS-RM). This is the largest spectroscopic study of quasar variability to date: our study includes 29 spectroscopic epochs from SDSS-RM over $6$ months, containing 357 quasars with MgII and 41 quasars with Hbeta . On longer timescales, the study is also supplemented with two-epoch data from SDSS-I/II. The SDSS-I/II data include an additional $2854$ quasars with MgII and 572 quasars with Hbeta. The MgII emission line is significantly variable ($\Delta f/f$ 10% on 100-day timescales), indicating that it is feasible to use the broad MgII line for reverberation mapping studies. The data also confirm that continuum variability increases with timescale and decreases with luminosity, and the continuum light curves are consistent with a damped random-walk model on rest-frame timescales of $\gtrsim 5$ days. We compare the emission-line and continuum variability to investigate the structure of the broad-line region. Broad-line variability shows a shallower increase with timescale compared to the continuum emission, demonstrating that the broad-line transfer function is not a $\delta$-function. Hbeta is more variable than MgII (roughly by a factor of $1.5$), suggesting different excitation mechanisms, optical depths and/or geometrical configuration for each emission line. The ensemble spectroscopic variability measurements enabled by the SDSS-RM project have important consequences for future studies of reverberation mapping and black hole mass estimation of $1<z<2$ quasars.
Over the past decades hollow-cathode lamps have been calibration standards for spectroscopic measurements. Advancing to cm/s radial velocity precisions with the next generation of instruments requires more suitable calibration sources with more lines and less dynamic range problems. Fabry-Perot interferometers provide a regular and dense grid of lines and homogeneous amplitudes making them good candidates for next generation calibrators. We investigate the usefulness of Fabry-Perot etalons in wavelength calibration, present an algorithm to incorporate the etalon spectrum in the wavelength solution and examine potential problems. The quasi periodic pattern of Fabry-Perot lines is used along with a hollow-cathode lamp to anchor the numerous spectral features on an absolute scale. We test our method with the HARPS spectrograph and compare our wavelength solution to the one derived from a laser frequency comb. The combined hollow-cathode lamp/etalon calibration overcomes large distortion (50 m/s) in the wavelength solution of the HARPS data reduction software. Direct comparison to the laser frequency comb bears differences of only maximum 10 m/s. Combining hollow-cathode lamps with Fabry-Perot Interferometers can lead to substantial improvements in the wavelength calibration of echelle spectrographs. Etalons can provide economical alternatives to the laser frequency comb, especially for smaller projects.
We present a metallicity analysis of 83 late-type giants within the central 1 pc of the Milky Way. K-band spectroscopy of these stars were obtained with the medium-spectral resolution integral-field spectrograph NIFS on Gemini North using laser-guide star adaptive optics. Using spectral template fitting with the MARCS synthetic spectral grid, we find that there is large variation in metallicity, with stars ranging from [M/H] $<$ -1.0 to above solar metallicity. About 6\% of the stars have [M/H] $<$ -0.5. This result is in contrast to previous observations, with smaller samples, that show stars at the Galactic center have approximately solar metallicity with only small variations. Our current measurement uncertainties are dominated by systematics in the model, especially at [M/H] $>$ 0, where there are stellar lines not represented in the model. However, the conclusion that there are low metallicity stars, as well as large variations in metallicity is robust. The metallicity may be an indicator of the origin of these stars. The low-metallicity population is consistent with that of globular clusters in the Milky Way, but their small fraction likely means that globular cluster infall is not the dominant mechanism for forming the Milky Way nuclear star cluster. The majority of stars are at or above solar metallicity, which suggests they were formed closer to the Galactic center or from the disk. In addition, our results indicate that it will be important for star formation history analyses using red giants at the Galactic center to consider the effect of varying metallicity.
Oscillatory double-diffusive convection (ODDC) (also known as semi- convection) refers to a type of double diffusive instability that occurs in regions of planetary and stellar interiors which have a destabilizing thermal stratification and a stabilizing mean molecular weight stratification. In this series of papers, we use an extensive suite of three-dimensional (3D) numerical simulations to quantify the transport of heat and chemical species by ODDC. Rosenblum et al. (2011) first showed that ODDC can either spontaneously form layers, which significantly enhance the transport of heat and chemical species compared to mi- croscopic transport, or remain in a state dominated by large scale gravity waves, in which there is a more modest enhancement of the turbulent transport rates. Subsequent studies in this series have focused on identifying under what condi- tions layers form (Mirouh et al. 2012), and quantifying transport through layered systems (Wood et al. 2013). Here we proceed to characterize transport through systems that are unstable to the ODDC instability, but do not undergo spon- taneous layer formation. We measure the thermal and compositional fluxes in non-layered ODDC from both 2D and 3D numerical simulations and show that 3D simulations are well approximated by similar simulations in a 2D domain. We find that the turbulent mixing rate in this regime is weak and can, to a first level approximation, be neglected. We conclude by summarizing the findings of papers I through III into a single prescription for transport by ODDC.
The 11 Mpc H-alpha and Ultraviolet Galaxy (11HUGS) Survey traces the star formation activity of nearby galaxies. In addition within this volume the detection completeness of core-collapse supernovae (CCSNe) is high therefore by comparing these observed stellar births and deaths we can make a sensitive test of our understanding of how stars live and die. In this paper, we use the results of the Binary Population and Spectral Synthesis (BPASS) code to simulate the 11HUGS galaxies H-alpha and far-ultraviolet (FUV) star formation rate indicators (SFRIs) and simultaneously match the core-collapse supernova (CCSN) rate. We find that stellar population including interacting binary stars makes little difference to the total CCSN rate but increases the H-alpha and FUV fluxes for a constant number of stars being formed. In addition they significantly increase the predicted rate of type Ibc supernovae (SNe) relative to type II SNe to the level observed in the 11HUGS galaxies. We also find that instead of assuming a constant star formation history (SFH) for the galaxies our best fitting models have a star formation rate (SFR) that peaked more than 3 Myrs ago.
The large-scale structure of the magnetic field in the solar corona provides the energy to power large-scale solar eruptive events. Our physical understanding of this structure, and hence our ability to predict these events, is limited by the type of data currently available. It is shown that the multifractal spectrum is a powerful tool to study this structure, by providing a physical connection between the details of photospheric magnetic gradients and current density at all size scales. This uses concepts associated with geometric measure theory and the theory of weakly differentiable functions to compare Amp\`{e}re's law to the wavelet-transform modulus maximum method. The H\"{o}lder exponent provides a direct measure of the rate of change of current density across spatial size scales. As this measure is independent of many features of the data (pixel resolution, data size, data type, presence of quiet-Sun data), it provides a unique approach to studying magnetic-field complexity and hence a potentially powerful tool for a statistical prediction of solar-flare activity. Three specific predictions are provided to test this theory: the multifractal spectra will not be dependent on the data type or quality; quiet-Sun gradients will not persist with time; structures with large current densities at large size scale will be the source of energy storage for solar eruptive events.
The infrared-to-X-ray (IRX) flux ratio traces the relative importance of dust cooling to gas cooling in astrophysical plasma such as supernova remnants (SNRs). We derive IRX ratios of SNRs in the LMC using Spitzer and Chandra SNR survey data and compare them with those of Galactic SNRs. IRX ratios of all the SNRs in the sample are found to be moderately greater than unity, indicating that dust grains are a more efficient coolant than gas although gas cooling may not be negligible. The IRX ratios of the LMC SNRs are systematically lower than those of the Galactic SNRs. As both dust cooling and gas cooling pertain to the properties of the interstellar medium, the lower IRX ratios of the LMC SNRs may reflect the characteristics of the LMC, and the lower dust-to- gas ratio (a quarter of the Galactic value) is likely to be the most significant factor. The observed IRX ratios are compared with theoretical predictions that yield IRX ratios an order of magnitude larger. This discrepancy may originate from the dearth of dust in the remnants due to either the local variation of the dust abundance in the preshock medium with respect to the canonical abundance or the dust destruction in the postshock medium. The non-equilibrium ionization cooling of hot gas, in particular for young SNRs, may also cause the discrepancy. Finally, we discuss implications for the dominant cooling mechanism of SNRs in low-metallicity galaxies.
The forthcoming Extremely Large Telescopes all require adaptive optics systems for their successful operation. The real-time control for these systems becomes computationally challenging, in part limited by the memory bandwidths required for wavefront reconstruction. We investigate new POWER8 processor technologies applied to the problem of real-time control for adaptive optics. These processors have a large memory bandwidth, and we show that they are suitable for operation of first-light ELT instrumentation, and propose some potential real-time control system designs. A CPU-based real-time control system significantly reduces complexity, improves maintainability, and leads to increased longevity for the real-time control system.
In recent years, detectors with sub-electron readout noise have been used very effectively in astronomical adaptive optics systems. Here, we compare readout noise models for the two key faint flux level detector technologies that are commonly used: EMCCD and scientific CMOS (sCMOS) detectors. We find that in almost all situations, EMCCD technology is advantageous, and that the commonly used simplified model for EMCCD readout is appropriate. We also find that the commonly used simple models for sCMOS readout noise are optimistic, and recommend that a proper treatment of the sCMOS rms readout noise probability distribution should be considered during instrument performance modelling and development.
We study the spherical collapse in the Parametrized Post-Friedmannian (PPF) scheme. We use a general form of the PPF parameter related to the Poisson equation and found the equations to solve that includes a non-trivial fifth force coming from the convolution of the modified gravity term in the k-space. In order to compute a concrete model, we use the parametrization proposed by Bertschinger and Zukin. The equations of the spherical collapse are solved assuming a Gaussian density profile and we show there is no shell crossing before reaching the turn around point. We show that the fifth force does not satisfy the Birkhoff's theorem and introduces different behaviors for the density threshold $\delta_{c}$, which in this case depends on the size and shape of the initial density profile, and therefore one expects a different statistic of the collapsed objects in the universe.
Extreme scattering events (ESEs) in the interstellar medium (ISM) were first observed in regular flux measurements of compact extragalactic sources. They are characterized by a flux variation over a period of weeks, suggesting the passage of a "diverging plasma lens" across the line of sight. Modeling the refraction of such a lens indicates that the structure size must be of order AU and the electron density of order 10s of cm^{-3}. Similar structures have been observed in measurements of pulsar intensity scintillation and group delay. Here we report observations of two ESEs showing increases in both intensity scintillation and dispersion made with the Parkes Pulsar Timing Array (PPTA). These allow us to make more complete models of the ESE, including an estimate of the "outer-scale" of the turbulence in the plasma lens. These observations show clearly that the ESE structure is fully turbulent on an AU scale. They provide some support for the idea that the structures are extended along the line of sight, such as would be the case for a scattering shell. The dispersion measurements also show a variety of AU scale structures which would not be called ESEs, yet involve electron density variations typical of ESEs and likely have the same origin.
Muons produced in atmospheric cosmic ray showers account for the by far
dominant part of the event yield in large-volume underground particle
detectors. The IceCube detector, with an instrumented volume of about a cubic
kilometer, has the potential to conduct unique investigations on atmospheric
muons by exploiting the large collection area and the possibility to track
particles over a long distance. Through detailed reconstruction of energy
deposition along the tracks, the characteristics of muon bundles can be
quantified, and individual particles of exceptionally high energy identified.
The data can then be used to constrain the cosmic ray primary flux and the
contribution to atmospheric lepton fluxes from prompt decays of short-lived
hadrons.
In this paper, techniques for the extraction of physical measurements from
atmospheric muon events are described and first results are presented. The
multiplicity spectrum of TeV muons in cosmic ray air showers for primaries in
the energy range from the knee to the ankle is derived and found to be
consistent with recent results from surface detectors. The single-muon energy
spectrum is determined up to PeV energies and shows a clear indication for the
emergence of a distinct spectral component from prompt decays of short-lived
hadrons. The magnitude of the prompt flux, which should include a substantial
contribution from light vector meson di-muon decays, is consistent with current
theoretical predictions.
The variety of measurements and high event statistics can also be exploited
for the evaluation of systematic effects. In the course of this study, internal
inconsistencies were found which indicate the presence of an unexplained effect
outside the range of detector systematics. The underlying cause could be
related to the hadronic interaction models used to describe muon production in
air showers.
How do peculiar velocities affect observed voids? To answer this question we use the VIDE toolkit to identify voids in mock galaxy populations embedded within an N-body simulation both with and without peculiar velocities included. We compare the resulting void populations to assess the impact on void properties. We find that void abundances and spherically-averaged radial density profiles are mildly affected by peculiar velocities. However, peculiar velocities can distort by up to 10% the shapes for a particular subset of voids depending on the void size and density contrast, which can lead to increased variance in Alcock-Paczy\'nski test. We offer guidelines for performing optimal cuts on the void catalogue to reduce this variance by removing the most severely affected voids while preserving the unaffected ones. In addition, since this shape distortion is largely limited to the line of sight, we show that the void radii are only affected at the $\sim$ 10% level and the macrocenter positions at the $\sim$ 20% (even before performing cuts), meaning that cosmological probes based on the Integrated Sachs-Wolfe and gravitational lensing are not severely impacted by peculiar velocities.
We present first measurements of the degree of linear polarization of distant comets C/2010 S1 (LINEAR) and C/2010 R1 (LINEAR) at heliocentric distances r= 5.9 - 7.0 AU. Observations were carried out with the SCORPIO-2 focal reducer at the 6-m telescope of the SAO RAS. Both comets showed considerable level of activity beyond a zone where water ice sublimation is negligible (up to 5 AU). Significant spatial variations both in the intensity and polarization are found in both comets. The slope of radial profiles of intensity changes gradually with the distance from the photocenter: from - 0.7 near the nucleus up to about - 1.3 for larger distances (up to 100000 km). The variation in polarization profiles indicates the non uniformity in the polarization distribution over the coma. The polarization degree over the coma gradually increases (in absolute value) with increasing the photocentric distance from of about - 1.9% up to - 3% for comet C/2010 S1 (LINEAR), and from of about - 2.5% up to - 3.5% for comet C/2010 R1 (LINEAR). These polarization values are significantly higher than typical value of the whole coma polarization (-1.5%) for comets at heliocentric distances less than 5 AU. The obtained photometric and polarimetric data are compared with those derived early for other comets at smaller heliocentric distances. Numerical modeling of light scattering characteristics was performed for media composed of particles with different refractive index, shape, and size. The computations were made by using the superposition T-matrix method. We obtained that for comet C/2010 S1 (LINEAR), the dust in the form of aggregates of overall radius R ~ 1.3 {\mu}m composed of N = 1000 spherical monomers with radius a = 0.1 {\mu}m, refractive index m = 1.65 + i 0.05, allows to obtain a satisfactory agreement between the results of polarimetric observations of comet C/2010 S1 and computations.
We analyse FORS2/VLT I-band imaging data to monitor the motions of both components in the most nearby known binary brown dwarf WISE J104915.57-531906.1AB (LUH16) over one year. The astrometry is dominated by parallax and proper motion, but with a precision of $\sim$0.2 milli-arcsecond per epoch we accurately measure the relative position change caused by the orbital motion of the pair. This allows us to directly determine a mass ratio of $q=0.78\pm0.10$ for this system. We also search for the signature of a planetary-mass companion around either of the A and B component and exclude at 3-$\sigma$ the presence of planets with masses larger than $2\,M_\mathrm{Jup}$ and orbital periods of 20-300 d. We update the parallax of LUH16 to $500.51\pm0.11$ mas, i.e. just within 2 pc. This study yields the first direct constraint on the mass ratio of LUH16 and shows that the system does not harbour any close-in giant planets.
We present observations of a 4 squared degree area toward the Gemini cloud obtained using J = 1-0 transitions of $^{12}$CO, $^{13}$CO and C$^{18}$O. No C$^{18}$O emission was detected. This region is composed of 36 core candidates of $^{13}$CO. These core candidates have a characteristic diameter of 0.25 pc, excitation temperatures of 7.9 K, line width of 0.54 km s$^{-1}$ and a mean mass of 1.4 M$_{\sun}$. They are likely to be starless core candidates, or transient structures, which probably disperse after $\sim$10$^6$ yr.
A flare and fast coronal mass ejection originated between solar active regions NOAA 11514 and 11515 on July 1, 2012 in response to flux emergence in front of the leading sunspot of the trailing region 11515. Analyzing the evolution of the photospheric magnetic flux and the coronal structure, we find that the flux emergence triggered the eruption by interaction with overlying flux in a non-standard way. The new flux neither had the opposite orientation nor a location near the polarity inversion line, which are favorable for strong reconnection with the arcade flux under which it emerged. Moreover, its flux content remained significantly smaller than that of the arcade (approximately 40 %). However, a loop system rooted in the trailing active region ran in part under the arcade between the active regions, passing over the site of flux emergence. The reconnection with the emerging flux, leading to a series of jet emissions into the loop system, caused a strong but confined rise of the loop system. This lifted the arcade between the two active regions, weakening its downward tension force and thus destabilizing the considerably sheared flux under the arcade. The complex event was also associated with supporting precursor activity in an enhanced network near the active regions, acting on the large-scale overlying flux, and with two simultaneous confined flares within the active regions.
We determine rotation periods of a sample of 48 late F-type to mid-M dwarf stars using time-series high-resolution spectroscopy of the Ca II H&K and H-alpha chromospheric activity indicators. We find good agreement between the rotation periods obtained from each of these two indicators. An empirical relationship between the level of chromospheric emission measured by log (R'HK) and the spectroscopic rotation periods is reported. This relation is largely independent of the spectral type and the metallicity of the stars and can be used to make a reliable prediction of rotation periods for late K to mid-M dwarfs with low levels of activity. For some stars in the sample, the measured spectroscopic rotation periods coincide, or are very close, to the orbital periods of postulated planets. In such cases, further studies are needed to clarify whether the associated periodic radial velocity signals reveal the existence of planets or are due to magnetic activity.
Among active galactic nuclei, BL Lac objects show extreme properties that have been interpreted as the effect of relativistic beaming on the emission from a plasma jet oriented close to the line of sight. The Doppler amplification of the jet emission makes them ideal targets for studying jet physics. In particular, low-power BL Lacs (LPBL) are very interesting because they probe the jet formation and emission processes at the lowest levels of accretion. However, they are difficult to identify since their emission is swamped by the radiation from the host galaxy in most observing bands. In this paper we propose a new LPBL selection method based on the mid-infrared emission, in addition to the traditional optical indices. We considered the radio-selected sample of Best & Heckman (2012, MNRAS, 421, 1569) and cross-matched it with the WISE all-sky survey. In a new diagnostic plane including the W2-W3 color and the Dn(4000) index, LPBL are located in a region scarcely populated by other sources. By filtering objects with small emission line equivalent width, we isolated 36 LPBL candidates up to redshift 0.15. Their radio luminosity at 1.4 GHz spans the range log L_r = 39.2-41.5 [erg/s]. Considering the completeness of our sample, we analyzed the BL Lac luminosity function (RLF), finding a dramatic paucity of LPBL with respect to the extrapolation of the RLF toward low power. This requires a break in the RLF located at log L_r~40.6 [erg/s]. The consequent peak in the BL Lacs number density is possibly the manifestation of a minimum power required to launch a relativistic jet.
We present early high resolution spectroscopic observations of the nova V1369 Cen. We have detected an absorption feature at 6695.6 \AA\, that we have identified as blue--shifted $^7$Li I $\lambda$6708 \AA. The absorption line, moving at -550 km/s, was observed in five high-resolution spectra of the nova obtained at different epochs. On the basis of the intensity of this absorption line we infer that a single nova outburst can inject in the Galaxy $M_{Li} =$ 0.3 - 4.8 $\times 10^{-10}$ M$_{\odot}$. Given the current estimates of Galactic nova rate, this amount is sufficient to explain the puzzling origin of the overabundance of Lithium observed in young star populations.
The origin of a new kinematically identified metal-poor stellar stream, the KFR08 stream, has not been established. We present stellar parameters, stellar ages, and detailed elemental abundances for Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Ni, Zn, Sr, Y, Zr, Ba, La, and Eu for 16 KFR08 stream members based on analysis of high resolution spectra. Based on the abundance ratios of 14 elements, we use the chemical tagging method to identify the stars which have the same chemical composition, and thus, might have a common birthplace, such as a cluster. Although three stars were tagged with similar elemental abundances ratios, we find that, statistically, it is not certain that they originate from a dissolved star cluster. This conclusion is consistent with the large dispersion of [Fe/H] ($\sigma_{\rm{[Fe/H]}} = 0.29$) among the 16 stream members. We find that our stars are $\alpha$ enhanced and that the abundance patterns of the stream members are well matched to the thick disk. In addition, most of the stream stars have estimated stellar ages larger than 11 Gyr. These results, together with the hot kinematics of the stream stars, suggest that the KFR08 stream is originated from the thick disk population which was perturbed by a massive merger in the early universe.
Hapke proposed a convenient and widely used analytical model to describe the spectro-photometry of granular materials. Using a compilation of the published data, Hapke (2012, Icarus, 221, 1079-1083) recently studied the relationship of b and c for natural examples and proposed the hockey stick relation (excluding b>0.5 and c>0.5). For the moment, there is no theoretical explanation for this relationship. One goal of this article is to study a possible bias due to the retrieval method. We expand here an innovative Bayesian inversion method in order to study into detail the uncertainties of retrieved parameters. On Emission Phase Function (EPF) data, we demonstrate that the uncertainties of the retrieved parameters follow the same hockey stick relation, suggesting that this relation is due to the fact that b and c are coupled parameters in the Hapke model instead of a natural phenomena. Nevertheless, the data used in the Hapke (2012) compilation generally are full Bidirectional Reflectance Diffusion Function (BRDF) that are shown not to be subject to this artifact. Moreover, the Bayesian method is a good tool to test if the sampling geometry is sufficient to constrain the parameters (single scattering albedo, surface roughness, b, c, opposition effect). We performed sensitivity tests by mimicking various surface scattering properties and various single image-like/disk resolved image, EPF-like and BRDF-like geometric sampling conditions. The second goal of this article is to estimate the favorable geometric conditions for an accurate estimation of photometric parameters in order to provide new constraints for future observation campaigns and instrumentations.
We argue that the lack of power exhibited by cosmic microwave background (CMB) anisotropies at large angular scales might be linked to the onset of inflation. We highlight observational features and theoretical hints that support this view, and present a preliminary estimate of the physical scale that would underlie the phenomenon.
In the absence of a fundamental theory that precisely predicts values for observable parameters, anthropic reasoning attempts to constrain probability distributions over those parameters in order to facilitate the extraction of testable predictions. The utility of this approach has been vigorously debated of late, particularly in light of theories that claim we live in a multiverse, where parameters may take differing values in regions lying outside our observable horizon. Within this cosmological framework, we investigate the efficacy of top-down anthropic reasoning based on the weak anthropic principle. We argue contrary to recent claims that it is not clear one can either dispense with notions of typicality altogether or presume typicality, in comparing resulting probability distributions with observations. We show in a concrete, top-down setting related to dark matter, that assumptions about typicality can dramatically affect predictions, thereby providing a guide to how errors in reasoning regarding typicality translate to errors in the assessment of predictive power. We conjecture that this dependence on typicality is an integral feature of anthropic reasoning in broader cosmological contexts, and argue in favour of the explicit inclusion of measures of typicality in schemes invoking anthropic reasoning, with a view to extracting predictions from multiverse scenarios.
The detailed shapes of spectral line profiles provide valuable information about the emitting plasma, especially when the plasma contains an unresolved mixture of velocities, temperatures, and densities. As a result of finite spectral resolution, the intensity measured by a spectrometer is the average intensity across a wavelength bin of non-zero size. It is assigned to the wavelength position at the center of the bin. However, the actual intensity at that discrete position will be different if the profile is curved, as it invariably is. Standard fitting routines (spline, Gaussian, etc.) do not account for this difference, and this can result in significant errors when making sensitive measurements. Detection of asymmetries in solar coronal emission lines is one example. Removal of line blends is another. We have developed an iterative procedure called Intensity Conserving Spline Interpolation (ICSI) that corrects for this effect. As its name implies, it conserves the observed intensity within each wavelength bin, which ordinary fits do not. Given the rapid convergence, speed of computation, and ease of use, we suggest that ICSI be made a standard component of the processing pipeline for spectroscopic data.
In the standard model of solar flares, energy deposition by a beam of electrons drives strong chromospheric evaporation leading to a significantly denser corona and much brighter emission across the spectrum. Chromospheric evaporation was examined in great detail by Fisher, Canfield, & McClymont (1985a,b,c), who described a distinction between two different regimes, termed explosive and gentle evaporation. In this work, we examine the importance of electron energy and stopping depths on the two regimes and on the atmospheric response. We find that with explosive evaporation, the atmospheric response does not depend strongly on electron energy. In the case of gentle evaporation, lower energy electrons are significantly more efficient at heating the atmosphere and driving up-flows sooner than higher energy electrons. We also find that the threshold between explosive and gentle evaporation is not fixed at a given beam energy flux, but also depends strongly on the electron energy and duration of heating. Further, at low electron energies, a much weaker beam flux is required to drive explosive evaporation.
Recent observations of the Crab Nebula (Rudy et al 2015) have maintained its reputation for high energy astrophysical enlightenment and its use as a testbed for theories of the behaviour of magnetized, relativistic plasma. In particular, new observations of the inner knot located 0.65'' SE from the pulsar confirm that it is compact, elongated transversely to the symmetry axis and curved concave towards the pulsar. 60 percent polarization has been measured along the symmetry axis (Moran et al 2013). The knot does not appear to be involved in the gamma ray flares. The new observations both reinforce the interpretation of the knot as dissipation of the pulsar wind at a strong shock and challenge the details of existing models of this process. In particular, it is argued that the compactness, high polarization and curvature are difficult to reconcile with simple relativistic shock models. Alternative possibilities include deflection of the outflow ahead of the shock and spatial variation in which the knot is interpreted as a caustic. Some future observations are proposed and new theoretical investigations are suggested.
The long-term behaviours of the pulsation and Blazhko periods of RR Lyr are investigated by means of Kepler and ground-based observations. The difficulties in detecting additional modes in the Cepheids monitored with CoRoT are discussed.
We are presenting here a study of the cold dust in the ring nebula Gum 31. We aim at deriving the physical properties of the molecular gas and dust associated with the nebula, and investigating its correlation with the star formation in the region, that was probably triggered by the expansion of the ionization front. We use 870 microns data obtained with LABOCA to map the dust emission. The obtained LABOCA image was compared to archival IR,radio continuum, and optical images. The 870 microns emission follows the 8 microns (Spitzer), 250 microns, and 500 microns (Herschel) emission distributions showing the classical morphology of a spherical shell. We use the 870 microns and 250 microns images to identify 60 dust clumps in the collected layers of molecular gas using the Gaussclumps algorithm. The clumps have effective deconvolved radii between 0.16 pc and 1.35 pc, masses between 70 Mo and 2800 Mo, and volume densities between 1.1x10^3 cm^-3 and 2.04x10^5 cm^-3. The total mass of the clumps is 37600 Mo. The dust temperature of the clumps is in the range from 21 K to 32 K, while inside the HII region reaches ~ 40 K. The clump mass distribution is well-fitted by a power law dN/dlog(M/Mo) proportional to M^(-alpha), with alpha=0.93+/-0.28. The slope differs from those obtained for the stellar IMF in the solar neighborhood, suggesting that the clumps are not direct progenitors of single stars/protostars. The mass-radius relationship for the 41 clumps detected in the 870 microns emission shows that only 37% of them lie in or above the high-mass star formation threshold, most of them having candidate YSOs projected inside. A comparison of the dynamical age of the HII region with the fragmentation time, allowed us to conclude that the collect and collapse mechanism may be important for the star formation at the edge of Gum 31, although other processes may also be acting.
We analyze two multi-chord stellar occultations by Pluto observed on July 18th, 2012 and May 4th, 2013, and monitored respectively from five and six sites. They provide a total of fifteen light-curves, twelve of them being used for a simultaneous fit that uses a unique temperature profile, assuming a clear (no-haze) and pure N_2 atmosphere, but allowing for a possible pressure variation between the two dates. We find a solution that fits satisfactorily (i.e. within the noise level) all the twelve light-curves, providing atmospheric constraints between ~1,190 km (pressure ~ 11 \mubar) and ~ 1,450 km (pressure ~0.1 \mubar) from Pluto's center. Our main results are: (1) the best-fitting temperature profile shows a stratosphere with strong positive gradient between 1,190 km (at 36 K, 11 \mubar) and r = 1,215 km (6.0 \mubar), where a temperature maximum of 110 K is reached; above it is a mesosphere with negative thermal gradient of -0.2 K/km up to ~ 1,390 km (0.25 \mubar), where, the mesosphere connects itself to a more isothermal upper branch around 81 K; (2) the pressure shows a small (6 %) but significant increase (6-\sigma level) between the two dates; (3) without troposphere, Pluto's radius is found to be R_P = 1,190 +/- 5km. Allowing for a troposphere, R_P is constrained to lie between 1,168 and 1,195 km; (4) the currently measured CO abundance is too small to explain the mesospheric negative thermal gradient. Cooling by HCN is possible, but only if this species is largely saturated; Alternative explanations like zonal winds or vertical compositional variations of the atmosphere are unable to explain the observed mesospheric trend.
We present a detailed analysis of an astrophysical mechanism that generates cosmological magnetic fields during the Epoch of Reionization. It is based on the photoionization of the Intergalactic Medium by the first sources formed in the Universe. First the induction equation is derived, then the characteristic length and time scales of the mechanism are identified, and finally numerical applications are carried out for first stars, primordial galaxies and distant powerful quasars. In these simple examples, the strength of the generated magnetic fields varies between the order of $10^{-23}$ G on hundreds of kiloparsecs to $10^{-19}$ G on hundreds of parsecs in the neutral Intergalactic Medium between the Str\"omgren spheres of the sources. Thus this mechanism contributes to the premagnetization of the whole Universe before large scale structures are in place. It operates with any ionizing source, at any time during the Epoch of Reionization. Finally, the generated fields possess a characteristic spatial configuration which may help discriminate these seeds from those produced by different mechanisms.
The mixing of materials due to the Richtmyer-Meshkov instability and the ensuing turbulent behavior is of intense interest in a variety of physical systems including inertial confinement fusion, combustion, and the final stages of stellar evolution. Extensive numerical and laboratory studies of shock-driven mixing have demonstrated the rich behavior associated with the onset of turbulence due to the shocks. Here we report on progress in understanding shock-driven mixing at interfaces between fluids of differing densities through 3D numerical simulations using the RAGE code in the implicit large eddy simulation context. We consider a shock tube configuration with a band of high density gas (SF$_6$) embedded in low density gas (air). Shocks with a Mach number of 1.26 are passed through SF$_6$ bands, resulting in transition to turbulence driven by the Richtmyer-Meshkov instability. The system is followed as a rarefaction wave and a reflected secondary shock from the back wall pass through the SF$_6$ band. We apply a variety of initial perturbations to the interfaces between the two fluids in which the physical standard deviation, wave number range, and the spectral slope of the perturbations are held constant, but the number of modes initially present is varied. By thus decreasing the density of initial spectral modes of the interface, we find that we can achieve as much as 25\% less total mixing at late times. This has potential direct implications for the treatment of initial conditions applied to material interfaces in both 3D and reduced dimensionality simulation models.
"The Lord made me a very great favor in an imaginary vision" wrote Maria de Agreda in the seventeenth century, "His Majesty put me at the foot of a beautiful Ladder, and showed me I had to climb it." These words refer to the spiritual ascent, present in the Judeo-Christian tradition, and crystallized in the visions of prophets and Catholic saints. Genesis (18: 10-22) narrates that Jacob, going to Haran, slept on some stones and saw a ladder between heaven and earth along which angels were ascending and descending. From this dream, the symbolic union between heaven and earth has been figured with stairs, ascribing to it different meanings over the centuries. On the steps of the ladder people saw a metaphor for the graduality of ascent; Benedict used a ladder of twelve steps of humility in his Regula, and in the seventh century AD John Climacus, Bishop of Sinai, established a thirty-step Scala Paradisi of meditation leading to God. In this work we discuss the historical echoes of the Benedictine rule, together with Climacus' voice in the desert and the visualization of celestial mysteries, in the case of the Cuzco school painting Allegory of the firmament, with the representation of the planets' seven heavens (XVIII century). In this way we try and analyze the intersection between science and mysticism in the representation of the heavenly stairs, in order to show the cultural anchorage of the symbology employed in these cases [abridged].
The loop quantization of the Schwarzschild interior region, as described by a homogenous anisotropic Kantowski-Sachs model, is re-examined. As several studies of different --inequivalent-- loop quantizations have shown, to date there exists no fully satisfactory quantum theory for this model. This fact posses challenges to the validity of some scenarios to address the black hole information problem. Here we put forward a novel viewpoint to construct the quantum theory that builds from some of the models available in the literature. The final picture is a quantum theory that is both independent of any auxiliary structure and possesses a correct low curvature limit. It represents a subtle but non-trivial modification of the original prescription given by Ashtekar and Bojowald. It is shown that the quantum gravitational constraint is well defined past the singularity and that its effective dynamics possesses a bounce into an expanding regime. The classical singularity is avoided, and a semiclassical spacetime satisfying vacuum Einstein's equations is recovered on the "other side" of the bounce. We argue that such metric represents the interior region of a white-hole spacetime, but for which the corresponding "white-hole mass" differs from the original black hole mass. Furthermore, we find that the value of the white-hole mass is proportional to the third power of the starting black hole mass. We discuss possible implications of this phenomena.
The recent observation by the IceCube experiment of cosmic neutrinos at energies up to a few PeV heralds the beginning of neutrino astronomy. At such high energies, the conventional neutrino flux is suppressed and the prompt component from charm meson decays is expected to become the dominant background to astrophysical neutrinos. Charm production at high energies is however theoretically uncertain, both since the charm mass is at the boundary of applicability of perturbative QCD, and also because the calculations are sensitive to the poorly-known gluon PDF at small-x. In this work we provide detailed perturbative QCD predictions for charm and bottom production in the forward region, and validate them by comparing with recent data from the LHCb experiment at 7 TeV. Finding good agreement between data and theory, we use the LHCb measurements to constrain the small-x gluon PDF, achieving a substantial reduction in its uncertainties. Using these improved PDFs, we provide predictions for charm and bottom production at LHCb at 13 TeV, as well as for the ratio of cross-sections between 13 and 7 TeV. The same calculations are used to compute the energy distribution of neutrinos from charm decays in pA collisions, a key ingredient towards achieving a theoretically robust estimate of charm-induced backgrounds at neutrino telescopes.
