Warm gas and dust surround the innermost regions of active galactic nuclei (AGN). They provide the material for accretion onto the super-massive black hole and they are held responsible for the orientation-dependent obscuration of the central engine. The AGN-heated dust distributions turn out to be very compact with sizes on scales of about a parsec in the mid-infrared. Only infrared interferometry currently provides the necessary angular resolution to directly study the physical properties of this dust. Size estimates for the dust distributions derived from interferometric observations can be used to construct a size--luminosity relation for the dust distributions. The large scatter about this relation suggests significant differences between the dust tori in the individual galaxies, even for nuclei of the same class of objects and with similar luminosities. This questions the simple picture of the same dusty doughnut in all AGN. The Circinus galaxy is the closest Seyfert 2 galaxy. Because its mid-infrared emission is well resolved interferometrically, it is a prime target for detailed studies of its nuclear dust distribution. An extensive new interferometric data set was obtained for this galaxy. It shows that the dust emission comes from a very dense, disk-like structure which is surrounded by a geometrically thick, similarly warm dust distribution as well as significant amounts of warm dust within the ionisation cone.
Using X-ray stacking analyses we estimate the average amounts of supermassive black hole (SMBH) growth taking place in star-forming galaxies (SFGs) at z~1 and z~2 as a function of galaxy stellar mass (M*). We find the average rate of SMBH growth taking place in SFGs follows remarkably similar trends with both M* and redshift as the average star-formation rates (SFRs) of these galaxies (i.e., dM_BH/dt ~ M*^(0.86+/-0.39) for the z~1 sample and dM_BH/dt ~ M*^(1.05+/-0.36) for the z~2 sample). It follows that the ratio of SMBH growth rate to SFR is (a) flat with respect to galaxy stellar mass (b) not evolving with redshift and (c) close to the ratio required to maintain/establish a SMBH to stellar mass ratio of ~10^(-3) as also inferred from today's M_BH-M_Bulge relationship. We interpret this as evidence that SMBHs have, on average, grown in-step with their host galaxies since at least z~2, irrespective of host galaxy mass and AGN triggering mechanism and that the relative growth rates are more important in establishing inferred M_BH-M* relationships than the seed SMBH masses or merger history. Based on these results we speculate that it is the availability of gas reservoirs that regulates both cosmological SMBH growth and star-formation.
We use the relations between aperture stellar velocity dispersion (\sigma_ap), stellar mass (M_sps), and galaxy size (R_e) for a sample of 150,000 early-type galaxies from SDSS/DR7 to place constraints on the stellar initial mass function (IMF) and dark halo response to galaxy formation. We build LCDM based mass models that reproduce, by construction, the relations between size, light concentration and stellar mass. Reproducing the median \sigma_ap vs M_sps relation is not possible in models that have {\it both} a universal IMF and a universal dark halo response. Significant departures from a universal IMF and/or dark halo response are required. We show that this degeneracy can be broken using the strength of the correlation between residuals of the velocity-mass (\Delta log \sigma_ap) and size-mass (\Delta log R_e) relations. The slope of this correlation, d_vr = \Delta log\sigma_ap/\Delta log R_e, varies systematically with galaxy mass from -0.45 at M_sps \sim 10^{10} M_sun, to -0.15 at M_sps \sim 10^{11.6}M_sun. The virial fundamental plane (FP) has d_vr=-1/2, and thus we find the tilt of the FP is mass dependent. Reproducing this tilt requires {\it both} a non-universal IMF and a non-universal halo response. Our best model has mass-follows-light at low masses (M_sps < 10^{11.2}M_sun) and unmodified NFW haloes at M_sps \sim 10^{11.5}M_sun. The stellar masses imply a mass dependent IMF which is "lighter" than Salpeter at low masses and "heavier" than Salpeter at high masses.
We present the first analysis of the X-ray warm absorber and nuclear obscuration in the Seyfert 1.8 galaxy ESO 113-G010. We used archival data from a 100 ks XMM-Newton observation made in 2005. From high resolution spectroscopy analysis of the RGS data, we detect absorption lines originating from a warm absorber consisting of two distinct phases of ionisation, with log xi ~ 3.2 and 2.3 respectively. The higher-ionised component has a larger column density and outflow velocity (N_H ~ 1.6 x 10^22 cm^-2, v ~ -1100 km/s) than the lower-ionised component (N_H ~ 0.5 x 10^22 cm^-2, v ~ -700 km/s). The shape of the optical-UV continuum and the large Balmer decrement (H_alpha/H_beta ~ 8) indicate significant amount of reddening is taking place in our line of sight in the host galaxy of the AGN; however, the X-ray spectrum is not absorbed by cold neutral gas intrinsic to the source. We discuss different explanations for this discrepancy between the reddening and the X-ray absorption, and suggest that the most likely solution is a dusty warm absorber. We show that dust can exist in the lower-ionised phase of the warm absorber, which causes the observed reddening of the optical-UV emission, whereas the X-rays remain unabsorbed due to lack of cold neutral gas in the ionised warm absorber. Furthermore, we have investigated the uncertainties in the construction of the Spectral Energy Distribution (SED) of this object due to obscuration of the nuclear source and the effects this has on the photoionisation modelling of the warm absorber. We show how the assumed SEDs influence the thermal stability of each phase and whether or not the two absorber phases in ESO 113-G010 can co-exist in pressure equilibrium.
We have vastly increased the CIV statistics at intermediate redshift by surveying the thousands of quasars in the Sloan Digital Sky Survey Data-Release 7. We visually verified over 16,000 CIV systems with 1.46 < z < 4.55---a sample size that renders Poisson error negligible. Detailed Monte Carlo simulations show we are approximately 50% complete down to rest equivalent widths W_r ~ 0.6 \AA. We analyzed the sample as a whole and in ten small redshift bins with approximately 1500 doublets each. The equivalent width frequency distributions f(W_r) were well modeled by an exponential, with little evolution in shape. In contrast with previous studies that modeled the frequency distribution as a single power law, the fitted exponential gives a finite mass density for the CIV ions. The co-moving line density dN_CIV/dX evolved smoothly with redshift, increasing by a factor of 2.36+/-0.08 from z = 4.55 to 1.96, then plateauing at dN_CIV/dX ~ 0.34 for z = 1.96 to 1.46. Comparing our SDSS sample with z < 1 (ultraviolet) and z > 5 (infrared) surveys, we see an approximately ten-fold increase in dN_CIV/dX over z ~ 6 --> 0, for W_r >= 0.6 \AA. This suggests a monotonic and significant increase in the enrichment of gas outside galaxies over the 12 Gyr lifetime of the universe.
We construct a sample of 75,863 star forming galaxies with robust metallicity and star formation rate measurements from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), from which we select a clean sample of compact group (CG) galaxies. The CGs are defined to be close configurations of at least 4 galaxies that are otherwise apparently isolated. Our selection results in a sample of 112 spectroscopically identified compact group galaxies, which can be further divided into groups that are either embedded within a larger structure, such as a cluster or large group, or truly isolated systems. The compact groups then serve as a probe into the influence of large scale environment on a galaxy's evolution, while keeping the local density fixed at high values. We find that the star formation rates (SFRs) of star forming galaxies in compact groups are significantly different between isolated and embedded systems. Galaxies in isolated systems show significantly enhanced SFR, relative to a control sample matched in mass and redshift, a trend not seen in the embedded systems. Galaxies in isolated systems exhibit a median SFR enhancement at fixed stellar mass of +0.07 \pm 0.03 dex. These dependences on large scale environment are small in magnitude relative to the apparent influence of local scale effects found in previous studies, but the significance of the difference in SFRs between our two samples constrains the effect of large scale environment to be non-zero. We find no significant change in the gas-phase interstellar metallicity for either the isolated or embedded compact group sample relative to their controls. However, simulated samples that include artificial offsets indicate that we are only sensitive to metallicity changes of log O/H >0.13 dex (at 99% confidence), which is considerably larger than the typical metallicity differences seen in previous environmental studies.
We present 3D-HST, a near-infrared spectroscopic Treasury program with the Hubble Space Telescope for studying the processes that shape galaxies in the distant Universe. 3D-HST provides rest-frame optical spectra for a sample of ~7000 galaxies at 1<z<3.5, the epoch when 60% of all star formation took place, the number density of quasars peaked, the first galaxies stopped forming stars, and the structural regularity that we see in galaxies today must have emerged. 3D-HST will cover 3/4 (625 sq.arcmin) of the CANDELS survey area with two orbits of primary WFC3/G141 grism coverage and two to four parallel orbits with the ACS/G800L grism. In the IR these exposure times yield a continuum signal-to-noise of ~5 per resolution element at H~23.1 and a 5sigma emission line sensitivity of 5x10-17 erg/s/cm2 for typical objects, improving by a factor of ~2 for compact sources in images with low sky background levels. The WFC3/G141 spectra provide continuous wavelength coverage from 1.1-1.6 um at a spatial resolution of ~0."13, which, combined with their depth, makes them a unique resource for studying galaxy evolution. We present the preliminary reduction and analysis of the grism observations, including emission line and redshift measurements from combined fits to the extracted grism spectra and photometry from ancillary multi-wavelength catalogs. The present analysis yields redshift estimates with a precision of sigma(z)=0.0034(1+z), or sigma(v)~1000 km/s. We illustrate how the generalized nature of the survey yields near-infrared spectra of remarkable quality for many different types of objects, including a quasar at z=4.7, quiescent galaxies at z~2, and the most distant T-type brown dwarf star known. The CANDELS and 3D-HST surveys combined will provide the definitive imaging and spectroscopic dataset for studies of the 1<z<3.5 Universe until the launch of the James Webb Space Telescope.
Using about 450,000 galaxies in the Deep Lens Survey, we present a detection of the gravitational magnification of z>4 Lyman Break Galaxies by massive foreground galaxies with 0.4<z<1, grouped by redshift. The magnification signal is detected at S/N greater than 20, and rigorous checks confirm that it is not contaminated by any galaxy sample overlap in redshift. The inferred galaxy mass profiles are consistent with earlier lensing analyses at lower redshift. We then explore the tomographic lens magnification signal by splitting our foreground galaxy sample into 7 redshift bins. Combining galaxy-magnification cross-correlations and galaxy angular auto-correlations, we develop a bias-independent estimator of the tomographic signal. As a diagnostic of magnification tomography, the measurement of this estimator rejects a flat dark matter dominated Universe at >9\sigma\ and is found to be consistent with the expected redshift-dependence of the WMAP7 \Lambda CDM cosmology.
In this paper we examine the percentage of type 1 AGN which require the inclusion of a soft excess component and/or significant cold absorption in the modelling of their X-ray spectra obtained by XMM-Newton. We do this by simulating spectra which mimic typical spectral shapes in order to find the maximum detectability expected at different count levels. We then apply a correction to the observed percentages found for the Scott et al. (2011) sample of 761 sources. We estimate the true percentage of AGN with a soft excess component to be 75+/-23%, suggesting that soft excesses are ubiquitous in the X-ray spectra of type 1 AGN. By carrying out joint fits on groups of low count spectra in narrow z bins in which additional spectral components were not originally detected, we show that the soft excess feature is recovered with a mean temperature kT and blackbody to power-law normalisation ratio consistent with those of components detected in individual high count spectra. Cold absorption with nH values broadly consistent with those reported in individual spectra are also recovered. We suggest such intrinsic cold absorption is found in a minimum of ~5% of type 1 AGN and may be present in up to ~10%.
An important issue in cosmology is reconstructing the effective dark energy equation of state directly from observations. With few physically motivated models, future dark energy studies cannot only be based on constraining a dark energy parameter space, as the errors found depend strongly on the parameterisation considered. We present a new non-parametric approach to reconstructing the history of the expansion rate and dark energy using Gaussian Processes, which is a fully Bayesian approach for smoothing data. We present a pedagogical introduction to Gaussian Processes, and discuss how it can be used to robustly differentiate data in a suitable way. Using this method we show that the Dark Energy Survey - Supernova Survey (DES) can accurately recover a slowly evolving equation of state to sigma_w = +-0.04 (95% CL) at z=0 and +-0.2 at z=0.7, with a minimum error of +-0.015 at the sweet-spot at z~0.14, provided the other parameters of the model are known. Errors on the expansion history are an order of magnitude smaller, yet make no assumptions about dark energy whatsoever. A code for calculating functions and their first three derivatives using Gaussian processes has been developed and is available for download at this http URL .
Recently, the number of detected galaxy counterparts of z > 2 Damped Lyman-alpha Absorbers in QSO spectra has increased substantially so that we today have a sample of 10 detections. M{\o}ller et al. in 2004 made the prediction, based on a hint of a luminosity-metallicity relation for DLAs, that HI size should increase with increasing metallicity. In this paper we investigate the distribution of impact parameter and metallicity that would result from the correlation between galaxy size and metallicity. We compare our observations with simulated data sets given the relation of size and metallicity. The observed sample presented here supports the metallicity-size prediction: The present sample of DLA galaxies is consistent with the model distribution. Our data also show a strong relation between impact parameter and column density of HI. We furthermore compare the observations with several numerical simulations and demonstrate that the observations support a scenario where the relation between size and metallicity is driven by feedback mechanisms controlling the star-formation efficiency and outflow of enriched gas.
We use a recently-developed analytic model for the ISM structure from scales of GMCs through star-forming cores to explore how the pre-stellar core mass function (CMF) and, by extrapolation, stellar initial mass function (IMF) should depend on both local and galactic properties. If the ISM is supersonically turbulent, the statistical properties of the density field follow from the turbulent velocity spectrum, and the excursion set formalism can be applied to analytically calculate the mass function of collapsing cores on the smallest scales on which they are self-gravitating (non-fragmenting). Two parameters determine the model: the disk-scale Mach number M_h (which sets the shape of the CMF), and the absolute velocity (to assign an absolute scale). For 'normal' variation in disk properties and core gas temperatures in the MW and local galaxies, there is almost no variation in the predicted high-mass behavior of the CMF/IMF. The slope is always close to Salpeter down to <1 M_sun. We predict modest variation in the sub-solar regime, mostly from variation in M_h, but within the observed scatter in sub-solar IMFs in local regions. For fixed galaxy properties, there is little variation in shape or 'upper mass limit' with parent GMC mass. However, in extreme starbursts (e.g. ULIRGs) we predict a bottom-heavy CMF. This agrees with the IMF inferred for the centers of Virgo ellipticals, believed to form in such a nuclear starburst. The CMF is bottom heavy despite the gas temperature being an order of magnitude larger, because M_h is also much larger. Larger M_h values make the 'parent' cloud mass (turbulent Jeans mass) larger, but promote fragmentation to smaller scales; this steepens the slope of the low-mass CMF and shifts the turnover mass. The model may predict a top-heavy CMF for the sub-pc disks around Sgr A*, but the relevant input parameters are uncertain.
We report on Chandra X-ray and Parkes radio observations of IGR J11014-6103, which is a possible pulsar wind nebula with a complex X-ray morphology and a likely radio counterpart. With the superb angular resolution of Chandra, we find evidence that a portion of the extended emission may be related to a bow shock due to the putative pulsar moving through the interstellar medium. The inferred direction of motion is consistent with IGR J11014-6103 having been born in the event that produced the supernova remnant (SNR) MSH 11-61A. If this association is correct, then previous constraints on the expansion of MSH 11-61A imply a transverse velocity for IGR J11014-6103 of 2,400-2,900 km/s, depending on the SNR model used. This would surpass the kick velocities of any known pulsars and rival or surpass the velocities of any compact objects that are associated with SNRs. While it is important to confirm the nature of the source, our radio pulsation search did not yield a detection.
The spectra of several high-redshift (z>6) quasars have shown evidence for a Gunn-Peterson (GP) damping wing, indicating a substantial mean neutral hydrogen fraction (x_HI > 0.03) in the z ~ 6 intergalactic medium (IGM). However, previous analyses assumed that the IGM was uniformly ionized outside of the quasar's HII region. Here we relax this assumption and model patchy reionization scenarios for a range of IGM and quasar parameters. We quantify the impact of these differences on the inferred x_HI, by fitting the spectra of three quasars: SDSS J1148+5251 (z=6.419), J1030+0524 (z=6.308), and J1623+3112 (z=6.247). We find that the best-fit values of x_HI in the patchy models agree well with the uniform case. More importantly, we confirm that the observed spectra favor the presence of a GP damping wing, with peak likelihoods decreasing by factors of > few - 10 when the spectra are modeled without a damping wing. We also find that the Ly alpha absorption spectra, by themselves, cannot distinguish the damping wing in a relatively neutral IGM from a damping wing in a highly ionized IGM, caused either by an isolated neutral patch, or by a damped Ly alpha absorber (DLA). However, neutral patches in a highly ionized universe (x_HI < 0.01), and DLAs with the large required column densities (N_HI > few x 10^{20} cm^{-2}) are both rare. As a result, when we include reasonable prior probabilities for the line of sight (LOS) to intercept either a neutral patch or a DLA at the required distance of ~ 40-60 comoving Mpc away from the quasar, we find strong lower limits on the neutral fraction in the IGM, x_HI > 0.1 (at 95% confidence). This strengthens earlier claims that a substantial global fraction of hydrogen in the z~6 IGM is in neutral form.
Despite astrophysical importance of binary star systems, detections are limited to those located in small ranges of separations, distances, and masses and thus it is necessary to use a variety of observational techniques for a complete view of stellar multiplicity across a broad range of physical parameters. In this paper, we report the detections and measurements of 2 binaries discovered from observations of microlensing events MOA-2011-BLG-090 and OGLE-2011-BLG-0417. Determinations of the binary masses are possible by simultaneously measuring the Einstein radius and the lens parallax from analyses of the well-resolved caustic-crossing parts of the light curve and the long-term deviation induced by the orbital motion of the Earth around the Sun, respectively. The measured masses of the binary components are 0.43 $M_{\odot}$ and 0.39 $M_{\odot}$ for MOA-2011-BLG-090 and 0.57 $M_{\odot}$ and 0.17 $M_{\odot}$ for OGLE-2011-BLG-0417 and thus both lens components of MOA-2011-BLG-090 and one component of OGLE-2011-BLG-0417 are M dwarfs, demonstrating the usefulness of microlensing in detecting binaries composed of low-mass components. From modeling of the light curves considering full Keplerian motion of the lens, we also measure the orbital parameters of the binaries. For both events, the caustic-crossing parts of the light curves, which are critical for determining the physical lens parameters, were resolved by high-cadence survey observations and thus it is expected that the number of microlensing binaries with measured physical parameters will increase in the future.
The newsletter of the Australian Astronomical Observatory. In this issue: Using 2dF and AAOmega to Harness the Full Power of the Supernova Legacy Survey; Emission Lines in the Near Infrared: Tracing the Violent ISM; Dancing Starbugs: vacuum adhesion, field rotation and other progress; A message of progress from HERMES; Imaging with the 2dF Focal Plane Imager; and all the usual columns and news from the Observatory.
Proposed space-based gravitational-wave (GW) detectors such as DECIGO and BBO will detect $\sim10^6$ neutron-star (NS) binaries and determine the luminosity distances to the binaries with high precision. Combining the luminosity distances with cosmologically-induced phase corrections on the GWs, cosmological expansion out to high redshift can be measured without the redshift determinations of host galaxies by electromagnetic observation and can be a unique probe for dark energy. This article is based on the results obtained in [1] where we investigated constraining power of the GW standard siren without redshift information on the equation of state of dark energy with future space-based GW detectors. We also compare the results with those obtained with other instruments and methods.
From the first published z>3 survey of 21-cm absorption within the hosts of radio galaxies and quasars, Curran et al. (2008b) found an apparent dearth of cool neutral gas at high redshift. From a detailed analysis of the photometry, each object is found to have a 1216 Angstrom continuum luminosity in excess of L > 1e23 W/Hz, a critical value above which 21-cm has never been detected at any redshift. For a variety of gas density distributions, we show that by placing a quasar within a galaxy of gas there is always an ultra-violet luminosity above which all of the gas in the galaxy is excited (and most likely ionised). Above this critical luminosity the hydrogen cannot be detected in the absorption of the 21-cm transition (and possibly Lyman-alpha) and while in this state the gas cannot engage in star formation. Applying the mean ionising photon rate of all of the sources searched, we find, using canonical values for the gas density and recombination rate coefficient, that the observed critical luminosity gives a scale-length (3 kpc) similar that of the neutral hydrogen (HI) in the Milky Way, a large spiral galaxy. This demonstrates that these galaxies are truly devoid of star-forming material, rather the non-detection of 21-cm being due to the sensitivity limits of current radio telescopes.