We derive novel limits on the masses of the light and heavy Majorana neutrinos by requiring successful leptogenesis in seesaw models of minimal flavour violation (MFV). Taking properly into account radiative flavour effects and avoiding the limitations due to a no-go theorem on leptonic asymmetries, we find that the mass of the lightest of the observable neutrinos must be smaller than $\sim 0.05$ eV, whilst the Majorana scale of lepton number violation should be higher than $\sim 10^{12}$ GeV. The latter lower bound enables one to probe the existence of possible new scales of MFV, up to energies of $\sim 100$ TeV, in low-energy experiments, such as $\mu \to e\gamma$ and $\mu \to e$ conversion in nuclei. Possible realizations of MFV leptogenesis in Grand Unified Theories are briefly discussed.
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We present simulations of the tidal disruption of a solar mass star by a $10^6M_{\odot}$ black hole. These, for the first time, cover the full time evolution of the tidal disruption event, starting well before the initial encounter and continuing until more than 90% of the bound material has returned to the vicinity of the hole. Our results are compared to the analytical prediction for the rate at which tidally-stripped gas falls back. We find that, for our chosen parameters, the overall scaling of the fallback rate, $\dot{M}_{\rm{fb}}$, closely follows the canonical $t^{-5/3}$ power-law. However, our simulations also show that the self-gravity of the tidal stream, which dominates the tidal gravity of the hole at large distances, causes some of the debris to recollapse into bound fragments before returning to the hole. This causes $\dot{M}_{\rm{fb}}$ to vary significantly around the $t^{-5/3}$ average. We discuss the implications of our findings in the context of the event Swift J1644+57.
Cold gas entering the central $1$ to $10^2$ pc of a galaxy fragments and condenses into clouds. The stability of the clouds determines whether they will be turned into stars or can be delivered to the central supermassive black hole (SMBH) to turn on an active galactic nucleus (AGN). The conventional criteria to assess the stability of these clouds, such as the Jeans criterion and Roche (or tidal) limit, are insufficient here, because they assume the dominance of self-gravity in binding a cloud, and neglect external agents, such as pressure and tidal forces, which are common in galactic nuclei. We formulate a new scheme for judging this stability. We first revisit the conventional Virial theorem, taking into account an external pressure, to identify the correct range of masses that lead to stable clouds. We then extend the theorem to include an external tidal field, crucial for the stability in the region of interest -- in dense star clusters, around SMBHs. We apply our extended Virial theorem to find the correct solutions to practical problems that until now were controversial, namely, the stability of the gas clumps in AGN tori, the circum-nuclear disk in the Galactic Center, and the central molecular zone of the Milky Way. The masses we derive for these structures are orders of magnitude smaller than the commonly-used Virial masses (equivalent to the Jeans mass). Moreover, we prove that these clumps are stable, contrary to what one would naively deduce from the Roche (tidal) limit.
Globular clusters (GCs) and Nuclear Stellar Clusters (NSCs) are typically composed by several stellar generations, characterized by different ages and chemical compositions. The youngest populations in NSCs appear to reside in disk-like structures, as observed in our Galaxy and in M31. Gas infall followed by formation of second generation (SG) stars in GCs may similarly form disk-like structures in the clusters nuclei. Here we explore this possibility and follow the long term evolution of stellar disks embedded in GCs, and study their affects on the evolution of the clusters. We study disks with different masses by means of detailed N-body simulations and explore their morphological and kinematic signatures on the GC structures. We find that as a second generation disk relaxes, the old, first generation, stellar population flattens and becomes more radially anisotropic, making the GC structure become more elliptical. The second generation stellar population is characterized by a lower velocity dispersion, and a higher rotational velocity, compared with the primordial older population. The strength of these kinematic signatures depends both on the relaxation time of the system and on the fractional mass of the second generation disk. We therefore conclude that SG populations formed in flattened configurations will give rise to two systematic trends: (1) Positive correlation between GC ellipticity and fraction of SG population (2) Positive correlation between GC relaxation time and ellipticity. Thereby GC ellipticities and rotation could be related to the formation of SG stars and their initial configuration.
We present $U_{336}V_{606}J_{125}H_{160}$ follow-up $HST$ observations of 16 $z\sim3$ candidate LyC emitters in the HS1549+1933 field. With these data, we obtain high spatial-resolution photometric redshifts of all sub-arcsecond components of the LyC candidates in order to eliminate foreground contamination and identify robust candidates for leaking LyC emission. Of the 16 candidates, we find one object with a robust LyC detection that is not due to foreground contamination. This object (MD5) resolves into two components; we refer to the LyC-emitting component as MD5b. MD5b has an observed 1500\AA\ to 900\AA\ flux-density ratio of $(F_{UV}/F_{LyC})_{obs}=4.0\pm2.0$, compatible with predictions from stellar population synthesis models. Neglecting IGM absorption, this ratio corresponds to lower limits to the relative (absolute) escape fraction of $f_{esc,rel}^{MD5b}=75\%\pm38\%$ ($f_{esc,abs}^{MD5b}=14\%\pm7\%$). The stellar population fit to MD5b indicates an age of $\lesssim50$Myr, which is in the youngest 10% of the $HST$ sample and the youngest third of typical $z\sim3$ Lyman break galaxies, and may be a contributing factor to its LyC detection. We obtain a revised, contamination-free estimate for the comoving specific ionizing emissivity at $z=2.85$, indicating (with large uncertainties) that star-forming galaxies provide roughly the same contribution as QSOs to the ionizing background at this redshift. Our results show that foreground contamination prevents ground-based LyC studies from obtaining a full understanding of LyC emission from $z\sim3$ star-forming galaxies. Future progress in direct LyC searches is contingent upon the elimination of foreground contaminants through high spatial-resolution observations, and upon acquisition of sufficiently deep LyC imaging to probe ionizing radiation in high-redshift galaxies.
We investigate the possibility of observing monochromatic neutrino lines originating from annihilation of dark matter. We analyse several astrophysical sources with overdensities of dark matter that can amplify the signal. As a case study, we consider mixed left and right handed sneutrino dark matter. We demonstrate that in the physically viable region of the model, one can obtain a prominent monochromatic neutrino line. We propose a search strategy to observe these neutrino lines in future generations of neutrino telescopes that is especially sensitive to dwarf spheroidal galaxies. We demonstrate that the presence of massive black holes in the cores of dwarfs as well as of more massive galaxies substantially boosts any putative signal. In particular, dark matter in dwarf galaxies spiked by IMBH provides a powerful means of probing low annihilation cross-sections well below $10^{-26} \rm cm^3 s^{-1}$ that are otherwise inaccessible by any future direct detection or collider experiment.
We present a spectroscopic survey of 318 faint $(R\sim 27$, $L\sim0.1L_*)$, Ly{\alpha}-emission-selected galaxies (LAEs) at 2.5<z<3. A sample of 32 LAEs with rest-frame optical spectra from Keck/MOSFIRE are used to interpret the LAE spectra in the context of their systemic redshifts. We find that the Ly{\alpha} emission of LAEs is typically less spectrally extended than among samples of more luminous continuum-selected galaxies (LBGs) at similar redshifts. Using the MOSFIRE subsample, we find that the peak of the Ly{\alpha} line is shifted by +200 km/s with respect to systemic across a diverse set of galaxies including both LAEs and LBGs. We also find a small number of objects with significantly blueshifted Ly{\alpha} emission, a potential indicator of accreting gas. The Ly{\alpha}-to-H{\alpha} line ratios suggest that the LAEs have Ly{\alpha} escape fractions $f_{\rm esc,Ly{\alpha}} \approx 30$%, significantly higher than typical LBG samples. Using redshifts calibrated by our MOSFIRE sample, we construct composite LAE spectra, finding the first evidence for metal-enriched outflows in such intrinsically-faint high-redshift galaxies. These outflows have smaller continuum covering fractions $(f_c \approx 0.3)$ and velocities $(v_{\rm ave} \approx 100-200$ km/s, $v_{\rm max} \approx 500$ km/s$)$ than those associated with typical LBGs, suggesting that gas covering fraction is a likely driver of the high Ly{\alpha} and Ly-continuum escape fractions of LAEs. Our results suggest a similar scaling of outflow velocity with star formation rate as is observed at lower redshifts $(v_{\rm outflow} \sim {\rm SFR}^{0.25})$ and indicate that a substantial fraction of gas is ejected with $v > v_{esc}$.
The expected gamma-ray flux coming from dark matter annihilation in dwarf spheroidal (dSph) galaxies depends on the so-called 'J-factor', the integral of the squared dark matter density along the line-of-sight. We examine the degree to which estimates of J are sensitive to contamination (by foreground Milky Way stars and stellar streams) of the stellar-kinematic samples that are used to infer dark matter densities in 'ultrafaint' dSphs. Applying standard kinematic analyses to hundreds of mock data sets that include varying levels of contamination, we find that mis-classified contaminants can cause J-factors to be overestimated by orders of magnitude. Stellar-kinematic data sets for which we obtain such biased estimates tend 1) to include relatively large fractions of stars with ambiguous membership status, and 2) to give estimates for J that are sensitive to specific choices about how to weight and/or to exclude stars with ambiguous status. Comparing publicly-available stellar-kinematic samples for the nearby dSphs Reticulum II and Segue I, we find that only the latter displays both of these characteristics. Estimates of Segue I's J-factor should therefore be regarded with a larger degree of caution when planning and interpreting gamma-ray observations.
We describe the design, operation, and first results of a photometric calibration project, called DICE (Direct Illumination Calibration Experiment), aiming at achieving precise instrumental calibration of optical telescopes. The heart of DICE is an illumination device composed of 24 narrow-spectrum, high-intensity, light-emitting diodes (LED) chosen to cover the ultraviolet-to-near-infrared spectral range. It implements a point-like source placed at a finite distance from the telescope entrance pupil, yielding a flat field illumination that covers the entire field of view of the imager. The purpose of this system is to perform a lightweight routine monitoring of the imager passbands with a precision better than 5 per-mil on the relative passband normalisations and about 3{\AA} on the filter cutoff positions. The light source is calibrated on a spectrophotometric bench. As our fundamental metrology standard, we use a photodiode calibrated at NIST. The radiant intensity of each beam is mapped, and spectra are measured for each LED. All measurements are conducted at temperatures ranging from 0{\deg}C to 25{\deg}C in order to study the temperature dependence of the system. The photometric and spectroscopic measurements are combined into a model that predicts the spectral intensity of the source as a function of temperature. We find that the calibration beams are stable at the $10^{-4}$ level -- after taking the slight temperature dependence of the LED emission properties into account. We show that the spectral intensity of the source can be characterised with a precision of 3{\AA} in wavelength. In flux, we reach an accuracy of about 0.2-0.5% depending on how we understand the off-diagonal terms of the error budget affecting the calibration of the NIST photodiode. With a routine 60-mn calibration program, the apparatus is able to constrain the passbands at the targeted precision levels.
The Galaxy And Mass Assembly (GAMA) survey is one of the largest contemporary spectroscopic surveys of low-redshift galaxies. Covering an area of ~286 deg^2 (split among five survey regions) down to a limiting magnitude of r < 19.8 mag, we have collected spectra and reliable redshifts for 238,000 objects using the AAOmega spectrograph on the Anglo-Australian Telescope. In addition, we have assembled imaging data from a number of independent surveys in order to generate photometry spanning the wavelength range 1 nm - 1 m. Here we report on the recently completed spectroscopic survey and present a series of diagnostics to assess its final state and the quality of the redshift data. We also describe a number of survey aspects and procedures, or updates thereof, including changes to the input catalogue, redshifting and re-redshifting, and the derivation of ultraviolet, optical and near-infrared photometry. Finally, we present the second public release of GAMA data. In this release we provide input catalogue and targeting information, spectra, redshifts, ultraviolet, optical and near-infrared photometry, single-component S\'ersic fits, stellar masses, H$\alpha$-derived star formation rates, environment information, and group properties for all galaxies with r < 19.0 mag in two of our survey regions, and for all galaxies with r < 19.4 mag in a third region (72,225 objects in total). The database serving these data is available at this http URL
The most accurate measurements of magnetic fields in star-forming gas are based on the Zeeman observations analyzed by Crutcher et al. (2010). We show that their finding that the 3D magnetic field scales approximately as density$^{0.65}$ can also be obtained from analysis of the observed line-of-sight fields. We present two large-scale AMR MHD simulations of several thousand $M_\odot$ of turbulent, isothermal, self-gravitating gas, one with a strong initial magnetic field (Alfven Mach number $M_{A,0}= 1$) and one with a weak initial field ($M_{A,0}=10$). We construct samples of the 100 most massive clumps in each simulation and show that they exhibit a power-law relation between field strength and density in excellent agreement with the observed one. Our results imply that the average field in molecular clumps in the interstellar medium is $<B_{tot}> \sim 42 n_{H,4}^{0.65} \mu$G. Furthermore, the median value of the ratio of the line-of-sight field to density$^{0.65}$ in the simulations is within a factor of about (1.3, 1.7) of the observed value for the strong and weak field cases, respectively. The median value of the mass-to-flux ratio, normalized to the critical value, is 70% of the line-of-sight value. This is larger than the 50% usually cited for spherical clouds because the actual mass-to-flux ratio depends on the volume-weighted field, whereas the observed one depends on the mass-weighted field. Our results indicate that the typical molecular clump in the ISM is significantly supercritical (~ factor of 3). The results of our strong-field model are in very good quantitative agreement with the observations of Li et al. (2009), which show a strong correlation in field orientation between small and large scales. Because there is a negligible correlation in the weak-field model, we conclude that molecular clouds form from strongly magnetized (although magnetically supercritical) gas.
We present the results of a 135-arcmin$^2$ search for high-redshift galaxies lensed by clusters from the MAssive Cluster Survey. We use relatively shallow images obtained with the Hubble Space Telescope in four passbands, namely, F606W, F814W, F110W, and F140W. We identify 124 F814W dropouts as candidates for galaxies at $z \ge 6$. In order to fit the available broad-band photometry to galaxy spectral energy distribution templates, we develop a prior for the level of dust extinction at various redshifts. We also investigate the systematic biases incurred by the use of SED-fit software. The fits we obtain yield an estimate of 27 Lyman-break galaxies with photometric redshifts from $z \sim 7$ to 9. In addition, our survey has identified over 70 candidates with a significant probability of being lower-redshift ($z \sim 2$) interlopers. We conclude that even as few as four broad-band filters -- when combined with fitting the SEDs -- are capable of isolating promising objects. Such surveys are thus ideal both for investigating the bright end ($M_{1500} \le -19$) of the high-redshift UV luminosity function and for identifying candidate massive evolved galaxies at lower redshifts.
A new astronomical photo-polarimeter that can measure linear polarization of point sources simultaneously in three spectral bands was designed and built in Indian Institute of Astrophysics. The polarimeter has a Calcite beam-displacement prism as the analyzer. The ordinary and extra-ordinary emerging beams in each spectral band are quasi-simultaneously detected by the same photomultiplier by using a high speed rotating chopper. The effective chopping frequency can be set to as high as 200 Hz. A rotating superachromatic Pancharatnam halfwave plate is used to modulate the light incident on the analyzer. The spectral bands are isolated using appropriate dichroic and glass filters. A detailed analysis shows that the reduction of 50% in the efficiency of the polarimeter because of the fact that the intensities of the two beams are measured alternately is partly compensated by the reduced time to be spent on the observation of the sky background. The position angle of polarization produced by the Glan-Taylor prism in the light path is found to be slightly wavelength dependent, indicating that the fixed super-achromatic halfwave plate in the beam does not fully compensate for the variation in the position angle of the effective optical axis of the rotating plate. However, the total amplitude of variation in the U-I spectral region is only 0.92 degree. The polarization efficiency is also found to be wavelength-dependent with a total amplitude of 0.271% in the U-I region; its mean value is 99.211%. The instrumental polarization is found to be very low. It is nearly constant in the V-I spectral region (~0.04%), and apparently, it increases slightly towards the ultraviolet. The observations of polarized stars show that the agreement between the measured polarization values and those available in the literature to be excellent.
Magnetic reconnection, a change of magnetic field connectivity, is a fundamental physical process in which magnetic energy is released explosively. It is responsible for various eruptive phenomena in the universe. However, this process is difficult to observe directly. Here, the magnetic topology associated with a solar reconnection event is studied in three dimensions (3D) using the combined perspectives of two spacecraft. The sequence of extreme ultraviolet (EUV) images clearly shows that two groups of oppositely directed and non-coplanar magnetic loops gradually approach each other, forming a separator or quasi-separator and then reconnecting. The plasma near the reconnection site is subsequently heated from $\sim$1 to $\ge$5 MK. Shortly afterwards, warm flare loops ($\sim$3 MK) appear underneath the hot plasma. Other observational signatures of reconnection, including plasma inflows and downflows, are unambiguously revealed and quantitatively measured. These observations provide direct evidence of magnetic reconnection in a 3D configuration and reveal its origin.
We consider the best today available observations of the Sun free of turbulent Earth atmospheric effects, taken with the Solar Optical Telescope (SOT) onboard the Hinode spacecraft. Both the instrumental smearing and the observed stray light are analyzed in order to improve the resolution. The Point Spread Function (PSF) corresponding to the blue continuum Broadband Filter Imager (BFI) near 450 nm is deduced by analyzing i/ the limb of the Sun and ii/ images taken during the transit of the planet Venus in 2012. A combination of Gaussian and Lorentzian functions is selected to construct a PSF in order to remove both smearing due to the instrumental diffraction effects (PSF core) and the large-angle stray light due to the spiders and central obscuration (wings of the PSF) that are responsible for the parasitic stray light. A Max-likelihood deconvolution procedure based on an optimum number of iterations is discussed. It is applied to several solar field images, including the granulation near the limb. The normal non-magnetic granulation is compared to the abnormal granulation which we call magnetic. A new feature appearing for the first time at the extreme- limb of the disk (the last 100 km) is discussed in the context of the definition of the solar edge and of the solar diameter. A single sunspot is considered in order to illustrate how effectively the restoration works on the sunspot core. A set of 125 consecutive deconvolved images is assembled in a 45 min long movie illustrating the complexity of the dynamical behavior inside and around the sunspot.
Aims: We explore the cosmological implications of two types of baryon
acoustic oscillation (BAO) data that are extracted by using the spherically
averaged one-dimensional galaxy clustering (GC) statistics (hereafter BAO1) and
the anisotropic two-dimensional GC statistics (hereafter BAO2), respectively.
Methods: Firstly, making use of the BAO1 and the BAO2 data, as well as the
SNLS3 type Ia supernovae sample and the Planck distance priors data, we
constrain the parameter spaces of the $\Lambda$CDM, the $w$CDM, and the
Chevallier-Polarski-Linder (CPL) model. Then, we discuss the impacts of
different BAO data on parameter estimation, equation of state $w$, figure of
merit and deceleration-acceleration transition redshift. At last, we use
various dark energy diagnosis, including Hubble diagram $H(z)$, deceleration
diagram $q(z)$, statefinder hierarchy $\{S^{(1)}_3, S^{(1)}_4\}$, composite
null diagnosic (CND) $\{S^{(1)}_3, \epsilon(z)\}$ and $\{S^{(1)}_4,
\epsilon(z)\}$, to distinguish the differences between the results given by
different BAO data.
Results: We find that, for all the models, BAO2 data always give a smaller
fractional matter density $\Omega_{m0}$, a larger fractional curvature density
$\Omega_{k0}$, and a larger Hubble constant $h$; for the $w$CDM and the CPL
model, BAO2 data always give a slightly smaller $w$. In addition, BAO1 data
always yield a cosmological result that is closer to the $\Lambda$CDM model,
while BAO2 data give a cosmological constraint that has a slightly better
accuracy. Moreover, we find that using the $H(z)$ and the $q(z)$ diagram have
difficulty to distinguish the differences between different BAO data; in
contrast, both the statefinder hierarchy $\{S^{(1)}_3, S^{(1)}_4\}$, the CND
$\{S^{(1)}_3, \epsilon(z)\}$ and $\{S^{(1)}_4, \epsilon(z)\}$ are powerful
tools that have the ability to distinguish the impacts of different BAO data.
Diskoseismology, the theoretical study of normal mode oscillations in geometrically thin, optically thick accretion disks, is a strong candidate to explain some QPOs in the power spectra of many black hole X-ray binary systems. The existence of g-modes, presumably the most robust and visible of the modes, depends on general relativistic gravitational trapping in the hottest part of the disk. As the existence of the required cavity in the presence of magnetic fields has been put into doubt by theoretical calculations, we will explore in greater generality what the inclusion of magnetic fields has to say on the existence of g-modes. We use an analytical perturbative approach on the equations of MHD to assess the impact of such effects. Our main conclusion is that there appears to be no compelling reason to discard g-modes. In particular, the inclusion of a non-zero {\it radial} component of the magnetic field enables a broader scenario for cavity non-destruction, especially taking into account recent simulations' saturation values for the magnetic field.
A recent analysis of UV data from the Interface Region Imaging Spectrograph {\em IRIS} reports plasma "bombs" with temperatures near \hot{} within the solar photosphere. This is a curious result, firstly because most bomb plasma pressures $p$ (the largest reported case exceeds $10^3$ dyn~cm$^{-2}$) fall well below photospheric pressures ($> 7\times10^3$), and secondly, UV radiation cannot easily escape from the photosphere. In the present paper the {\em IRIS} data is independently analyzed. I find that the bombs arise from plasma originally at pressures between $\lta80$ and 800 dyne~cm$^{-2}$ before explosion, i.e. between $\lta850$ and 550 km above $\tau_{500}=1$. This places the phenomenon's origin in the low-mid chromosphere or above. I suggest that bomb spectra are more compatible with Alfv\'enic turbulence than with bi-directional reconnection jets.
Energy dissipation is highly intermittent in turbulent plasmas, being localized in coherent structures such as current sheets. The statistical analysis of spatial dissipative structures is an effective approach to studying turbulence. In this paper, we generalize this methodology to investigate four-dimensional spatiotemporal structures, i.e., dissipative processes representing sets of interacting coherent structures, which correspond to flares in astrophysical systems. We develop methods for identifying and characterizing these processes, and then perform a statistical analysis of dissipative processes in numerical simulations of driven magnetohydrodynamic turbulence. We find that processes are often highly complex, long-lived, and weakly asymmetric in time. They exhibit robust power-law probability distributions and scaling relations, including a distribution of dissipated energy with power-law index near -1.75, indicating that intense dissipative events dominate the overall energy dissipation. We compare our results with the previously observed statistical properties of solar flares.
In this work, we investigate if gravitational microlensing can magnify the polarization signal of a stellar spot and make it be observable. A stellar spot on a source star of microlensing makes polarization signal through two channels of Zeeman effect and breaking circular symmetry of the source surface brightness due to its temperature contrast. We first explore the characteristics of perturbations in polarimetric microlensing during caustic-crossing of a binary lensing as follows: (a) The cooler spots over the Galactic bulge sources have the smaller contributions in the total flux, although they have stronger magnetic fields. (b) The maximum deviation in the polarimetry curve due to the spot happens when the spot is located near the source edge and the source spot is first entering the caustic whereas the maximum photometric deviation occurs for the spots located at the source center. (c) There is a (partial) degeneracy for indicating spot's size, its temperature contrast and its magnetic induction from the deviations in light or polarimetric curves. (d) If the time when the photometric deviation due to spot becomes zero (between positive and negative deviations) is inferred from microlensing light curves, we can indicate the magnification factor of the spot, characterizing the spot properties except its temperature contrast. The stellar spots alter the polarization degree as well as strongly change its orientation which gives some information about the spot position. Although, the photometry observations are more efficient in detecting stellar spots than the polarimetry ones, but polarimetry observations can specify the magnetic field of the source spots.
We have performed an unbiased deep near-infrared survey toward the Aquila molecular cloud with a sky coverage of ~1 deg2. We identified 45 molecular hydrogen emission-line objects(MHOs), of which only 11 were previously known. Using the Spitzer archival data we also identified 802 young stellar objects (YSOs) in this region. Based on the morphology and the location of MHOs and YSO candidates, we associate 43 MHOs with 40 YSO candidates. The distribution of jet length shows an exponential decrease in the number of outflows with increasing length and the molecular hydrogen outflows seem to be oriented randomly. Moreover, there is no obvious correlation between jet lengths, jet opening angles, or jet H2 1-0 S(1) luminosities and spectral indices of the possible driving sources in this region. We also suggest that molecular hydrogen outflows in the Aquila molecular cloud are rather weak sources of turbulence, unlikely to generate the observed velocity dispersion in the region of survey.
We developed an efficient algorithm integrated in our 3D modeling tool, GX Simulator (Nita et al. 2015), allowing quick computation of the synthetic intensity and polarization maps of solar active regions (AR) in the ALMA spectral range. The algorithm analyzes the photospheric input (white light and magnetogram) to classify a given photospheric pixel to belong to a given photospheric structure. Then, a 1D chromospheric model (Fontenla et al. 2009) is added on top of each pixel, which forms a chromospheric model of the AR. Next step is computation of the mm and sub-mm emission produced from this chromosphere model. A huge advantage of this approach is that emission from any given AR can be synthesized very fast, on the order of a few minutes after the AR selection. Using the GX Simulator tool it is also possible to produce synthetic maps of the microwave (gyroresonance) and EUV emission from the same AR model and compare them with the ALMA synthetic maps and with the corresponding observed microwave and/or EUV data.
Symplectic integrators are widely used for long-term integration of
conservative astrophysical problems due to their ability to preserve the
constants of motion; however, they cannot in general be applied in the presence
of nonconservative interactions. In this Letter, we develop the "slimplectic"
integrator, a new type of numerical integrator that shares many of the benefits
of traditional symplectic integrators yet is applicable to general
nonconservative systems. We utilize a fixed time-step variational integrator
formalism applied to the principle of stationary nonconservative action
developed in Galley, 2013; Galley, Tsang & Stein, 2014. As a result, the
generalized momenta and energy (Noether current) evolutions are well-tracked.
We discuss several example systems, including damped harmonic oscillators,
Poynting-Robertson drag, and gravitational radiation reaction, by utilizing our
new publicly available code to demonstrate the slimplectic integrator
algorithm.
Slimplectic integrators are well-suited for integrations of systems where
nonconservative effects play an important role in the long-term dynamical
evolution. As such they are particularly appropriate for cosmological or
celestial N-body dynamics problems where nonconservative interactions, e.g.
dynamical friction or dissipative tides, can play an important role.
The unusual GRB 110709B triggered Swift/BAT twice, with a time difference of $\sim 11$ minutes. Its light curve presented three noticeable peaks but only two were originally identified. In this work, we describe each peak as due to a different central-engine phase: the first one is the millisecond-protomagnetar stage, the second one is the BH-formation collapse phase and the last one is the Collapsar scenario with a Blandford-Znajek engine. Additionally, we analyze and explain the afterglow phase evoking the standard fireball model. Our model can successfully describe the timescales, fluxes and spectral indices observed for GRB 110709B.
We explore the generation of large-scale magnetic fields in the so-called moduli inflation. The hypercharge electromagnetic fields couple to not only a scalar field but also a pseudoscalar one, so that the conformal invariance of the hypercharge electromagnetic fields can be broken. We explicitly analyze the strength of the magnetic fields on the Hubble horizon scale at the present time, the local non-Gaussianity of the curvature perturbations originating from the massive gauge fields, and the tensor-to-scalar ratio of the density perturbations. As a consequence, we find that the local non-Gaussianity and the tensor-to-scalar ratio are compatible with the recent Planck results.
As one of the probes of universe, strong gravitational lensing systems allow us to compare different cosmological models and constrain vital cosmological parameters. This purpose can be reached from the dynamic and geometry properties of strong gravitational lensing systems, for instance, time-delay $\Delta\tau$ of images, the velocity dispersion $\sigma$ of the lensing galaxies and the combination of these two effects, $\Delta\tau/\sigma^2$. In this paper, in order to carry out one-on-one comparisons between $\Lambda$CDM universe and $R_h=ct$ universe, we use a sample containing 36 strong lensing systems with the measurement of velocity dispersion from the SLACS and LSD survey. Concerning the time-delay effect, 12 two-image lensing systems with $\Delta\tau$ are also used. In addition, Monte Carlo (MC) simulations are used to compare the efficiency of the three methods as mentioned above. From simulations, we estimate the number of lenses required to rule out one model at the $99.7\%$ confidence level. Comparing with constraints from $\Delta\tau$ and the velocity dispersion $\sigma$, we find that using $\Delta\tau/\sigma^2$ can improve the discrimination between cosmological models. Despite the independence tests of these methods reveal a correlation between $\Delta\tau/\sigma^2$ and $\sigma$, $\Delta\tau/\sigma^2$ could be considered as an improved method of $\sigma$ if more data samples are available.
We attempt to propose a method for automatically detecting the solar filament chirality and barb bearing. We first introduce the unweighted undirected graph concept and adopt the Dijkstra shortest-path algorithm to recognize the filament spine. Then, we use the polarity inversion line (PIL) shift method for measuring the polarities on both sides of the filament, and employ the connected components labeling method to identify the barbs and calculate the angle between each barb and the spine to determine the bearing of the barbs, i.e., left or right. We test the automatic detection method with H-alpha filtergrams from the Big Bear Solar Observatory (BBSO) H-alpha archive and magnetograms observed with the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). Four filaments are automatically detected and illustrated to show the results. The barbs in different parts of a filament may have opposite bearings. The filaments in the southern hemisphere (northern hemisphere) mainly have left-bearing (right-bearing) barbs and positive (negative) magnetic helicity, respectively. The tested results demonstrate that our method is efficient and effective in detecting the bearing of filament barbs. It is demonstrated that the conventionally believed one-to-one correspondence between filament chirality and barb bearing is not valid. The correct detection of the filament axis chirality should be done by combining both imaging morphology and magnetic field observations.
Two dedicated asteroid rotation-period surveys have been carried out using data taken on January 6-9 and February 20-23 of 2014 by the Intermediate Palomar Transient Factory (iPTF) in the $R$~band with $\sim 20$-min cadence. The total survey area covered 174~deg$^2$ in the ecliptic plane. Reliable rotation periods for 1,438 asteroids are obtained from a larger data set of 6,551 mostly main-belt asteroids, each with $\geq 10$~detections. Analysis of 1751, PTF based, reliable rotation periods clearly shows the "spin barrier" at $\sim 2$~hours for "rubble-pile" asteroids. We also found a new large-sized super-fast rotator, 2005 UW163 (Chang et al., 2014), and other five candidates as well. Our spin-rate distributions of asteroids with $3 < D < 15$~km shows number decrease when frequency greater than 5 rev/day, which is consistent to that of the Asteroid Light Curve Database (LCDB, Warner et al., 2009) and the result of (Masiero et al., 2009). We found the discrepancy in the spin-rate distribution between our result and (Pravec et al., 2008, update 2014-04-20) is mainly from asteroids with $\Delta m < 0.2$ mag that might be primarily due to different survey strategies. For asteroids with $D \leq 3$~km, we found a significant number drop at $f = 6$ rev/day. The YORP effect timescale for small-sized asteroid is shorter that makes more elongate objets spun up to reach their spin-rate limit and results in break-up. The K-S test suggests a possible difference in the spin-rate distributions of C- and S-type asteroids. We also find that C-type asteroids have a smaller spin-rate limit than the S-type, which agrees with the general sense that the C-type has lower bulk density than the S-type.
The magnetar 4U~0142+61 has been well studied at optical and infrared wavelengths and is known to have a complicated broad-band spectrum over the wavelength range. Here we report the result from our linear imaging polarimetry of the magnetar at optical $I$-band. From the polarimetric observation carried out with the 8.2-m Subaru telescope, we determine the degree of linear polarization $P=1.0\pm$3.4\%, or $P\leq$5.4\% (90\% confidence level). Considering models suggested for optical emission from magnetars, we discuss the implications of our result. The upper limit measurement indicates that different from radio pulsars, magnetars probably would not have strongly polarized optical emission if the emission arises from their magnetosphere as suggested.
In quantum gravity, a foamy structure of space-time leads to Lorentz invariance violation (LIV). As the most energetic astrophysical processes in the Universe, gamma-ray bursts (GRBs) provide an effective way to probe quantum gravity effects. We use continuous spectra of 20 short GRBs detected by the Swift satellite to give a conservative lower limit of quantum gravity energy scale $M_\textrm{QG} $. Due to the LIV effect, photons with different energy have different velocities. This will lead to the delayed arrival of high energy photons relative to the low energy ones. Based on the fact that the LIV-induced time delay can't be longer than the duration of a GRB, we present the most conservative estimation of the quantum gravity energy scales from 20 short GRBs. The most strict constraint, $M_\textrm{QG}>5.05\times10^{14}$ GeV, is from GRB 140622A.
We have monitored the 2014 superoutburst of the WZ Sge-type transient PNV J03093063+2638031 for more than four months, from V=11.0 maximum brightness down to V=18.4 mag, close to quiescence value, by obtaining BVRI photometry and low resolution fluxed spectroscopy. The evolution was normal and no late-time `echo' outbursts were observed. The absolute integrated flux of emission lines kept declining along the superoutburst, and their increasing contrast with the underlying continuum was simply the result of the faster decline of the continuum compared to the emission lines. Inspection of historical Harvard plates covering the 1899-1981 period did not reveal previous outbursts, neither `normal' nor 'super'. We discovered an extended emission nebula (radius ~1 arcmin) around PNV J03093063+2638031, that became visible for a few months as the result of photo-ionization from the superoutburst of the central star. It is not present on Palomar I and II sky survey images and it quickly disappeared when the outburst was over. From the rate at wich the inization front swept through the nebula, we derive a distance of ~120 pc to the system. The nebula is density bounded with an outer radius of 0.03 pc, and the absolute magnitude of the central star in quiescence is M(V)~14.2 mag. The electron density in the nebula is estimated to be 10(+5) cm(-3) from the observed recombination time scale. Given the considerable substructures seen across the nebula, a low filling factor is inferred. Similar nebulae have not been reported for other WZ Sge objects and the challenges posed to models are considered.
As new scientists and engineers join the SKA project and as the pressures come on to maintain costs within a chosen envelope it is worth restating and updating the rationale for the 'Exploration of the Unknown' (EoU). Maintaining an EoU philosophy will prove a vital ingredient for realizing the SKA's discovery potential. Since people make the discoveries enabled by technology a further axis in capability parameter space, the'human bandwidth' is emphasised. Using the morphological approach pioneered by Zwicky, a currently unexploited region of observational parameter space can be identified viz: time variable spectral patterns on all spectral and angular scales, one interesting example would be 'spectral transients'. We should be prepared to build up to 10 percent less collecting area for a given overall budget in order to enhance the ways in which SKA1 can be flexibly utilized.
We use the gravitational instability formation scenario of cometesimals to derive the aggregate size that can be released by the gas pressure from the nucleus of comet 67P/Churyumov-Gerasimenko for different heliocentric distances and different volatile ices. To derive the ejected aggregate sizes, we developed a model based on the assumption that the entire heat absorbed by the surface is consumed by the sublimation process of one volatile species. The calculations were performed for the three most prominent volatile materials in comets, namely, H_20 ice, CO_2 ice, and CO ice. We find that the size range of the dust aggregates able to escape from the nucleus into space widens when the comet approaches the Sun and narrows with increasing heliocentric distance, because the tensile strength of the aggregates decreases with increasing aggregate size. The activity of CO ice in comparison to H_20 ice is capable to detach aggregates smaller by approximately one order of magnitude from the surface. As a result of the higher sublimation rate of CO ice, larger aggregates are additionally able to escape from the gravity field of the nucleus. Our model can explain the large grains (ranging from 2 cm to 1 m in radius) in the inner coma of comet 67P/Churyumov-Gerasimenko that have been observed by the OSIRIS camera at heliocentric distances between 3.4 AU and 3.7 AU. Furthermore, the model predicts the release of decimeter-sized aggregates (trail particles) close to the heliocentric distance at which the gas-driven dust activity vanishes. However, the gas-driven dust activity cannot explain the presence of particles smaller than ~1 mm in the coma because the high tensile strength required to detach these particles from the surface cannot be provided by evaporation of volatile ices. These smaller particles can be produced for instance by spin-up and centrifugal mass loss of ejected larger aggregates.
We present an analysis of the effects of beam deconvolution on noise properties in CMB measurements. The analysis is built around the artDeco beam deconvolver code. We derive a low-resolution noise covariance matrix that describes the residual noise in deconvolution products, both in harmonic and pixel space. The matrix models the residual correlated noise that remains in time-ordered data after destriping, and the effect of deconvolution on it. To validate the results, we generate noise simulations that mimic the data from the Planck LFI instrument. A $\chi^2$ test for the full 70 GHz covariance in multipole range $\ell=0-50$ yields a mean reduced $\chi^2$ of 1.0037. We compare two destriping options, full and independent destriping, when deconvolving subsets of available data. Full destriping leaves substantially less residual noise, but leaves data sets intercorrelated. We derive also a white noise covariance matrix that provides an approximation of the full noise at high multipoles, and study the properties on high-resolution noise in pixel space through simulations.
Partially depleted cores, as measured by core-Sersic model "break radii", are typically tens to a few hundred parsecs in size. Here we investigate the unusually large (cusp radius of 4.57 kpc) depleted core recently reported for Holm 15A, the brightest cluster galaxy of Abell 85. We model the 1D light profile, and also the 2D image (using GALFIT-CORSAIR, a tool for fitting the core-Sersic model in 2D). We find good agreement between the 1D and 2D analyses, with minor discrepancies attributable to intrinsic ellipticity gradients. We show that a simple Sersic profile (with a low index n and no depleted core) plus the known outer exponential "halo" provide a good description of the stellar distribution. We caution that while almost every galaxy light profile will have a radius where the negative logarithmic slope of the intensity profile equals 0.5, this alone does not imply the presence of a partially depleted core within this radius.
The Of?p star CPD -28 2561 was monitored at high energies with XMM-Newton and HST. In X-rays, this magnetic oblique rotator displays bright and hard emission that varies by ~55% with rotational phase. These changes occur in phase with optical variations, as expected for magnetically confined winds; there are two maxima and two minima in X-rays during the 73d rotational period of CPD -28 2561. However, contrary to previously studied cases, no significant hardness variation is detected between minima and maxima, with the exception of the second minimum which is slightly distinct from the first one. In the UV domain, broad-band fluxes remain stable while line profiles display large variations. Stronger absorptions at low velocities are observed when the magnetic equator is seen edge-on, which can be reproduced by a detailed 3D model. However, a difference in absorption at high velocities in the CIV and NV lines is also detected for the two phases where the confined wind is seen nearly pole-on. This suggests the presence of strong asymmetries about the magnetic equator, mostly in the free-flowing wind (rather than in the confined dynamical magnetosphere).
A sunspot emanates from a growing pore or protospot. In order to trigger the formation of a penumbra, large inclinations at the outskirts of the protospot are necessary. The penumbra develops and establishes by colonising both umbral areas and granulation. Evidence for a unique stable boundary value for the vertical component of the magnetic field strength, $B^{\rm stable}_{\rm ver}$, was found along the umbra-penumbra boundary of developed sunspots. We use broadband G-band images and spectropolarimetric GFPI/VTT data to study the evolution of and the vertical component of the magnetic field on a forming umbra-penumbra boundary. For comparison with stable sunspots, we also analyse the two maps observed by Hinode/SP on the same spot after the penumbra formed. The vertical component of the magnetic field, $B_{\rm ver}$, at the umbra-penumbra boundary increases during penumbra formation owing to the incursion of the penumbra into umbral areas. After 2.5 hours, the penumbra reaches a stable state as shown by the GFPI data. At this stable stage, the simultaneous Hinode/SP observations show a $B_{\rm ver}$ value comparable to that of umbra-penumbra boundaries of fully fledged sunspots. We confirm that the umbra-penumbra boundary, traditionally defined by an intensity threshold, is also characterised by a distinct canonical magnetic property, namely by $B^{\rm stable}_{\rm ver}$. During the penumbra formation process, the inner penumbra extends into regions where the umbra previously prevailed. Hence, in areas where $B_{\rm ver} < B^{\rm stable}_{\rm ver}$, the magneto-convection mode operating in the umbra turns into a penumbral mode. Eventually, the inner penumbra boundary settles at $B^{\rm stable}_{\rm ver}$, which hints toward the role of $B_{\rm ver}^{\rm stable}$ as inhibitor of the penumbral mode of magneto-convection.
The so-called drag-based model (DBM) simulates analytically the propagation of coronal mass ejections (CMEs) in interplanetary space and allows the prediction of their arrival times and impact speeds at any point in the heliosphere ("target"). The DBM is based on the assumption that beyond a distance of about 20 solar radii from the Sun, the dominant force acting on CMEs is the "aerodynamic" drag force. In the standard form of DBM, the user provisionally chooses values for the model input parameters, by which the kinematics of the CME over the entire Sun--"target" distance range is defined. The choice of model input parameters is usually based on several previously undertaken statistical studies. In other words, the model is used by ad hoc implementation of statistics-based values of the input parameters, which are not necessarily appropriate for the CME under study. Furthermore, such a procedure lacks quantitative information on how well the simulation reproduces the coronagraphically observed kinematics of the CME, and thus does not provide an estimate of the reliability of the arrival prediction. In this paper we advance the DBM by adopting it in a form that employs the CME observations over a given distance range to evaluate the most suitable model input parameters for a given CME by means of the least-squares fitting. Furthermore, the new version of the model automatically responds to any significant change of the conditions in the ambient medium (solar wind speed, density, CME--CME interactions, etc.) by changing the model input parameters according to changes in the CME kinematics. The advanced DBM is shaped in a form that can be readily employed in an operational system for real-time space-weather forecasting by promptly adjusting to a successively expanding observational dataset, thus providing a successively improving prediction of the CME arrival.
The formation of massive stars and their arrival on the zero-age main-sequence occurs hidden behind dense clouds of gas and dust. In the giant Hii region NGC 3603, the radiation of a young cluster of OB stars has dispersed dust and gas in its vicinity. At a projected distance of 2:5 pc from the cluster, a bright mid-infrared (mid-IR) source (IRS 9A) had been identified as a massive young stellar object (MYSO), located on the side of a molecular clump (MM2) of gas facing the cluster. We investigated the physical conditions in MM2, based on APEX sub-mm observations using the SABOCA and SHFI instruments, and archival ATCA 3 mm continuum and CS spectral line data. We resolved MM2 into several compact cores, one of them closely associated with IRS 9A. These are likely infrared dark clouds as they do not show the typical hot-core emission lines and are mostly opaque against the mid-IR background. The compact cores have masses of up to several hundred times the solar mass and gas temperatures of about 50 K, without evidence of internal ionizing sources. We speculate that IRS 9A is younger than the cluster stars, but is in an evolutionary state after that of the compact cores.
We compute the dynamics and emission of dissipative shells that are subject to a strong Compton drag, under simplifying assumptions about the dissipation mechanism. We show that under conditions prevailing in blazars, substantial deceleration is anticipated on sub-parsec and parsec scales in cases of rapid dissipation. Such episodes may be the origin of some of the flaring activity occasionally observed in gamma ray blazars. The shape of the light curves thereby produced reflects the geometry of the emitting surface if the deceleration is very rapid, or the dynamics of the shell if the deceleration is delayed, or initially more gradual, owing, e.g., to continuous injection of energy and momentum.
Aims: We present a multiwavelength study of the Be/X-ray binary system V0332+53 with the main goal of better characterizing its behavior during a low luminosity X-ray event. We also aim to shed light on the mechanism/s which trigger the X-ray activity for this source. Methods: V0332+53 was observed by RXTE and Swift during the decay of the normal X-ray outburst of 2008, as well as with Suzaku before the rising of the third normal outburst of the 2010 series. In addition, this source has been monitored from the ground-based astronomical observatories of El Teide (Tenerife, Spain) during August 2014 to February 2015, Roque de los Muchachos (La Palma, Spain) during July and September 2012 and Sierra Nevada (Granada, Spain) since October 2012, and from the TUBITAK National Observatory (Antalya, Turkey) since September 2006. We have performed spectral and photometric temporal analyses in order to investigate the transient behavior of this binary system during Type I outbursts. Results: Our optical study revealed that continuous mass ejection episodes from the Be star have been since 2006 and another one is currently ongoing. The broad-band 1-60 keV X-ray spectrum of the neutron star during the decay of the 2008 outburst was well fitted with standard phenomenological models, enhanced by an absorption feature of unknown origin at about 10 keV and a narrow iron K-alpha fluorescence line at 6.4 keV. In contrast to previous works, we tentatively see an increase of the cyclotron line energy with increasing flux (although further and more sensitive observations are needed to confirm this). Regarding the fast aperiodic variability, we detect a Quasi-Periodic Oscillation (QPO) at 227+-9$ mHz only during the lowest luminosities. The latter fact might indicate that the inner regions surrounding the neutron star are more visible during the lowest flux states.
A very general cosmological consideration suggests that, along with galactic dark matter halos, much smaller dark matter structures may exist. These structures are usually called 'clumps', and their mass extends to $10^{-6} M_\odot$ or even lower. The clumps should give the main contribution into the signal of dark matter annihilation, provided that they have survived until the present time. Recent observations favor a cored profile for low-mass astrophysical halos. We consider cored clumps and show that they are significantly less firm than the standard NFW ones. In contrast to the standard scenario, the cored clumps should have been completely destroyed inside $\sim 20$ kpc from the Milky Way center. The dwarf spheroidals should not contain any dark matter clumps as well. On the other hand, even under the most pessimistic assumption about the clump structure, the clumps should have survived in the Milky Way at a distance exceeding $50$ kpc from the center, as well as in low-density cosmic structures. There they significantly boost the dark matter annihilation.
We present the high resolution spectroscopic study of five -3.9<=[Fe/H]<=-2.5 stars in the Local Group dwarf spheroidal, Sculptor, thereby doubling the number of stars with comparable observations in this metallicity range. We carry out a detailed analysis of the chemical abundances of alpha, iron peak, light and heavy elements, and draw comparisons with the Milky Way halo and the ultra faint dwarf stellar populations. We show that the bulk of the Sculptor metal-poor stars follows the same trends in abundance ratios versus metallicity as the Milky Way stars. This suggests similar early conditions of star formation and a high degree of homogeneity of the interstellar medium. We find an outlier to this main regime, which seems to miss the products of the most massive of the TypeII supernovae. In addition to its value to help refining galaxy formation models, this star provides clues to the production of cobalt and zinc. Two of our sample stars have low odd-to-even barium isotope abundance ratios, suggestive of a fair proportion of s-process; we discuss the implication for the nucleosynthetic origin of the neutron capture elements.
Galactic Archeology is about exploring the Milky Way as a galaxy by, mainly, using its (old) stars as tracers of past events and thus figure out the formation and evolution of our Galaxy. I will briefly outline some of the key scientific aspects of Galactic Archeology and then discuss the associated instrumentations. Gaia will forever change the way we approach this subject. However, Gaia on its own is not enough. Ground-based complementary spectroscopy is necessary to obtain full phase-space information and elemental abundances for stars fainter than the top few percent of the bright part of the Gaia catalogue. I will review the requirement on instrumentation for Gaia follow-up that Galactic Archeology sets. In particular, I will discuss the requirements on radial velocity and elemental abundance determination, including a brief look at potential pit-falls in the abundance analysis (e.g., NLTE, atomic diffusion). This contribution also provides a non-exhaustive comparison of the various current and future spectrographs for Galactic Archeology. Finally, I will discuss the needs for astrophysical calibrations for the surveys and inter-survey calibrations.
We estimate the energy reservoir available in the deconfinement phase transition induced collapse of a neutron star to its hybrid star mass twin on the "third family" branch, using a recent equation of state of dense matter. The available energy corresponding to the mass-energy difference between configurations is comparable with energies of the most violent astrophysical burst processes. An observational outcome of such a dynamical transition might be fast radio bursts, specifically a recent example of a FRB with a double-peak structure in its light curve.
We present a model of spontaneous (or dynamical) C and CP violation where it is possible to generate domains of matter and antimatter separated by cosmologically large distances. Such C(CP) violation existed only in the early universe and later it disappeared with the only trace of generated baryonic and/or antibaryonic domains. So the problem of domain walls in this model does not exist. These features are achieved through a postulated form of interaction between inflaton and a new scalar field, realizing short time C(CP) violation.
In this work, we present, for the first time, a numerical study of the Bondi-Hoyle accretion with density gradients in the fully relativistic regime. In this context, we consider accretion onto a Kerr Black Hole (BH) of a supersonic ideal gas, which has density gradients perpendicular to the relative motion. The set of parameters of interest in this study are the Mach number, M, the spin of the BH, a, and the density-gradient parameter of the gas, {\rho} . We show that, unlike in the Newtonian case, all the studied cases, especially those with density gradient, approach a stationary flow pattern. To illustrate that the system reaches steady state we calculate the mass and angular momentum accretion rates on a spherical surface located almost at the event horizon. In the particular case of M = 1, {\rho} = 0.5 and BH spin a = 0.5, we observe a disk-like configuration surrounding the BH. Finally, we present the gas morphology and some of its properties.
We study the photospheric magnetic field of ~2000 active regions in solar
cycle 23 to search for parameters indicative of energy build-up and subsequent
release as a solar flare. We extract three sets of parameters: snapshots in
space and time- total flux, magnetic gradients, and neutral lines; evolution in
time- flux evolution; structures at multiple size scales- wavelet analysis.
This combines pattern recognition and classification techniques via a relevance
vector machine to determine whether a region will flare. We consider
classification performance using all 38 extracted features and several feature
subsets. Classification performance is quantified using both the true positive
rate and the true negative rate. Additionally, we compute the true skill score
which provides an equal weighting to true positive rate and true negative rate
and the Heidke skill score to allow comparison to other flare forecasting work.
We obtain a true skill score of ~0.5 for any predictive time window in the
range 2-24hr, with a TPR of ~0.8 and a TNR of ~0.7. These values do not appear
to depend on the time window, although the Heidke skill score (<0.5) does.
Features relating to snapshots of the distribution of magnetic gradients show
the best predictive ability over all predictive time windows. Other
gradient-related features and the instantaneous power at various wavelet scales
also feature in the top five ranked features in predictive power. While the
photospheric magnetic field governs the coronal non-potentiality (and
likelihood of flaring), photospheric magnetic field alone is not sufficient to
determine this uniquely. Furthermore we are only measuring proxies of the
magnetic energy build up. We still lack observational details on why energy is
released at any particular point in time. We may have discovered the natural
limit of the accuracy of flare predictions from these large scale studies.
We present Spitzer 4.5\micron\ light curve observations, Keck NIRSPEC radial velocity observations, and LCOGT optical light curve observations of PTFO~8-8695, which may host a Jupiter-sized planet in a very short orbital period (0.45 days). Previous work by \citet{vaneyken12} and \citet{barnes13} predicts that the stellar rotation axis and the planetary orbital plane should precess with a period of $300 - 600$ days. As a consequence, the observed transits should change shape and depth, disappear, and reappear with the precession. Our observations indicate the long-term presence of the transit events ($>3$ years), and that the transits indeed do change depth, disappear and reappear. The Spitzer observations and the NIRSPEC radial velocity observations (with contemporaneous LCOGT optical light curve data) are consistent with the predicted transit times and depths for the $M_\star = 0.34\ M_\odot$ precession model and demonstrate the disappearance of the transits. An LCOGT optical light curve shows that the transits do reappear approximately 1 year later. The observed transits occur at the times predicted by a straight-forward propagation of the transit ephemeris. The precession model correctly predicts the depth and time of the Spitzer transit and the lack of a transit at the time of the NIRSPEC radial velocity observations. However, the precession model predicts the return of the transits approximately 1 month later than observed by LCOGT. Overall, the data are suggestive that the planetary interpretation of the observed transit events may indeed be correct, but the precession model and data are currently insufficient to confirm firmly the planetary status of PTFO~8-8695b.
Intrinsic alignment (IA) of source galaxies is one of the major astrophysical systematics for ongoing and future weak lensing surveys. This paper presents the first forecasts of the impact of IA on cosmic shear measurements for current and future surveys (DES, Euclid, LSST, WFIRST) using simulated likelihood analyses and realistic covariances that include higher-order moments of the density field in the computation. We consider a range of possible IA scenarios and test mitigation schemes, which parameterize IA by the fraction of red galaxies, normalization, luminosity and redshift dependence of the IA signal (for a subset we consider joint IA and photo-z uncertainties). Compared to previous studies we find smaller biases in time-dependent dark energy models if IA is ignored in the analysis; the amplitude and significance of these biases vary as a function of survey properties (depth, statistical uncertainties), luminosity function, and IA scenario: Due to its small statistical errors and relatively shallow observing strategy Euclid is significantly impacted by IA. LSST and WFIRST benefit from their increased survey depth, while the larger statistical errors for DES decrease IA's relative impact on cosmological parameters. The proposed IA mitigation scheme removes parameter biases due to IA for DES, LSST, and WFIRST even if the shape of the IA power spectrum is only poorly known; successful IA mitigation for Euclid requires more prior information. We explore several alternative IA mitigation strategies for Euclid; in the absence of alignment of blue galaxies we recommend the exclusion of red (IA contaminated) galaxies in cosmic shear analyses. We find that even a reduction of 20% in the number density of galaxies only leads to a 4-10% loss in cosmological constraining power.
We show that the cool gas masses of galactic discs reach a steady state that lasts many Gyr after their last major merger in cosmological hydrodynamic simulations. The mass of disc gas, M$_{\rm gas}$, depends upon a galaxy halo's spin and virial mass, but not upon stellar feedback. Halos with low spin have high star formation efficiency and lower disc gas mass. Similarly, lower stellar feedback leads to more star formation so the gas mass ends up nearly the same irregardless of stellar feedback strength. Even considering spin, the M$_{\rm gas}$ relation with halo mass, M$_{200}$ only shows a factor of 3 scatter. The M$_{\rm gas}$--M$_{200}$ relation show a break at M$_{200}$=$2\times10^{11}$ M$_\odot$ that corresponds to an observed break in the M$_{\rm gas}$--M$_\star$ relation. The constant disc mass stems from a shared halo gas density profile in all the simulated galaxies. In their outer regions, the profiles are isothermal. Where the profile rises above $n=10^{-3}$ cm$^{-3}$, the gas readily cools and the profile steepens. Inside the disc, rotation supports gas with a flatter density profile except where supernova explosions disrupt the disc. Energy injection from stellar feedback also provides pressure support to the halo gas to prevent runaway cooling flows. The resulting constant gas mass makes simpler models for galaxy formation possible, either using a "bathtub" model for star formation rates or when modeling chemical evolution.
The Bipolar Spherical Harmonics (BipoSH) form a natural basis to study the CMB two point correlation function in a non-statistically isotropic (non-SI) universe. The coefficients of expansion in this basis are a generalisation of the well known CMB angular power spectrum and contain complete information of the statistical properties of a non-SI but Gaussian random CMB sky. We use these coefficients to describe the weak lensing of CMB photons in a non-SI universe. Finally we show that the results reduce to the standard weak lensing results in the isotropic limit.
Recently, Goodman et al. (2014) argued that the very long, very thin infrared dark cloud "Nessie" lies directly in the Galactic mid-plane and runs along the Scutum-Centaurus arm in position-position-velocity ($p-p-v$) space as traced by lower density $\rm {CO}$ and higher density ${\rm NH}_3$ gas. Nessie was presented as the first "bone" of the Milky Way, an extraordinarily long, thin, high-contrast filament that can be used to map our Galaxy's "skeleton." Here, we present evidence for additional bones in the Milky Way Galaxy, arguing that Nessie is not a curiosity but one of several filaments that could potentially trace Galactic structure. Our ten bone candidates are all long, filamentary, mid-infrared extinction features which lie parallel to, and no more than 20 pc from, the physical Galactic mid-plane. We use $\rm {CO}$, ${\rm N}_2{\rm H}^+$, $\rm {HCO}^+$, and ${\rm NH}_3$ radial velocity data to establish the three-dimensional location of the candidates in ${\it p-p-v}$ space. Of the ten candidates, six also: have a projected aspect ratio of $\geqq$50:1; run along, or extremely close to, the Scutum-Centaurus arm in p-p-v space; and exhibit no abrupt shifts in velocity. Evidence suggests that these candidates are marking the locations of significant spiral features, with the bone called filament 5 ("BC_18.88-0.09") being a close analog to Nessie in the Northern Sky. As molecular spectral-line and extinction maps cover more of the sky at increasing resolution and sensitivity, it should be possible to find more bones in future studies, ultimately to create a global-fit to the Galaxy's spiral arms by piecing together individual skeletal features.
In this paper we generalize the kinetic mixing idea to time reparametrization invariant theories, namely, relativistic point particles and cosmology in order to obtain new insights for dark matter and energy. In the first example, two relativistic particles interact through an appropriately chosen coupling term. It is shown that the system can be diagonalized by means of a non-local field redefinition, and, as a result of this procedure, the mass of one the particles gets rescaled. In the second case, inspired by the previous example, two cosmological models (each with its own scale factor) are made to interact in a similar fashion. The equations of motion are solved numerically in different scenarios (dust, radiation or a cosmological constant coupled to each sector of the system). When a cosmological constant term is present, kinetic mixing rescales it to a lower value which may be more amenable to observations.
We consider the possibility of solar neutrino decay as a sub-leading effect on their propagation between production and detection. Using current oscillation data, we set a new lower bound to the $\nu_2$ neutrino lifetime at $\tau_2\, /\, m_2 \geq 7.2 \times 10^{-4}\,\,\hbox{s}\,.\,\hbox{eV}^{-1}$ at $99\%\,$C.L.. Also, we show how seasonal variations in the solar neutrino data can give interesting additional information about neutrino lifetime.
Recent measurements of PeV energy neutrinos at IceCube and a 3.5 keV X-ray line in the spectra of several galaxies are both tantalizing signatures of new physics. This paper shows that one or both of these observations can be explained within an extended supersymmetric neutrino sector. Obtaining light active neutrino masses as well as phenomenologically interesting (keV-GeV) sterile neutrino masses without any unnaturally small parameters hints at a new symmetry in the neutrino sector that is broken at the PeV scale, presumably tied to supersymmetry breaking. The same symmetry and structure can sufficiently stabilize an additional PeV particle, produce its abundance through the freeze-in mechanism, and lead to decays that can give the energetic neutrinos observed by IceCube. The lightest sterile neutrino, if at 7 keV, is a non-resonantly produced fraction of dark matter, and can account for the 3.5 keV X-ray line. The two signals could therefore be the first probes of an extended supersymmetric neutrino sector.
We study the sensitivity of multi ton-scale time projection chambers using a liquid xenon target, e.g., the proposed DARWIN instrument, to spin-independent and spin-dependent WIMP-nucleon scattering interactions. Taking into account realistic backgrounds from the detector itself as well as from neutrinos, we examine the impact of exposure, energy threshold, background rejection efficiency and energy resolution on the dark matter sensitivity. With an exposure of 200 t x y and assuming detector parameters which have been already demonstrated experimentally, spin-independent cross sections as low as $2.5 \times 10^{-49}$ cm$^2$ can be probed for WIMP masses around 40 GeV/$c^2$. Additional improvements in terms of background rejection and exposure will further increase the sensitivity, while the ultimate WIMP science reach will be limited by neutrinos scattering coherently off the xenon nuclei.
The long-standing problem of the asymmetry between matter and antimatter in the Universe is, in this paper, analysed in the context of the modified theories of gravity. In particular we study two models of $f(R)$ theories of gravitation that, with the opportune choice of the free parameters, introduce little perturbation to the scale factor of the Universe in the radiation dominated (RD) phase predicted by general relativity (GR), i.e., $a(t)\sim t^{1/2}$. This little perturbation generates a Ricci scalar different by zero, i.e., $R\neq 0$ that reproduces the correct magnitude for the asymmetry factor $\eta$ computed in the frame of the theories of the gravitational baryogenesis and gravitational leptogenesis. The opportune choice of the free parameters is discussed in order to obtain results coherent with experimental data. Furthermore, the form of the potential $V$, for the scalar-tensor theory conformally equivalent to the $f(R)$ theory which reproduces the right asymmetry factor, is here obtained.
We argue that the full conversion of a hadronic star into a quark or a hybrid star occurs within two different regimes separated by a critical value of the density of the hadronic phase $\overline{n_h}$. The first stage, occurring for $n_h>\overline{n_h}$, is characterized by turbulent combustion and lasts typically a few ms. During this short time-scale neutrino cooling is basically inactive and the star heats up thanks to the heat released in the conversion. In the second stage, occurring for $n_h<\overline{n_h}$, turbulence is not active anymore, and the conversion proceeds on a much longer time scale (of the order of tens of seconds), with a velocity regulated by the diffusion and the production of strange quarks. At the same time, neutrino cooling is also active. The interplay between the heating of the star due to the slow conversion of its outer layers (with densities smaller than $\overline{n_h}$) and the neutrino cooling of the forming quark star leads to a quasi-plateau in the neutrino luminosity which, if observed, would possibly represent a unique signature for the existence of quark matter inside compact stars. We will discuss the phenomenological implications of this scenario in particular in connection with the time structure of long gamma-ray-bursts.
We investigate a calculation method for solving the Mukhanov-Sasaki equation in slow-roll $k$-inflation based on the uniform approximation in conjunction with an expansion scheme for slow-roll parameters with respect to the number of $e$-folds about the so-called turning point. Earlier works on this method has so far gained sensible calculation results for the resulting expression for power spectra among others, up to second order with respect to the Hubble and sound flow parameters, when compared to other semi-analytical approaches (e.g., Green's function and WKB methods). However, a closer inspection is suggestive that this may not hold when higher-order parts of the power spectra are considered; residual logarithmic divergences may come out that would make the prediction problematic. Looking at this possibility, we map out up to what order with respect to the mentioned parameters several physical quantities can be calculated before hitting a logarithmically divergent result. It turns out that the power spectra are limited up to second order, the tensor-to-scalar ratio up to third order, and the spectral indices and running can be calculated up to any order.
We show that observation of the time-dependent effect of microlensing of relativistically broadened emission lines (such as e.g. the Fe Kalpha line in X-rays) in strongly lensed quasars could provide data on celestial mechanics of circular orbits in the direct vicinity of the horizon of supermassive black holes. This information can be extracted from the observation of evolution of red / blue edge of the magnified line just before and just after the period of crossing of the innermost stable circular orbit by the microlensing caustic. The functional form of this evolution is insensitive to numerous astrophysical parameters of the accreting black hole and of the microlensing caustics network system (as opposed to the evolution the full line spectrum). Measurement of the temporal evolution of the red / blue edge could provide a precision measurement of the radial dependence of the gravitational redshift and of velocity of the circular orbits, down to the innermost stable circular orbit. These measurements could be used to discriminate between the General Relativity and alternative models of the relativistic gravity in which the dynamics of photons and massive bodies orbiting the gravitating centre is different from that of the geodesics in the Schwarzschild or Kerr space-times.
We present a brief overview of a new generation of high-precision laboratory and astrophysical measurements to search for ultralight (sub-eV) axion, axion-like pseudoscalar and scalar dark matter, which form either a coherent condensate or topological defects (solitons). In these new detection methods, the sought effects are linear in the interaction constant between dark matter and ordinary matter, which is in stark contrast to traditional searches for dark matter, where the sought effects are quadratic or higher order in the underlying interaction constants (which are extremely small).
The transition between the supersonic solar wind and the subsonic heliosheath, the termination shock (TS), was observed by Voyager 2 (V2) on 2007 August 31-September 1 at a distance of 84 AU from the Sun. The data reveal multiple crossings of a complex, quasi-perpendicular supercritical shock. These experimental data are the starting point for a more sophisticated analysis that includes computer modeling of a shock in the presence of pickup ions (PUIs). here, we present two-dimensional (2-D) particle-in-cell (PIC) simulations of the TS including PUIs self-consistently. We also report the ion velocity distribution across the TS using the Faraday cup data from V2. A relatively complete plasma and magnetic field data set from V2 gives us the opportunity to do a full comparison between the experimental data and PIC simulation results. Our results show that: (1) The nonstationarity of the shock front is mainly caused by the ripples along the shock front and these ripples from even if the percentage of PUIs is high. (2) PUIs play a key role in the energy dissipation of the TS, and most of the incident ion dynamic energy is transferred to the thermal energy of PUIs instead of solar wind ions (SWIs). (3) The simulated composite heliosheath ion velocity distribution function is a superposition of a cold core formed by transmitted SWIs, the shoulders contributed by the hot reflected SWIs and directly transmitted PUIs, and the wings of the distribution dominated by the very hot reflected PUIs. (4) The V2 Faraday cups observed the cool core of the distribution, so they saw only a tip of the iceberg. For the evolution of the cool core distribution function across the TS, the computed results agree reasonably well with the V2experimental results.
We compute the radiation emitted by a particle on the innermost stable circular orbit of a rapidly spinning black hole both (a) analytically, working to leading order in the deviation from extremality and (b) numerically, with a new high-precision Teukolsky code. We find excellent agreement between the two methods. We confirm previous estimates of the overall scaling of the power radiated, but show that there are also small oscillations all the way to extremality. Furthermore, we reveal an intricate mode-by-mode structure in the flux to infinity, with only certain modes having the dominant scaling. The scaling of each mode is controlled by its conformal weight, a quantity that arises naturally in the representation theory of the enhanced near-horizon symmetry group. We find relationships to previous work on particles orbiting in precisely extreme Kerr, including detailed agreement of quantities computed here with conformal field theory calculations performed in the context of the Kerr/CFT correspondence.
The effect of the Gauss-Bonnet term on the existence and dynamical stability
of thin-shell wormholes as negative tension branes is studied in the arbitrary
dimensional spherically, planar, and hyperbolically symmetric spacetimes. We
consider radial perturbations against the shell for the solutions which have
the Z${}_2$ symmetry and admit the general relativistic limit. It is shown that
the Gauss-Bonnet term shrinks the parameter region admitting static wormholes.
The effect of the Gauss-Bonnet term on the stability depends on the spacetime
symmetry. For planar symmetric wormholes, the Gauss-Bonnet term does not affect
their stability.
If the coupling constant is positive but small, the Gauss-Bonnet term tends
to destabilize spherically symmetric wormholes, while it stabilizes
hypebolically symmetric wormholes. The Gauss-Bonnet term can destabilize
hypebolically symmetric wormholes as a non-perturbative effect, however,
spherically symmetric wormholes cannot be stable.
The disformal transformation of metric $g_{\mu \nu} \to \Omega^2 (\phi)g_{\mu \nu}+\Gamma(\phi,X) \partial_{\mu}\phi \partial_{\nu}\phi$, where $\phi$ is a scalar field with the kinetic energy $X= \partial_{\mu}\phi \partial^{\mu}\phi/2$, preserves the Lagrangian structure of Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories (which is the minimum extension of Horndeski theories). In the presence of matter, this transformation gives rise to a kinetic-type coupling between the scalar field $\phi$ and matter. We consider the Einstein frame in which the second-order action of tensor perturbations on the isotropic cosmological background is of the same form as that in General Relativity and study the role of couplings at the levels of both background and linear perturbations. We show that the effective gravitational potential felt by matter perturbations in the Einstein frame can be conveniently expressed in terms of the sum of a General Relativistic contribution and couplings induced by the modification of gravity. For the theories in which the transformed action belongs to a class of Horndeski theories, there is no anisotropic stress between two gravitational potentials in the Einstein frame due to a gravitational de-mixing. We propose a concrete dark energy model encompassing Brans-Dicke theories as well as theories with the tensor propagation speed $c_{\rm t}$ different from 1. We clarify the correspondence between physical quantities in the Jordan/Einstein frames and study the evolution of gravitational potentials and matter perturbations from the matter-dominated epoch to today in both analytic and numerical approaches.
We show that very general scalar-tensor theories of gravity (including, e.g., Horndeski models) are generically invariant under disformal transformations. However there is a special subset, when the transformation is not invertible, that yields new equations of motion which are a generalization of the so-called "mimetic" dark matter theory recently introduced by Chamsedinne and Mukhanov. These new equations of motion can also be derived from an action containing an additional Lagrange multiplier field. The general mimetic scalar-tensor theory has the same number of derivatives in the equations of motion as the original scalar-tensor theory. As an application we show that the simplest mimetic scalar-tensor model is able to mimic the cosmological background of a flat FLRW model with an irrotational barotropic perfect fluid with any constant equation of state.