We present a Newtonian multi-fluid formalism for superfluid neutron star cores, focussing on the additional dissipative terms that arise when one takes into account the individual dynamical degrees of freedom associated with the coupled "fluids". The problem is of direct astrophysical interest as the nature of the dissipative terms can have significant impact on the damping of the various oscillation modes of the star and the associated gravitational-wave signatures. A particularly interesting application concerns the gravitational-wave driven instability of f- and r-modes. We apply the developed formalism to two specific three-fluid systems: (i) a hyperon core in which both Lambda and Sigma^- hyperons are present, and (ii) a core of deconfined quarks in the colour-flavour-locked phase in which a population of neutral K^0 kaons is present. The formalism is, however, general and can be applied to other problems in neutron-star dynamics (such as the effect of thermal excitations close to the superfluid transition temperature) as well as laboratory multi-fluid systems.
We present a multiwavelength study of the NGC 281 complex which contains the young cluster IC 1590 at the center, using deep wide-field optical UBVI_c photometry, slitless spectroscopy along with archival data sets in the near-infrared (NIR) and X-ray. The extent of IC 1590 is estimated to be ~6.5 pc. The cluster region shows a relatively small amount of differential reddening. The majority of the identified young stellar objects (YSOs) are low mass PMS stars having age <1-2 Myr and mass 0.5-3.5 M_\odot. The slope (\Gamma) of the mass function for IC 1590, in the mass range 2 < M/M_\odot \le 54, is found to be -1.11+-0.15. The slope of the K-band luminosity function (0.37+-0.07) is similar to the average value (~0.4) reported for young clusters. The distribution of gas and dust obtained from the IRAS, CO and radio maps indicates clumpy structures around the central cluster. The radial distribution of the young stellar objects, their ages, \Delta(H-K) NIR-excess, and the fraction of classical T Tauri stars suggest triggered star formation at the periphery of the cluster region. However, deeper optical, NIR and MIR observations are needed to have a conclusive view of star formation scenario in the region. The properties of the Class 0/I and Class II sources detected by using the Spitzer mid-infrared observations indicate that a majority of the Class II sources are X-ray emitting stars, whereas X-ray emission is absent from the Class 0/I sources. The spatial distribution of Class 0/I and Class II sources reveals the presence of three sub-clusters in the NGC 281 West region.
We observed four "water fountain" sources in the CO J=3-2 line emission with the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope in 2010-2011. The water fountain sources are evolved stars that form high-velocity collimated jets traced by water maser emission. The CO line was detected only from IRAS 16342-3814. The present work confirmed that the ^{12}CO to ^{13}CO line intensity ratio is ~1.5 at the systemic velocity. We discuss the origins of the very low ^{12}CO to ^{13}CO intensity ratio, as possible evidence for the "hot-bottom burning" in an oxygen-rich star, and the CO intensity variation in IRAS 16342-3814.
Most theoretical models invoke quasar driven outflows to quench star formation in massive galaxies, this feedback mechanism is required to account for the population of old and passive galaxies observed in the local universe. The discovery of massive, old and passive galaxies at z=2, implies that such quasar feedback onto the host galaxy must have been at work very early on, close to the reionization epoch. We have observed the [CII]158um transition in SDSSJ114816.64+525150.3 that, at z=6.4189, is one of the most distant quasars known. We detect broad wings of the line tracing a quasar-driven massive outflow. This is the most distant massive outflow ever detected and is likely tracing the long sought quasar feedback, already at work in the early Universe. The outflow is marginally resolved on scales of about 16 kpc, implying that the outflow can really affect the whole galaxy, as required by quasar feedback models. The inferred outflow rate, dM/dt > 3500 Msun/yr, is the highest ever found. At this rate the outflow can clean the gas in the host galaxy, and therefore quench star formation, in a few million years.
We present both timing and spectral analysis of the outburst of 4U 0115+63 in April -- May 2008 with INTEGRAL and RXTE observations. We have determined the spin period of the neutron star at $\sim 3.61430 \pm 0.00003$ s, and a spin up rate during the outburst of $\dot{P}=(-7.24 \pm 0.03)\times10^{-6} {\rm s d^{-1}}$, the angle of periapsis $\omega=48.67^\circ \pm 0.04^\circ$ in 2008 and its variation (apsidal motion) $\dot{\omega} = 0.048^\circ \pm 0.003^\circ {\rm yr}^{-1}$. We also confirm the relation of spin-up torque versus luminosity in this source during the giant outburst. The hard X-ray spectral properties of 4U 0115+63 during the outburst are studied with INTEGRAL and RXTE. Four cyclotron absorption lines are detected using the spectra from combined data of IBIS and JEM-X aboard INTEGRAL in the energy range of 3 -- 100 keV. The 5 -- 50 keV luminosities at an assumed distance of 7 kpc are determined to be in the range of $(1.5-12)\times 10^{37} {\rm ergs s^{-1}}$ during the outburst. The fundamental absorption line energy varies during the outburst: around 15 keV during the rising phase, and transiting to $\sim 10$ keV during the peak of the outburst, and further coming back to $\sim 15$ keV during the decreasing phase. The variations of photon index show the correlation with the fundamental line energy changes: the source becomes harder around the peak of the outburst and softer in both rising and decreasing phases. This correlation and transition processes during the outburst need further studies in both observations and theoretical work. The known relation of the fundamental line energy and X-ray luminosity is confirmed by our results, however, our discoveries suggest that some other factors besides luminosity play the important role in fundamental line energy variations and spectral transitions.
We present Herschel/SPIRE images at 250, 350, and 500 {\mu}m of NGC 4244, a typical low-mass, disk-only and edge-on spiral galaxy. The dust disk is clumpy and shows signs of truncation at the break radius of the stellar disk. This disk coincides with the densest part of the Hi disk. We compare the Spectral Energy Distribution, including the new SPIRE fluxes, to 3D radiative transfer models; a smooth model disk and a clumpy model with embedded heating. Each model requires a very high value for the dust scale-length (h(dust) = 2 - 5 h(stars)), higher dust masses than previous models of NGC 4244 (Md = 0.47 - 1.39 \times 10e7 Msun) and a face-on optical depth of {\tau}(V) = 0.4 - 1.12, in agreement with previous disk opacity studies. The vertical scales of stars and dust are similar. The clumpy model much better mimics the general morphology in the submm images and the general SED. The inferred gas-to-dust mass ratio is compatible with those of similar low-mass disks. The relatively large radial scale-length of the dust disk points to radial mixing of the dusty ISM within the stellar disk. The large vertical dust scale and the clumpy dust distribution of our SED model are both consistent with a scenario in which the vertical structure of the ISM is dictated by the balance of turbulence and self-gravity.
The presence of a well-defined and narrow dust lane in an edge-on spiral galaxy is the observational signature of a thin and dense molecular disk, in which gravitational collapse has overcome turbulence. Using a sample of galaxies out to z~1 extracted from the COSMOS survey, we identify the fraction of massive disks that display a dust lane. Our goal is to explore the evolution in the stability of the molecular ISM disks in spiral galaxies over a cosmic timescale. We check the reliability of our morphological classifications against changes in restframe wavelength, resolution, and cosmic dimming with (artificially redshifted) images of local galaxies from SDSS. We find that the fraction of L* disks with dust lanes in COSMOS is consistent with the local fraction (~80%) out to z~0.7. At z=0.8, the dust lane fraction is only slightly lower. A somewhat lower dust lane fraction in starbursting galaxies tentatively supports the notion that a high specific star formation rate can efficiently destroy or inhibit a dense molecular disk. A small subsample of higher redshift COSMOS galaxies display low internal reddening (E[B-V]), as well as a low incidence of dust lanes. These may be disks in which the growth of the dusty ISM disk lags behind that of the stellar disk. We note that at z=0.8, the most massive galaxies display a lower dust lane fraction than lower mass galaxies. A small contribution of recent mergers or starbursts to this most massive population may be responsible. The fact that the fraction of galaxies with dust lanes in COSMOS is consistent with little or no evolution implies that models to explain the Spectral Energy Distribution or the host galaxy dust extinction of supernovae based on local galaxies are still applicable to higher redshift spirals. It also suggests that dust lanes are long lived phenomena or can be reformed over very short time-scales.
We monitored the 22 GHz maser line in the lensed quasar MG J0414+0534 at z=2.64 with the 300-m Arecibo telescope for almost two years to detect possible additional maser components and to measure a potential velocity drift of the lines. The main maser line profile is complex and can be resolved into a number of broad features with line widths of 30-160 km/s. A new maser component was tentatively detected in October 2008 at a velocity of +470 km/s. After correcting for the estimated lens magnification, we find that the H2O isotropic luminosity of the maser in MG J0414+0534 is about 26,000 solar luminosities, making this source the most luminous ever discovered. Both the main line peak and continuum flux densities are surprisingly stable throughout the period of the observations. An upper limit on the velocity drift of the main peak of the line has been estimated from our observations and is of the order of 2 km/s per year. We discuss the results of the monitoring in terms of the possible nature of the maser emission, associated with an accretion disk or a radio jet. This is the first time that such a study is performed in a water maser source at high redshift, potentially allowing us to study the parsec-scale environment around a powerful radio source at cosmological distances.
Spicules were recently found to exist as two types when a new class of so-called type II spicules was discovered at the solar limb with Hinode. The type II spicules have been linked with on-disk observations of Rapid Blue-shifted Excursions (RBEs) in the Ha and Ca 8542 lines. Here we analyze observations optimized for the detection of RBEs in both Ha and Ca 8542 simultaneously at a high temporal cadence taken with CRISP at the SST. This study used a high-quality time sequence for RBEs at different blue-shifts and employed an automated detection routine to detect a large number of RBEs in order to expand on the statistics of RBEs. We find that the number of detected RBEs is dependent on the Doppler velocity of the images on which the search is performed. Detection of RBEs at lower velocities increases the estimated number of RBEs to the same order of magnitude expected from limb spicules. This shows that RBEs and type II spicules are exponents of the same phenomenon. We provide evidence that Ca 8542 RBEs are connected to Ha RBEs and are located closer to the network regions with the Ha RBEs being the continuation, and show that RBEs have an average lifetime of 83.9 s when observed in both spectral lines with Doppler velocity ranges of 10-25 km/s in Ca 8542 and 30-50 km/s in Ha. In addition, we determine the transverse motion of a much larger sample of RBEs than previous studies and find that like type II spicules, RBEs undergo significant transverse motions, 5-10 km/s. Finally, we find that the intergranular jets discovered in BBSO are a subset of RBEs.
We perform global time-dependent simulations of an accretion disc around a young stellar object with a dead zone (a region where the magneto-rotational instability cannot drive turbulence because the material is not sufficiently ionised). For infall accretion rates on to the disc of around 10^-7 Msun/yr, dead zones occur if the critical magnetic Reynolds number is larger than about 10^4. We model the collapse of a molecular gas cloud. At early times when the infall accretion rate is high, the disc is thermally ionised and fully turbulent. However, as the infall accretion rate drops, a dead zone may form if the critical magnetic Reynolds number is sufficiently large, otherwise the disc remains fully turbulent. With a dead zone the disc can become unstable to the gravo-magneto instability. The mass of the star grows in large accretion outbursts that may explain FU Orionis events. At late times there is not sufficient mass in the disc for outbursts to occur but the dead zone becomes even more prominent as the disc cools. Large inner dead zones in the later stages of disc evolution may help to explain observations of transition discs with an inner hole.
We briefly discuss the method of population synthesis to calculate theoretical delay time distributions of type Ia supernova progenitors. We also compare the results of the different research groups and conclude that although one of the main differences in the results for single degenerate progenitors is the retention efficiency with which accreted hydrogen is added to the white dwarf core, this cannot explain all the differences.
A new Monte Carlo simulation code for the propagation of Ultra High Energy Cosmic Rays is presented. The results of this simulation scheme are tested by comparison with results of another Monte Carlo computation as well as with the results obtained by directly solving the kinetic equation for the propagation of Ultra High Energy Cosmic Rays. A short comparison with the latest flux published by the Pierre Auger collaboration is also presented.
Magnetohydrodynamic (MHD) instabilities can play an important role in the structure and dynamics of the pulsar magnetosphere. We consider the instabilitycaused by differential rotation that is suggested by many theoretical models. Stability is considered by means of a linear analysis within the frane of the force-free MHD. We argue that differentially rotating magnetospheres are unstable for any particular geometry of the magnetic field and rotation law. The characteristic growth time of instability is of the order of the rotation period. The instability can lead to fluctuations of the emission and enhancement of diffusion in the magnetosphere.
We investigate gravitational lensing in the context of the MOG modified theory of gravity. Using a formulation of the theory with no adjustable or fitted parameters, we present the MOG equations of motion for slow, nonrelativistic test particles and for ultrarelativistic test particles, such as rays of light. We demonstrate how the MOG prediction for the bending of light can be applied to astronomical observations. Our investigation first focuses on a small set of strong lensing observations where the properties of the lensing objects are found to be consistent with the predictions of the theory. We also present an analysis of the colliding clusters 1E0657-558 (known also as the Bullet Cluster) and Abell 520; in both cases, the predictions of the MOG theory are in good agreement with observation.
There is substantial evidence for a connection between star formation in the nuclear region of a galaxy and growth of the central supermassive black hole. Furthermore, starburst activity in the region around an active galactic nucleus (AGN) may provide the obscuration required by the unified model of AGN. Molecular line emission is one of the best observational avenues to detect and characterize dense, star-forming gas in galactic nuclei over a range of redshift. This paper presents predictions for the carbon monoxide (CO) line features from models of nuclear starburst disks around AGN. These small scale ($\la 100$ pc), dense and hot starbursts have CO luminosities similar to scaled-down ultra-luminous infrared galaxies and quasar host galaxies. Nuclear starburst disks that exhibit a pc-scale starburst and could potentially act as the obscuring torus show more efficient CO excitation and higher brightness temperature ratios than those without such a compact starburst. In addition, the compact starburst models predict strong absorption when $J_{\mathrm{Upper}} \ga 10$, a unique observational signature of these objects. These findings allow for the possibility that CO SLEDs could be used to determine if starburst disks are responsible for the obscuration in $z \la 1$ AGN. Directly isolating the nuclear CO line emission of such compact regions around AGN from galactic-scale emission will require high resolution imaging or selecting AGN host galaxies with weak galactic-scale star formation. Stacking individual CO SLEDs will also be useful in detecting the predicted high-$J$ features.
Previous studies have shown that many post-AGB stars with dusty disks are associated with single-lined binary stars. To verify the binarity hypothesis on a larger sample, we started a high-resolution spectral monitoring of about 40 field giants, whose binarity was suspected based on either a light curve, an infrared excess, or a peculiar chemical composition. Here we report on the discovery of the periodic RV variations in BD+46 442, a high-latitude F giant with a disk. We interpret the variations due to the motion around a faint companion, and deduce the following orbital parameters: Porb = 140.77 d, e = 0.083, asini=0.31 AU. We find it to be a moderately metal-poor star ([M/H]=-0.7) without a strong depletion pattern in the photospheric abundances. Interestingly, many lines show periodic changes with the orbital phase: Halpha switches between a double-peak emission and a PCyg-like profiles, while strong metal lines appear split during the maximum redshift. Similar effects are likely visible in the spectra of other post-AGB binaries, but their regularity is not always realized due to sporadic observations. We propose that these features result from an ongoing mass transfer from the evolved giant to the companion. In particular, the blue-shifted absorption in Halpha, which occurs only at superior conjunction, may result from a jet originating in the accretion disk around the companion and seen in absorption towards the luminous primary.
The recently discovery of a massive neutron star (PSR J1614-2230 of $1.97\pm0.04M_{\odot}$) rules out the soft equation of states (EOSs) such as those included hyperons or kaon condensates at high densities, while the nuclear theory or the terrestrial laboratory data prefer a soft EOS. Here we propose one possible mechanism to allow that the observed massive neutron star can be supported by a soft EOS, that is, if the the gravitational constant $G$ varies at super strong field, a soft EOS can support the massive neutron stars.
We present an analysis of simultaneous X-Ray and UV observations ofcomet
C/2007 N3 (Lulin) taken on three days between January 2009 and March 2009 using
the Swift observatory. For our X-ray observations, we used basic transforms to
account for the movement of the comet to allow the combination of all available
data to produce an exposure-corrected image. We fit a simple model to the
extracted spectrum and measured an X-ray flux of 4.3+/-1.3 * 10^-13 ergs cm-2
s-1 in the 0.3 to 1.0 keV band. In the UV, we acquired large-aperture
photometry and used a coma model to derive water production rates given
assumptions regarding the distribution of water and its dissociation into OH
molecules about the comet's nucleus.
We compare and discuss the X-ray and UV morphology of the comet. We show that
the peak of the cometary X-ray emission is offset sunward of the UV peak
emission, assumed to be the nucleus, by approximately 35,000 km. The offset
observed, the shape of X-ray emission and the decrease of the X-ray emission
comet-side of the peak, suggested that the comet was indeed collisionally thick
to charge exchange, as expected from our measurements of the comet's water
production rate (6--8 10^28 mol. s-1). The X-ray spectrum is consistent with
solar wind charge exchange emission, and the comet most likely interacted with
a solar wind depleted of very highly ionised oxygen. We show that the measured
X-ray lightcurve can be very well explained by variations in the comet's gas
production rates, the observing geometry and variations in the solar wind flux.
Strong quasi-periodic oscillations in the tails of the giant gamma-ray flares seen in SGR 1806-20 and SGR 1900+14 are thought to be produced by starquakes in the flaring magnetar. However, the large fractional amplitudes (up to ~20%) observed are difficult to reconcile with predicted amplitudes of starquakes. Here we demonstrate that the steeply pulsed emission profile in the tail of the giant flare can enhance the observed amplitude of the underlying oscillation, analogously to a beam of light oscillating in and out of the line of sight. This mechanism will also broaden the feature in the power spectrum and introduce power at harmonics of the oscillation. The observed strength of the oscillation depends on the amplitude of the underlying starquake, the orientation and location of the emission on the surface of the star, and the gradient of the light curve profile. While the amplification of the signal can be significant, we demonstrate that even with uncertainties in the emission geometry, this effect is not sufficient to produce the observed QPOs. This result excludes the direct observation of a starquake, and suggests that the observed variations come from modulations in the intensity of the emission.
We present a data model describing the structure of spectrophotometric datasets with spectral and temporal coordinates and associated metadata. This data model may be used to represent spectra, time series data, segments of SED (Spectral Energy Distributions) and other spectral or temporal associations.
We discuss a new interacting model for the cosmological dark sector in which the attenuated dilution of cold dark matter scales as $a^{-3}f(a)$, where f(a) is an arbitrary function of the cosmic scale factor $a$. From thermodynamic arguments, we show that f(a) is proportional to entropy source of the particle creation process. In order to investigate the cosmological consequences of this kind of interacting models, we expand f(a) in a power series and viable cosmological solutions are obtained. Finally, we use current observational data to place constraints on the interacting function f(a).
We have imaged the ejecta of GK Persei (Nova Persei 1901 A.D.) with the Hubble Space Telescope (HST), revealing hundreds of cometary-like structures. One or both ends of the structures often show a brightness enhancement relative to the structures' middle sections, but there is no simple regularity to their morphologies (in contrast with the Helix nebula). Some of the structures' morphologies suggest the presence of slow-moving or stationary material with which the ejecta is colliding, while others suggest shaping from a wind emanating from GK Per itself. A detailed expansion map of the nova's ejecta was created by comparing HST images taken in successive years. WFPC2 narrowband images and STIS spectra demonstrate that the physical conditions in the ejecta vary strongly on spatial scales much smaller than those of the ejecta. Directly measuring accurate densities and compositions, and hence masses of this and other nova shells, will demand data at least as resolved spatially as those presented here. The filling factor the ejecta is < 1%, and the nova ejecta mass must be less than $10^{-4} \Msun$. A few of the nebulosities vary in brightness by up to a factor of two on timescales of one year. Finally, we present the deepest images yet obtained of a jet-like feature outside the main body of GK Per nebulosity, and the first spectrum of that feature. Dominated by strong, narrow emission lines of [NII], [OII], [OIII], and [SII], this feature is probably a shock due to ejected material running into stationary ISM, slowly moving ejecta from a previous nova episode, or circum-binary matter present before 1901. An upper limit to the mass of the jet is of order a few times $10^{-6} \Msun$. The jet might be an important, or even dominant mass sink from the binary system. The jet's faintness suggests that similar features could easily have been missed in other cataclysmic binaries.