We present derivation of the basic equations and boundary conditions for relativistic static spherically symmetric stars (SSSS) in the model of minimal dilatonic gravity (MDG) which offers an alternative and simultaneous description of the effects of dark matter (DM) and dark energy (DE) using one dilaton field $\Phi$. The numerical results for a realistic equation of state (EOS) MPA1 of neutron matter are represented for the first time. The existing three very different scales: the Compton length of the scalar field $\lambda_\Phi$, the star's radius $r^*$, and the finite radius of MDG Universe $r_{U}$ are a source of numerical difficulties. Owing to introduction of a new dark scalar field $\varphi=\ln(1+\ln\Phi)$ we were able to study numerically an unprecedentedly large interval of $\lambda_\Phi$ and discovered existence of $\lambda_\Phi^{crit}\approx 2.1\, km$ for NS with MPA1 EOS. It is related with bifurcation of the physical domain in phase space of the system. Some novel physical consequences are discussed.
We give here a list of exact classical solutions of a large class of weakly nonlocal theories of gravity, which are unitary and super-renormalizable (or finite) at quantum level. It is explicitly shown that flat and Ricci-flat spacetimes as well as maximally symmetric manifolds are exact solutions of the equation of motion. Therefore, well-known physical spacetimes like Schwarzschild, Kerr, (Anti-) de Sitter serve as solutions for standard matter content. In dimension higher than four we can also have Anti-de Sitter solutions in the presence of positive cosmological constant. We pedagogically show how to obtain these exact solutions. Furthermore, for another version of the theory, written in the Weyl basis, Friedmann-Robertson-Walker (FRW) spacetimes are also exact solutions, when the matter content is given by conformal matter (radiation). We also comment on the presence of singularities and possible resolution of them in finite and conformally invariant theories. "Delocalization" is proposed as a way to solve the black hole singularity problem. In order to solve the problem of cosmological singularities it seems crucial to have a conformally invariant or asymptotically free quantum gravitational theory.
Neutrino oscillations in a hot and dense astrophysical environment such as a core-collapse supernova pose a challenging, seven-dimensional flavor transport problem. To make the problem even more difficult (and interesting), neutrinos can experience collective oscillations through nonlinear refraction in the dense neutrino medium in this environment. Significant progress has been made in the last decade towards the understanding of collective neutrino oscillations in various simplified neutrino gas models with imposed symmetries and reduced dimensions. However, a series of recent studies seem to have "reset" this progress by showing that these models may not be compatible with collective neutrino oscillations because the latter can break the symmetries spontaneously if they are not imposed. We review some of the key concepts of collective neutrino oscillations by using a few simple toy models. We also elucidate the breaking of spatial and directional symmetries in these models because of collective oscillations.
We solve the field equations of modified gravity for $f(R)$ model in metric formalism. Further, we obtain the fixed points of the dynamical system in phase space analysis of $f(R)$ models, both with and without the effects of radiation. Stability of these points is studied by invoking perturbations about them. We apply the conditions on the eigenvalues of the matrix obtained in the linearized first-order differential equations for stability of points. Following this, these fixed points are used for the dynamics of different phases of the universe. Certain linear and quadratic forms of $f(R)$ are determined from the geometrical and physical considerations and the dynamics of the scale factor is found for those forms. Further, we determine the Hubble parameter $H(t)$, Ricci scalar $R$ for radiation-, matter- and acceleration-dominated phases of the universe, whose time-ordering may explain an arrow of time throughout the cosmic evolution.
This article deals with the study of Bianchi type-I universe in the context of f(R,T) gravity. Einstein's fi?eld equations in f(R,T) gravity has been solved in presence of cosmological constant ? and quadratic equation of state. Here we have discussed two classes of f(R,T) gravity i.e. f(R,T) = R + 2f(T) and f(R,T) = f_1(R) + f_2(T). A set of models has been taken into consideration based on the plausible relation. Also we have studied the some physical and kinematical properties of the models.
The microphysics of relativistic collisionless sheared flows is investigated in a configuration consisting of a globally neutral, relativistic $e^-e^+$ beam streaming through a hollow plasma/dielectric channel. We show through multidimensional PIC simulations that this scenario excites the Mushroom instability (MI), a transverse shear instability on the electron-scale, when there is no overlap (no contact) between the $e^-e^+$ beam and the walls of the hollow plasma channel. The onset of the MI leads to the conversion of the beam's kinetic energy into magnetic (and electric) field energy, effectively slowing down a globally neutral body in the absence of contact. The collisionless shear physics explored in this configuration may operate in astrophysical environments, particularly in highly relativistic and supersonic settings where macroscopic shear processes are stable.
The $1 ^3\Sigma_u^- \leftarrow X^3\Sigma_g^-$ transition of linear HC$_5$H (A) has been observed in a neon matrix and gas phase. The assignment is based on mass-selective experiments, extrapolation of previous results of the longer HC$_{2n+1}$H homologues, and density functional and multi-state CASPT2 theoretical methods. Another band system starting at 303 nm in neon is assigned as the $1 ^1 A_1 \leftarrow X ^1 A_1$ transition of the cumulene carbene pentatetraenylidene H$_2$C$_5$ (B).
Measurements of double photoelectron emission (DPE) probabilities as a function of wavelength are reported for Hamamatsu R8778, R8520, and R11410 VUV-sensitive photomultiplier tubes (PMTs). In DPE, a single photon strikes the PMT photocathode and produces two photoelectrons instead of a single one. It was found that the fraction of detected photons that result in DPE emission is a function of the incident photon wavelength, and manifests itself below $\sim$250 nm. For the xenon scintillation wavelength of 175 nm, a DPE probability of 18--24\% was measured depending on the tube and measurement method. This wavelength-dependent single photon response has implications for the energy calibration and photon counting of current and future liquid xenon detectors such as LUX, LZ, XENON100/1T, Panda-X and XMASS.
Cosmological parameters deduced from the Planck measurements of anisotropies in the cosmic microwave background are at some tension with direct astronomical measurements of various parameters at low redshifts. Very recently, it has been conjectured that this discrepancy can be reconciled if a certain fraction of dark matter is unstable and decays between recombination and the present epoch. Herein we show that if the superheavy relics have a branching into neutrinos B (X \to \nu \bar \nu) \sim 5 \times 10^{-8}, then this scenario can also accommodate the recently discovered extraterrestrial flux of neutrinos, relaxing the tension between IceCube results and Fermi LAT data. The model is fully predictive and can be confronted with future IceCube data. We demonstrate that in 10 years of observation IceCube will be able to distinguish the mono-energetic signal from X decay at the 3\sigma level. In a few years of data taking with the upgraded IceCube-Gen2 enough statistics will be gathered to elucidate the dark matter--neutrino connection at the 5\sigma level.
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The paucity of observed supermassive black hole binaries (SMBHBs) may imply that the gravitational wave background (GWB) from this population is anisotropic, rendering existing analyses sub-optimal. We present the first constraints on the angular distribution of a nanohertz stochastic GWB from circular, inspiral-driven SMBHBs using the $2015$ European Pulsar Timing Array data [Desvignes et al. (in prep.)]. Our analysis of the GWB in the $\sim 2 - 90$ nHz band shows consistency with isotropy, with the strain amplitude in $l>0$ spherical harmonic multipoles $\lesssim 40\%$ of the monopole value. We expect that these more general techniques will become standard tools to probe the angular distribution of source populations.
The dwarf planet Pluto is known to host an extended system of five co-planar satellites. Previous studies have explored the formation and evolution of the system in isolation, neglecting perturbative effects by the Sun. Here we show that secular evolution due to the Sun can strongly affect the evolution of outer satellites and rings in the system, if such exist. Although precession due to extended gravitational potential from the inner Pluto-Charon binary quench such secular evolution up to $a_{crit}\sim0.0035$ AU ($\sim0.09$ $R_{Hill}$ the Hill radius; including all of the currently known satellites), outer orbits can be significantly altered. In particular, we find that \emph{co-planar} rings and satellites should not exist beyond $a_{crit}$; rather, satellites and dust particles in these regions secularly evolve on timescales ranging between $10^{4}-10^{6}$ yrs, and quasi-periodically change their inclinations and eccentricities through secular evolution (Lidov-Kozai oscillations). Such oscillations can lead to high inclinations and eccentricities, constraining the range where such satellites (and dust particles) can exist without crossing the orbits of the inner satellites, or crossing the outer Hill stability range. Outer satellites, if such exist are therefore likely to be \emph{irregular} satellites, with orbits limited to be non-circular and/or highly inclined. These could be potentially detected and probed by the New-Horizon mission, possibly providing direct evidence for the secular evolution of the Pluto satellite system, and shedding new light on its origins.
Infrared (IR) luminosity is fundamental to understanding the cosmic star formation history and AGN evolution, since their most intense stages are often obscured by dust. Japanese infrared satellite, AKARI, provided unique data sets to probe these both at low and high redshifts. The AKARI performed an all sky survey in 6 IR bands (9, 18, 65, 90, 140, and 160$\mu$m) with 3-10 times better sensitivity than IRAS, covering the crucial far-IR wavelengths across the peak of the dust emission. Combined with a better spatial resolution, AKARI can measure the total infrared luminosity ($L_{TIR}$) of individual galaxies much more precisely, and thus, the total infrared luminosity density of the local Universe. In the AKARI NEP deep field, we construct restframe 8$\mu$m, 12$\mu$m, and total infrared (TIR) luminosity functions (LFs) at 0.15$<z<$2.2 using 4128 infrared sources. A continuous filter coverage in the mid-IR wavelength (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24$\mu$m) by the AKARI satellite allows us to estimate restframe 8$\mu$m and 12$\mu$m luminosities without using a large extrapolation based on a SED fit, which was the largest uncertainty in previous work. By combining these two results, we reveal dust-hidden cosmic star formation history and AGN evolution from $z$=0 to $z$=2.2, all probed by the AKARI satellite. The next generation space infrared telescope, SPICA, will revolutionize our view of the infrared Universe with superb sensitivity of the cooled 3m space telescope. We conclude with our survey proposal and future prospects with SPICA.
We present infrared galaxy luminosity functions (LFs) in the AKARI North Ecliptic Pole (NEP) deep field using recently-obtained, wider CFHT optical/near-IR images. AKARI has obtained deep images in the mid-infrared (IR), covering 0.6 deg$^2$ of the NEP deep field. However, our previous work was limited to the central area of 0.25 deg$^2$ due to the lack of optical coverage of the full AKARI NEP survey. To rectify the situation, we recently obtained CFHT optical and near-IR images over the entire AKARI NEP deep field. These new CFHT images are used to derive accurate photometric redshifts, allowing us to fully exploit the whole AKARI NEP deep field. AKARI's deep, continuous filter coverage in the mid-IR wavelengths (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24$\mu$m) exists nowhere else, due to filter gaps of other space telescopes. It allows us to estimate restframe 8$\mu$m and 12$\mu$m luminosities without using a large extrapolation based on spectral energy distribution (SED) fitting, which was the largest uncertainty in previous studies. Total infrared luminosity (TIR) is also obtained more reliably due to the superior filter coverage. The resulting restframe 8$\mu$m, 12$\mu$m, and TIR LFs at $0.15<z<2.2$ are consistent with previous works, but with reduced uncertainties, especially at the high luminosity-end, thanks to the wide field coverage. In terms of cosmic infrared luminosity density ($\Omega_{\mathrm{IR}}$), we found that the $\Omega_{\mathrm{IR}}$ evolves as $\propto (1+z)^{4.2\pm 0.4}$.
CIZA J2242.8+5301 ($z = 0.188$, nicknamed 'Sausage') is an extremely massive ($M_{200}\sim 2.0 \times 10^{15}M_\odot$ ), merging cluster with shock waves towards its outskirts, which was found to host numerous emission-line galaxies. We performed extremely deep Westerbork Synthesis Radio Telescope HI observations of the 'Sausage' cluster to investigate the effect of the merger and the shocks on the gas reservoirs fuelling present and future star formation (SF) in cluster members. By using spectral stacking, we find that the emission-line galaxies in the 'Sausage' cluster have, on average, as much HI gas as field galaxies (when accounting for the fact cluster galaxies are more massive than the field galaxies), contrary to previous studies. Since the cluster galaxies are more massive than the field spirals, they may have been able to retain their gas during the cluster merger. The large HI reservoirs are expected to be consumed within $\sim0.75-1.0$ Gyr by the vigorous SF and AGN activity and/or driven out by the out-flows we observe. We find that the star-formation rate in a large fraction of H$\alpha$ emission-line cluster galaxies correlates well with the radio broad band emission, tracing supernova remnant emission. This suggests that the cluster galaxies, all located in post-shock regions, may have been undergoing sustained SFR for at least 100 Myr. This fully supports the interpretation proposed by Stroe et al. (2015) and Sobral et al. (2015) that gas-rich cluster galaxies have been triggered to form stars by the passage of the shock.
Using the relativistic equations of radiation hydrodynamics in the viscous limit, we analyze the boundary layers that develop between radiation-dominated jets and their environments. In this paper we present the solution for the self-similar, 2-D, plane-parallel two-stream problem, wherein the jet and the ambient medium are considered to be separate, interacting fluids, and we compare our results to those of previous authors. (In a companion paper we investigate an alternative scenario, known as the free-streaming jet model.) Consistent with past findings, we show that the boundary layer that develops between the jet and its surroundings creates a region of low-density material. These models may be applicable to sources such as super-Eddington tidal disruption events and long gamma-ray bursts.
We study explosion characteristics of ultra-stripped supernovae (SNe), which are candidates of SNe generating binary neutron stars (NSs). As a first step, we perform stellar evolutionary simulations of bare carbon-oxygen cores of mass from 1.45 to 2.0 $M_\odot$ until the iron cores become unstable and start collapsing. We then perform axisymmetric hydrodynamics simulations with spectral neutrino transport using these stellar evolution outcomes as initial conditions. All models exhibit successful explosions driven by neutrino heating. The diagnostic explosion energy, ejecta mass, Ni mass, and NS mass are typically $\sim 10^{50}$ erg, $\sim 0.1 M_\odot$, $\sim 0.01M_\odot$, and $\approx 1.3 M_\odot$, which are compatible with observations of rapidly-evolving and luminous transient such as SN 2005ek. We also find that the ultra-stripped SN is a candidate for producing the secondary low-mass NS in the observed compact binary NSs like PSR J0737-3039.
Motivated by the recent, serendipitous discovery of the densest known galaxy, M60-UCD1, we present two initial findings from a follow-up search, using the Sloan Digital Sky Survey, Subaru/Suprime-Cam and Hubble Space Telescope imaging, and SOAR/Goodman spectroscopy. The first object discovered, M59-UCD3, has a similar size to M60-UCD1 (half-light radius of r_h ~ 20 pc) but is 40% more luminous (M_V ~ -14.6), making it the new densest-known galaxy. The second, M85-HCC1, has a size like a typical globular cluster r_h ~ 1.8 pc) but is much more luminous (M_V ~ -12.5). This hypercompact cluster is by far the densest confirmed free-floating stellar system, and is equivalent to the densest known nuclear star clusters. From spectroscopy, we find that both objects are relatively young (~9 Gyr and ~3 Gyr, respectively), with metal-abundances that resemble those of galaxy centers. Their host galaxies show clear signs of large-scale disturbances, and we conclude that these dense objects are the remnant nuclei of recently accreted galaxies. M59-UCD3 is an ideal target for follow-up with high-resolution imaging and spectroscopy to search for an overweight central supermassive black hole as was discovered in M60-UCD1. These findings also emphasize the potential value of ultra-compact dwarfs and massive globular clusters as tracers of the assembly histories of galaxies.
We present a series of hydrodynamic simulations of isolated galaxies with stellar mass of $10^{9} \, \rm{M}_{\odot}$. The models use a resolution of $750 \, \rm{M}_{\odot}$ per particle and include a treatment for the full non-equilibrium chemical evolution of ions and molecules (157 species in total), along with gas cooling rates computed self-consistently using the non-equilibrium abundances. We compare these to simulations evolved using cooling rates calculated assuming chemical (including ionisation) equilibrium, and we consider a wide range of metallicities and UV radiation fields, including a local prescription for self-shielding by gas and dust. We find higher star formation rates and stronger outflows at higher metallicity and for weaker radiation fields, as gas can more easily cool to a cold (few hundred Kelvin) star forming phase under such conditions. Contrary to variations in the metallicity and the radiation field, non-equilibrium chemistry generally has no strong effect on the total star formation rates or outflow properties. However, it is important for modelling molecular outflows. For example, the mass of H$_{2}$ outflowing with velocities $> 50 \, \rm{km} \, \rm{s}^{-1}$ is enhanced by a factor $\sim 20$ in non-equilibrium. We also compute the observable line emission from CII and CO. Both are stronger at higher metallicity, while CII and CO emission are higher for stronger and weaker radiation fields respectively. We find that CII is generally unaffected by non-equilibrium chemistry. However, emission from CO varies by a factor of $\sim 2 - 4$. This has implications for the mean $X_{\rm{CO}}$ conversion factor between CO emission and H$_{2}$ column density, which we find is lowered by up to a factor $\sim 2.3$ in non-equilibrium, and for the fraction of CO-dark molecular gas.
Strong encounters between single stars and binaries play a pivotal role in the evolution of star clusters. Such encounters can also dramatically modify the orbital parameters of binaries, exchange partners in and out of binaries, and are a primary contributor to the rate of physical stellar collisions in star clusters. Often, these encounters are studied under the approximation that they happen quickly enough and within a small enough volume to be considered isolated from the rest of the cluster. In this paper, we study the validity of this assumption through the analysis of a large grid of single - binary and binary - binary scattering experiments. For each encounter we evaluate the encounter duration, and compare this with the expected time until another single or binary star will join the encounter. We find that for lower-mass clusters, similar to typical open clusters in our Galaxy, the percent of encounters that will be "interrupted" by an interloping star or binary may be 20-40% (or higher) in the core, though for typical globular clusters we expect <1% of encounters to be interrupted. Thus, the assumption that strong encounters occur in relative isolation breaks down for certain clusters. Instead, many strong encounters develop into more complex "mini-clusters", which must be accounted for in studying, for example, the internal dynamics of star clusters, and the physical stellar collision rate.
In this work we analyse the properties of cosmic voids in standard and coupled dark energy cosmologies. Using large numerical simulations, we investigate the effects produced by the dark energy coupling on three statistics: the filling factor, the size distribution and the stacked profiles of cosmic voids. We find that the bias of the tracers of the density field used to identify the voids strongly influences the properties of the void catalogues, and, consequently, the possibility of using the identified voids as a probe to distinguish coupled dark energy models from the standard $\Lambda $CDM cosmology. In fact, on one hand coupled dark energy models are characterised by an excess of large voids in the cold dark matter distribution as compared to the reference standard cosmology, due to their higher normalisation of linear perturbations at low redshifts. Specifically, these models present an excess of large voids with $R_{eff}>20, 15, 12$ Mpc h^{-1}, at $z=0, 0.55, 1$, respectively. On the other hand, we do not find any significant difference in the properties of the void detected in the distribution of collapsed dark matter halos. These results imply that the tracer bias has a significant impact on the possibility of using cosmic void catalogues to probe cosmology.
We explore the structures of protoclusters and their relationship with high redshift clusters using the Millennium Simulation combined with a semi-analytic model. We find that protoclusters are very extended, with 90 per cent of their mass spread across $\sim35\,h^{-1}{\rm Mpc}$ comoving at $z=2$ ($\sim30\, \rm{arcmin}$). The `main halo', which can manifest as a high redshift cluster or group, is only a minor feature of the protocluster, containing less than 20 per cent of all protocluster galaxies at $z=2$. Furthermore, many protoclusters do not contain a main halo that is massive enough to be identified as a high redshift cluster. Protoclusters exist in a range of evolutionary states at high redshift, independent of the mass they will evolve to at $z=0$. We show that the evolutionary state of a protocluster can be approximated by the mass ratio of the first and second most massive haloes within the protocluster, and the $z=0$ mass of a protocluster can be estimated to within 0.2 dex accuracy if both the mass of the main halo and the evolutionary state is known. We also investigate the biases introduced by only observing star-forming protocluster members within small fields. The star formation rate required for line-emitting galaxies to be detected is typically high, which leads to the artificial loss of low mass galaxies from the protocluster sample. This effect is stronger for observations of the centre of the protocluster, where the quenched galaxy fraction is higher. This loss of low mass galaxies, relative to the field, distorts the size of the galaxy overdensity, which in turn can contribute to errors in predicting the $z=0$ evolved mass.
We present a study of the cosmological Ly$\alpha$ emission signal at $z > 4$. Our goal is to predict the power spectrum of the spatial fluctuations that could be observed by an intensity mapping survey. The model uses the latest data from the HST legacy fields and the abundance matching technique to associate UV emission and dust properties with the halos, computing the emission from the interstellar medium (ISM) of galaxies and the intergalactic medium (IGM), including the effects of reionization, self-consistently. The Ly$\alpha$ intensity from the diffuse IGM emission is 1.3 (2.0) times more intense than the ISM emission at $z = 4(7)$; both components are fair tracers of the star-forming galaxy distribution. However the power spectrum is dominated by ISM emission on small scales ($k > 0.01 h{\rm Mpc}^{-1}$) with shot noise being significant only above $k = 1 h{\rm Mpc}^{-1}$. At very lange scales ($k < 0.01h{\rm Mpc}^{-1}$) diffuse IGM emission becomes important. The comoving Ly$\alpha$ luminosity density from IGM and galaxies, $\dot \rho_{{\rm Ly}\alpha}^{\rm IGM} = 8.73(6.51) \times 10^{40} {\rm erg}{\rm s}^{-1}{\rm Mpc}^{-3}$ and $\dot \rho_{{\rm Ly}\alpha}^{\rm ISM} = 6.62(3.21) \times 10^{40} {\rm erg}{\rm s}^{-1}{\rm Mpc}^{-3}$ at $z = 4(7)$, is consistent with recent SDSS determinations. We predict a power $k^3 P^{{\rm Ly}\alpha}(k, z)/2\pi^2 = 9.76\times 10^{-4}(2.09\times 10^{-5}){\rm nW}^2{\rm m}^{-4}{\rm sr}^{-2}$ at $z = 4(7)$ for $k = 0.1 h {\rm Mpc}^{-1}$.
We present seven epochs of spectropolarimetry of the Type IIb supernova (SN) 2011dh in M51, spanning 86 days of its evolution. The first epoch was obtained 9 days after the explosion, when the photosphere was still in the depleted hydrogen layer of the stripped-envelope progenitor. Continuum polarization is securely detected at the level of P~0.5% through day 14 and appears to diminish by day 30, which is different from the prevailing trends suggested by studies of other core-collapse SNe. Time-variable modulations in P and position angle are detected across P-Cygni line features. H-alpha and HeI polarization peak after 30 days and exhibit position angles roughly aligned with the earlier continuum, while OI and CaII appear to be geometrically distinct. We discuss several possibilities to explain the evolution of the continuum and line polarization, including the potential effects of a tidally deformed progenitor star, aspherical radioactive heating by fast-rising plumes of Ni-56 from the core, oblique shock breakout, or scattering by circumstellar material. While these possibilities are plausible and guided by theoretical expectations, they are not unique solutions to the data. The construction of more detailed hydrodynamic and radiative-transfer models that incorporate complex aspherical geometries will be required to further elucidate the nature of the polarized radiation from SN 2011dh and other Type IIb supernovae.
The goal of this paper is to test whether the formation rate of star clusters is proportional to the star formation rate (SFR) in galaxies. As a first step, we present the mass functions of compact clusters younger than 10 Myr in seven star-forming galaxies of diverse masses, sizes, and morphologies: the Large and Small Magellanic Clouds, NGC 4214, NGC 4449, M83, M51, and the Antennae. These cluster mass functions (CMFs) are well represented by power laws, dN/dM~M^b, with similar exponents b=-1.92+/-0.27, but with amplitudes that differ by factors up to ~10^3, corresponding to vast differences in the sizes of the cluster populations in these galaxies. We then normalize these CMFs by the SFRs in the galaxies, derived from dust-corrected H-alpha luminosities, and find that the spread in the amplitudes collapses, with a remaining rms deviation of only sigma_(logA)= 0.2. This is close to the expected dispersion from random uncertainties in the CMFs and SFRs. Thus, the data presented here are consistent with exact proportionality between the formation rates of stars and clusters. However, the data also permit weak deviations from proportionality, at the factor of two level, within the statistical uncertainties. We find the same spread in amplitudes when we normalize the mass functions of much older clusters, with ages in the range 100 to 400 Myr, by the current SFR. This is another indication of the general similarity among the cluster populations of different galaxies.
The aim of the project is to characterise both components of the nearest brown dwarf sytem to the Sun, WISE J104915.57-531906.1 (=Luhman16AB) at optical and near-infrared wavelengths. We obtained high signal-to-noise intermediate-resolution (R~6000-11000) optical (600-1000 nm) and near-infrared (1000-2480nm) spectra of each component of Luhman16AB, the closest brown dwarf binary to the Sun, with the X-Shooter instrument on the Very Large Telescope. We classify the primary and secondary of the Luhman16 system as L6-L7.5 and T0+/-1, respectively, in agreement with previous measurements published in the literature. We present measurements of the lithium pseudo-equivalent widths, which appears of similar strength on both components (8.2+/-1.0 Angstroms and 8.4+/-1.5 Angstroms for the L and T components, respectively). The presence of lithium (Lithium 7) in both components imply masses below 0.06 Msun while comparison with models suggests lower limits of 0.04 Msun. The detection of lithium in the T component is the first of its kind. Similarly, we assess the strength of other alkali lines (e.g. pseudo-equivalent widths of 6-7 Angstroms for RbI and 4-7 Angstroms for CsI) present in the optical and near-infrared regions and compare with estimates for L and T dwarfs. We also derive effective temperatures and luminosities of each component of the binary: -4.66+/-0.08 dex and 1305(+180)(-135) for the L dwarf and -4.68+/-0.13 dex and 1320(+185)(-135) for the T dwarf, respectively. Using our radial velocity determinations, the binary does not appear to belong to any of the well-known moving group. Our preliminary theoretical analysis of the optical and J-band spectra indicates that the L- and T-type spectra can be reproduced with a single temperature and gravity but different relative chemical abundances which impact strongly the spectral energy distribution of L/T transition objects.
We report the discovery of a microlensing exoplanet OGLE-2012-BLG-0563Lb with the planet-star mass ratio ~1 x 10^{-3}. Intensive photometric observations of a high-magnification microlensing event allow us to detect a clear signal of the planet. Although no parallax signal is detected in the light curve, we instead succeed at detecting the flux from the host star in high-resolution JHK'-band images obtained by the Subaru/AO188 and IRCS instruments, allowing us to constrain the absolute physical parameters of the planetary system. With the help of a spectroscopic information of the source star obtained during the high-magnification state by Bensby et al. (2013), we find that the lens system is located at 1.3^{+0.6}_{-0.8} kpc from us, and consists of an M dwarf (0.34^{+0.12}_{-0.20} M_sun) orbited by a Saturn-mass planet (0.39^{+0.14}_{-0.23} M_Jup) at the projected separation of 0.74^{+0.26}_{-0.42} AU (close model) or 4.3^{+1.5}_{-2.5} AU (wide model). The probability of contamination in the host star's flux, which would reduce the masses by a factor of up to 3, is estimated to be 17%. This possibility can be tested by future high-resolution imaging. We also estimate the (J-Ks) and (H-Ks) colors of the host star, which are marginally consistent with a low-metallicity mid-to-early M dwarf, although further observations are required for the metallicity to be conclusive. This is the fifth sub-Jupiter-mass (0.2<m_p/M_Jup<1) microlensing planet around an M dwarf with the mass well constrained. The relatively rich harvest of sub-Jupiters around M dwarfs is contrasted with a possible paucity of ~1--2 Jupiter-mass planets around the same type of star, which can be explained by the planetary formation process in the core accretion scheme.
A free-space laser communication system has been designed and partially developed as an alternative to standard RF links from UAV to ground stations. This project belongs to the SINTONIA program (acronym in Spanish for low environmental-impact unmanned systems), led by BR&TE (Boeing Research and Technology Europe) with the purpose of boosting Spanish UAV technology. A MEMS-based modulating retroreflector has been proposed as a communication terminal onboard the UAV, allowing both the laser transmitter and the acquisition, tracking and pointing subsystems to be eliminated. This results in an important reduction of power, size and weight, moving the burden to the ground station. In the ground station, the ATP subsystem is based on a GPS-aided two-axis gimbal for tracking and coarse pointing, and a fast steering mirror for fine pointing. A beacon-based system has been designed, taking advantage of the retroreflector optical principle, in order to determine the position of the UAV in real-time. The system manages the laser power in an optimal way, based on a distance-dependent beam-divergence control and by creating two different optical paths within the same physical path using different states of polarization.
Big bang nucleosynthesis in a modified gravity model of $f(R)\propto R^n$ is investigated. The only free parameter of the model is a power-law index $n$. We find cosmological solutions in a parameter region of $1< n \leq (4+\sqrt{6})/5$. We calculate abundances of $^4$He, D, $^3$He, $^7$Li, and $^6$Li during big bang nucleosynthesis. We compare the results with the latest observational data. It is then found that the power-law index is constrained to be $(n-1)=(-0.86\pm 1.19)\times 10^{-4}$ (95 % C.L.) mainly from observations of deuterium abundance as well as $^4$He abundance.
We present an absorption-line survey of optically thick gas clouds -- Lyman Limit Systems (LLSs) -- observed at high dispersion with spectrometers on the Keck and Magellan telescopes. We measure column densities of neutral hydrogen NHI and associated metal-line transitions for 157 LLSs at z=1.76-4.39 restricted to 10^17.3 < NHI < 10^20.3. An empirical analysis of ionic ratios indicates an increasing ionization state of the gas with decreasing NHI and that the majority of LLSs are highly ionized, confirming previous expectations. The Si^+/H^0 ratio spans nearly four orders-of-magnitude, implying a large dispersion in the gas metallicity. Fewer than 5% of these LLSs have no positive detection of a metal transition; by z~3, nearly all gas that is dense enough to exhibit a very high Lyman limit opacity has previously been polluted by heavy elements. We add new measurements to the small subset of LLS (~5-10) that may have super-solar abundances. High Si^+/Fe^+ ratios suggest an alpha-enhanced medium whereas the Si^+/C^+ ratios do not exhibit the super-solar enhancement inferred previously for the Lya forest.
This manuscript describes the design, usage, and data-reduction pipeline developed for the Magellan Inamori Kyocera Echelle (MIKE) spectrometer used with the Magellan telescope at the Las Campanas Observatory. We summarize the basic characteristics of the instrument and discuss observational procedures recommended for calibrating the standard data products. We detail the design and implementation of an IDL based data-reduction pipeline for MIKE data (since generalized to other echelle spectrometers, e.g. Keck/HIRES, VLT/UVES). This includes novel techniques for flat-fielding, wavelength calibration, and the extraction of echelle spectroscopy. Sufficient detail is provided in this manuscript to enable inexperienced observers to understand the strengths and weaknesses of the instrument and software package and an assessment of the related systematics.
We present first results from a high resolution multi-band survey of the Westerlund 2 region with the Hubble Space Telescope. Specifically, we imaged Westerlund 2 with the Advanced Camera for Surveys through the $F555W$, $F814W$, and $F658N$ filters and with the Wide Field Camera 3 in the $F125W$, $F160W$, and $F128N$ filters. We derive the first high resolution pixel-to-pixel map of the color excess $E(B-V)_g$ of the gas associated with the cluster, combining the H$\alpha$ ($F658N$) and Pa$\beta$ ($F128N$) line observations. We demonstrate that, as expected, the region is affected by significant differential reddening with a median of $E(B-V)_g=1.87$~mag. After separating the populations of cluster members and foreground contaminants using a $(F814W-F160W)$ vs. $F814W$ color-magnitude diagram, we identify a pronounced pre-main-sequence population in Westerlund 2 showing a distinct turn-on. After dereddening each star of Westerlund 2 individually in the color-magnitude diagram we find via over-plotting PARSEC isochrones that the distance is in good agreement with the literature value of $\sim4.16 \pm 0.33$~kpc. With zero-age-main-sequence fitting to two-color-diagrams, we derive a value of total to selective extinction of $R_V=3.95 \pm 0.135$. A spatial density map of the stellar content reveals that the cluster might be composed of two clumps. We estimate the same age of 0.5-2.0 Myr for both clumps. While the two clumps appear to be coeval, the northern clump shows a $\sim 20 \%$ lower stellar surface density.
We investigate the consequences of general curved trajectories in multi-field inflation. After setting up a completely general formalism using the mass basis, which naturally accommodates the notion of light and heavy modes, we study in detail the simple case of two successive turns in two-field system. We find the power spectrum of the curvature perturbation receives corrections that exhibit oscillatory features sinusoidal in the logarithm of the comoving wavenumber without slow-roll suppression. We show that this is because of the resonance of the heavy modes inside and outside the mass horizon.
We have used the radiative transfer code HDUST to analyze and interpret the long-term photometric behavior of the Be star omega CMa, considering four complete cycles of disk formation and dissipation. This is the first time in which a full lightcurve of a Be star was investigated and modeled including both disk build-up and dissipation phases. Based on the quite good fit of the observed data we were able to derive the history of stellar mass decretion rates (including long- and short-term changes) during the disk formation and dissipation phases in all four cycles.
Magnetic fields are usually observed in the quiet Sun as small-scale elements that cover the entire solar surface (the `salt and pepper' patterns in line-of-sight magnetograms). By using 3D radiative MHD numerical simulations we find that these fields result from a local dynamo action in the top layers of the convection zone, where extremely weak 'seed' magnetic fields (e.g., from a $10^{-6}$ G) can locally grow above the mean equipartition field, to a stronger than 2000~G field localized in magnetic structures. Our results reveal that the magnetic flux is predominantly generated in regions of small-scale helical downflows. We find that the local dynamo action takes place mostly in a shallow, about 500~km deep, subsurface layer, from which the generated field is transported into the deeper layers by convective downdrafts. We demonstrate that the observed dominance of vertical magnetic fields at the photosphere and horizontal fields above the photosphere can be explained by small-scale magnetic loops produced by the dynamo. Such small-scale loops play an important role in the structure and dynamics of the solar atmosphere and that their detection in observations is critical for understanding the local dynamo action on the Sun.