The classical problem of spherical homologous gravitational collapse with a polytropic equation of state for pressure is examined in Lagrangian fluid coordinate, where the position of each initial fluid element {\eta} = r(0) is followed in time by the evolution function y(t). In this Lagrangian description, the fluid velocity v = dr/dt = {\eta}dy/dt is not a fluid variable, contrary to the commonly used Eulerian fluid description. As a result, the parameter space is one dimensional in {\eta}, in contrast to the (x, v) two-parameter space of Eulerian formulation. In terms of Lagrangian coordinate, the evolution function y(t), which is not limited to a linear time scaling, agrees with the well established parametric form of Mestel (Mestel 1965) for cold cloud collapse. The spatial structure is described by an equation which corresponds to the one derived by Goldreich and Weber (Goldreich & Weber 1980). The continuous self-similar density distribution presents a peaked central core followed by oscillations with decreasing amplitude, somewhat reminiscent to the expansion-wave inside-out collapse of Shu (Shu 1977). This continuous solution could account for the planetary system of a protostar. There is also a disconnected density distribution, which could be relevant to cavity formation between the highly peaked central core and the external infalling envelope of a magnetar-in-a-cavity pre-supernova configuration.
Using SDSS Stripe82 data we have obtained deep radial surface brightness profiles of 7 face-on to intermediate inclined late-type spirals down to \sim 30 mag arcsec^-2 in the r'-band. We do not find any evidence for a sharp cut-off of the light distribution of the disks but a smooth continuation into the stellar halos of galaxies. Stellar halos start to affect the surface brightness profiles of the galaxies at \sim 28 mag arcsec^-2, and at a radial distance of \sim 4-10 inner scale-lengths. We find that the light contribution from the stellar halo could be responsible of previous classification of surface brightness profiles as Type III in late-type galaxies. In order to estimate the contribution of the stellar halo light to the total galaxy light, we carried out a Bulge/Disk/Stellar Halo decomposition by simoultaneously fitting all components. The light contribution of the halo to the total galaxy light varies from ~ 1% to ~ 5%, but in case of ongoing mergers, the halo light fraction can be as high as ~ 10%, independently of the luminosities of the galaxies. We have also explored the integrated (g'-r') color of the stellar halo of our galaxies. We find (g'-r') colors ranging from ~ 0.4 to ~ 1.2. By confronting these colors with model predictions, we encounter problems to fit our very red colors onto stellar population grids with conventional IMFs. Very red halo colors can be attributed to stellar populations dominated by very low mass stars of low to intermediate metallicity produced by bottom-heavy IMFs.
Based on the Veneziano ghost theory of QCD, we estimate the cosmological constant $\Lambda$, which is related to the vacuum energy density, $\rho_{\Lambda}$, by $\Lambda = \frac{8\pi G}{3} \rho_{\Lambda}$. In the current Veneziano ghost theory $\rho_{\Lambda}$ is given by the absolute value of the product of the local quark condensate and quark current mass:$\rho_{\Lambda} = \frac{2N_{f}H}{m_{\eta'}}c |m_{q}<0|:\bar{q}q:|0>|$. By solving Dyson-Schwinger Equations for a dressed quark propagator, we found the local quark condensate $<0|:\bar{q}q:|0> \simeq -(235 MeV)^{3}$, the generally accepted value. The quark current mass, predicted by use of chiral perturbation theory is $m_{q} \simeq 3.29 - 6.15$. This gives the same result for $\rho_{\Lambda}$ as found by previous authors, which is somewhat larger than the observed value. However, when we make use of the nonlocal quark condensate, $<0|:\bar{q}(x)q(0):|0>= g(x)<0|:\bar{q}q:|0>$, with g(x) estimated from our previous work, we find $\Lambda$ is in a good agreement with the observations.
We study the cosmological evolution of an induced gravity model with a scale symmetry breaking potential for the scalar field. The radiation to matter transition, following inflation and reheating, influences the dynamics of such a field through its non minimal coupling. We illustrate how, under certain conditions on the potential, such a dynamics can lead to a suitable amount of dark energy explaining the present accelerated expansion.
We extend our investigation of soft graviton effects on the microscopic dynamics of matter fields in de Sitter space. We evaluate the quantum equation of motion in generic gauge theories. We find that the Lorentz invariance can be respected and the velocity of light is not renormalized at the one-loop level. The gauge coupling constant is universally screened by soft gravitons and diminishes with time. These features are in common with other four dimensional field theories with dimensionless couplings. In particular the couplings scale with time with definite scaling exponents. Although individual scaling exponents are gauge dependent, we argue that the relative scaling exponents are gauge independent and should be observable. We also mention soft graviton effects on CMB.
The properties of a spherically symmetric static space-time permeated of dark energy are worked out. Dark energy is viewed as the strain energy of an elastically deformable four dimensional manifold. The metric is worked out in the vacuum region around a central spherical mass/defect in the linear approximation. We discuss analogies and differences with the analogue in the de Sitter space time and how these competing scenarios could be differentiated on an observational ground. The comparison with the tests at the solar system scale puts upper limits to the parameters of the theory, consistent with the values obtained applying the classical cosmological tests.
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We investigate the structure of the stalled supernova shock in both 2D and 3D and explore the differences in the effects of neutrino heating and the standing accretion shock instability (SASI). Early after bounce, the amplitude of the dipolar mode of the shock is factors of $\sim2-$3 smaller in 3D than in 2D. However, later in both 3D and 2D the monopole and dipole modes start to grow until explosion. Whereas in 2D the $(l,m) = (1,0)$ mode changes sign quasi-periodically, producing the "up-and-down" motion always seen in modern 2D simulations, in 3D this almost never happens. Rather, when the dipolar mode starts to grow in 3D, it grows in magnitude and wanders stochastically in direction until settling before explosion to a particular patch of solid angle. The amplitude growth of this unidirectional dipole mode can precede that of the average shock radius. Furthermore, in 2D when neutrino heating is turned off, the amplitudes of the characteristic axisymmetric sloshing mode are a factor of $\sim3-$4 smaller than when neutrino heating is on. This suggests that it is neutrino-driven convection, not the SASI, which is responsible for the prominent dipolar mode seen in detailed 2D simulations, and that the SASI is at most a minor feature of supernova dynamics. The quasi-steady increase in the average shock radius and the (unoscillating) dipole, even hundreds of milliseconds before the explosion commences, may be distinctive and important signatures of 3D supernova behavior in the neutrino-driven context.
We present the results of deep, high-resolution, 5 GHz Expanded Very Large Array (EVLA) observations of the nearby, dwarf lenticular galaxy and intermediate mass black hole candidate (M ~4.5 x 10^5 M_sun), NGC 404. For the first time, radio emission at frequencies above 1.4 GHz has been detected in this galaxy. We found a modestly resolved source in the NGC 404 nucleus with a total radio luminosity of 7.6 +/- 0.7 x 10^17 W/Hz at 5 GHz and a spectral index from 5 to 7.45 GHz of alpha = -0.88 +/- 0.30. NGC 404 is only the third central intermediate mass black hole candidate detected in the radio regime with subarcsecond resolution. The position of the radio source is consistent with the optical center of the galaxy and the location of a known, hard X-ray point source (Lx ~1.2 x 10^37 erg/s). The faint radio and X-ray emission could conceivably be produced by an X-ray binary, star formation, a supernova remnant or a low-luminosity AGN powered by an intermediate mass black hole. In light of our new EVLA observations, we find that the most likely scenario is an accreting intermediate mass black hole, with other explanations incompatible with the observed X-ray and/or radio luminosities or statistically unlikely.
The fermionic dark matter (DM) phase-space density Q(r) = rho(r)/sigma^3(r) must be smaller than K m^4/\hbar^3 where m is the DM particle mass, sigma(r) is the DM velocity dispersion and K is a pure number of order one which we estimate. This bound follows from the Pauli principle which restricts the phase-space distribution function of fermionic spin-1/2 dark matter (DM) particles to be f(r,p) < 2. Cusped profiles from N-body galaxy simulations produce a divergent Q(r) at r = 0 violating this quantum bound. Combining this quantum bound with the behavior of Q(r) from simulations and with galaxy observational data on Q, implies that classical galaxy dynamics breaks down for fermionic DM at a distance from the centre of at least r_q. For keV scale WDM r_q turns to be in the parsec scale. For cold dark matter (CDM), r_q is between dozens of kilometers and a few meters, astronomically compatible with zero. For fermionic hot dark matter (HDM) r_q is from kpc to Mpc. This quantum bound rules out the presence of galaxy cusps for fermionic WDM. This is in agreement with astronomical observations which show that the DM halos are cored. The formation of cusps would be allowed for bosonic DM for which the Pauli principle does not apply. Hence, bosonic DM is strongly disfavored by the observation of galaxy cores. Quantum dynamical calculations become necessary to compute galaxy structures at kpc scales and below. N-body simulations can be used at scales larger than a kpc and matched with the quantum evolution.The Thomas-Fermi quantum approximation to self-gravitating fermions with masses in the keV scale yields galaxy properties as halo radius, mass and velocity dispersion consistent with the observations. Namely, fermionic WDM treated quantum mechanically, as it must be, reproduces the observed DM cores of galaxies.
The Panchromatic Hubble Andromeda Treasury (PHAT) survey is an on-going Hubble Space Telescope (HST) multi-cycle program to obtain high spatial resolution imaging of one-third of the M31 disk at ultraviolet through near-infrared wavelengths. In this paper, we present the first installment of the PHAT stellar cluster catalog. When completed, the PHAT cluster catalog will be among the largest and most comprehensive surveys of resolved star clusters in any galaxy. The exquisite spatial resolution achieved with HST has allowed us to identify hundreds of new clusters that were previously inaccessible with existing ground-based surveys. We identify 601 clusters in the Year 1 sample, representing more than a factor of four increase over previous catalogs within the current survey area (390 arcmin^2). This work presents results derived from the first \sim25% of the survey data; we estimate that the final sample will include \sim2500 clusters. For the Year 1 objects, we present a catalog with positions, radii, and six-band integrated photometry. Along with a general characterization of the cluster luminosities and colors, we discuss the cluster luminosity function, the cluster size distributions, and highlight a number of individually interesting clusters found in the Year 1 search.
We present the first science results from our Hubble Space Telescope Survey for Lyman limit absorption systems (LLS) using the low dispersion spectroscopic modes of the Advanced Camera for Surveys and the Wide Field Camera 3. Through an analysis of 71 quasars, we determine the incidence frequency of LLS per unit redshift and per unit path length, l(z) and l(x) respectively, over the redshift range 1 < z< 2.6, and find a weighted mean of l(x)=0.29 +/-0.05 for 2.0 < z < 2.5 through a joint analysis of our sample and that of Ribaudo et al. (2011). Through stacked spectrum analysis, we determine a median (mean) value of the mean free path to ionizing radiation at z=2.4 of lambda_mfp = 243(252)h^(-1) Mpc, with an error on the mean value of +/- 43h^(-1) Mpc. We also re-evaluate the estimates of lambda_mfp from Prochaska et al. (2009) and place constraints on the evolution of lambda_mfp with redshift, including an estimate of the "breakthrough" redshift of z = 1.6. Consistent with results at higher z, we find that a significant fraction of the opacity for absorption of ionizing photons comes from systems with N_HI <= 10^{17.5} cm^(-2) with a value for the total Lyman opacity of tau_lyman = 0.40 +/- 0.15. Finally, we determine that at minimum, a 5-parameter (4 power-law) model is needed to describe the column density distribution function f(N_HI, X) at z \sim 2.4, find that f(N_HI,X) undergoes no significant change in shape between z \sim 2.4 and z \sim 3.7, and provide our best fit model for f(N_HI,X).
New data are reported from the operation of a 4.0 kg CF$_{3}$I bubble chamber in the 6800 foot deep SNOLAB underground laboratory. The effectiveness of ultrasound analysis in discriminating alpha decay background events from single nuclear recoils has been confirmed, with a lower bound of $>$99.3% rejection of alpha decay events. Twenty single nuclear recoil event candidates and three multiple bubble events were observed during a total exposure of 553 kg-days distributed over three different bubble nucleation thresholds. The effective exposure for single bubble recoil-like events was 437.4 kg-days. A neutron background internal to the apparatus, of known origin, is estimated to account for five single nuclear recoil events and is consistent with the observed rate of multiple bubble events. This observation provides world best direct detection constraints on WIMP-proton spin-dependent scattering for WIMP masses $>$20 GeV/c$^{2}$ and demonstrates significant sensitivity for spin-independent interactions.
The Elliptical Isolated X-ray (ElIXr) Galaxy Survey is a volume-limited (<110Mpc) study of optically selected, isolated, Lstar elliptical galaxies, to provide an X-ray census of galaxy-scale (virial mass, Mvir < 1e13 Msun) objects, and identify candidates for detailed hydrostatic mass modelling. In this paper, we present a Chandra and XMM study of one such candidate, NGC1521, and constrain its distribution of dark and baryonic matter. We find a morphologically relaxed hot gas halo, extending almost to R500, that is well described by hydrostatic models similar to the benchmark, baryonically closed, Milky Way-mass elliptical galaxy NGC720. We obtain good constraints on the enclosed gravitating mass (M500=3.8e12+/-1e12 Msun, slightly higher than NGC\thin 720), and baryon fraction (fb500=0.13+/-0.03). We confirm at 8.2-sigma the presence of a dark matter (DM) halo consistent with LCDM. Assuming a Navarro-Frenk-White DM profile, our self-consistent, physical model enables meaningful constraints beyond R500, revealing that most of the baryons are in the hot gas. Within the virial radius, fb is consistent with the Cosmic mean, suggesting that the predicted massive, quasi-hydrostatic gas halos may be more common than previously thought. We confirm that the DM and stars conspire to produce an approximately powerlaw total mass profile (rho \propto r^-alpha) that follows the recently discovered scaling relation between alpha and optical effective radius. Our conclusions are insensitive to modest, observationally motivated, deviations from hydrostatic equilibrium. Finally, after correcting for the enclosed gas fraction, the entropy profile is close to the self-similar prediction of gravitational structure formation simulations, as observed in massive galaxy clusters.
We present dynamical and structural scaling relations of quiescent galaxies at z=2, including the dynamical mass-size relation and the first constraints on the fundamental plane (FP). The backbone of the analysis is a new, very deep VLT/X-shooter spectrum of a massive, compact, quiescent galaxy at z=2.0389. We detect the continuum between 3700-22000A and several strong absorption features (Balmer series, Ca H+K, G-band), from which we derive a stellar velocity dispersion of 318 +/- 53 km/s. We perform detailed modeling of the continuum emission and line indices and derive strong simultaneous constraints on the age, metallicity, and stellar mass. The galaxy is a dusty (A_V=0.77 (+0.36,-0.32)) solar metallicity (log(Z/Zsun) = 0.02 (+0.20,-0.41)) post starburst galaxy, with a mean luminosity weighted log(age/yr) of 8.9 +/- 0.1. The galaxy formed the majority of its stars at z>3 and currently has little or no ongoing star formation. We compile a sample of three other z~2 quiescent galaxies with measured velocity dispersions, two of which are also post starburst like. Their dynamical mass-size relation is offset significantly less than the stellar mass-size relation from the local early type relations, which we attribute to a lower central dark matter fraction. Recent cosmological merger simulations qualitatively agree with the data, but can not fully account for the evolution in the dark matter fraction. The z~2 FP requires additional evolution beyond passive stellar aging, to be in agreement with the local FP. The structural evolution predicted by the cosmological simulations is insufficient, suggesting that additional, possibly non-homologous structural evolution is needed.
In this short review we present the developments over the last 5 decades that have led to the use of Graphics Processing Units (GPUs) for astrophysical simulations. Since the introduction of NVIDIA's Compute Unified Device Architecture (CUDA) in 2007 the GPU has become a valuable tool for N-body simulations and is so popular these days that almost all papers about high precision N-body simulations use methods that are accelerated by GPUs. With the GPU hardware becoming more advanced and being used for more advanced algorithms like gravitational tree-codes we see a bright future for GPU like hardware in computational astrophysics.
We present Spitzer IRAC and MIPS observations of the star-forming region containing intermediate-mass young stellar object (YSO) AFGL 490. We supplement these data with near-IR 2MASS photometry and with deep SQIID observations off the central high extinction region. We have more than doubled the known membership of this region to 57 Class I and 303 Class II YSOs via the combined 1-24 um photometric catalog derived from these data. We construct and analyze the minimum spanning tree of their projected positions, isolating one locally over-dense cluster core containing 219 YSOs (60.8% of the region's members). We find this cluster core to be larger yet less dense than similarly analyzed clusters. Although the structure of this cluster core appears irregular, we demonstrate that the parsec-scale surface densities of both YSOs and gas are correlated with a power law slope of 2.8, as found for other similarly analyzed nearby molecular clouds. We also explore the mass segregation implications of AFGL 490's offset from the center of its core, finding that it has no apparent preferential central position relative to the low-mass members.
Using the planned antenna locations of the 128 antenna buildout of the Murchison Widefield Array (MWA), we accurately calculate its sensitivity to the Epoch of Reionization (EoR) power spectrum of redshifted 21 cm emission. Our calculation takes into account synthesis rotation, chromatic and asymmetrical baseline effects, and excludes modes that will be contaminated by foreground subtraction. With one full season of observation on two fields (900 and 700 hours), the MWA will be capable of a 14$\sigma$ detection of the EoR signal along with slope constraints.
Being able to measure each merger's sky location, distance, component masses, and conceivably spins, ground-based gravitational-wave detectors will provide a extensive and detailed sample of coalescing compact binaries (CCBs) in the local and, with third-generation detectors, distant universe. These measurements will distinguish between competing progenitor formation models. In this paper we develop practical tools to characterize the amount of experimentally accessible information available, to distinguish between two a priori progenitor models. Using a simple time-independent model, we demonstrate the information content scales strongly with the number of observations. The exact scaling depends on how significantly mass distributions change between similar models. We develop phenomenological diagnostics to estimate how many models can be distinguished, using first-generation and future instruments. Finally, we emphasize that multi-observable distributions can be fully exploited only with very precisely calibrated detectors, search pipelines, parameter estimation, and Bayesian model inference.
We report on the development of W-band (75-110 GHz) heterodyne receiver technology for large-format astronomical arrays. The receiver system is designed to be both mass-producible, so that the designs could be scaled to thousands of receiver elements, and modular. Most of the receiver function- ality is integrated into compact Monolithic Microwave Integrated Circuit (MMIC) amplifier-based multichip modules. The MMIC modules include a chain of InP MMIC low-noise amplifiers, coupled-line bandpass filters and sub-harmonic Schottky diode mixers. The receiver signals will be routed to and from the MMIC modules on a multilayer high frequency laminate, which includes splitters, amplifiers, and frequency doublers. A prototype MMIC module has exhibited a band-averaged noise temperature of 41 K from 82-100 GHz and a gain of 29 dB at 15 K, which is the state- of-the-art for heterodyne multi-chip modules.
The radial velocity-discovered exoplanet HD 97658b was recently announced to transit, with a derived planetary radius of 2.93 $\pm$ 0.28 R$_{\oplus}$. As a transiting super-Earth orbiting a bright star, this planet would make an attractive candidate for additional observations, including studies of its atmospheric properties. We present and analyze follow-up photometric observations of the HD 97658 system acquired with the MOST space telescope. Our results show no transit with the depth and ephemeris reported in the announcement paper. For the same ephemeris, we rule out transits for a planet with radius larger than 1.87 R$_{\oplus}$. We also report new radial velocity measurements which continue to support the existence of an exoplanet with a period of 9.5 days, and obtain improved orbital parameters.