As the size of images and data products derived from astronomical data continues to increase, new tools are needed to visualize and interact with that data in a meaningful way. Motivated by our own astronomical images taken with the Dark Energy Camera (DECam) we present Toyz, an open source Python package for viewing and analyzing images and data stored on a remote server or cluster. Users connect to the Toyz web application via a web browser, making it an convenient tool for students to visualize and interact with astronomical data without having to install any software on their local machines. In addition it provides researchers with an easy-to-use tool that allows them to browse the files on a server and quickly view very large images ($>$ 2 Gb) taken with DECam and other cameras with a large FOV and create their own visualization tools that can be added on as extensions to the default Toyz framework.
NASA's re-purposed Kepler mission -- dubbed K2 -- has brought new scientific opportunities that were not anticipated for the original Kepler mission. One science goal that makes optimal use of K2's capabilities, in particular its 360-degree ecliptic field of view, is galactic archaeology -- the study of the evolution of the Galaxy from the fossil stellar record. The thrust of this research is to exploit high-precision, time-resolved photometry from K2 in order to detect oscillations in red giant stars. This asteroseismic information can provide estimates of stellar radius (hence distance), mass and age of vast numbers of stars across the Galaxy. Here we present the initial analysis of a subset of red giants, observed towards the North Galactic Gap, during the mission's first full science campaign. We investigate the feasibility of using K2 data for detecting oscillations in red giants that span a range in apparent magnitude and evolutionary state (hence intrinsic luminosity). We demonstrate that oscillations are detectable for essentially all cool giants within the $\log g$ range $\sim 1.9-3.2$. Our detection is complete down to $\mathit{Kp}\sim 14.5$, which results in a seismic sample with little or no detection bias. This sample is ideally suited to stellar population studies that seek to investigate potential shortcomings of contemporary Galaxy models.
We show the effects of AGN-driven outflows on the ejection of heavy elements using our cosmological simulations, where super-massive black holes originate from the first stars. In the most massive galaxy, we have identified two strong outflows unambiguously driven by AGN feedback. These outflows have a speed greater than $\sim 8000$ km\,s$^{-1}$ near the AGN, and travel out to a half Mpc with $\sim 3000$ km\,s$^{-1}$. These outflows remove the remaining gas ($\sim 3$ per cent of baryons) and significant amounts of metals ($\sim 2$ per cent of total produced metals) from the host galaxy, chemically enriching the circumgalactic medium (CGM) and the intergalactic medium (IGM). 17.6 per cent of metals from this galaxy, and 18.4 per cent of total produced metals in the simulation, end up in the CGM and IGM, respectively. The metallicities of the CGM and IGM are higher with AGN feedback, while the mass--metallicity relation of galaxies is not affected very much. We also find `selective' mass-loss where iron is more effectively ejected than oxygen because of the time-delay of Type Ia Supernovae. AGN-driven outflows play an essential role not only in quenching of star formation in massive galaxies to match with observed down-sizing phenomena, but also in a large-scale chemical enrichment in the Universe. Observational constraints of metallicities and elemental abundance ratios in outflows are important to test the modelling of AGN feedback in galaxy formation.
Transverse magnetohydrodynamic (MHD) waves have been shown to be ubiquitous in the solar atmosphere and can in principle carry sufficient energy to generate and maintain the Sun's million-degree outer atmosphere or corona. However, direct evidence of the dissipation process of these waves and subsequent heating has not yet been directly observed. Here we report on high spatial, temporal, and spectral resolution observations of a solar prominence that show a compelling signature of so-called resonant absorption, a long hypothesized mechanism to efficiently convert and dissipate transverse wave energy into heat. Aside from coherence in the transverse direction, our observations show telltale phase differences around 180 degrees between transverse motions in the plane-of-sky and line-of-sight velocities of the oscillating fine structures or threads, and also suggest significant heating from chromospheric to higher temperatures. Comparison with advanced numerical simulations support a scenario in which transverse oscillations trigger a Kelvin-Helmholtz instability (KHI) at the boundaries of oscillating threads via resonant absorption. This instability leads to numerous thin current sheets in which wave energy is dissipated and plasma is heated. Our results provide direct evidence for wave-related heating in action, one of the candidate coronal heating mechanisms.
We study the physical and evolutionary properties of the "WD family" of AM CVn stars by computing realistic models of IDD systems. We evaluate self-consistently both the mass transfer rate from the donor, as determined by GW emission and interaction with the binary companion, and the thermal response of the accretor to mass deposition. We find that, after the onset of mass transfer, all the considered systems undergo a strong non-dynamical He-flash. However, due to the compactness of these systems, the expanding accretors fill their Roche lobe very soon, thus preventing the efficient heating of the external layers of the accreted CO WDs. Moreover, due to the loss of matter from the systems, the orbital separations enlarge and mass transfer comes to a halt. The further evolution depends on the value of \mdot\, after the donors fill again their lobe. On one hand, if the accretion rate, as determined by the actual value of (M_don,M_acc), is high enough, the accretors experience several He-flashes of decreasing strength and then quiescent He-burning sets in. Later on, since the mass transfer rate in IDD is a permanently decreasing function of time, accretors experience several recurrent strong flashes. On the other hand, for intermediate and low values of the accretion rate, the accretors enter the strong flashes accretion regime. As expected, in all the considered systems the last He-flash is the strongest one, even if the physical a dynamical event never occurs. When the mass accretion rate decreases below (2-3 10^{-8}Msun/yr, the compressional heating of the He-shell becomes less efficient than the neutrino cooling, so that all the accretors in the considered systems evolve into massive degenerate objects. Our results suggest that SNe .Ia or type Ia Supernovae due to Edge-Lit Detonation in the WD family of AM CVn stars should be much more rare than previously expected.
Galaxy merging is widely accepted to be a key driving factor in galaxy formation and evolution, while the feedback from AGN is thought to regulate the BH-bulge coevolution and the star formation process. In this context, we focused on 1SXPSJ050819.8+172149, a local (z=0.0175) Seyfert 1.9 galaxy (L_bol~4x10^43 ergs/s). The source belongs to an IR-luminous interacting pair of galaxies, characterized by a luminosity for the whole system (due to the combination of star formation and accretion) of log(L_IR/L_sun)=11.2. We present the first detailed description of the 0.3-10keV spectrum of 1SXPSJ050819.8+172149, monitored by Swift with 9 pointings performed in less than 1 month. The X-ray emission of 1SXPSJ050819.8+172149 is analysed by combining all the Swift pointings, for a total of ~72ks XRT net exposure. The averaged Swift-BAT spectrum from the 70-month survey is also analysed. The slope of the continuum is ~1.8, with an intrinsic column density NH~2.4x10^22 cm-2, and a deabsorbed luminosity L(2-10keV)~4x10^42 ergs/s. Our observations provide a tentative (2.1sigma) detection of a blue-shifted FeXXVI absorption line (rest-frame E~7.8 keV), suggesting the discovery for a new candidate powerful wind in this source. The physical properties of the outflow cannot be firmly assessed, due to the low statistics of the spectrum and to the observed energy of the line, too close to the higher boundary of the Swift-XRT bandpass. However, our analysis suggests that, if the detection is confirmed, the line could be associated with a high-velocity (vout~0.1c) outflow most likely launched within 80r_S. To our knowledge this is the first detection of a previously unknown ultrafast wind with Swift. The high NH suggested by the observed equivalent width of the line (EW~ -230eV, although with large uncertainties), would imply a kinetic output strong enough to be comparable to the AGN bolometric luminosity.
Aims Determining the intensity of lines and continuum airglow emission in the H-band is important for the design of faint-object infrared spectrographs. Existing spectra at low/medium resolution cannot disentangle the true sky-continuum from instrumental effects (e.g. diffuse light in the wings of strong lines). We aim to obtain, for the first time, a high resolution infrared spectrum deep enough to set significant constraints on the continuum emission between the lines in the H-band. Methods During the second commissioning run of the GIANO high-resolution infrared spectrograph at La Palma Observatory, we pointed the instrument directly to the sky and obtained a deep spectrum that extends from 0.97 to 2.4 micron. Results The spectrum shows about 1500 emission lines, a factor of two more than in previous works. Of these, 80% are identified as OH transitions; half of these are from highly excited molecules (hot-OH component) that are not included in the OH airglow emission models normally used for astronomical applications. The other lines are attributable to O2 or unidentified. Several of the faint lines are in spectral regions that were previously believed to be free of line emission. The continuum in the H-band is marginally detected at a level of about 300 photons/m^2/s/arcsec^2/micron, equivalent to 20.1 AB-mag/arcsec^2. The observed spectrum and the list of observed sky-lines are published in electronic format. Conclusions Our measurements indicate that the sky continuum in the H-band could be even darker than previously believed. However, the myriad of airglow emission lines severely limits the spectral ranges where very low background can be effectively achieved with low/medium resolution spectrographs. We identify a few spectral bands that could still remain quite dark at the resolving power foreseen for VLT-MOONS (R ~6,600).
Magnetic helicity has the remarkable property of being a conserved quantity of ideal magnetohydrodynamics (MHD). Therefore, it could be used as an effective tracer of the magnetic field evolution of magnetized plasmas. Theoretical estimations indicate that magnetic helicity is also essentially conserved with non-ideal MHD processes, e.g. magnetic reconnection. This conjecture has however been barely tested, either experimentally or numerically. Thanks to recent advances in magnetic helicity estimation methods, it is now possible to test numerically its dissipation level in general three-dimensional datasets. We first revisit the general formulation of the temporal variation of relative magnetic helicity on a fully bounded volume when no hypothesis on the gauge are made. We introduce a method to precisely estimate its dissipation independently of the type of non-ideal MHD processes occurring. In a solar-like eruptive event simulation, using different gauges, we compare its estimation in a finite volume with its time-integrated flux through the boundaries, hence testing the conservation and dissipation of helicity. We provide an upper bound of the real dissipation of magnetic helicity: It is quasi-null during the quasi-ideal MHD phase. Even when magnetic reconnection is acting the relative dissipation of magnetic helicity is also very small (<2.2%), in particular compared to the relative dissipation of magnetic energy (>30 times larger). We finally illustrate how the helicity-flux terms involving velocity components are gauge dependent, hence limiting their physical meaning.
A method is presented for Bayesian model selection without explicitly computing evidences, by using a combined likelihood and introducing an integer model selection parameter $n$ so that Bayes factors, or more generally posterior odds ratios, may be read off directly from the posterior of $n$. If the total number of models under consideration is specified a priori, the full joint parameter space $(\theta, n)$ of the models is of fixed dimensionality and can be explored using standard MCMC or nested sampling methods, without the need for reversible jump MCMC techniques. The posterior on $n$ is then obtained by straightforward marginalisation. We demonstrate the efficacy of our approach by application to several toy models. We then apply it to constraining the dark energy equation-of-state using a free-form reconstruction technique. We show that $\Lambda$CDM is significantly favoured over all extensions, including the simple $w(z){=}{\rm constant}$ model.
We obtained an ALMA Cycle 0 spectral scan of the dusty LIRG NGC 4418, spanning a total of 70.7 GHz in bands 3, 6, and 7. We use a combined local thermal equilibrium (LTE) and non-LTE (NLTE) fit of the spectrum in order to identify the molecular species and derive column densities and excitation temperatures. We derive molecular abundances and compare them with other Galactic and extragalactic sources by means of a principal component analysis. We detect 317 emission lines from a total of 45 molecular species, including 15 isotopic substitutions and six vibrationally excited variants. Our LTE/NLTE fit find kinetic temperatures from 20 to 350 K, and densities between 10$^5$ and 10$^7$ cm$^{-3}$. The spectrum is dominated by vibrationally excited HC$_3$N, HCN, and HNC, with vibrational temperatures from 300 to 450 K. We find high abundances of HC$_3$N, SiO, H$_2$S, and c-HCCCH and a low CH$_3$OH abundance. A principal component analysis shows that NGC 4418 and Arp 220 share very similar molecular abundances and excitation, which clearly set them apart from other Galactic and extragalactic environments. The similar molecular abundances observed towards NCG 4418 and Arp 220 are consistent with a hot gas-phase chemistry, with the relative abundances of SiO and CH$_3$OH being regulated by shocks and X-ray driven dissociation. The bright emission from vibrationally excited species confirms the presence of a compact IR source, with an effective diameter $<$5 pc and brightness temperatures $>$350 K. The molecular abundances and the vibrationally excited spectrum are consistent with a young AGN/starburst system. We suggest that NGC 4418 may be a template for a new kind of chemistry and excitation, typical of compact obscured nuclei (CON). Because of the narrow line widths and bright molecular emission, NGC 4418 is the ideal target for further studies of the chemistry in CONs.
This paper presents a librational solution for evolutions of parameters averaged over a synodic period in mean motion resonances in planar circular restricted three-body problem (PCR3BP) with non-gravitational effects taken into account. The librational solution is derived from a linearization of modified Lagrange's planetary equations. The presented derivation respects properties of orbital evolutions in the mean motion resonances within the framework of the PCR3BP. All orbital evolutions in the PCR3BP with the non-gravitational effects can be described by four varying parameters. We used the semimajor axis, eccentricity, longitude of pericenter and resonant angular variable. The evolutions are found for all four parameters. The solution can be applied also in the case without the non-gravitational effects. We compared numerically and analytically obtained evolutions in the case when the non-gravitational effects are the Poynting-Robertson effect and the radial stellar wind. The librational solution is good approximation when the libration amplitude of the resonant angular variable is small.
The evolution of a supernova remnant in a cloudy medium as a function of the volume filling factor of the clouds is studied in a three-dimensional axially symmetrical model. The model includes the mixing of heavy elements (metals) ejected by the supernova and their contribution to radiative losses. The interaction of the supernova envelope with the cloudy phase of the interstellar medium leads to nonsimultaneous, and on average earlier, onsets of the radiative phase in different parts of the supernova envelope. Growth in the volume filling factor $f$ leads to a decrease in the time for the transition of the envelope to the radiative phase and a decrease in the envelope's mean radius, due to the increased energy losses by the envelope in the cloudy medium. When the development of hydrodynamical instabilities in the supernova envelope is efficient, the thermal energy falls as $E_t\sim t^{-2.3}$, for the propagation of the supernova remnant through either a homogeneous or a cloudy medium. When the volume filling factor is $f\simgt 0.1$, a layer with excess kinetic energy andmomentumforms far behind the global shock front from the supernova, which traps the hot gas of the cavity in the central part of the supernova remnant. Metals ejected by the supernova are also enclosed in the central region of the remnant, where the initial (high) metallicity is essentially preserved. Thus, the interaction of the supernova envelope with the cloudy interstellar medium appreciably changes the dynamics and structure of the distribution of the gas in the remnant. This affects the observational characteristics of the remnant, in particularly, leading to substantial fluctuations of the emission measure of the gas with $T>10^5$~K and the velocity dispersion of the ionized gas.
The excess of high energy neutrinos observed by the IceCube collaboration might originate from baryon number violating decays of heavy shadow baryons from dark mirror sector which produce shadow neutrinos. These sterile neutrino species then oscillate into ordinary neutrinos transferring to them specific features of their spectrum. In particular, this scenario can explain the end of the spectrum above 2 PeV and the presence of the energy gap between 400 TeV and 1 PeV.
The problem of the formation of the Moon is still not explained satisfactorily. While it is a generally accepted scenario that the last giant impact on Earth between some 50 to 100 million years after the starting of the formation of the terrestrial planets formed our natural satellite, there are still many open questions like the isotopic composition which is identical for these two bodies. In our investigation we will not deal with these problems of chemical composition but rather undertake a purely dynamical study to find out the probability of a Mars-sized body to collide with the Earth shortly after the formation of the Earth-like planets. For that we assume an additional massive body between Venus and Earth, respectively Earth and Mars which formed there at the same time as the other terrestrial planets. We have undertaken massive n-body integrations of such a planetary system with 4 inner planets (we excluded Mercury but assumed one additional body as mentioned before) for up to tens of millions of years. Our results led to a statistical estimation of the collision velocities as well as the collision angles which will then serve as the basis of further investigation with detailed SPH computations. We find a most probable origin of the Earth impactor at a semi-major axis of approx. 1.16 AU.
We report on the optical spectroscopic analysis of a sample of 99 low-luminosity quasi-stellar objects (LLQSOs) at $z\leq 0.06$ base the Hamburg/ESO QSO survey (HES). The LLQSOs presented here offer the possibility of studying the faint end of the QSO population at smaller cosmological distances and, therefore, in greater detail. A small number of our LLQSO present no broad component. Two sources show double broad components, whereas six comply with the classic NLS1 requirements. As expected in NLR of broad line AGNs, the [S{\sc{ii}}]$-$based electron density values range between 100 and 1000 N$_{e}$/cm$^{3}$. Using the optical characteristics of Populations A and B, we find that 50\% of our sources with H$\beta$ broad emission are consistent with the radio-quiet sources definition. The remaining sources could be interpreted as low-luminosity radio-loud quasar. The BPT-based classification renders an AGN/Seyfert activity between 50 to 60\%. For the remaining sources, the possible star burst contribution might control the LINER and HII classification. Finally, we discuss the aperture effect as responsible for the differences found between data sets, although variability in the BLR could play a significant role as well.
Carbon-rich grains with isotopic anomalies compared to the Sun are found in primitive meteorites. They were made by stars, and carry the original stellar nucleosynthesis signature. Silicon carbide grains of Type X and C, and low-density graphites condensed in the ejecta of core-collapse supernovae. We present a new set of models for the explosive He shell and compare them with the grains showing 12C/13C and 14N/15N ratios lower than solar. In the stellar progenitor H was ingested into the He shell and not fully destroyed before the explosion. Different explosion energies and H concentrations are considered. If the SN shock hits the He-shell region with some H still present, the models can reproduce the C and N isotopic signatures in C-rich grains. Hot-CNO cycle isotopic signatures are obtained, including a large production of 13C and 15N. The short-lived radionuclides 22Na and 26Al are increased by orders of magnitude. The production of radiogenic 22Ne from the decay of 22Na in the He shell might solve the puzzle of the Ne-E(L) component in low-density graphite grains. This scenario is attractive for the SiC grains of type AB with 14N/15N ratios lower than solar, and provides an alternative solution for SiC grains originally classified as nova grains. Finally, this process may contribute to the production of 14N and 15N in the Galaxy, helping to produce the 14N/15N ratio in the solar system.
CONTEXT: Asymptotic giant branch (AGB) stars are in one of the latest
evolutionary stages of low to intermediate-mass stars. Their vigorous mass loss
has a significant effect on the stellar evolution, and is a significant source
of heavy elements and dust grains for the interstellar medium. The mass-loss
rate can be well traced by carbon monoxide (CO) line emission.
AIMS: We present new \textit{Herschel} HIFI and IRAM 30m telescope CO line
data for a sample of 53 galactic AGB stars. The lines cover a fairly large
range of excitation energy from the $J=1\to0$ line to the $J=9\to8$ line, and
even the $J=14\to13$ line in a few cases. We perform radiative transfer
modelling for 38 of these sources to estimate their mass-loss rates.
METHODS: We used a radiative transfer code based on the Monte Carlo method to
model the CO line emission. We assume spherically symmetric circumstellar
envelopes that are formed by a constant mass-loss rate through a smoothly
accelerating wind.
RESULTS: We find models that are consistent across a broad range of CO lines
for most of the stars in our sample, i.e., a large number of the circumstellar
envelopes can be described with a constant mass-loss rate. We also find that an
accelerating wind is required to fit, in particular, the higher-J lines and
that a velocity law will have a significant effect on the model line
intensities. The results cover a wide range of mass-loss rates ($\sim 10^{-8}$
to $2\times 10^{-5}~\mathrm{M}_\odot~\mathrm{ yr}^{-1}$) and gas expansion
velocities (2 to $21.5$~ km s$^{-1}$), and include M-, S-, and C-type AGB
stars. Our results generally agree with those of earlier studies, although we
tend to find slightly lower mass-loss rates by about 40\%, on average. We also
present "bonus" lines detected during our CO observations.
Stellar activity may induce Doppler variability at the level of a few m/s which can then be confused by the Doppler signal of an exoplanet orbiting the star. To first order, linear correlations between radial velocity measurements and activity indices have been proposed to account for any such correlation. The likely presence of two super-Earths orbiting Kapteyn's star was reported in Anglada et al. (2014, MNRAS 443L, 89A), but this claim was recently challenged by Robertson et al. (2015, ApJ 805L, 22R) arguing evidence of a rotation period (143 days) at three times the orbital period of one of the proposed planets (Kapteyn's b, P=48.6 days), and the existence of strong linear correlations between its Doppler signal and activity data. By re-analyzing the data using global optimization methods and model comparison, we show that such claim is incorrect given that; 1) the choice of a rotation period at 143 days is unjustified, and 2) the presence of linear correlations is not supported by the data. We conclude that the radial velocity signals of Kapteyn's star remain more simply explained by the presence of two super-Earth candidates orbiting it. We also advocate for the use of global optimization procedures and objective arguments, instead of claims lacking of a minimal statistical support.
We employ an automated detection algorithm to perform a global study of solar prominence characteristics. We process four months of TESIS observations in the He II 304 \AA\ line taken close to the solar minimum of 2008-2009 and focus mainly on quiescent and quiescent-eruptive prominences. We detect a total of 389 individual features ranging from 25$\times$25 to 150$\times$500 Mm$^2$ in size and obtain distributions of many their spatial characteristics, such as latitudinal position, height, size and shape. To study their dynamics, we classify prominences as either stable or eruptive and calculate their average centroid velocities, which are found to be rarely exceeding 3 km/s. Besides, we give rough estimates of mass and gravitational energy for every detected prominence and use these values to evaluate the total mass and gravitational energy of all simultaneously existing prominences (10$^{12}$-10$^{14}$ kg and 10$^{29}$-10$^{31}$ erg, respectively). Finally, we investigate the form of the gravitational energy spectrum of prominences and derive it to be a power-law of index -1.1$\pm$0.2.
Transverse magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere and may be responsible for generating the Sun's million-degree outer atmosphere. However, direct evidence of the dissipation process and heating from these waves remains elusive. Through advanced numerical simulations combined with appropriate forward modeling of a prominence flux tube, we provide the observational signatures of transverse MHD waves in prominence plasmas. We show that these signatures are characterized by thread-like substructure, strong transverse dynamical coherence, an out-of-phase difference between plane-of-the-sky motions and LOS velocities, and enhanced line broadening and heating around most of the flux tube. A complex combination between resonant absorption and Kelvin-Helmholtz instabilities (KHI) takes place in which the KHI extracts the energy from the resonant layer and dissipates it through vortices and current sheets, which rapidly degenerate into turbulence. An inward enlargement of the boundary is produced in which the turbulent flows conserve the characteristic dynamics from the resonance, therefore guaranteeing detectability of the resonance imprints. We show that the features described in the accompanying paper (Okamoto et al. 2015) through coordinated Hinode and IRIS observations match well the numerical results.
SNIA and CMB datasets have shown both of evolving Newton's "constant" and a signature of the coupling of scalar field to matter. These observations motivate the consideration of the scalar-matter coupling in Jordan frame in the framework of scalar-tensor gravity. So far, majority of the works on the coupling of scalar matter has performed in Einstein frame in the framework of minimally coupled scalar fields. In this work, we generalize the original scalar-tensor theories of gravity introducing a direct coupling of scalar to matter in the Jordan frame. The combined consideration of both evolving Newton's constant and scalar-matter coupling using the recent observation datasets, shows features different from the previous works. The analysis shows a vivid signature of the scalar-matter coupling. The variation rate of the Newton's constant is obtained rather greater than that determined in the previous works.
The simplest standard ray tracing scheme employing the Born and Limber approximations and neglecting lens-lens coupling is used for computing the convergence along individual rays in mock N-body data based on Szekeres swiss cheese and onion models. The results are compared with the exact convergence computed using the exact Szekeres metric combined with the Sachs formalism. A comparison is also made with an extension of the simple ray tracing scheme which includes the Doppler convergence. The exact convergence is reproduced very precisely as the sum of the gravitational and Doppler convergences along rays in LTB swiss cheese and single void models. This is not the case when the swiss cheese models are based on non-symmetric Szekeres models. For such models, there is a significant deviation between the exact and ray traced paths and hence also the corresponding convergences. There is also a clear deviation between the exact and ray tracing results obtained when studying both non-symmetric and spherically symmetric Szekeres onion models.
Following the basic principles of a charge separated pulsar magnetosphere \citep{goldreich1969}, we consider the magnetosphere be stationary in space, instead of corotating, and the electric field be uploaded from the potential distribution on the pulsar surface, set up by the unipolar induction. Consequently, the plasma of the magnetosphere undergoes guiding center drifts of the gyro motion due to the transverse forces to the magnetic field. These forces are the electric force, magnetic gradient force, and field line curvature force. Since these plasma velocities are of drift nature, there is no need to introduce an emf along the field lines, which would contradict the $E_{\parallel}=\vec E\cdot\vec B=0$ plasma condition. Furthermore, there is also no need to introduce the critical field line separating the electron and ion open field lines. We present a self-consistent description where the magnetosphere is described in terms of electric and magnetic fields and also in terms of plasma velocities. The fields and velocities are then connected through the space charge densities self-consistently. We solve the pulsar equation analytically for the fields and construct the standard steady state pulsar magnetosphere. By considering the unipolar induction inside the pulsar and the magnetosphere outside the pulsar as one coupled system, and under the condition that the unipolar pumping rate exceeds the Poynting flux in the open field lines, plasma pressure can build up in the magnetosphere, in particular in the closed region. This could cause a periodic openning up of the closed region, leading to a pulsating magnetosphere, which could be an alternative for pulsar beacons. The closed region can also be openned periodically by the build-up of toroidal magnetic field through a positive feedback cycle.
Massive rotating single stars with an initial metal composition appropriate for the dwarf galaxy I Zw 18 ([Fe/H]=$-$1.7) are modelled during hydrogen burning for initial masses of 9-300 M$_{\odot}$ and rotational velocities of 0-900 km s$^{-1}$. Internal mixing processes in these models were calibrated based on an observed sample of OB-type stars in the Magellanic Clouds. Even moderately fast rotators, which may be abundant at this metallicity, are found to undergo efficient mixing induced by rotation resulting in quasi chemically-homogeneous evolution. These homogeneously-evolving models reach effective temperatures of up to 90 kK during core hydrogen burning. This, together with their moderate mass-loss rates, make them Transparent Wind Ultraviolet INtense stars (TWUIN star), and their expected numbers might explain the observed HeII ionizing photon flux in I Zw 18 and other low-metallicity HeII galaxies. Our slowly rotating stars above $\sim$80 M$_{\odot}$ evolve into late B- to M-type supergiants during core hydrogen burning, with visual magnitudes up to 19$^{\mathrm{m}}$ at the distance of I Zw 18. Both types of stars, TWUIN stars and luminous late-type supergiants, are only predicted at low metallicity. Massive star evolution at low metallicity is shown to differ qualitatively from that in metal-rich environments. Our grid can be used to interpret observations of local star-forming dwarf galaxies and high-redshift galaxies, as well as the metal-poor components of our Milky Way and its globular clusters.
The energy reconstruction of extensive air showers measured with the LOFAR Radboud Air Shower Array (LORA) is presented in detail. LORA is a particle detector array located in the center of the LOFAR radio telescope in the Netherlands. The aim of this work is to provide an accurate and independent energy measurement for the air showers measured through their radio signal with the LOFAR antennas. The energy reconstruction is performed using a parameterized relation between the measured shower size and the cosmic-ray energy obtained from air shower simulations. In order to illustrate the capabilities of LORA, the all-particle cosmic-ray energy spectrum has been reconstructed, assuming that cosmic rays are composed only of protons or iron nuclei in the energy range between $\sim2\times10^{16}$ and $2\times10^{18}$ eV. The results are compatible with literature values and a changing mass composition in the transition region from a galactic to an extragalactic origin of cosmic rays.
Blazars have been suggested as possible neutrino sources long before the recent IceCube discovery of high-energy neutrinos. We re-examine this possibility within a new framework built upon the blazar simplified view and a self-consistent modelling of neutrino emission from individual sources. The former is a recently proposed paradigm that explains the diverse statistical properties of blazars adopting minimal assumptions on blazars' physical and geometrical properties. This view, tested through detailed Monte Carlo simulations, reproduces the main features of radio, X-ray, and gamma-ray blazar surveys and also the extragalactic gamma-ray background at energies > 10 GeV. Here we add a hadronic component for neutrino production and estimate the neutrino emission from BL Lacs as a class, "calibrated" by fitting the spectral energy distributions of a preselected sample of BL Lac objects and their (putative) neutrino spectra. Unlike all previous papers on this topic, the neutrino background is then derived by summing up at a given energy the fluxes of each BL Lac in the simulation, all characterised by their own redshift, synchrotron peak energy, gamma-ray flux, etc. Our main result is that BL Lacs as a class can explain the neutrino background seen by IceCube above ~ 0.5 PeV while they only contribute ~ 10% at lower energies, leaving room to some other population(s)/physical mechanism. However, one cannot also exclude the possibility that individual BL Lacs still make a contribution at the ~ 20% level to the IceCube low-energy events. Our scenario makes specific predictions testable in the next few years.
This paper presents a model for the dark halos of galaxy clusters in the framework of Weyl geometric scalar tensor theory with a MOND-like approximation in the weak field static limit. The basics of this approach are introduced in the first part of the paper; then a three component halo model is derived (without presupposing prior knowledge of Weyl geometric gravity). The cluster halo is constituted by the scalar field energy and the phantom energy of the gravitational structure, thus transparent rather than "dark". It is completely determined by the baryonic mass distribution of hot gas and stars. The model is tested against recent observational data for 19 clusters. The total mass of Coma and 15 other clusters is correctly predicted on the basis of data on baryonic mass in the bounds of the error intervals (1 sigma); one cluster lies in the 2 sigma interval, two more in 3 sigma.
In this paper we consider the issue of paradigm evaluation by applying Bayes' theorem along the following nested chain of progressively more complex structures: i) parameter estimation (within a model), ii) model selection and comparison (within a paradigm), iii) paradigm evaluation. In such a chain the Bayesian evidence works both as the posterior's normalization at a given level and as the likelihood function at the next level up. Whilst raising no objections to the standard application of the procedure at the two lowest levels, we argue that it should receive an essential modification when evaluating paradigms, in view of the issue of falsifiability. By considering toy models we illustrate how unfalsifiable models and paradigms are always favoured by the Bayes factor. We argue that the evidence for a paradigm should not only be high for a given dataset, but exceptional with respect to what it would have been, had the data been different. We propose a measure of falsifiability (which we term predictivity), and a prior to be incorporated into the Bayesian framework, suitably penalising unfalsifiability. We apply this measure to inflation seen as a whole, and to a scenario where a specific inflationary model is hypothetically deemed as the only one viable as a result of information alien to cosmology (e.g. Solar System gravity experiments, or particle physics input). We conclude that cosmic inflation is currently difficult to falsify and thus to be construed as a scientific theory, but that this could change were external/additional information to cosmology to select one of its many models. We also compare this state of affairs to bimetric varying speed of light cosmology.
We generalize ERA method of PSF correction for more realistic situations. The method re-smears the observed galaxy image(galaxy image smeared by PSF) and PSF image by an appropriate function called Re-Smearing Function(RSF) to make new images which have the same ellipticity with the lensed (before smeared by PSF) galaxy image. It has been shown that the method avoids a systematic error arising from an approximation in the usual PSF correction in moment method such as KSB for simple PSF shape. By adopting an idealized PSF we generalize ERA method applicable for arbitrary PSF. This is confirmed with simulated complex PSF shapes. We also consider the effect of pixel noise and found that the effect causes systematic overestimation.
The rate of tidal evolution of asteroidal binaries is defined by the dynamical Love numbers divided by quality factors. Common is the (often illegitimate) approximation of the dynamical Love numbers with their static counterparts. As the static Love numbers are, approximately, proportional to the inverse rigidity, this renders a popular fallacy that the tidal evolution rate is determined by the product of the rigidity by the quality factor: $\,k_l/Q\propto 1/(\mu Q)\,$. In reality, the dynamical Love numbers depend on the tidal frequency and all rheological parameters of the tidally perturbed body (not just rigidity). We demonstrate that in asteroidal binaries the rigidity of their components plays virtually no role in tidal friction and tidal lagging, and thereby has almost no influence on the intensity of tidal interactions (tidal torques, tidal dissipation, tidally induced changes of the orbit). A key quantity that determines the tidal evolution is a product of the effective viscosity $\,\eta\,$ by the tidal frequency $\,\chi\,$. The functional form of the torque's dependence on this product depends on who wins in the competition between viscosity and self-gravitation. Hence a quantitative criterion, to distinguish between two regimes. For higher values of $\,\eta\chi\,$ we get $\,k_l/Q\propto 1/(\eta\chi)\;$; $\,$while for lower values we obtain $\,k_l/Q\propto \eta\chi\,$. Our study rests on an assumption that asteroids can be treated as Maxwell bodies. Applicable to rigid rocks at low frequencies, this approximation is used here also for rubble piles, due to the lack of a better model. In the future, as we learn more about mechanics of granular mixtures in a weak gravity field, we may have to amend the tidal theory with other rheological parameters, ones that do not show up in the description of viscoelastic bodies.
We study tachyon inflation within the $N$--formalism, which takes a prescription for the small Hubble flow slow--roll parameter $\epsilon_1$ as a function of the large number of $e$-folds $N$. This leads to a classification of models through their behaviour at large-$N$. In addition to the perturbative $N$ class, we introduce the polynomial and exponential classes for the $\epsilon_1$ parameter. With this formalism we reconstruct a large number of potentials used previously in the literature for tachyon field inflation. We also obtain new families of potentials form the polynomial class. We characterize the realizations of Tachyon inflation by computing the usual cosmological observables at first and second order in the Hubble flow slow--roll parameters. This allows us to look at observable differences between tachyon and canonical scalar field inflation. The analysis of observables in light of the Planck 2015 data shows the viability of some of these models, mostly for certain realization of the polynomial and exponential classes.