We investigate the environment in the vicinity of the supernova remnant (SNR) G59.5+0.1 and identify all young stellar objects (YSOs) around the SNR, to derive the physical properties, obtain insight into the star-formation history, and further see whether SNR G59.5+0.1 can trigger star formation in this region. We have performed the submillimeter/millimeter observations in CO lines toward the southeast of SNR G59.5+0.1 with the KOSMA 3m Telescope. High integrated CO line intensity ratio R(CO 3-2/CO 2-1) is identified as one good signature of SNR-MCs (molecular clouds) interacting system. To investigate the impact of SNR G59.5+0.1 on the process of star formation, we used GLIMPSE I Catalog to select YSOs (including class I and class II sources). CO emission in an arc-like shape and mid-infrared 8.28 um emission are well coincident with SNR G59.5+0.1, which has the total mass of 1.1*10^{4}Msun and fully cover open cluster NGC 6823. Three molecular clumps were identified in the CO molecular arc, each clump shows the broad line wing emission, indicating that there are three outflows motion. The integrated CO line intensity ratio (R(CO 3-2/CO 2-1) for the whole molecular arc is between 0.48 and 1.57. The maximum value is 1.57, which is much higher than previous measurements of individual Galactic MCs. The CO molecular arc has a line intensity ratio gradient. SNR G59.5+0.1 is in adiabatic expansion phase. The age of the SNR is 8.6*10^{4} yr. Based on GLIMPSE I Catalog 625 young stellar objects (YSOs) candidates (including 176 class I sources and 449 class II sources) are selected. The timescales for class 0, class I and class II sources are <10^{4} yr, ~10^{5} yr, and ~10^{6} yr, respectively. The number of YSOs are significantly enhanced in the interacting regions, indicating the presence of some recently formed stars.
Modeling extinction along anomalous/non-CCM sightlines, which are characterized by a broad $217.5 nm$ bump and steep far-ultraviolet (FUV) rise, is reported. The extinction along these sightlines, viz. {HD 210121}, {HD 204827}, {HD 29647} and {HD 62542}, is difficult to reproduce using standard silicate and graphite grains. Very good match with the observed extinction is obtained by considering nanodiamond component as part of carbonaceous matter. Most of these sightlines are rich in carbon and are invariably backed by a young hot stellar object. Nanodiamond is taken as core within amorphous carbon and graphite. These core-mantle particles taken as additional components along with graphite and silicates lead to reduction in the silicate requirement. The abundance of carbonaceous matter is not affected as a very small fraction of nanodiamond is required. Extinction along sightlines that show steep FUV is also reported demonstrating the importance of nanodiamond component in all such regions.
Solar-like oscillations have been observed by Kepler and CoRoT in several
solar-type stars, thereby providing a way to probe the stars using
asteroseismology.
We provide the mode frequencies required for performing comparison with those
obtained from stellar modelling.
Time series of 9 months of data have been used. The power spectra of 61
main-sequence and subgiant stars have been analysed using both Maximum
Likelihood Estimators and Bayesian estimators, providing individual mode
characteristics such as frequencies, linewidths, and mode heights. We {{\bf
derived and describe}} a methodology for extracting a single set of mode
frequencies from multiple sets derived by different methods and individuals. We
report on how one can assess the quality of the fitted parameters using the
likelihood ratio test and the posterior probabilities.
Here we give the mode frequencies of 61 stars (with their 1-sigma error
bars), as well as their associated \'echelle diagrams.
Weak gravitational lensing by galaxy clusters on faint higher redshift galaxies has been traditionally used to study the cluster mass distribution and as a tool to identify clusters as peaks in the shear maps. However, it becomes soon clear that peaks statistics can also be used as a way to constrain the underlying cosmological model due to its dependence on both the cosmic expansion rate and the growth rate of structures. This feature makes peak statistics particularly interesting from the point of view of discriminating between General Relativity and modified gravity. Here we consider a general class of f(R) theories and compute the observable mass function based on the aperture mass statistics. We complement our theoretical analysis with a Fisher matrix forecast of the constraints that an Euclid - like survey can impose on the f(R) model parameters. We show that peak statistics alone can in principle discriminate between General Relativity and f(R) models and strongly constrain the f(R) parameters that are sensitive to the non - linear growth of structure. However, we also find a degeneracy between f(R) and dark energy models and the adopted relation between cluster mass and concentration.
We present the results of complex seismic modelling of the Slowly Pulsating B-type star HD74560. The star pulsates in five frequencies detected in photometric observations. For all these frequencies, we identify the mode degree, $\ell$. For two of them, found also in spectroscopic data, we are able to derived the empirical values of the complex nonadiabatic parameter $f$. We test effects of chemical composition and opacity data. Our results show that the properties of seismic models of SPB stars differ significantly from those of the more massive $\beta$ Cephei stars.
I present a brief review of the properties of jets from X-ray binaries, highlighting the disk-jet connection, in which there are strong correlations between X-ray and radio power for black holes and for neutron star in low/hard spectral states, and reduced emission in soft states. I discuss how some of the new "deviant" black hole systems which follow the relation normally found for neutron stars might fit into such a picture. I close by highlighting a few open questions which might be best addressed with soft gamma-ray observations.
Radio and X-ray emission of AGN appears to be correlated. The details of the underlying physical processes, however, are still not fully understood, i.e., to what extent is the X-ray and radio emission originating from the same relativistic particles or from the accretion-disk or corona or both. We study the cm radio emission of an SDSS/ROSAT/FIRST matched sample of 13 X-raying AGN in the redshift range 0.11< z < 0.37 at high angular resolution with the goal of searching for jet structures or diffuse, extended emission on sub-kpc scales. We use MERLIN at 18 cm for all objects and Western EVN at 18 cm for four objects to study the radio emission on scales of ~500 pc and ~40 pc for the MERLIN and EVN observations, respectively. The detected emission is dominated by compact nuclear radio structures. We find no kpc collimated jet structures. The EVN data indicate for compact nuclei on 40 pc scales, with brightness temperatures typical for accretion-disk scenarios. Comparison with FIRST shows that the 18 cm emission is resolved out up to 50% by MERLIN. Star-formation rates based on large aperture SDSS spectra are generally too small to produce considerable contamination of the nuclear radio emission. We can, therefore, assume the 18 cm flux densities to be produced in the nuclei of the AGN. Together with the ROSAT soft X-ray luminosities and black hole mass estimates from the literature, our sample objects follow closely the Merloni et al. (2003) fundamental plane relation, which appears to trace the accretion processes. Detailed X-ray spectral modeling from deeper hard X-ray observations and higher angular resolution at radio wavelengths are required to further proceed in the disentangling of jet and accretion related processes.
I find the common envelope (CE) energy formalism, the CE \alpha-prescription, to be inadequate to predict the final orbital separation of the CE evolution in massive envelopes. I find that when the orbital separation decreases to ~10 times the final orbital separation predicted by the CE \alpha-prescription, the companion has not enough mass in its vicinity to carry away its angular momentum. The core-secondary binary system must get rid of its angular momentum by interacting with mass further out. The binary system interacts gravitationally with a rapidly-rotating flat envelope, in a situation that resembles planet-migration in protoplanetary disks. The envelope convection of the giant carries energy and angular momentum outward. The basic assumption of the CE \alpha-prescription, that the binary system gravitational energy goes to unbind the envelope, breaks-down. Based on that, I claim that merger is a common outcome of the CE evolution of AGB and red super-giants stars with an envelope to secondary mass ratio of M_{env}/M_2 >~5. I discuss some other puzzling observations that might be explained by the migration and merger processes.
Numerous nuclear reactions in the crust of accreting neutron stars are strongly affected by dense plasma environment. Simulations of superbursts, deep crustal heating and other nuclear burning phenomena in neutron stars require astrophysical S-factors for these reactions (as a function of center-of-mass energy E of colliding nuclei). A large database of S-factors is created for about 5000 non-resonant fusion reactions involving stable and unstable isotopes of Be, B, C, N, O, F, Ne, Na, Mg, and Si. It extends the previous database of about 1000 reactions involving isotopes of C, O, Ne, and Mg. The calculations are performed using the Sao Paulo potential and the barrier penetration formalism. All calculated S-data are parameterized by an analytic model for S(E) proposed before [Phys. Rev. C 82, 044609 (2010)] and further elaborated here. For a given reaction, the present S(E)-model contains three parameters. These parameters are easily interpolated along reactions involving isotopes of the same elements with only seven input parameters, giving an ultracompact, accurate, simple, and uniform database. The S(E) approximation can also be used to estimate theoretical uncertainties of S(E) and nuclear reaction rates in dense matter, as illustrated for the case of the 34Ne+34Ne reaction in the inner crust of an accreting neutron star.
We investigate the possibility that the galactic dark matter exists in the phantom field responsible for the dark energy. We obtain the statically and spherically exact solution for this kind of the galaxy system with a supermassive black hole at its center. The solution of the metric functions is satisfied with $g_{tt} = - g_{rr}^{-1}$. Constrained by the observation of the rotational stars moving in circular orbits with nearly constant tangential speed in a spiral galaxy, the background of the phantom field which is spatially inhomogeneous has an exponential potential. The absorption cross section of the low-energy $S$-wave excitations, arising from the phantom dark energy, into the central black hole is shown to be the horizontal area of the central black hole. Because the infalling phantom particles have a total negative energy, the accretion of the phantom energy is companied with the decrease of the black hole mass which is estimated to be much less than a solar mass in the lifetime of the Universe. Using a simple model with the cold dark matters very weakly coupled to the phantom particles which are generated from the background, we show that these two densities can be stable in the galaxy.
New aspects of the slow solar wind turbulent heating and acceleration are investigated. A physical meaning of the lower boundary of the Alfv\'en wave turbulent spectra in the solar atmosphere and the solar wind is studied and the significance of this natural parameter is demonstrated. Via an analytical and quantitative treatment of the problem we show that a truncation of the wave spectra from the lower frequency side, which is a consequence of the solar magnetic field structure and its cyclic changes, results in a significant reduction of the heat production and acceleration rates. An appropriate analysis is presented regarding the link of the considered problem with existing observational data and slow solar wind initiation scenarios.