We present a spectral analysis of the UV-bright star vZ 1128 in M3 based on observations with the Far Ultraviolet Spectroscopic Explorer (FUSE), the Space Telescope Imaging Spectrograph (STIS), and the Keck HIRES echelle spectrograph. By fitting the H I, He I, and He II lines in the Keck spectrum with non-LTE H-He models, we obtain Teff = 36,600 K, log g = 3.95, and log N(He)/N(H) = -0.84. The star's FUSE and STIS spectra show photospheric absorption from C, N, O, Al, Si, P, S, Fe, and Ni. No stellar features from elements beyond the iron peak are observed. Both components of the N V 1240 doublet exhibit P~Cygni profiles, indicating a weak stellar wind, but no other wind features are seen. The star's photospheric abundances appear to have changed little since it left the red giant branch (RGB). Its C, N, O, Al, Si, Fe, and Ni abundances are consistent with published values for the red-giant stars in M3, and the relative abundances of C, N, and O follow the trends seen on the cluster RGB. In particular, its low C abundance suggests that the star left the asymptotic giant branch before the onset of third dredge-up.
The B-mode polarization of the cosmic microwave background on large scales has been considered as a probe of gravitational waves from the cosmic inflation. Ongoing and future experiments will, however, suffer from contamination due to the B-modes of non-primordial origins, one of which is the lensing induced B-mode polarization. Subtraction of the lensing B-modes, usually referred to as delensing, will be required for further improvement of detection sensitivity of the gravitational waves. In such experiments, knowledge of statistical properties of the B-modes after delensing is indispensable to likelihood analysis particularly because the lensing B-modes are known to be non-Gaussian. In this paper, we study non-Gaussian structure of the delensed B-modes on large scales, comparing them with those of the lensing B-modes. In particular, we investigate the power spectrum correlation matrix and the probability distribution function (PDF) of the power spectrum amplitude. Assuming an experiment in which the quadratic delensing is an almost optimal method, we find that delensing reduces correlations of the lensing B-mode power spectra between different multipoles, and that the PDF of the power spectrum amplitude is well described as a normal distribution function with a variance larger than that in the case of a Gaussian field. These features are well captured by an analytic model based on the 4th order Edgeworth expansion. As a consequence of the non-Gaussianity, the constraint on the tensor-to-scalar ratio after delensing is degraded within approximately a few percent, which depends on the multipole range included in the analysis.
A spacecraft pushed by radiation has the major advantage that the power source is not included in the accelerated mass, making it the preferred technique for reaching relativistic speeds. There are two main technical challenges. First, to get significant acceleration, the sail must be both extremely light weight and capable of operating at high intensities of the incident beam and the resulting high temperatures. Second, the transmitter must emit high power beams through huge apertures, many kilometers in diameter, in order to focus radiation on the sail across the long distances needed to achieve high final speeds. Existing proposals for the sail use carbon or aluminum films, but aluminum is limited by a low melting point, and both have low mechanical strength requiring either a distributed payload or complex rigging. We propose here a graphene sail, which offers high absorption per unit weight, high temperature operation, and the mechanical strength to support simple rigging to a lumped mass payload. For the transmitter, existing proposals use a compact high power source, and focus the energy with a large (hundreds to thousands of km) space-based lens. Existing optical drive proposals also require launch from the outer solar system, have severe pointing restrictions, and require difficult maneuvering of the beam source. Instead we propose an active Fresnel lens, allowing smaller apertures of less mass, easier pointing with fewer restrictions, and probe launch from the inner solar system. The technologies for both the sail and the transmitter are already under development for other reasons. Worked examples, physically smaller and less massive than those suggested so far, range from a 1kg payload launched to 10\% of the speed of light by a transmitter only 25 times the mass of ISS, to a larger system that can launch a 1000 kg payload to 50\% of the speed of light.
Primordial black holes are studied in the Bose-Einstein condensate description of space-time. The question of baryon-number conservation is investigated with emphasis on possible formation of bound states of the system's remaining captured baryons. This leads to distinct predictions for both the formation time, which for the naively natural assumptions is shown to lie between $10^{-12}\.\srm$ to $10^{12}\.\srm$ after Big Bang, as well as for the remnant's mass, yielding approximately $3 \cdot 10^{23}\.{\rm kg}$ in the same scheme. The consequences for astrophysically formed black holes are also considered.
Using limits on photon flux from Dwarf Spheroidal galaxies, we place bounds on the parameter space of models in which Dark Matter annihilates into multiple final state particle pair channels. We derive constraints on effective operator models with Dark Matter couplings to third generation fermions and to pairs of Standard Model vector bosons. We present limits in various slices of model parameter space along with estimations of the region of maximal validity of the effective operator approach for indirect detection. We visualize our bounds for models with multiple final state annihilations by projecting parameter space constraints onto triangles, a technique familiar from collider physics; and we compare our bounds to collider limits on equivalent models.
In the early seventies, Alan Sandage defined cosmology as the search for two
numbers: Hubble parameter ${{H}_{0}}$ and deceleration parameter ${{q}_{0}}$.
The first of the two basic cosmological parameters (the Hubble parameter)
describes the linear part of the time dependence of the scale factor. Treating
the Universe as a dynamical system it is natural to assume that it is
non-linear: indeed, linearity is nothing more than approximation, while
non-linearity represents the generic case. It is evident that future models of
the Universe must take into account different aspects of its evolution. As soon
as the scale factor is the only dynamical variable, the quantities which
determine its time dependence must be essentially present in all aspects of the
Universe' evolution. Basic characteristics of the cosmological evolution, both
static and dynamical, can be expressed in terms of the parameters ${{H}_{0}}$
and ${{q}_{0}}$. The very parameters (and higher time derivatives of the scale
factor) enable us to construct model-independent kinematics of the cosmological
expansion.
Time dependence of the scale factor reflects main events in history of the
Universe. Moreover it is the deceleration parameter who dictates the expansion
rate of the Hubble sphere and determines the dynamics of the observable galaxy
number variation: depending on the sign of the deceleration parameter this
number either grows (in the case of decelerated expansion), or we are going to
stay absolutely alone in the cosmos (if the expansion is accelerated).
The intended purpose of the report is reflected in its title --- "Cosmology
in terms of the deceleration parameter". We would like to show that practically
any aspect of the cosmological evolution is tightly bound to the deceleration
parameter. It is the second part of the report. The first part see here
this http URL
The XMASS project is designed for multiple physics goals using highly-purified liquid xenon scintillator in an ultra-low radioactivity environment. As the first stage of the project, the detector with 835 kg of liquid xenon was constructed and is being operated. In this paper, we present results from our commissioning data, current status of the experiment, and a next step of the project.
We explore the systematics of the density dependence of nuclear matter symmetry energy in the ambit of microscopic calculations with various energy density functionals, and find that the symmetry energy from subsaturation density to supra-saturation density can be well determined by three characteristic parameters of the symmetry energy at saturation density $\rho_0 $, i.e., the magnitude $E_{\text{sym}}({\rho_0 })$, the density slope $L$ and the density curvature $K_{\text{sym}}$. This finding opens a new window to constrain the supra-saturation density behavior of the symmetry energy from its (sub-)saturation density behavior. In particular, we obtain $L=46.7 \pm 12.8$ MeV and $K_{\text{sym}}=-166.9 \pm 168.3$ MeV as well as $E_{\text{sym}}({2\rho _{0}}) \approx 40.2 \pm 12.8$ MeV and $L({2\rho _{0}}) \approx 8.9 \pm 108.7$ MeV based on the present knowledge of $E_{\text{sym}}({\rho_{0}}) = 32.5 \pm 0.5$ MeV, $E_{\text{sym}}({\rho_c}) = 26.65 \pm 0.2$ MeV and $L({\rho_c}) = 46.0 \pm 4.5$ MeV at $\rho_{\rm{c}}= 0.11$ fm$^{-3}$ extracted from nuclear mass and the neutron skin thickness of Sn isotopes. Our results indicate that the symmetry energy cannot be stiffer than a linear density dependence.In addition, we also discuss the quark matter symmetry energy since the deconfined quarks could be the right degree of freedom in dense matter at high baryon densities.
Binary black holes on quasicircular orbits with spins aligned with their orbital angular momentum have been testbeds for analytic and numerical relativity for decades, not least because symmetry ensures that such configurations are equilibrium solutions to the spin-precession equations. In this work, we show that these solutions can be unstable when the spin of the higher-mass black hole is aligned with the orbital angular momentum and the spin of the lower-mass black hole is anti-aligned. Spins in these configurations are unstable to precession to large misalignment when the binary separation $r$ is between the values $r_{\rm ud\pm}= (\sqrt{\chi_1} \pm \sqrt{q \chi_2})^4 (1-q)^{-2} M$, where $M$ is the total mass, $q \equiv m_2/m_1$ is the mass ratio, and $\chi_1$ ($\chi_2$) is the dimensionless spin of the more (less) massive black hole. This instability exists for a wide range of spin magnitudes and mass ratios and can occur in the strong-field regime near merger. We describe the origin and nature of the instability using recently developed analytical techniques to characterize fully generic spin precession. This instability provides a channel to circumvent astrophysical spin alignment at large binary separations, allowing significant spin precession prior to merger affecting both gravitational-wave and electromagnetic signatures of stellar-mass and supermassive binary black holes.
We obtain a gauge-invariant relativistic quantum geometry by using a Weylian-like integrable manifold with a geometric scalar field which provides a gauge-invariant relativistic quantum theory in which the algebra of the Weylian-like field depends on observers. An example for a Reisnn\"er-Nordstr\"om black-hole is studied.
We present the simplest nuclear energy density functional (NEDF) to date, determined by only 4 significant phenomenological parameters, yet capable of fitting measured nuclear masses with better accuracy than the Bethe-Weizs\"acker mass formula, while also describing density structures (charge radii, neutron skins etc.) and time-dependent phenomena (induced fission, giant resonances, low energy nuclear collisions, etc.). The 4 significant parameters are necessary to describe bulk nuclear properties (binding energies and charge radii); an additional 2 to 3 parameters have little influence on the bulk nuclear properties, but allow independent control of the density dependence of the symmetry energy and isovector excitations, in particular the Thomas-Reiche-Kuhn sum rule. This Hohenberg-Kohn-style of density functional theory successfully realizes Weizs\"acker's ideas and provides a computationally tractable model for a variety of static nuclear properties and dynamics, from finite nuclei to neutron stars, where it will also provide a new insight into the physics of the r-process, nucleosynthesis, and neutron star crust structure. This new NEDF clearly separates the bulk geometric properties - volume, surface, symmetry, and Coulomb energies which amount to 8MeV per nucleon or up to 2000MeV per nucleus for heavy nuclei - from finer details related to shell effects, pairing, isospin breaking, etc. which contribute at most a few MeV for the entire nucleus. Thus it provides a systematic framework for organizing various contributions to the NEDF. Measured and calculated physical observables - symmetry and saturation properties, the neutron matter equation of state, and the frequency of giant dipole resonances - lead directly to new terms not considered in current NEDF parameterizations.
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We report the discovery of a new young stellar cluster in the outer Galaxy
located at the position of an IRAS PSC source that has been previously
mis-identified as an external galaxy. The cluster is seen in our near-infrared
imaging towards IRAS 04186+5143 and in archive Spitzer images confirming the
young stellar nature of the sources detected. There is also evidence of
sub-clustering seen in the spatial distributions of young stars and of gas and
dust.
Near- and mid-infrared photometry indicates that the stars exhibit colours
compatible with reddening by interstellar and circumstellar dust and are likely
to be low- and intermediate-mass YSOs with a large proportion of Class I YSOs.
Ammonia and CO lines were detected, with the CO emission well centred near
the position of the richest part of the cluster. The velocity of the CO and
NH$_3$ lines indicates that the gas is Galactic and located at a distance of
about 5.5 kpc, in the outer Galaxy.
Herschel data of this region characterise the dust environment of this
molecular cloud core where the young cluster is embedded. We derive masses,
luminosities and temperatures of the molecular clumps where the young stars
reside and discuss their evolutionary stages.
We combined the spectroscopic information from the 3D-HST survey with the PEP/Herschel data to characterize the H\alpha dust attenuation properties of a sample of 79 normal star-forming galaxies at $0.7\leq z\leq1.5$ in the GOODS-S field. The sample was selected in the far-IR, at \lambda=100 and/or 160 \mu m, and only includes galaxies with a secure H\alpha detection (S/N>3). From the low resolution 3D-HST spectra we measured z and F(H\alpha) for the whole sample, rescaling the observed flux by a constant factor of 1.2 to remove the contamination by [NII]. The stellar masses, infrared and UV luminosities were derived from the SEDs by fitting multi-band data from GALEX near-UV to SPIRE500 \mu m. We derived the continuum extinction Estar(B-V) from both the IRX ratio and the UV-slope, and found an excellent agreement among them. Galaxies in the sample have 2.6x10^9$\leq$M*$\leq$3.5x10^11 Msun, intense infrared luminosity (L_IR>1.2x10^10 Lsun), high level of dust obscuration (0.1$\leq$Estar(B-V)$\leq$1.1) and strong H\alpha emission (typical observed fluxes Fobs(H\alpha)$\geq$4.1x10^-17 erg/s/cm2). The nebular extinction was estimated by comparing the observed SFR_H\alpha and the SFR_UV. We obtained f=Estar(B-V)/Eneb(B-V)=0.93$\pm$0.06, i.e. higher than the value measured in the local Universe. This result could be partially due to the adopted selection criteria, picking up the most obscured but also the H\alpha brightest sources. The derived dust correction produces a good agreement between H\alpha and IR+UV SFRs for objects with SFR$\gtrsim$20 Msun/yr and M*$\gtrsim$5x10^10 Msun, while sources with lower SFR and M* seem to require a smaller f-factor (i.e. higher H\alpha extinction correction). Our results then imply that for our sample the nebular and optical-UV extinctions are comparable and suggest that the f-factor is a function of both M* and SFR, according with previous studies.
We present a new integral-field spectroscopic dataset of the central part of the Orion Nebula (M 42), observed with the MUSE instrument at the ESO VLT. We reduced the data with the public MUSE pipeline. The output products are two FITS cubes with a spatial size of ~5.9'x4.9' (corresponding to ~0.76 pc x 0.63 pc) and a contiguous wavelength coverage of 4595...9366 Angstrom, spatially sampled at 0.2". We provide two versions with a sampling of 1.25 Angstrom and 0.85 Angstrom in dispersion direction. Together with variance cubes these files have a size of 75 and 110 GiB on disk. They represent one of the largest integral field mosaics to date in terms of information content. We make them available for use in the community. To validate this dataset, we compare world coordinates, reconstructed magnitudes, velocities, and absolute and relative emission line fluxes to the literature and find excellent agreement. We derive a two-dimensional map of extinction and present de-reddened flux maps of several individual emission lines and of diagnostic line ratios. We estimate physical properties of the Orion Nebula, using the emission line ratios [N II] and [S III] (for the electron temperature $T_e$) and [S II] and [Cl III] (for the electron density $N_e$), and show two-dimensional images of the velocity measured from several bright emission lines.
We analyze the interaction of a radiation-dominated jet and its surroundings using the equations of radiation hydrodynamics in the viscous limit. In a previous paper we considered the two-stream scenario, which treats the jet and its surroundings as distinct media interacting through radiation viscous forces. Here we present an alternative boundary layer model, known as the free-streaming jet model -- where a narrow stream of fluid is injected into a static medium -- and present solutions where the flow is ultrarelativistic and the boundary layer is dominated by radiation. It is shown that these jets entrain material from their surroundings and that their cores have a lower density of scatterers and a harder spectrum of photons, leading to observational consequences for lines of sight that look "down the barrel of the jet." These jetted outflow models may be applicable to the jets produced during long gamma-ray bursts and super-Eddington phases of tidal disruption events.
We present photometric observations from the {\it Stratospheric Observatory for Infrared Astronomy (SOFIA)} at 11.1 $\mu$m of the Type IIn supernova (SN IIn) 2010jl. The SN is undetected by {\it SOFIA}, but the upper limits obtained, combined with new and archival detections from {\it Spitzer} at 3.6 \& 4.5 $\mu$m allow us to characterize the composition of the dust present. Dust in other Type IIn SNe has been shown in previous works to reside in a circumstellar shell of material ejected by the progenitor system in the few millenia prior to explosion. Our model fits show that the dust in the system shows no evidence for the strong, ubiquitous 9.7 $\mu$m feature from silicate dust, suggesting the presence of carbonaceous grains. The observations are best fit with 0.01-0.05 $\msun$ of carbonaceous dust radiating at a temperature of $\sim 550-620$ K. The dust composition may reveal clues concerning the nature of the progenitor system, which remains ambiguous for this subclass. Most of the single star progenitor systems proposed for SNe IIn, such as luminous blue variables, red supergiants, yellow hypergiants, and B[e] stars, all clearly show silicate dust in their pre-SN outflows. However, this post-SN result is consistent with the small sample of SNe IIn with mid-IR observations, none of which show signs of emission from silicate dust in their IR spectra.
We present SIGAME (SImulator of GAlaxy Molecular Emission), a new numerical code designed to simulate the 12CO rotational line emission spectrum of galaxies. Using sub-grid physics recipes to post-process the outputs of smoothed particle hydrodynamics (SPH) simulations, a molecular gas phase is condensed out of the initial hot and partly ionised SPH gas and distributed in Giant Molecular Cloud (GMCs). The GMCs are subjected to far-UV radiation fields and cosmic ray ionisation rates which scale with the local star formation rate volume density, thereby ensuring that the thermal state of the gas is directly coupled to the in situ star formation conditions. Level populations as well as line radiative transport of the CO rotational lines are solved for with the 3-D radiative transfer code LIME. We have applied SIGAME to cosmological SPH simulations of three disk galaxies at z=2 with stellar masses in the range ~(0.5-2)x10^11 Msun and star formation rates ~40-140 Msun/yr, for which we predict a low-excitation gas with CO intensity peaks at the CO J=3-2 transition and total CO(3-2) luminosities within the range of observations of corresponding star-forming galaxies at z~1-2.5. Global CO-H2 conversion factors (alpha_CO) range from 1.4 to 1.6 Msun*pc^2/(K*km/s), i.e. about a third of the Galactic value. On resolved scales, the model galaxies display an increase in CO(J-(J-1))/CO(1-0) brightness temperature line ratios at J>=3, but a decrease in alpha_CO towards the central regions, in agreement with observations of nearby galaxies. Adopting a steeper GMC radial density profile or a more shallow mass spectrum leads to increased alpha_CO factors, though still below the Galactic value. The inclusion of high pressure (P_ext/k_B>10^4K/cm^3) environments descreases line ratios at high-J.
We present a multi-wavelength analysis of the history of star formation in the W3 complex. Using deep, near-infrared ground-based images, combined with images obtained with Spitzer and Chandra observatories, we identified and classified young embedded sources. We identified the principal clusters in the complex, and determined their structure and extension. We constructed extinction-limited samples for five principal clusters, and constructed K-band luminosity functions (KLF) that we compare with those of artificial clusters with varying ages. This analysis provided mean ages and possible age spreads for the clusters. We found that IC 1795, the centermost cluster of the complex, still hosts a large fraction of young sources with circumstellar disks. This indicates that star formation was active in IC 1795 as recently as 2 Myr ago, simultaneous to the star forming activity in the flanking embedded clusters, W3-Main and W3(OH). A comparison with carbon monoxide emission maps indicates strong velocity gradients in the gas clumps hosting W3-Main and W3(OH) and show small receding clumps of gas at IC 1795, suggestive of rapid gas removal (faster than the T Tauri timescale) in the cluster forming regions. We discuss one possible scenario for the progression of cluster formation in the W3 complex. We propose that early processes of gas collapse in the main structure of the complex could have defined the progression of cluster formation across the complex with relatively small age differences from one group to another. However, triggering effects could act as catalysts for enhanced efficiency of formation at a local level, in agreement with previous studies.
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a multipurpose high-contrast imaging platform designed for the discovery and detailed characterization of exoplanetary systems and serves as a testbed for high-contrast imaging technologies for ELTs. It is a multi-band instrument which makes use of light from 600 to 2500nm allowing for coronagraphic direct exoplanet imaging of the inner 3 lambda/D from the stellar host. Wavefront sensing and control are key to the operation of SCExAO. A partial correction of low-order modes is provided by Subaru's facility adaptive optics system with the final correction, including high-order modes, implemented downstream by a combination of a visible pyramid wavefront sensor and a 2000-element deformable mirror. The well corrected NIR (y-K bands) wavefronts can then be injected into any of the available coronagraphs, including but not limited to the phase induced amplitude apodization and the vector vortex coronagraphs, both of which offer an inner working angle as low as 1 lambda/D. Non-common path, low-order aberrations are sensed with a coronagraphic low-order wavefront sensor in the infrared (IR). Low noise, high frame rate, NIR detectors allow for active speckle nulling and coherent differential imaging, while the HAWAII 2RG detector in the HiCIAO imager and/or the CHARIS integral field spectrograph (from mid 2016) can take deeper exposures and/or perform angular, spectral and polarimetric differential imaging. Science in the visible is provided by two interferometric modules: VAMPIRES and FIRST, which enable sub-diffraction limited imaging in the visible region with polarimetric and spectroscopic capabilities respectively. We describe the instrument in detail and present preliminary results both on-sky and in the laboratory.
In the current era of large spectroscopic surveys of the Milky Way, reference stars for calibrating astrophysical parameters and chemical abundances are of paramount importance. We determine elemental abundances of Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Co and Ni for our predefined set of Gaia FGK benchmark stars. By analysing high-resolution and high-signal to noise spectra taken from several archive datasets, we combined results of eight different methods to determine abundances on a line-by-line basis. We perform a detailed homogeneous analysis of the systematic uncertainties, such as differential versus absolute abundance analysis, as well as we assess errors due to NLTE and the stellar parameters in our final abundances. Our results are provided by listing final abundances and the different sources of uncertainties, as well as line-by-line and method-by-method abundances. The Gaia FGK benchmark stars atmospheric parameters are already being widely used for calibration of several pipelines applied to different surveys. With the added reference abundances of 10 elements this set is very suitable to calibrate the chemical abundances obtained by these pipelines.
MUSE, a giant integral field spectrograph, is about to become the newest facility instrument at the VLT. It will see first light in February 2014. Here, we summarize the properties of the instrument as built and outline functionality of the data reduction system, that transforms the raw data that gets recorded separately in 24 IFUs by 4k CCDs, into a fully calibrated, scientifically usable data cube. We then describe recent work regarding geometrical calibration of the instrument and testing of the processing pipeline, before concluding with results of the Preliminary Acceptance in Europe and an outlook to the on-sky commissioning.
We analyse whether a stellar atmosphere model computed with the code CMFGEN provides an optimal description of the stellar observations of WR 136 and simultaneously reproduces the nebular observations of NGC 6888, such as the ionization degree, which is modelled with the pyCloudy code. All the observational material available (far and near UV and optical spectra) were used to constrain such models. We found that even when the stellar luminosity and the mass-loss rate were well constrained, the stellar temperature T_* at tau = 20, can be in a range between 70 000 and 110 000 K. When using the nebula as an additional restriction we found that the stellar models with T_* \sim 70 000 K represent the best solution for both, the star and the nebula. Results from the photoionization model show that if we consider a chemically homogeneous nebula, the observed N^+/O^+ ratios found in different nebular zones can be reproduced, therefore it is not necessary to assume a chemical inhomogeneous nebula. Our work shows the importance of calculating coherent models including stellar and nebular constraints. This allowed us to determine, in a consistent way, all the physical parameters of both the star and its associated nebula. The chemical abundances derived are 12 + log(N/H) = 9.95, 12 + log(C/H) = 7.84 and 12 + log(O/H) = 8.76 for the star and 12 + log(N/H) = 8.40, 12 + log(C/H) = 8.86 and 12 + log(O/H) = 8.20. Thus the star and the nebula are largely N- and C- enriched and O-depleted.
We present high-dispersion spectroscopic data of the compact planetary nebula
Vy 1-2, where high expansion velocities up to 100 km/s are found in the Ha, [N
II] and [O III] emission lines. HST images reveal a bipolar structure. Vy 1-2
displays a bright ring-like structure with a size of 2.4"x3.2" and two faint
bipolar lobes in the west-east direction. A faint pair of knots is also found,
located almost symmetrically on opposite sides of the nebula at PA=305 degrees.
Furthermore, deep low-dispersion spectra are also presented and several
emission lines are detected for the first time in this nebula, such as the
doublet [Cl III] 5517, 5537 A, [K IV] 6101 A, C II 6461 A, the doublet C IV
5801, 5812 A. By comparison with the solar abundances, we find enhanced N,
depleted C and solar O. The central star must have experienced the hot bottom
burning (CN-cycle) during the 2nd dredge-up phase, implying a progenitor star
of higher than 3 solar masses. The very low C/O and N/O abundance ratios
suggest a likely post-common envelope close binary system.
A simple spherically symmetric geometry with either a blackbody or a
H-deficient stellar atmosphere model is not able to reproduce the ionisation
structure of Vy 1-2. The effective temperature and luminosity of its central
star indicate a young nebula located at a distance of ~9.7 kpc with an age of
~3500 years. The detection of stellar emission lines, C II 6461 A, the doublet
C IV {\lambda}{\lambda} 5801, 5812 A and O III 5592 A, emitted from a
H-deficient star, indicates the presence of a late-type Wolf-Rayet or a WEL
type central star.
Radial velocity measurements are presented for 85 late M- and L-type very low mass stars and brown dwarfs obtained with the Magellan Echellette (MagE) spectrograph. Targets primarily have distances within 20 pc of the Sun, with more distant sources selected for their unusual spectral energy distributions. We achieved precisions of 2--3 km/s, and combined these with astrometric and spectrophotometric data to calculate $UVW$ velocities. Most are members of the thin disk of the Galaxy, and velocity dispersions indicate a mean age of 5.2$\pm$0.2 Gyr for sources within 20 pc. We find significantly different kinematic ages between late-M dwarfs (4.0$\pm$0.2 Gyr) and L dwarfs (6.5$\pm$0.4 Gyr) in our sample that are contrary to predictions from prior simulations. This difference appears to be driven by a dispersed population of unusually blue L dwarfs which may be more prevalent in our local volume-limited sample than in deeper magnitude-limited surveys. The L dwarfs exhibit an asymmetric $U$ velocity distribution with a net inward flow, similar to gradients recently detected in local stellar samples. Simulations incorporating brown dwarf evolution and Galactic orbital dynamics are unable to reproduce the velocity asymmetry, suggesting non-axisymmetric perturbations or two distinct L dwarf populations. We also find the L dwarfs to have a kinematic age-activity correlation similar to more massive stars. We identify several sources with low surface gravities, and two new substellar candidate members of nearby young moving groups: the astrometric binary DENIS J08230313$-$4912012AB, a low-probability member of the $\beta$ Pictoris Moving Group; and 2MASS J15104786-2818174, a moderate-probability member of the 30-50 Myr Argus Association.
Hot channels (HCs), high temperature erupting structures in the lower corona of the Sun, have been proposed as a proxy of magnetic flux ropes (MFRs) since their initial discovery. However, it is difficult to make definitive proof given the fact that there is no direct measurement of magnetic field in the corona. An alternative way is to use the magnetic field measurement in the solar wind from in-situ instruments. On 2012 July 12, an HC was observed prior to and during a coronal mass ejection (CME) by the AIA high-temperature images. The HC is invisible in the EUVI low-temperature images, which only show the cooler leading front (LF). However, both the LF and an ejecta can be observed in the coronagraphic images. These are consistent with the high temperature and high density of the HC and support that the ejecta is the erupted HC. In the meanwhile, the associated CME shock was identified ahead of the ejecta and the sheath through the COR2 images, and the corresponding ICME was detected by \textit{ACE}, showing the shock, sheath and magnetic cloud (MC) sequentially, which agrees with the coronagraphic observations. Further, the MC contained a low-ionization-state center and a high-ionization-state shell, consistent with the pre-existing HC observation and its growth through magnetic reconnection. All of these observations support that the MC detected near the Earth is the counterpart of the erupted HC in the corona for this event. Therefore, our study provides strong observational evidence of the HC as an MFR.
The field of Galactic Archaeology aims to understand the origins and evolution of the stellar populations in the Milky Way, as a way to understand galaxy formation and evolution in general. The GALAH (Galactic Archaeology with HERMES) Survey is an ambitious Australian-led project to explore the Galactic history of star formation, chemical evolution, minor mergers and stellar migration. GALAH is using the HERMES spectrograph, a novel, highly multiplexed, four-channel high-resolution optical spectrograph, to collect high-quality R ~ 28,000 spectra for one million stars in the Milky Way. From these data we will determine stellar parameters, radial velocities and abundances for up to 29 elements per star, and carry out a thorough chemical tagging study of the nearby Galaxy. There are clear complementarities between GALAH and other ongoing and planned Galactic Archaeology surveys, and also with ancillary stellar data collected by of major cosmological surveys. Combined, these data sets will provide a revolutionary view of the structure and history of the Milky Way.
We study the environmental dependence of the strength of polycyclic aromatic hydrocarbon (PAH) emission by AKARI observations of RX J0152.7-1357, a galaxy cluster at z=0.84. PAH emission reflects the physical conditions of galaxies and dominates 8 um luminosity (L8), which can directly be measured with the L15 band of AKARI. L8 to infrared luminosity (LIR) ratio is used as a tracer of the PAH strength. Both photometric and spectroscopic redshifts are applied to identify the cluster members. The L15-band-detected galaxies tend to reside in the outskirt of the cluster and have optically green colour, R-z'~ 1.2. We find no clear difference of the L8/LIR behaviour of galaxies in field and cluster environment. The L8/LIR of cluster galaxies decreases with specific-star-formation rate divided by that of main-sequence galaxies, and with LIR, consistent with the results for field galaxies. The relation between L8/LIR and LIR is between those at z=0 and z=2 in the literature. Our data also shows that starburst galaxies, which have lower L8/LIR than main-sequence, are located only in the outskirt of the cluster. All these findings extend previous studies, indicating that environment affects only the fraction of galaxy types and does not affect the L8/LIR behaviour of star-forming galaxies.
In the absence of CMB precision measurements, a Taylor expansion has often been invoked to parametrize the Hubble flow function during inflation. The standard "horizon flow" procedure implicitly relies on this assumption. However, the recent Planck results indicate a strong preference for plateau inflation, which suggests the use of Pad\'e approximants instead. We propose a novel method that provides analytic solutions of the flow equations for a given parametrization of the Hubble function. This method is illustrated in the Taylor and Pad\'e cases, for low order expansions. We then present the results of a full numerical treatment scanning larger order expansions, and compare these parametrizations in terms of convergence, prior dependence, predictivity and compatibility with the data. Finally, we highlight the implications for potential reconstruction methods.
We searched for ultra-high energy (UHE) neutrinos from Gamma-Ray Bursts (GRBs) with the Askaryan Radio Array (ARA) Testbed station's 2011-2012 data set. Among 589 GRBs monitored by the Gamma Ray Coordinate Network (GCN) catalog from Jan. 2011 to Dec. 2012 over the entire sky, 57 GRBs were selected for analysis. These GRBs were chosen because they occurred during a period of low anthropogenic background and high stability of the station and fell within our geometric acceptance. We searched for UHE neutrinos from 57 GRBs and observed 0 events, which is consistent with 0.11 expected background events. With this result, we set the limits on the UHE GRB neutrino fluence and quasi-diffuse flux from $10^{16}$ to $10^{19}$~eV. This is the first limit on the UHE GRB neutrino quasi-diffuse flux at energies above $10^{16}$~eV.
The strong variability of blazars can be characterized by power spectral densities (PSDs) and Fourier frequency-dependent time lags. In previous work, we created a new theoretical formalism for describing the PSDs and time lags produced via a combination of stochastic particle injection and emission via the synchrotron, synchrotron self-Compton, and external Compton (EC) processes. This formalism used the Thomson cross section and simple $\delta$-function approximations to model the synchrotron and Compton emissivities. Here we expand upon this work, using the full Compton cross section and detailed and accurate emissivities. Our results indicate good agreement between the PSDs computed using the $\delta$-function approximations and those computed using the accurate expressions, provided the observed photons are produced primarily by electrons with energies exceeding the lower limit of the injected particle population. Breaks are found in the PSDs at frequencies corresponding to the cooling timescales of the electrons primarily responsible for the observed emission, and the associated time lags are related to the difference in electron cooling timescales between the two energy channels, as expected. If the electron cooling timescales can be determined from the observed time lags and/or the observed EC PSDs, then one could in principle use the method developed here to determine the energy of the external seed photon source for EC, which is an important unsolved problem in blazar physics.
We combine observations of the Coronal Multi-channel Polarimeter (CoMP) and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) to study the characteristic properties of (propagating) Alfvenic motions and quasi-periodic intensity disturbances in polar plumes. This unique combination of instruments highlights the physical richness of the processes taking place at the base of the (fast) solar wind. The (parallel) intensity perturbations with intensity enhancements around 1% have an apparent speed of 120 km/s (in both the 171A and 193A passbands) and a periodicity of 15 minutes, while the (perpendicular) Alfvenic wave motions have a velocity amplitude of 0.5 km/s, a phase speed of 830 km/s, and a shorter period of 5 minutes on the same structures. These observations illustrate a scenario where the excited Alfvenic motions are propagating along an inhomogeneously loaded magnetic field structure such that the combination could be a potential progenitor of the magnetohydrodynamic turbulence required to accelerate the fast solar wind.
Sco X-1 is the archetypal low mass X-ray binary (LMXB) and the brightest persistent extra-solar X-ray source in the sky. It was included in the K2 Campaign 2 field and was observed continuously for 71 days with 1 minute time resolution. In this paper we report these results and underline the potential of K2 for similar observations of other accreting compact binaries. We reconfirm that Sco X-1 shows a bimodal distribution of optical "high" and "low" states and rapid transitions between them on timescales less than 3 hours (or 0.15 orbits). We also find evidence that this behaviour has a typical systemic timescale of 4.8 days, which we interpret as a possible disc precession period in the system. Finally, we confirm the complex optical vs. X-ray correlation/anticorrelation behaviour for "high" and "low" optical states respectively.
We analyze HST spectra and Chandra observations of a sample of 21 LINERs, at least 18 of which genuine AGN. We find a correlation between the X-rays and emission lines luminosities, extending over three orders of magnitude and with a dispersion of 0.36 dex; no differences emerge between LINERs with and without broad lines, or between radio-loud and radio-quiet sources. The presence of such a strong correlation is remarkable considering that for half of the sample the X-ray luminosity can not be corrected for local absorption. This connection is readily understood since the X-ray light is associated with the same source producing the ionizing photons at the origin of the line emission. This implies that we have a direct view of the LINERs nuclei in the X-rays: the circumnuclear, high column density structure (the torus) is absent in these sources. Such a conclusion is also supported by mid-infrared data. We suggest that this is due to the general paucity of gas and dust in their nuclear regions that causes also their low rate of accretion and low bolometric luminosity.
Since 1995, more than 1500 exoplanets have been discovered around a large diversity of host stars (from M- to A-type stars). Tidal dissipation in stellar convective envelopes is a key actor that shapes the orbital architecture of short-period systems. Our objective is to understand and evaluate how tidal dissipation in the convective envelope of low-mass stars (from M to F types) depends on their mass, evolutionary stage and rotation. Using a simplified two-layer assumption, we compute analytically the frequency-averaged tidal dissipation in their convective envelope. This dissipation is due to the conversion into heat of the kinetic energy of tidal non wave-like/equilibrium flow and inertial waves because of the viscous friction applied by turbulent convection. Using grids of stellar models allows us to study the variation of the dissipation as a function of stellar mass and age on the Pre-Main-Sequence and on the Main-Sequence for stars with masses spanning from $0.4$ to $1.4M_{\odot}$. As shown by observations, tidal dissipation in stars varies over several orders of magnitude as a function of stellar mass, age and rotation. During their Pre-Main-Sequence, all low-mass stars have an increase of the frequency-averaged tidal dissipation for a fixed angular velocity in their convective envelope until they reach a critical aspect and mass ratios. Next, the dissipation evolves on the Main Sequence to an asymptotic value that becomes maximum for $0.6M_{\odot}$ K-type stars and that decreases by several orders of magnitude with increasing stellar mass. Finally, the rotational evolution of low-mass stars strengthens the importance of tidal dissipation during the Pre-Main-Sequence for star-planet and multiple star systems.
Context. Mass loss is an important property in evolution models of massive
stars. As up to 90% of the massive stars have a visual or spectroscopic
companion and many of them exhibit mass exchange, mass-loss rates can be
acquired through the period study of massive binaries.
Aims. Using our own photometric observations as well as archival data, we
look for variations in orbital periods of seven massive eclipsing binary
systems in the Cygnus OB2 association and estimate their mass-loss rates and
stellar parameters.
Methods. We use a Bayesian parameter estimation method to simultaneously fit
the period and period change to all available data and a stellar modelling tool
to model the binary parameters from photometric and radial-velocity data.
Results. Four out of the seven selected binaries show non-zero period change
values at two-sigma confidence level. We also report for the first time the
eclipsing nature of a star MT059.
In four-particle scattering processes with transfer of mass, unlike mergers in which mass can only increase, mass of the most massive galaxies may be reduced. Elementary model describing such process is considered. In this way, it is supposed to explain observed phenomenon of downsizing when increasing of characteristic mass the heaviest galaxies over cosmological time replaces by its reduction.
The atmosphere of a transiting planet shields the stellar radiation providing us with a powerful method to estimate its size and density. In particular, because of their high ionization energy, atoms with high atomic number (Z) absorb short-wavelength radiation in the upper atmosphere, undetectable with observations in visible light. One implication is that the planet should appear larger during a primary transit observed in high energy bands than in the optical band. The last Venus transit in 2012 offered a unique opportunity to study this effect. The transit has been monitored by solar space observations from Hinode and Solar Dynamics Observatory (SDO). We measure the radius of Venus during the transit in three different bands with subpixel accuracy: optical (4500A), UV (1600A, 1700A), Extreme UltraViolet (EUV, 171-335A) and soft X-rays (about 10A). We find that, while the Venus optical radius is about 80 km larger than the solid body radius (the expected opacity mainly due to clouds and haze), the radius increases further by more than 70 km in the EUV and soft X-rays. These measurements mark the densest ion layers of Venus' ionosphere, providing information about the column density of CO2 and CO. They are useful for planning missions in situ to estimate the dynamical pressure from the environment, and can be employed as a benchmark case for observations with future missions, such as the ESA Athena, which will be sensitive enough to detect transits of exoplanets in high-energy bands.
Cosmic voids may be very useful in testing fundamental aspects of cosmology. Yet observationally voids can only be seen as regions with a deficit of bright galaxies. To study how biased galaxies trace matter underdensities and how the properties of voids depend on those of the tracer galaxy population, we use a $\Lambda$CDM N-body simulation populated with mock galaxies based on the halo occupation distribution (HOD) model. We identify voids in these mocks using the ZOBOV void finder and measure their abundances, sizes, tracer densities, and dark matter content. To separate the effects of bias from those of sampling density, we do the same for voids traced by randomly down-sampled subsets of the dark matter particles in the simulation. We find that galaxy bias reduces the total number of voids by $\sim50\%$ and can dramatically change their size distribution. The matter content of voids in biased and unbiased tracers also differs. Using simulations to accurately estimate the cosmological constraints that can be obtained from voids therefore requires the use of realistic mock galaxy catalogues. We discuss aspects of the dark matter content of voids that can be deduced from properties of the tracer distribution, such as the void size and the minimum tracer number density. In particular we consider the compensation of the total mass deficit in voids and find that the distinction between over- and under-compensated voids is not a function of void size alone, as has previously been suggested. However, we find a simple linear relationship between the average density of tracers in the void and the total mass compensation on much larger scales. The existence of this linear relationship holds independent of the bias and sampling density of the tracers. This provides a universal tool to classify void environments and will be important for the use of voids in observational cosmology.
We present the Micro-channel X-ray Telescope (MXT), a new narrow-field (about 1{\deg}) telescope that will be flying on the Sino-French SVOM mission dedicated to Gamma-Ray Burst science, scheduled for launch in 2021. MXT is based on square micro pore optics (MPOs), coupled with a low noise CCD. The optics are based on a "Lobster Eye" design, while the CCD is a focal plane detector similar to the type developed for the seven eROSITA telescopes. MXT is a compact and light (<35 kg) telescope with a 1 m focal length, and it will provide an effective area of about 45 cmsq on axis at 1 keV. The MXT PSF is expected to be better than 4.2 arc min (FWHM) ensuring a localization accuracy of the afterglows of the SVOM GRBs to better than 1 arc min (90\% c.l. with no systematics) provided MXT data are collected within 5 minutes after the trigger. The MXT sensitivity will be adequate to detect the afterglows for almost all the SVOM GRBs as well as to perform observations of non-GRB astrophysical objects. These performances are fully adapted to the SVOM science goals, and prove that small and light telescopes can be used for future small X-ray missions.
We measure the location and energetics of a SIV BALQSO outflow. This ouflow has a velocity of 10,800 km s$^{-1}$ and a kinetic luminosity of $10^{45.7}$ erg s$^{-1}$, which is 5.2% of the Eddington luminosity of the quasar. From collisional excitation models of the observed SIV$/$SIV* absorption troughs, we measure a hydrogen number density of $n_\mathrm{\scriptscriptstyle H}=10^{4.3}$ cm$^{-3}$, which allows us to determine that the outflow is located 110 pc from the quasar. Since SIV is formed in the same ionization phase as CIV, our results can be generalized to the ubiquitous CIV BALs. Our accumulated distance measurements suggest that observed BAL outflows are located much farther away from the central source than is generally assumed (0.01-0.1 pc).
Our goal is to identify bipolar HII regions and to understand their morphology, their evolution, and the role they play in the formation of new generations of stars. We use the Spitzer and Herschel Hi-GAL surveys to identify bipolar HII regions. We search for their exciting star(s) and estimate their distances using near-IR data. Dense clumps are detected using Herschel-SPIRE data. MALT90 observations allow us to ascertain their association with the central HII region. We identify Class 0/I YSOs using their Spitzer and Herschel-PACS emissions. These methods will be applied to the entire sample of candidate bipolar HII regions. This paper focuses on two bipolar HII regions, one interesting in terms of its morphology, G319.88$+$00.79, and one in terms of its star formation, G010.32$-$00.15. Their exciting clusters are identified and their photometric distances estimated to be 2.6 kpc and 1.75 kpc, respectively. We suggest that these regions formed in dense and flat structures that contain filaments. They have a central ionized region and ionized lobes perpendicular to the parental cloud. The remains of the parental cloud appear as dense (more than 10^4 per cm^3) and cold (14-17 K) condensations. The dust in the PDR is warm (19-25 K). Dense massive clumps are present around the central ionized region. G010.32-00.14 is especially remarkable because five clumps of several hundred solar masses surround the central HII region; their peak column density is a few 10^23 per cm^2, and the mean density in their central regions reaches several 10^5 per cm^3. Four of them contain at least one massive YSO; these clumps also contain extended green objects and Class II methanol masers. This morphology suggests that the formation of a second generation of massive stars has been triggered by the central bipolar HII region. It occurs in the compressed material of the parental cloud.
We monitored the Dusty S-cluster object (DSO/G2) during its closest approach to the Galactic Center supermassive black hole in 2014 with ESO VLT/SINFONI. We report on our findings, i.e. ionized-hydrogen emission from the DSO that remains spatially compact before and after the peribothron passage. The detection of DSO/G2 object as a compact single-peak emission line source is in contradiction with the original hypothesis of a core-less cloud that is necessarily tidally stretched, hence producing double-peak emission line profile around the pericentre passage. This strengthens the evidence that the DSO/G2 source is a dust-enshrouded young star. The accretion of material from the circumstellar disc onto the stellar surface can contribute significantly to the emission of Br$\gamma$ line as well as to the observed large line width of the order of 10 angstroms.
Context. Heating the solar corona to several million degrees requires the conversion of magnetic energy into thermal energy. In this paper, we investigate whether an unstable magnetic thread within a coronal loop can destabilise a neighbouring magnetic thread. Aims. By running a series of simulations, we aim to understand under what conditions the destabilisation of a single magnetic thread can also trigger a release of energy in a nearby thread. Methods. The 3D magnetohydrodynamics code, Lare3d, is used to simulate the temporal evolution of coronal magnetic fields during a kink instability and the subsequent relaxation process. We assume that a coronal magnetic loop consists of non-potential magnetic threads that are initially in an equilibrium state. Results. The non-linear kink instability in one magnetic thread forms a helical current sheet and initiates magnetic reconnection. The current sheet fragments, and magnetic energy is released throughout that thread. We find that, under certain conditions, this event can destabilise a nearby thread, which is a necessary requirement for starting an avalanche of energy release in magnetic threads. Conclusions. It is possible to initiate an energy release in a nearby, non-potential magnetic thread, because the energy released from one unstable magnetic thread can trigger energy release in nearby threads, provided that the nearby structures are close to marginal stability.
Aims: In a recent study, we derived individual distances for 109 pre-main
sequence stars that define the Lupus kinematic association of young stars.
Here, we use these new distances to derive the masses and ages of Lupus T Tauri
stars with the aim of better constraining the lifetime of their circumstellar
disks.
Methods: Using the photometric and spectroscopic information available in the
literature, we computed the photospheric luminosity of 92 T Tauri stars in the
Lupus association. Then, we estimated their masses and ages from theoretical
evolutionary models. Based on Monte Carlo simulations and statistical tests, we
compare the mass and age distribution of the classical T Tauri stars (CTTS) and
weak-line T Tauri (WTTS) in our sample.
Results: We show that the CTTSs are on average younger than the WTTSs and
that the probability that both T~Tauri subclasses are drawn from the same mass
and age parental distribution is very low. Our results favor the scenario
proposed earlier for the Taurus-Auriga association, where the CTTSs evolve into
WTTSs when their disks are fully accreted by the star. Based on an empirical
disk model, we find that the average disk lifetime for the T Tauri stars in the
Lupus association is $\tau_{d}=3\times10^{6}\,(M_*/M_{\odot})^{0.55}$ yr.
Conclusions: We find evidence that the average lifetime of the circumstellar
disks in the Lupus association is shorter than in the Taurus-Auriga association
and discuss the implications of this result.
We present narrow-band optical and near-IR imaging and optical long-slit spectroscopic observations of Hu1-2, a Galactic planetary nebula (PN) with a pair of [N II]-bright, fast-moving (> 340 km/s) bipolar knots. Intermediate-dispersion spectra are used to derive physical conditions and abundances across the nebula, and high-dispersion spectra to study the spatio-kinematical structure. Generally Hu1-2 has high He/H (~0.14) and N/O ratios (~0.9), typical of Type I PNe. On the other hand, its abundances of O, Ne, S, and Ar are low as compared with the average abundances of Galactic bulge and disc PNe. The position-velocity maps can be generally described as an hour-glass shaped nebula with bipolar expansion, although the morphology and kinematics of the innermost regions cannot be satisfactorily explained with a simple, tilted equatorial torus. The spatio-kinematical study confines the inclination angle of its major axis to be within 10 degrees of the plane of sky. As in the irradiated bow-shocks of IC4634 and NGC7009, there is a clear stratification in the emission peaks of [O III], H_alpha, and [N II] in the northwest (NW) knot of Hu1-2. Fast collimated outflows in PNe exhibit higher excitation than other low-ionization structures. This is particularly the case for the bipolar knots of Hu1-2, with He II emission levels above those of collimated outflows in other Galactic PNe. The excitation of the knots in Hu1-2 is consistent with the combined effects of shocks and UV radiation from the central star. The mechanical energy and luminosity of the knots are similar to those observed in the PNe known to harbor a post-common envelope (post-CE) close binary central star.
We calculate non-axisymmetric oscillations of neutron stars magnetized by purely poloidal magnetic fields. We use polytropes of index $n=1$ and 1.5 as a background model, where we ignore the equilibrium deformation due to the magnetic field. Since separation of variables is not possible for the oscillation of magnetized stars, we employ finite series expansions for the perturbations using spherical harmonic functions. Solving the oscillation equations as the boundary and eigenvalue problem, we find two kinds of discrete magnetic modes, that is, stable (oscillatory) magnetic modes and unstable (monotonically growing) magnetic modes. For isentropic models, the frequency or the growth rate of the magnetic modes is exactly proportional to $B_{\rm S}$, the strength of the field at the surface. The oscillation frequency and the growth rate are affected by the buoyant force in the interior, and the stable stratification tends to stabilize the unstable magnetic modes.
Recently, we have generalized the Bekenstein-Hawking entropy formula for black holes embedded in expanding Friedmann universes. In this letter, we begin the study of this new formula to obtain the first law of thermodynamics for dynamical apparent horizons. In this regard we obtain a generalized expression for the internal energy $U$ together with a distinction between the dynamical temperature $T_D$ of apparent horizons and the related one due to thermodynamics formulas. Remarkable, when the expression for $U$ is applied to the apparent horizon of the universe, we found that this internal energy is a constant of motion. Our calculations thus show that the total energy of our spatially flat universe including the gravitational contribution, when calculated at the apparent horizon, is an universal constant that can be set to zero from simple dimensional considerations. This strongly support the holographic principle.
We explore the systematics of the density dependence of nuclear matter symmetry energy in the ambit of microscopic calculations with various energy density functionals, and find that the symmetry energy from subsaturation density to supra-saturation density can be well determined by three characteristic parameters of the symmetry energy at saturation density $\rho_0 $, i.e., the magnitude $E_{\text{sym}}({\rho_0 })$, the density slope $L$ and the density curvature $K_{\text{sym}}$. This finding opens a new window to constrain the supra-saturation density behavior of the symmetry energy from its (sub-)saturation density behavior. In particular, we obtain $L=46.7 \pm 12.8$ MeV and $K_{\text{sym}}=-166.9 \pm 168.3$ MeV as well as $E_{\text{sym}}({2\rho _{0}}) \approx 40.2 \pm 12.8$ MeV and $L({2\rho _{0}}) \approx 8.9 \pm 108.7$ MeV based on the present knowledge of $E_{\text{sym}}({\rho_{0}}) = 32.5 \pm 0.5$ MeV, $E_{\text{sym}}({\rho_c}) = 26.65 \pm 0.2$ MeV and $L({\rho_c}) = 46.0 \pm 4.5$ MeV at $\rho_{\rm{c}}= 0.11$ fm$^{-3}$ extracted from nuclear mass and the neutron skin thickness of Sn isotopes. Our results indicate that the symmetry energy cannot be stiffer than a linear density dependence.In addition, we also discuss the quark matter symmetry energy since the deconfined quarks could be the right degree of freedom in dense matter at high baryon densities.
In this paper, a modified Eddington-inspired-Born-Infeld (EiBI) theory with a pure trace term $g_{\mu\nu}R$ being added to the determinantal action is analysed from a cosmological point of view. It corresponds to the most general action constructed from a rank two tensor that contains up to first order terms in curvature. This term can equally be seen as a conformal factor multiplying the metric $g_{\mu\nu}$. This very interesting type of amendment has not been considered within the Palatini formalism despite the large amount of works on the Born-Infeld-inspired theory of gravity. This model can provide smooth bouncing solutions which were not allowed in the EiBI model for the same EiBI coupling. Most interestingly, for a radiation filled universe there are some regions of the parameter space that can naturally lead to a de Sitter inflationary stage without the need of any exotic matter field. Finally, in this model we discover a new type of cosmic "quasi-sudden" singularity, where the cosmic time derivative of the Hubble rate becomes very large but finite at a finite cosmic time.
The Peccei-Quinn mechanism suffers from the problem of the isocurvature perturbations. The isocurvature perturbations are suppressed if the Peccei-Quinn breaking scale is large during inflation. The oscillation of the Peccei-Quinn breaking field after inflation, however, leads to the formation of domain walls due to the parametric resonance effect. In this paper, we discuss the evolution of the Peccei-Quinn breaking field after inflation in detail, and propose a model where the parametric resonance is ineffective and hence domain walls are not formed. We also discuss consistency of our model with supersymmetric theory.
We discuss how a cyclic model for the flat universe can be constructively derived from Loop Quantum Gravity. This model has a lower bounce, at small values of the scale factor, which shares many similarities with that of Loop Quantum Cosmology. We find that quantum gravity corrections can be also relevant at energy densities much smaller than the Planckian one and that they can induce an upper bounce at large values of the scale factor.
We discuss initial conditions for the recently proposed Imperfect Dark Matter (Modified Dust). We show that they are adiabatic under fairly moderate assumptions about the cosmological evolution of the Universe at the relevant times.
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After two ALMA observing cycles, only a handful of [CII] $158\,\mu m$ emission line searches in z>6 galaxies have reported a positive detection, questioning the applicability of the local [CII]-SFR relation to high-z systems. To investigate this issue we use the Vallini et al. 2013 (V13) model, based on high-resolution, radiative transfer cosmological simulations to predict the [CII] emission from the interstellar medium of a z~7 (halo mass $M_h=1.17\times10^{11}M_{\odot}$) galaxy. We improve the V13 model by including (a) a physically-motivated metallicity (Z) distribution of the gas, (b) the contribution of Photo-Dissociation Regions (PDRs), (c) the effects of Cosmic Microwave Background on the [CII] line luminosity. We study the relative contribution of diffuse neutral gas to the total [CII] emission ($F _{diff}/F_{tot}$) for different SFR and Z values. We find that the [CII] emission arises predominantly from PDRs: regardless of the galaxy properties, $F _{diff}/F_{tot}\leq 10$% since, at these early epochs, the CMB temperature approaches the spin temperature of the [CII] transition in the cold neutral medium ($T_{CMB}\sim T_s^{CNM}\sim 20$ K). Our model predicts a high-z [CII]-SFR relation consistent with observations of local dwarf galaxies ($0.02<Z/Z_{\odot}<0.5$). The [CII] deficit suggested by actual data ($L_{CII}<2.0\times 10^7 L_{\odot}$ in BDF3299 at z~7.1) if confirmed by deeper ALMA observations, can be ascribed to negative stellar feedback disrupting molecular clouds around star formation sites. The deviation from the local [CII]-SFR would then imply a modified Kennicutt-Schmidt relation in z>6 galaxies. Alternatively/in addition, the deficit might be explained by low gas metallicities ($Z<0.1 Z_{\odot}$).
At bright radio powers ($P_{\rm 1.4 GHz} > 10^{25}$ W/Hz) the space density of the most powerful sources peaks at higher redshift than that of their weaker counterparts. This paper establishes whether this luminosity-dependent evolution persists for sources an order of magnitude fainter than those previously studied, by measuring the steep--spectrum radio luminosity function (RLF) across the range $10^{24} < P_{\rm 1.4 GHz} < 10^{28}$ W/Hz, out to high redshift. A grid-based modelling method is used, in which no assumptions are made about the RLF shape and high-redshift behaviour. The inputs to the model are the same as in Rigby et al. (2011): redshift distributions from radio source samples, together with source counts and determinations of the local luminosity function. However, to improve coverage of the radio power vs. redshift plane at the lowest radio powers, a new faint radio sample is introduced. This covers 0.8 sq. deg., in the Subaru/XMM-Newton Deep Field, to a 1.4 GHz flux density limit of $S_{\rm 1.4 GHz} \geq 100~\mu$Jy, with 99% redshift completeness. The modelling results show that the previously seen high-redshift declines in space density persist to $P_{\rm 1.4 GHz} < 10^{25}$ W/Hz. At $P_{\rm 1.4 GHz} > 10^{26}$ W/Hz the redshift of the peak space density increases with luminosity, whilst at lower radio luminosities the position of the peak remains constant within the uncertainties. This `cosmic downsizing' behaviour is found to be similar to that seen at optical wavelengths for quasars, and is interpreted as representing the transition from radiatively efficient to inefficient accretion modes in the steep-spectrum population. This conclusion is supported by constructing simple models for the space density evolution of these two different radio galaxy classes; these are able to successfully reproduce the observed variation in peak redshift.
We compare DNS calculations of homogeneous isotropic turbulence with the statistical properties of intra-cluster turbulence from the Matryoshka Run (Miniati 2014) and find remarkable similarities between their inertial ranges. This allowed us to use the time dependent statistical properties of intra-cluster turbulence to evaluate dynamo action in the intra-cluster medium, based on earlier results from numerically resolved nonlinear magneto-hydrodynamic turbulent dynamo (Beresnyak 2012). We argue that this approach is necessary (a) to properly normalize dynamo action to the available intra-cluster turbulent energy and (b) to overcome the limitations of low Re affecting current numerical models of the intra-cluster medium. We find that while the properties of intra-cluster magnetic field are largely insensitive to the value and origin of the seed field, the resulting values for the Alfven speed and the outer scale of the magnetic field are consistent with current observational estimates, basically confirming the idea that magnetic field in today's galaxy clusters is a record of its past turbulent activity.
We estimate the incidence of multiply-imaged AGNs among the optical counterparts of X-ray selected point-like sources in the XXL field. We also derive the expected statistical properties of this sample, such as the redshift distribution of the lensed sources and of the deflectors that lead to the formation of multiple images, modelling the deflectors using both spherical (SIS) and ellipsoidal (SIE) singular isothermal mass distributions. We further assume that the XXL survey sample has the same overall properties as the smaller XMM-COSMOS sample restricted to the same flux limits and taking into account the detection probability of the XXL survey. Among the X-ray sources with a flux in the [0.5-2] keV band larger than 3.0x10$^{-15}$ erg cm$^{-2}$ s$^{-1}$ and with optical counterparts brighter than an r-band magnitude of 25, we expect ~20 multiply-imaged sources. Out of these, ~16 should be detected if the search is made among the seeing-limited images of the X-ray AGN optical counterparts and only one of them should be composed of more than two lensed images. Finally, we study the impact of the cosmological model on the expected fraction of lensed sources.
We investigate the supernova-driven galactic wind of the barred spiral galaxy NGC 7552, using both ground-based optical nebular emission lines and far-ultraviolet absorption lines measured with the Hubble Space Telescope Cosmic Origins Spectrograph. We detect broad (~300 km/s) blueshifted (-40 km/s) optical emission lines associated with the galaxy's kpc-scale star-forming ring. The broad line kinematics and diagnostic line ratios suggest that the H-alpha emission comes from clouds of high density gas entrained in a turbulent outflow. We compare the H-alpha emission line profile to the UV absorption line profile measured along a coincident sight line and find significant differences. The maximum blueshift of the H-alpha-emitting gas is ~290 km/s, whereas the UV line profile extends to blueshifts upwards of 1000 km/s. The mass outflow rate estimated from the UV is roughly nine times greater than that estimated from H-alpha. We argue that the H-alpha emission traces a cluster-scale outflow of dense, low velocity gas at the base of the large-scale wind. We suggest that UV absorption line measurements are therefore more reliable tracers of warm gas in starburst-driven outflows.
We study the sources of biases and systematics in the derivation of galaxy properties of observational studies, focusing on stellar masses, star formation rates, gas/stellar metallicities, stellar ages and magnitudes/colors. We use hydrodynamical cosmological simulations of galaxy formation, for which the real quantities are known, and apply observational techniques to derive the observables. We also make an analysis of biases that are relevant for a proper comparison between simulations and observations. For our study, we post-process the simulation outputs to calculate the galaxies' spectral energy distributions (SEDs) using Stellar Population Synthesis models and also generating the fully-consistent far UV-submillimeter wavelength SEDs with the radiative transfer code SUNRISE. We compared the direct results of simulations with the observationally-derived quantities obtained in various ways, and found that systematic differences in all studied galaxy properties appear, which are caused by: (1) purely observational biases (e.g. fiber size for single-fiber spectroscopic surveys), (2) the use of mass-weighted/luminosity-weighted quantities, with preferential sampling of more massive/luminous regions, (3) the different ways to construct the template of models when a fit to the spectra is performed, and (4) variations due to the use of different calibrations, most notably in the cases of the gas metallicities and star formation rates. Our results show that large differences, in some cases of more than an order of magnitude, can appear depending on the technique used to derive galaxy properties. Understanding these differences is of primary importance both for simulators, to allow a better judgement on similarities/differences with observations, and for observers, to allow a proper interpretation of the data which inevitably suffers from observational biases which vary from survey to survey.
We present the results of a study of the low-mass X-ray binary 4U 1636-536. We have performed temporal analysis of all available RXTE/ASM, Swift/BAT and MAXI data. We have confirmed the previously discovered quasi-periodicity of ~45 d present during ~2004, however we found it continued to 2006. At other epochs, the quasi-periodicity is only transient, and the quasi-period, if present, drifts. We have then applied a time-dependent accretion disc model to the interval with the significant X-ray quasi-periodicity. For our best model, the period and the amplitude of the theoretical light curve agree well with that observed. The modelled quasi-periodicity is due to the hydrogen thermal-ionization instability occurring in outer regions of the accretion disc. The model parameters are the average mass accretion rate (estimated from the light curves), and the accretion disc viscosity parameters, for the hot and cold phases. Our best model gives relatively low values of viscosity parameter for cold phase 0.01 and for hot phase 0.03.
We use a sample of 37 of the densest clusters and protoclusters across $1.3 \le z \le 3.2$ from the Clusters Around Radio-Loud AGN (CARLA) survey to study the formation of massive cluster galaxies. We use optical $i'$-band and infrared 3.6$\mu$m and 4.5$\mu$m images to statistically select sources within these protoclusters and measure their median observed colours; $\langle i'-[3.6] \rangle$. We find the abundance of massive galaxies within the protoclusters increases with decreasing redshift, suggesting these objects may form an evolutionary sequence, with the lower redshift clusters in the sample having similar properties to the descendants of the high redshift protoclusters. We find that the protocluster galaxies have an approximately unevolving observed-frame $i'-[3.6]$ colour across the examined redshift range. We compare the evolution of the $\langle i'-[3.6] \rangle$ colour of massive cluster galaxies with simplistic galaxy formation models. Taking the full cluster population into account, we show that the formation of stars within the majority of massive cluster galaxies occurs over at least 2Gyr, and peaks at $z \sim 2$-3. From the median $i'-[3.6]$ colours we cannot determine the star formation histories of individual galaxies, but their star formation must have been rapidly terminated to produce the observed red colours. Finally, we show that massive galaxies at $z>2$ must have assembled within 0.5Gyr of them forming a significant fraction of their stars. This means that few massive galaxies in $z>2$ protoclusters could have formed via dry mergers.
We test the long-term kinematical stability of a Galactic stellar halo model, due to Kafle, et al. (2012), who study the kinematics of approximately 5000 blue horizontal branch (BHB) stars in the Sloan Digital Sky Survey (SDSS). The velocity dispersion $\sigma$ and anisotropy parameter $\beta$ of the stars have been determined as functions of Galactocentric radius, over the range $6<R_\mathrm{GC} < 25$ kpc, and show a strong dip in the anisotropy profile at $R_\mathrm{GC}\sim17$ kpc. By directly integrating orbits of particles in a 3-D model of the Galactic potential with these characteristics, we show that the $\sigma$ and $\beta$ profiles quickly evolve on a time scale of a $\mathrm{few}\times10$ Myr whereas the density $\rho$ profile remains largely unaffected. We suggest that the feature is therefore transient. The origin of such features in the Galactic halo remains unclear.
We present SIGAME simulations of the [CII] 157.7 {\mu}m fine structure line emission from cosmological smoothed particle hydrodynamics (SPH) simulations of main sequence galaxies at z = 2. Using sub-grid physics prescriptions the gas in our galaxy simulations is modelled as a multi-phased interstellar medium (ISM) comprised of molecular gas residing in the inner regions of giant molecular clouds, an atomic gas phase associated with photodissociation regions at the surface of the clouds, and a diffuse, fully ionized gas phase. Adopting a density profile of the clouds and taking into account heating by the local FUV radiation field and cosmic rays - both scaled by the local star formation rate density - we calculate the [CII] emission from each of the aforementioned ISM phases using a large velocity gradient approach for each cloud, on resolved and global scales. The [CII] emission peaks in the central (<~ 1 kpc) regions of our galaxies where the star formation is most intense, and we find that the majority (>~ 60%) of the emission in this region originates in the molecular gas phase. At larger galactocentric distances (>~2 kpc), the atomic gas is the main contributor to the [CII] emission (>~ 80%), and at all radii the ionized gas provides a negligible amount (<~ 5%) to the [CII] budget. Our simulations predict a log-linear relationship between the integrated [CII] luminosity and star formation rate with a slope (0.80 +/- 0.12) in agreement with observationally determined slopes (~ 0.85 - 1.00) but with a ~ 3 times higher normalization than the observed z ~ 0 relation.
The Resonant Switch (RS) model of twin high-frequency quasi-periodic oscillations (HF QPOs) observed in neutron star binary systems, based on switch of the twin oscillations at a resonant point, has been applied to the atoll source 4U 1636-53 under assumption that the neutron star exterior can be approximated by the Kerr geometry. Strong restrictions of the neutron star parameters M (mass) and a (spin) arise due to fitting the frequency pairs admitted by the RS model to the observed data in the regions related to the resonant points. The most precise variants of the RS model are those combining the relativistic precession frequency relations with their modifications. Here, the neutron star mass and spin estimates given by the RS model are confronted with a variety of equations of state (EoS) governing structure of neutron stars in the framework of the Hartle-Thorne theory of rotating neutron stars applied for the observationally given rotation frequency f_rot~580 Hz (or alternatively f_rot~290 Hz) of the neutron star at 4U 1636-53. It is shown that only two variants of the RS model based on the Kerr approximation are compatible with two EoS applied in the Hartle-Thorne theory for f_rot~580 Hz, while no variant of the RS model is compatible for f_rot~290 Hz. The two compatible variants of the RS model are those giving the best fits of the observational data. However, a self-consistency test by fitting the observational data to the RS model with oscillation frequencies governed by the Hartle-Thorne geometry described by three spacetime parameters M, a and (quadrupole moment) q related by the two available EoS puts strong restrictions. The test admits only one variant of the RS model of twin HF QPOs for the Hartle-Thorne theory with the Gandolfi et al. (2010) EoS predicting the parameters of the neutron star $M \sim 2.10 \mathrm{M}_{\odot}$, $a \sim 0.208$, and $q/a^2 \sim 1.77$.
Kinematical parameterisations of disc galaxies, employing emission line observations, are indispensable tools for studying the formation and evolution of galaxies. Future large-scale HI surveys will resolve the discs of many thousands of galaxies, allowing a statistical analysis of their disc and halo kinematics, mass distribution and dark matter content. Here we present an automated procedure which fits tilted-ring models to Hi data cubes of individual, well-resolved galaxies. The method builds on the 3D Tilted Ring Fitting Code (TiRiFiC) and is called FAT (Fully Automated TiRiFiC). To assess the accuracy of the code we apply it to a set of 52 artificial galaxies and 25 real galaxies from the Local Volume HI Survey (LVHIS). Using LVHIS data, we compare our 3D modelling to the 2D modelling methods DiskFit and rotcur. A conservative result is that FAT accurately models the kinematics and the morphologies of galaxies with an extent of eight beams across the major axis in the inclination range 20$^{\circ}$-90$^{\circ}$ without the need for priors such as disc inclination. When comparing to 2D methods we find that velocity fields cannot be used to determine inclinations in galaxies that are marginally resolved. We conclude that with the current code tilted-ring models can be produced in a fully automated fashion. This will be essential for future HI surveys, with the Square Kilometre Array and its pathfinders, which will allow us to model the gas kinematics of many thousands of well-resolved galaxies. Performance studies of FAT close to our conservative limits, as well as the introduction of more parameterised models will open up the possibility to study even less resolved galaxies.
Type Ia supernovae (SNe Ia) are powerful cosmological "standardizable candles" and the most precise distance indicators. However, a limiting factor in their use for precision cosmology rests on our ability to correct for the dust extinction toward them. SN 2014J in the starburst galaxy M82, the closest detected SN~Ia in three decades, provides unparalleled opportunities to study the dust extinction toward an SN Ia. In order to derive the extinction as a function of wavelength, we model the color excesses toward SN 2014J, which are observationally derived over a wide wavelength range in terms of dust models consisting of a mixture of silicate and graphite. The resulting extinction laws steeply rise toward the far ultraviolet, even steeper than that of the Small Magellanic Cloud (SMC). We infer a visual extinction of $A_V \approx 1.9~\rm mag$, a reddening of $E(B-V)\approx1.1~ \rm mag$, and a total-to-selective extinction ratio of $R_V \approx 1.7$, consistent with that previously derived from photometric, spectroscopic, and polarimetric observations. The size distributions of the dust in the interstellar medium toward SN 2014J are skewed toward substantially smaller grains than that of the Milky Way and the SMC.
We present a new calibration of the Calcium II Triplet equivalent widths versus [Fe/H], constructed upon K giant stars in the Galactic bulge. This calibration will be used to derive iron abundances for the targets of the GIBS survey, and in general it is especially suited for solar and supersolar metallicity giants, typical of external massive galaxies. About 150 bulge K giants were observed with the GIRAFFE spectrograph at VLT, both at resolution R~20,000 and at R~6,000. In the first case, the spectra allowed us to perform direct determination of Fe abundances from several unblended Fe lines, deriving what we call here high resolution [Fe/H] measurements. The low resolution spectra allowed us to measure equivalent widths of the two strongest lines of the near infrared Calcium II triplet at 8542 and 8662 A. By comparing the two measurements we derived a relation between Calcium equivalent widths and [Fe/H] that is linear over the metallicity range probed here, -1<[Fe/H]<+0.7. By adding a small second order correction, based on literature globular cluster data, we derived the unique calibration equation [Fe/H]$_{CaT} = -3.150 + 0.432W' + 0.006W'^2$, with a rms dispersion of 0.197 dex, valid across the whole metallicity range -2.3<[Fe/H]<+0.7.
Ellerman bombs are transient brightenings of the extended wings of the solar Balmer lines in emerging active regions. We describe their properties in the ultraviolet lines sampled by the Interface Region Imaging Spectrograph (IRIS), using simultaneous imaging spectroscopy in H$\alpha$ with the Swedish 1-m Solar Telescope (SST) and ultraviolet images from the Solar Dynamics Observatory for Ellerman bomb detection and identification. We select multiple co-observed Ellerman bombs for detailed analysis. The IRIS spectra strengthen the view that Ellerman bombs mark reconnection between bipolar kilogauss fluxtubes with the reconnection and the resulting bi-directional jet located within the solar photosphere and shielded by overlying chromospheric fibrils in the cores of strong lines. The spectra suggest that the reconnecting photospheric gas underneath is heated sufficiently to momentarily reach stages of ionization normally assigned to the transition region and the corona. We also analyze similar outburst phenomena that we classify as small flaring arch filaments and ascribe to higher-located reconnection. They have different morphology and produce hot arches in million-Kelvin diagnostics.
The influence of dark matter particle decay on the baryon-to-photon ratio has been studied for different cosmological epochs. We consider different parameter values of dark matter particles such as mass, lifetime, the relative fraction of dark matter particles. It is shown that the modern value of the dark matter density $\Omega_{\rm CDM}=0.26$ is enough to lead to variation of the baryon-to-photon ratio up to $\Delta \eta / \eta \sim 0.01 \div 1$ for decays of the particles with masses 10 GeV $\div$ 1 TeV. However, such processes can also be accompanied by emergence of an excessive gamma ray flux. The observational data on the diffuse gamma ray background are used to making constraints on the dark matter decay models and on the maximum possible variation of the baryon-to-photon ratio $\Delta\eta/\eta\lesssim10^{-5}$. Detection of such variation of the baryon density in future cosmological experiments can serve as a powerful means of studying properties of dark matter particles.
The atmospheric parameters and chemical abundances of two neglected A-type stars, 28 Peg and HD 202240, were derived using high resolution spectra obtained at the TUBITAK National Observatory. We determined the photospheric abundances of eleven elements for 28 Peg and twenty for HD 202240, using equivalent-width measurement and spectral synthesis methods. Their abundance patterns are in good agreement with those of chemically normal A-type stars having similar atmospheric parameters. We pinpoint the position of these stars on the H-R diagram and estimate their masses and ages as; $2.60\pm0.10\ M_\odot$ and $650\pm50\ Myr$ for 28 Peg and $4.50\pm0.09\ M_\odot$ and $150\pm10\ Myr$ for HD 202240. To compare our abundance determinations with those of stars having similar ages and atmospheric parameters, we select members of open clusters. We notice that our target stars exhibit similar abundance patterns with these members.
We present ANNz2, a new implementation of the public software for photometric redshift (photo-z) estimation of Collister and Lahav (2004). Large photometric galaxy surveys are important for cosmological studies, and in particular for characterizing the nature of dark energy. The success of such surveys greatly depends on the ability to measure photo-zs, based on limited spectral data. ANNz2 utilizes multiple machine learning methods, such as artificial neural networks, boosted decision/regression trees and k-nearest neighbours. The objective of the algorithm is to dynamically optimize the performance of the photo-z estimation, and to properly derive the associated uncertainties. In addition to single-value solutions, the new code also generates full probability density functions (PDFs) in two different ways. In addition, estimators are incorporated to mitigate possible problems of spectroscopic training samples which are not representative or are incomplete. ANNz2 is also adapted to provide optimized solutions to general classification problems, such as star/galaxy separation. We illustrate the functionality of the code using data from the tenth data release of the Sloan Digital Sky Survey and the Baryon Oscillation Spectroscopic Survey. The code is available for download at https://github.com/IftachSadeh/ANNZ
Current and future radio interferometric arrays such as LOFAR and SKA are characterized by a paradox. Their large number of receptors (up to millions) allow theoretically unprecedented high imaging resolution. In the same time, the ultra massive amounts of samples makes the data transfer and computational loads (correlation and calibration) order of magnitudes too high to allow any currently existing image reconstruction algorithm to achieve, or even approach, the theoretical resolution. We investigate here decentralized and distributed image reconstruction strategies which select, transfer and process only a fraction of the total data. The loss in MSE incurred by the proposed approach is evaluated theoretically and numerically on simple test cases.
We have investigated the effect of stellar encounters on the formation and disruption of the Oort cloud using the classical impulse approximation. We calculate the evolution of a planetesimal disk into a spherical Oort cloud due to the perturbation from passing stars for 10 Gyr. We obtain the empirical fits of the $e$-folding time for the number of Oort cloud comets using the standard exponential and Kohlrausch formulae as functions of the stellar parameters and the initial semimajor axes of planetesimals. The $e$-folding time and the evolution timescales of the orbital elements are also analytically derived. In some calculations, the effect of the Galactic tide is additionally considered. We also show the radial variations of the $e$-folding times to the Oort cloud. From these timescales, we show that if the initial planetesimal disk has the semimajor axes distribution ${\rm d}n/{\rm d}a\propto a^{-2}$, which is produced by planetary scattering (Higuchi et al. 2006), the $e$-folding time for planetesimals in the Oort cloud is $\sim$10 Gyr at any heliocentric distance $r$. This uniform $e$-folding time over the Oort cloud means that the supply of comets from the inner Oort cloud to the outer Oort cloud is sufficiently effective to keep the comet distribution as ${\rm d}n/{\rm d}r\propto r^{-2}$. We also show that the final distribution of the semimajor axes in the Oort cloud is approximately proportional to $a^{-2}$ for any initial distribution.
In this presentation we summarize our previous results concerning the evolution of primordial magnetic fields with and without helicity during the expansion of the Universe. We address different magnetogenesis scenarios such as inflation, electroweak and QCD phase transitions magnetogenesis. A high Reynolds number in the early Universe ensures strong coupling between magnetic field and fluid motions. After generation the subsequent dynamics of the magnetic field is governed by decaying hydromagnetic turbulence. We claim that primordial magnetic fields can be considered as a seeds for observed magnetic fields in galaxies and clusters. Magnetic field strength bounds obtained in our analysis are consistent with the upper and lower limits of extragalactic magnetic fields.
The very short and bright flare of 3C 279 detected with {\it Fermi}-LAT in 2013 December is tested by a model with stochastic electron acceleration by turbulences. Our time-dependent simulation shows that the very hard spectrum and asymmetric lightcurve are successfully reproduced by changing only the magnetic field from the value in the steady period. The maximum energy of electrons drastically grows by the decrease of the magnetic field, which yields hard photon spectrum as observed. Succeeding rapid cooling due to the inverse Compton scattering with the external photons reproduces the decaying feature of the lightcurve. The inferred energy density of the magnetic field is much less than the electron and photon energy densities. The low magnetic field and short variability timescale are unfavorable for the jet acceleration model by the gradual Poynting flux dissipation.
The fields of solar radiophysics and solar system radio physics, or radio heliophysics, will benefit immensely from an instrument with the capabilities projected for SKA. Potential applications include interplanetary scintillation (IPS), radio-burst tracking, and solar spectral radio imaging with a superior sensitivity. These will provide breakthrough new insights and results in topics of fundamental importance, such as the physics of impulsive energy releases, magnetohydrodynamic oscillations and turbulence, the dynamics of post-eruptive processes, energetic particle acceleration, the structure of the solar wind and the development and evolution of solar wind transients at distances up to and beyond the orbit of the Earth. The combination of the high spectral, time and spatial resolution and the unprecedented sensitivity of the SKA will radically advance our understanding of basic physical processes operating in solar and heliospheric plasmas and provide a solid foundation for the forecasting of space weather events.
The origin of high velocity stars observed in the halo of our Galaxy is still unclear. In this work we test the hypothesis, raised by results of recent high precision $N$-body simulations, of strong acceleration of stars belonging to a massive globular cluster orbitally decayed in the central region of the host galaxy where it suffers of a close interaction with a super massive black hole, which, for these test cases, we assumed $10^8$ M$_\odot$ in mass.
As second-generation gravitational-wave detectors prepare to analyze data at unprecedented sensitivity, there is great interest in searches for unmodeled transients, commonly called bursts. Significant effort has yielded a variety of techniques to identify and characterize such transient signals, and many of these methods have been applied to produce astrophysical results using data from first-generation detectors. However, the computational cost of background estimation remains a challenging problem; it is difficult to claim a 5{\sigma} detection with reasonable computational resources without paying for efficiency with reduced sensitivity. We demonstrate a hierarchical approach to gravitational-wave transient detection, focusing on long-lived signals, which can be used to detect transients with significance in excess of 5{\sigma} using modest computational resources. In particular, we show how previously developed seedless clustering techniques can be applied to large datasets to identify high-significance candidates without having to trade sensitivity for speed.
We present the first study of the relationship between the column density distribution of molecular clouds within nearby Galactic spiral arms and their evolutionary status as measured from their stellar content. We analyze a sample of 195 molecular clouds located at distances below 5.5 kpc, identified from the ATLASGAL 870 micron data. We define three evolutionary classes within this sample: starless clumps, star-forming clouds with associated young stellar objects, and clouds associated with HII regions. We find that the N(H2) probability density functions (N-PDFs) of these three classes of objects are clearly different: the N-PDFs of starless clumps are narrowest and close to log-normal in shape, while star-forming clouds and HII regions exhibit a power-law shape over a wide range of column densities and log-normal-like components only at low column densities. We use the N-PDFs to estimate the evolutionary time-scales of the three classes of objects based on a simple analytic model from literature. Finally, we show that the integral of the N-PDFs, the dense gas mass fraction, depends on the total mass of the regions as measured by ATLASGAL: more massive clouds contain greater relative amounts of dense gas across all evolutionary classes.
Observations of the energetic neutral atoms (ENAs) of heliospheric origin by
IBEX differ from expectations based on heliospheric models. It was proposed
that the structure of the heliosphere may be similar to the "two-stream" model
derived in 1961 by Parker for the case of strong interstellar magnetic field.
Using MHD simulations, we examine possible structure of the heliosphere for a
wide range of interstellar magnetic field strengths, with different choices of
interstellar medium and solar wind parameters. For the model heliospheres, we
calculate the fluxes of ENAs created in the inner heliosheath, and compare with
IBEX observations.
We find that the plasma flow in the model heliospheres for strong
interstellar field ($\sim$20 $\mu$G) has a "two-stream" structure, which
remains visible down to $\sim$5 $\mu$G. The obtained ENA flux distribution show
the features similar to the "split tail" effect observed by IBEX. In our model,
the main cause of this effect is the two component (fast and slow) solar wind
structure.
The potential field approximation has been providing a fast, and computationally inexpensive estimation for the solar corona's global magnetic field geometry for several decades. In contrast, more physics-based global magnetohydrodynamic (MHD) models have been used for a similar purpose, while being much more computationally expensive. Here, we investigate the difference in the field geometry between a global MHD model and the potential field source surface model (PFSSM) by tracing individual magnetic field lines in the MHD model from the Alfven surface (AS), through the source surface (SS), all the way to the field line footpoint, and then back to the source surface in the PFSSM. We also compare the flux-tube expansion at two points at the SS and the AS along the same radial line. We study the effect of solar cycle variations, the order of the potential field harmonic expansion, and different magnetogram sources. We find that the flux-tube expansion factor is consistently smaller at the AS than at the SS for solar minimum and the fast solar wind, but it is consistently larger for solar maximum and the slow solar wind. We use the Wang--Sheeley--Arge (WSA) model to calculate the associated wind speed for each field line, and propagate these solar-wind speeds to 1AU. We find a more than five hours deviation in the arrival time between the two models for 20% of the field lines in the solar minimum case, and for 40% of the field lines in the solar maximum case.
Context: Features in the spectra of primary cosmic rays (CRs) provide
invaluable information on the propagation of these particles in the Galaxy. In
the rigidity region around a few hundred GV, such features have been measured
in the proton and helium spectra by the PAMELA experiment and later confirmed
with a higher significance by AMS-02. We investigate the implications of these
datasets for the scenario in which CRs propagate under the action of
self-generated waves.
Aims: We show that the recent data on the spectrum of protons and helium
nuclei as collected with AMS-02 and Voyager are in very good agreement with the
predictions of a model in which the transport of Galactic CRs is regulated by
self-generated waves. We also study the implications of the scenario for the
boron-to-carbon ratio: although a good overall agreement is found, at high
energy we find marginal support for a (quasi) energy independent contribution
to the grammage, that we argue may come from the sources themselves
Results: A break in the spectra of all nuclei is found at rigidity of a few
hundred GV, as a result of a transition from self-generated waves to
pre-existing waves with a Kolmogorov power spectrum. Neither the slope of the
diffusion coefficient, nor its normalisation are free parameters. Moreover, at
rigidities below a few GV, CRs are predicted to be advected with the
self-generated waves at the local Alfv\'en speed. This effect, predicted in our
previous work, provides an excellent fit to the Voyager data on the proton and
helium spectra at low energies, providing additional support to the model.
Context: Be/X-ray binaries show outbursts with peak luminosities up to a few times $10^{37}\,$erg/s, during which they can be observed and studied in detail. Most (if not all) Be/X-ray binaries harbour accreting pulsars, whose X-ray spectra in many cases contain cyclotron resonant scattering features related to the magnetic field of the sources. Spectral variations as a function of luminosity and of the rotational phase of the neutron star are observed in many accreting pulsars. Aims: We explore X-ray spectral and timing properties of the Be/X-ray binary GX 304-1 during an outburst episode. Specifically, we investigate the behavior of the cyclotron resonant scattering feature, the continuum spectral parameters, the pulse period, and the energy- and luminosity-resolved pulse profiles. We combine the luminosity-resolved spectral and timing analysis to probe the accretion geometry and the beaming patterns of the rotating neutron star. Methods: We analyze the INTEGRAL data from the two JEM-X modules, ISGRI and SPI, covering the January-February 2012 outburst, divided in six observations. We obtain pulse profiles in two energy bands, phase-averaged and phase-resolved spectra for each observation. Results: We confirm the positive luminosity-dependence of the cyclotron line energy in GX 304-1, and report a dependence of the photon index on luminosity. Using a pulse-phase connection technique, we find a pulse period solution valid for the entire outburst. Our pulse-phase resolved analysis shows, that the centroid energy of the cyclotron line is varying only slightly with pulse phase, while other spectral parameters show more pronounced variations. Our results are consistent with a scenario in which, as the pulsar rotates, we are exploring only a small portion of its beam pattern.
In this paper we calculate the potential sensitivity of the CUORE detector to axions produced in the Sun through the Primakoff process and detected by coherent Bragg conversion by the inverse Primakoff process. The conversion rate is calculated using density functional theory for the electron density and realistic expectations for the energy resolution and background of CUORE. Monte Carlo calculations for $5~$y$\times741~$kg=$3705~$kg y of exposure are analyzed using time correlation of individual events with the theoretical time-dependent counting rate and lead to an expected limit on the axion-photon coupling $g_{a\gamma\gamma}<3.83\times 10^{-10}~GeV^{-1}$ for axion masses less than several eV.
The pulsar wind model is applied to explain the variable timing behavior of PSR B0540-69 and PSR J1846-0258. For PSR B0540-69, a 36 percent relative increase in the spin down rate was reported recently. Similarly, a net decrease in the spin frequency $\Delta\nu \approx -10^{-4} \, \rm Hz$ after a large glitch and a lower braking index were detected for PSR J1846-0258. In the pulsar wind model, braking indices of these two pulsar which are all larger than 1 but smaller than 3 can be well explained. The particle density reflects the magnetospheric activity in real-time and may be responsible for the changing spin down behavior. A different state of particle density will result in increase (or decrease) in the spin down rate. Corresponding to the variable timing behavior of PSR B0540-69 and PSR J1846-0258, the relative increase in the particle density are respectively 88 percent and 44 percent in the vacuum gap model. A changing particle density will lead to a varying braking index. The changing particle density is $\dot{\kappa}=1.68 \times 10^{-9} \, \rm s^{-1}$ for PSR J1846-0258 corresponding to its lower braking index 2.19.
Using the observations from the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO), we investigate six X-class and twenty-nine M-class flares occurring in solar active region (AR) 12192 from October 18 to 29. Among them, thirty (including six X- and twenty-four M-class) flares originated from the AR core and the other five M-flares appeared at the AR periphery. Four of the X-flares exhibited similar flaring structures, indicating they were homologous flares with analogous triggering mechanism. The possible scenario is: photospheric motions of emerged magnetic fluxes lead to shearing of the associated coronal magnetic field, which then yields a tether-cutting favorable configuration. Among the five periphery M-flares, four were associated with jet activities. The HMI vertical magnetic field data show that the photospheric fluxes of opposite magnetic polarities emerged, converged and canceled with each other at the footpoints of the jets before the flares. Only one M-flare from the AR periphery was followed by a coronal mass ejection (CME). From October 20 to 26, the mean decay index of the horizontal background field within the height range of 40-105 Mm is below the typical threshold for torus instability onset. This suggests that a strong confinement from the overlying magnetic field might be responsible for the poor CME production of AR 12192.
The GAMA survey has now completed its spectroscopic campaign of over 250,000 galaxies ($r<19.8$mag), and will shortly complete the assimilation of the complementary panchromatic imaging data from GALEX, VST, VISTA, WISE, and Herschel. In the coming years the GAMA fields will be observed by the Australian Square Kilometer Array Pathfinder allowing a complete study of the stellar, dust, and gas mass constituents of galaxies within the low-z Universe ($z<0.3$). The science directive is to study the distribution of mass, energy, and structure on kpc-Mpc scales over a 3billion year timeline. This is being pursued both as an empirical study in its own right, as well as providing a benchmark resource against which the outputs from numerical simulations can be compared. GAMA has three particularly compelling aspects which set it apart: completeness, selection, and panchromatic coverage. The very high redshift completeness ($\sim 98$\%) allows for extremely complete and robust pair and group catalogues; the simple selection ($r<19.8$mag) minimises the selection bias and simplifies its management; and the panchromatic coverage, 0.2$\mu$m - 1m, enables studies of the complete energy distributions for individual galaxies, well defined sub-samples, and population assembles (either directly or via stacking techniques). For further details and data releases see: this http URL
According to the cosmological principle, Universal large-scale structure is
homogeneous and isotropic. The observable Universe, however, shows complex
structures even on very large scales. The recent discoveries of structures
significantly exceeding the transition scale of 370 Mpc pose a challenge to the
cosmological principle.
We report here the discovery of the largest regular formation in the
observable Universe; a ring with a diameter of 1720 Mpc, displayed by 9 gamma
ray bursts (GRBs), exceeding by a factor of five the transition scale to the
homogeneous and isotropic distribution. The ring has a major diameter of $43^o$
and a minor diameter of $30^o$ at a distance of 2770 Mpc in the 0.78<z<0.86
redshift range, with a probability of $2\times 10^{-6}$ of being the result of
a random fluctuation in the GRB count rate.
Evidence suggests that this feature is the projection of a shell onto the
plane of the sky. Voids and string-like formations are common outcomes of
large-scale structure. However, these structures have maximum sizes of 150 Mpc,
which are an order of magnitude smaller than the observed GRB ring diameter.
Evidence in support of the shell interpretation requires that temporal
information of the transient GRBs be included in the analysis.
This ring-shaped feature is large enough to contradict the cosmological
principle. The physical mechanism responsible for causing it is unknown.
The "Wide Area VISTA Extra-galactic Survey" (WAVES) is a 4MOST Consortium Design Reference Survey which will use the VISTA/4MOST facility to spectroscopically survey ~2million galaxies to $r_{\rm AB} < 22$ mag. WAVES consists of two interlocking galaxy surveys ("WAVES-Deep" and "WAVES-Wide"), providing the next two steps beyond the highly successful 1M galaxy Sloan Digital Sky Survey and the 250k Galaxy And Mass Assembly survey. WAVES will enable an unprecedented study of the distribution and evolution of mass, energy, and structures extending from 1-kpc dwarf galaxies in the local void to the morphologies of 200-Mpc filaments at $z\sim1$. A key aim of both surveys will be to compare comprehensive empirical observations of the spatial properties of galaxies, groups, and filaments, against state-of-the-art numerical simulations to distinguish between various Dark Matter models.
The local cosmic-ray (CR) spectra are calculated for typical characteristic regions of a cold dense molecular cloud, to investigate two so far neglected mechanisms of dust charging: collection of suprathermal CR electrons and protons by grains, and photoelectric emission from grains due to the UV radiation generated by CRs. The two mechanisms add to the conventional charging by ambient plasma, produced in the cloud by CRs. We show that the CR-induced photoemission can dramatically modify the charge distribution function for submicron grains. We demonstrate the importance of the obtained results for dust coagulation: While the charging by ambient plasma alone leads to a strong Coulomb repulsion between grains and inhibits their further coagulation, the combination with the photoemission provides optimum conditions for the growth of large dust aggregates in a certain region of the cloud, corresponding to the densities $n(\mathrm{H_2})$ between $\sim10^4$ cm$^{-3}$ and $\sim10^6$ cm$^{-3}$. The charging effect of CR is of generic nature, and therefore is expected to operate not only in dense molecular clouds but also in the upper layers and the outer parts of protoplanetary discs.
We have observed the Virgo Cluster spiral galaxy, NGC~4845, at 1.6 and 6 GHz using the Karl G. Jansky Very Large Array, as part of the `Continuum Halos in Nearby Galaxies -- an EVLA Survey' (CHANG-ES). The source consists of a bright unresolved core with a surrounding weak central disk (1.8 kpc diameter). The core is variable over the 6 month time scale of the CHANG-ES data and has increased by a factor of $\approx$ 6 since 1995. The wide bandwidths of CHANG-ES have allowed us to determine the spectral evolution of this core which peaks {\it between} 1.6 and 6 GHz (it is a GigaHertz-peaked spectrum source).We show that the spectral turnover is dominated by synchrotron self-absorption and that the spectral evolution can be explained by adiabatic expansion (outflow), likely in the form of a jet or cone. The CHANG-ES observations serendipitously overlap in time with the hard X-ray light curve obtained by Nikolajuk \& Walter (2013) which they interpret as due to a tidal disruption event (TDE) of a super-Jupiter mass object around a $10^5\, M_\odot$ black hole. We outline a standard jet model, provide an explanation for the observed circular polarization, and quantitatively suggest a link between the peak radio and peak X-ray emission via inverse Compton upscattering of the photons emitted by the relativistic electrons. We predict that it should be possible to resolve a young radio jet via VLBI as a result of this nearby TDE.
Streams of gas and dust in the inner parsec of the Galactic center form a distinct feature known as the Minispiral, which has been studied in radio waveband as well as in the infrared wavebands. A large fraction of the Minispiral gas is ionized by radiation of OB stars present in the Nuclear Star Cluster (NSC). Based on the inferred mass in the innermost parsec ($\sim 10^6$ solar masses), over $\sim 10^3$ -- $10^4$ neutron stars should move in the sphere of gravitational influence of the SMBH. We estimate that a fraction of them propagate through the denser, ionized medium concentrated mainly along the three arms of the Minispiral. Based on the properties of the gaseous medium, we discuss different interaction regimes of magnetised neutron stars passing through this region. Moreover, we sketch expected observational effects of these regimes. The simulation results may be applied to other galactic nuclei hosting NSC, where the expected distribution of the interaction regimes is different across different galaxy types.
Infrared (IR) excesses around K-type red giants (RGs) have previously been discovered using IRAS data, and past studies have suggested a link between RGs with overabundant Li and IR excesses, implying the ejection of circumstellar shells or disks. We revisit the question of IR excesses around RGs using higher spatial resolution IR data, primarily from WISE. Our goal was to elucidate the link between three unusual RG properties: fast rotation, enriched Li, and IR excess. We have 316 targets thought to be K giants, about 40% of which we take to be Li-rich. In 24 cases with previous detections of IR excess at low spatial resolution, we believe that source confusion is playing a role, in that either (a) the source that is bright in the optical is not responsible for the IR flux, or (b) there is more than one source responsible for the IR flux as measured in IRAS. We looked for IR excesses in the remaining sources, identifying 28 that have significant IR excesses by ~20 um (with possible excesses for 2 additional sources). There appears to be an intriguing correlation in that the largest IR excesses are all in Li-rich K giants, though very few Li-rich K giants have IR excesses (large or small). These largest IR excesses also tend to be found in the fastest rotators. There is no correlation of IR excess with the carbon isotopic ratio, 12C/13C. IR excesses by 20 um, though relatively rare, are at least twice as common among our sample of Li-rich K giants. If dust shell production is a common by-product of Li enrichment mechanisms, these observations suggest that the IR excess stage is very short-lived, which is supported by theoretical calculations. Conversely, the Li-enrichment mechanism may only occasionally produce dust, and an additional parameter (e.g., rotation) may control whether or not a shell is ejected.
Recent quantum mechanical calculations of rate coefficients for collisional transfer of population between the hyperfine states of 13CN enable their population densities to be determined. We have computed the relative populations of the hyperfine states of the N = 0, 1, 2 rotational states for kinetic temperatures 5 $\le$ T $\le$ 20 K and molecular hydrogen densities 1 $\le$ n(H2) $\le$10 10 cm --3. Spontaneous and induced radiative transitions were taken into account. Our calculations show that, if the lines are optically thin, the populations of the hyperfine states, F, within a given rotational manifold are proportional to their statistical weights, (2F + 1) -- i.e. in local thermodynamic equilibrium -- over the entire range of densities. We have re-analysed IRAM 30 m telescope observations of 13CN hyperfine transitions (N = 1 $\rightarrow$ 0) in four starless cores. A comparison of these observations with our calculations confirms that the hyperfine states are statistically populated in these sources.
Using the cosmological smoothed particle hydrodynamical code GADGET-3 we make a realistic assessment of the technique of using constant cumulative number density as a tracer of galaxy evolution at high redshift. We find that over a redshift range of $3\leq z \leq7$ one can on average track the growth of the stellar mass of a population of galaxies selected from the same cumulative number density bin to within $\sim 0.20$ dex. Over the stellar mass range we probe ($10^{10.39}\leq M_s/M_\odot \leq 10^{10.75}$ at $z =$ 3 and $10^{8.48}\leq M_s/M_\odot \leq 10^{9.55}$ at $z =$ 7) one can reduce this bias by selecting galaxies based on an evolving cumulative number density. We find the cumulative number density evolution exhibits a trend towards higher values which can be quantified by simple linear formulations going as $-0.10\Delta z$ for descendants and $0.12\Delta z$ for progenitors. Utilizing such an evolving cumulative number density increases the accuracy of descendant/progenitor tracking by a factor of $\sim2$. This result is in excellent agreement, within $0.10$ dex, with abundance matching results over the same redshift range. However, we find that our more realistic cosmological hydrodynamic simulations produce a much larger scatter in descendant/progenitor stellar masses than previous studies, particularly when tracking progenitors. This large scatter makes the application of either the constant cumulative number density or evolving cumulative number density technique limited to average stellar masses of populations only, as the diverse mass assembly histories caused by stochastic physical processes such as gas accretion, mergers, and star formation of individual galaxies will lead to a larger scatter in other physical properties such as metallicity and star-formation rate.
We study the predictions for structure formation in an induced gravity dark energy model with a quartic potential. By developing a dedicated Einstein-Boltzmann code, we study self-consistently the dynamics of homogeneous cosmology and of linear perturbations without using any parametrization. By evolving linear perturbations with initial conditions in the radiation era, we accurately recover the quasi-static analytic approximation in the matter dominated era. We use Planck 2013 data and a compilation of baryonic acoustic oscillation (BAO) data to constrain the coupling $\gamma$ to the Ricci curvature and the other cosmological parameters. By connecting the gravitational constant in the Einstein equation to the one measured in a Cavendish-like experiment, we find $\gamma < 0.0012$ at 95% CL with Planck 2013 and BAO data. This is the tightest cosmological constraint on $\gamma$ and on the corresponding derived post-Newtonian parameters. Because of a degeneracy between $\gamma$ and the Hubble constant $H_0$, we show how larger values for $\gamma$ are allowed, but not preferred at a significant statistical level, when local measurements of $H_0$ are combined in the analysis with Planck 2013 data.
We use Hubble Space Telescope Wide-Field Camera 3 (HST/WFC3) rest-frame optical imaging to select a pilot sample of star-forming galaxies in the redshift range z = 2.00-2.65 whose multi-component morphologies are consistent with expectations for major mergers. We follow up this sample of major merger candidates with Keck/NIRSPEC longslit spectroscopy obtained in excellent seeing conditions (FWHM ~ 0.5 arcsec) to obtain Halpha-based redshifts of each of the morphological components in order to distinguish spectroscopic pairs from false pairs created by projection along the line of sight. Of six pair candidates observed, companions (estimated mass ratios 5:1 and 7:1) are detected for two galaxies down to a 3sigma limiting emission-line flux of ~ 10^{-17} erg/s/cm2. This detection rate is consistent with a ~ 50% false pair fraction at such angular separations (1-2 arcsec), and with recent claims that the star-formation rate (SFR) can differ by an order of magnitude between the components in such mergers. The two spectroscopic pairs identified have total SFR, SFR surface densities, and stellar masses consistent on average with the overall z ~ 2 star forming galaxy population.
In the present paper we study the behavior of the normalized $I$-$Q$ relation for neutron stars in a particular class of $f(R)$ theories of gravity, namely the $R^2$ gravity that is one of the most natural and simplest extensions of general relativity in the strong field regime. We study both the slowly and rapidly rotating cases. The results show that the $I$-$Q$ relation remain nearly equation of state independent for fixed values of the normalized rotational parameter, but the deviations from universality can be a little bit larger compared to the general relativistic case. What is the most interesting in our studies, is that the differences with the pure Einstein's theory can be large reaching above 20\%. This is qualitative different from the majority of alternative theories of gravity, where the normalized $I$-$Q$ relations are almost indistinguishable from the general relativistic case, and can lead to observational constraints on the $f(R)$ theories in the future.
Recent observations reveal that magnetic turbulence in the nearly colisionless solar wind plasma extends to scales smaller than the plasma microscales, such as ion gyroradius and ion inertial length. Measured breaks in the spectra of magnetic and density fluctuations at high frequencies are thought to be related to the transition from large-scale hydromagnetic to small-scale kinetic turbulence. The scales of such transitions and the responsible physical mechanisms are not well understood however. In the present work we emphasize the crucial role of the plasma parameters in the transition to kinetic turbulence, such as the ion and electron plasma beta, the electron to ion temperature ratio, the degree of obliquity of turbulent fluctuations. We then propose an explanation for the spectral breaks reported in recent observations.
Here is proposed the idea of linking the dark matter issue, (considered as a major problem of contemporary research in physics) with two other open theoretical questions, one, almost centenary about the existence of an unavoidable ether in general relativity agreeing with the Mach's principle, and one more recent about the properties of the quantum vacuum of the quantum field theory of strong interactions, QuantumChromodynamics (QCD). According to this idea, on the one hand, dark matter and dark energy that, according to the current standard model of cosmology represent about 95% of the universe content, can be considered as two distinct forms of the Mach's ether, and, on the other hand, dark matter, as a perfect fluid emerging from the QCD vacuum could be modeled as a Bose Einstein condensate.
In this paper, we have considered a spatially flat FRW universe filled with pressureless matter and dark energy. We have considered a phenomenological parametrization of the deceleration parameter $q(z)$ and from this we have reconstructed the equation of state for dark energy $\omega_{\phi}(z)$. Using the combination of datasets (SN Ia + Hubble + BAO/CMB), we have constrained the transition redshift $z_t$ (at which the universe switches from a decelerating to an accelerating phase) and have found the best fit value of $z_t$. We have also found that the reconstructed results of $q(z)$ and $\omega_{\phi}(z)$ are in good agreement with the recent observations. The potential term for the present toy model is found to be functionally similar to a Higgs potential.
Disformal theories of gravity are scalar-tensor theories where the scalar couples derivatively to matter via the Jordan frame metric. These models have recently attracted interest in the cosmological context since they admit accelerating solutions. We derive the solution for a static isolated mass in generic disformal gravity theories and transform it into the parameterised post-Newtonian form. This allows us to investigate constraints placed on such theories by local tests of gravity. The tightest constraints come from preferred-frame effects due to the motion of the Solar System with respect to the evolving cosmological background field. The constraints we obtain improve upon the previous solar system constraints by two orders of magnitude, and constrain the scale of the disformal coupling for generic models to $\mathcal{M} \gtrsim 100$ eV. These constraints render all disformal effects irrelevant for cosmology.
We initiate a study of cosmological implications of sphaleron-mediated CP-violation arising from the electroweak vacuum angle under the reasonable assumption that the semiclassical suppression is lifted at finite temperature. In this article, we explore the implications for existing scenarios of baryogenesis. Many compelling models of baryogenesis rely on electroweak sphalerons to relax a $(B+L)$ charge asymmetry. Depending on the sign of the CP-violating parameter, it is shown that the erasure of positive $(B+L)$ will proceed more or less quickly than the relaxation of negative $(B+L)$. This is a higher order effect in the kinetic equation for baryon number, which we derive here through order $n_{B+L}^2$. Its impact on known baryogenesis models therefore seems minor, since phenomenologically $n_{B+L}$ is much smaller than the entropy density. However, there remains an intriguing unexplored possibility that baryogenesis could be achieved with the vacuum angle alone providing the required CP-violation.
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