We have conducted a statistical analysis of the ultra-luminous X-ray point sources (ULXs; L(X) >= 10^39 erg/s) in a sample of galaxies selected from the Arp Atlas of Peculiar Galaxies. We find a possible enhancement of a factor of ~2-4 in the number of ULXs per blue luminosity for the strongly interacting subset. Such an enhancement would be expected if ULX production is related to star formation, as interacting galaxies tend to have enhanced star formation rates on average. For most of the Arp galaxies in our sample, the total number of ULXs compared to the far-infrared luminosity is consistent with values found earlier for spiral galaxies. This suggests that for these galaxies, ULXs trace recent star formation. However, for the most infrared-luminous galaxies, we find a deficiency of ULXs compared to the infrared luminosity. For these very infrared-luminous galaxies, AGNs may contribute to powering the far-infrared; alternatively, ULXs may be highly obscured in the X-ray in these galaxies and therefore not detected by these Chandra observations. We determined local UV/optical colors within the galaxies in the vicinity of the candidate ULXs using GALEX UV and SDSS optical images. In most cases, the distributions of colors are similar to the global colors of interacting galaxies. However, the u - g and r - i colors at the ULX locations tend to be bluer on average than these global colors, suggesting that ULXs are preferentially found in regions with young stellar populations. In the Arp sample there is a possible enhancement of a factor of ~2 - 5 in the fraction of galactic nuclei that are X-ray bright compared to more normal spirals.
The realization of low-cost instruments with high technical performance is a goal which deserves some efforts in an epoch of fast technological developments: indeed such instruments can be easily reproduced and therefore allow to open new research programs in several Observatories. We realized a fast optical photometer based on the SiPM technology, using commercially available modules. Using low-cost components we have developed a custom electronic chain to extract the signal produced by a commercial MPPC module produced by Hamamatsu, in order to obtain sub millisecond sampling of the light curve of astronomical sources, typically pulsars. In the early February 2011 we observed the Crab Pulsar at the Cassini telescope with our prototype photometer, deriving its period, power spectrum and shape of its light curve in very good agreement with the results obtained in the past with other instruments.
The recent analysis of observations taken with the EIS instrument on Hinode suggests that well constrained measurements of the temperature distribution in solar active regions can finally be made. Such measurements are critical for constraining theories of coronal heating. Past analysis, however, has suffered from limited sample sizes and large uncertainties at temperatures between 5 and 10 MK. Here we present a systematic study of the differential emission cores. We focus on measurements in the "inter-moss" region, that is, the region between the loop footpoints, where the observations are easier to interpret. To reduce the uncertainties at the highest temperatures we present a new method for isolating the Fe XVIII emission in the AIA/SDO 94 channel. The resulting differential emission measure distributions confirm our previous analysis showing that the temperature distribution in an active region core is often strongly peaked near 4 MK. We characterize the properties of the emission distribution as a function of the total unsigned magnetic flux. We find that the amount of high temperature emission in the active region core is correlated with the total unsigned magnetic flux, while the emission at lower temperatures, in contrast, is inversely related. These results provide compelling evidence that high temperature active region emission is often close to equilibrium, although weaker active regions may be dominated by evolving million degree loops in the core.
Recent observations of z >~ 7 Ly{\alpha} emitters (LAEs) have derived a variety of Ly{\alpha} luminosity functions (LFs) with contradictory results, evolution or non-evolution from z <~ 6, the epoch after reionization. This could be because most of z >~ 7 LFs comprise photometric candidates and might include some contaminations. We conducted the Subaru Telescope Faint Object Camera And Spectrograph narrowband NB980 ({\lambda}c ~ 9800A, FWHM ~ 100A) imaging and spectroscopy survey of z=7-7.1 LAEs to compare its "contamination-free" result with z >~ 7 photometric Ly{\alpha} LFs previously derived. We imaged the Subaru Deep Field and the sky around a cluster MS 1520.1+3002 and found one LAE candidate, but spectroscopy did not reveal Ly{\alpha} though deep enough to detect it. We calculated the expected number of LAEs in our survey, using five z=7 and three z=7.7 Ly{\alpha} LFs from recent surveys. Seven of them are consistent with null detection (0.1^{+1.8}_{-0.1}-1.1^{+2.2}_{-1.0} LAEs) within errors including Poisson statistics and cosmic variance, but average values (0.7-1.1 LAEs) predicted from one z=7 and two z=7.7 LFs among the seven indicate nearly a single detection. The remaining one z=7 LF predicts 3.0^{+3.2}_{-2.0} LAEs. As to z=7, the discrepancy likely comes from different LAE selection criteria. For z=7.7, there are two possibilities; (1) If z=7.7 LAEs are somehow brighter in Ly{\alpha} luminosity than lower redshift LAEs, z=7.7 LF is observed to be similar to or higher than lower redshift LFs even if attenuated by neutral hydrogen. (2) All/most of the z=7.7 candidates are not LAEs. This supports the decline of LF from z ~ 6 to 7.7 and reionization at z ~ 6-7.7.
We searched for z=7.3 Ly{\alpha} emitters (LAEs) behind two lensing clusters, Abell 2390 and CL 0024, using the Subaru Telescope Suprime-Cam and a narrowband NB1006 ({\lambda}c ~ 1005 nm, FWHM ~ 21 nm). Combination of the fully depleted CCDs of the Suprime-Cam, sensitive to z ~ 7 Ly{\alpha} at ~ 1 {\mu}m, and magnification by the lensing clusters can be potentially a powerful tool to detect faint distant LAEs. Using NB1006 and deep optical-infrared images taken with the Hubble and Spitzer Space Telescopes, we investigated if there exist objects consistent with the color of z=7.3 LAEs behind the clusters. We could not detect any LAEs to the unlensed Ly{\alpha} flux limit F(Ly{\alpha}) ~ 6.9 x 10^{-18} erg s^{-1} cm^{-2}. Comparison with z ~ 7 LAE field searches suggests that a blank field survey covering an area sufficiently larger than lensing clusters is more efficient in finding a large number of z ~ 7 LAEs than both a lensing survey observing many clusters with shallow imaging and a lensing survey imaging one cluster to a deeper luminosity limit, expected from the bright end slope of several z ~ 7 Ly{\alpha} luminosity functions. We also investigated the NB1006 images of the three z ~ 7 z-dropout galaxy candidates previously detected in Abell 2390 and found that none of them are detected in NB1006. Two of them are consistent with predictions from the previous studies that they would be at lower redshifts. The other one has a photometric redshift of z ~ 7.3, and if we assume that it is at z=7.3, the unlensed Ly{\alpha} line flux would be very faint: F(Ly{\alpha}) < 4.4 x 10^{-18} erg s^{-1} cm^{-2} (1 {\sigma} upper limit) or rest frame equivalent width of W(Ly{\alpha}) < 26A. Its Ly{\alpha} emission might be attenuated by neutral hydrogen, as recent studies show that the fraction of Lyman break galaxies displaying strong Ly{\alpha} emission is lower at z ~ 7 than at z <~ 6.
The cosmic string is a useful probe of the early Universe and may give us a clue to physics at high energy scales where any artificial particle accelerators cannot reach. Although one of the most promising tools is the cosmic microwave background, the constraint from gravitational waves is becoming so stringent that one may not hope to detect its signatures in the cosmic microwave background. In this paper, we construct a scenario that contains cosmic strings observable in the cosmic microwave background while evading the constraint imposed by the recent pulsar timing data. We argue that cosmic strings with relatively large tension are allowed by delaying the onset of the scaling regime. We also show that this scenario is naturally realized in the context of chaotic inflation in supergravity, where the phase transition is governed by the Hubble induced mass.
SaVi, a program for visualizing satellite orbits, movement, and coverage, is maintained at the University of Surrey. This tool has been used for research in academic papers, and by industry companies designing and intending to deploy satellite constellations. It has also proven useful for demonstrating aspects of satellite constellations and their geometry, coverage and movement for educational and teaching purposes. SaVi is introduced and described briefly here.
We propose a disc-corona model in which a geometrically thin, optically thick disc surrounds a Kerr black hole, and magnetic fields exert a time-steady torque on the inner edge of the accretion disc. The analytical expression of the total gravitational power is derived from the thin-disc dynamics equations by using this new boundary condition. It is shown that the magnetic torque can considerably enhance the amount of energy released in the disc-corona system. Furthermore, the global solutions of this disc-corona system are obtained numerically. We find that the fraction of the power dissipated into the corona in the total for such disc-corona system increases with the increasing dimensionless black hole spin parameter $a_\ast $, but is insensitive on the $\Delta \varepsilon $ which is the additional radiative efficiency parameter relevant to magnetic torque, for $\Delta\varepsilon > 1$. In addition, the emerged spectra from this disc-corona system are simulated by using Monte-Carlo method, and the effect of the different parameters on the output spectra is discussed.
A jet acceleration model for extracting energy from disk-corona surrounding a rotating black hole is proposed. In the disk-corona scenario, we obtain the ratio of the power dissipated in the corona to the total for such disk-corona system by solving the disk dynamics equations. The analytical expression of the jet power is derived based on the electronic circuit theory of the magnetosphere. It is shown that jet power increases with the increasing black hole (BH) spin, and concentrates in the inner region of the disk-corona. In addition, we use a sample consisting of 37 radio loud quasars to explore their jet production mechanism, and show that our jet formation mechanism can simulate almost all sources with high power jet, that fail to be explained by the Blandford-Znajek (BZ) process.
We propose a model for the spectral formation of Gamma Ray Burst (GRB) prompt emission, where the phenomenological Band's function is usually applied to describe the GRB prompt emission. We suggest that the GRB prompt emission is mainly a result of two upscattering processes. The first process is the Comptonization of relatively cold soft photons of the star off electrons of a hot shell of plasma of temperature T_e of the order of 10^{9} K (or kT_e~100 keV) that moves sub-relativistically with the bulk velocity V_b substantially less than the speed of light c. In this phase, the Comptonization parameter Y is high and the interaction between a blackbody-like soft seed photon population and hot electrons leads to formation of a saturated Comptonization spectrum modified by the sub-relativistic bulk outflow. The second process is an upscattering of the previously Comptonized spectrum by the plasma outflow once it becomes relativistic. This process gives rise to the high-energy power-law component above the peak in the EF(E)-diagram where F(E) is the energy flux. The latter process can be described by a convolution of the Comptonized spectrum with a broken-power-law Green function. Possible physical scenarios for this second upscattering process are discussed. In the framework of our model, we give an interpretation of the Amati relation between the intrinsic spectral peak photon energy and radiated energy or luminosity, and we propose a possible explanation of the GRB temporal variability.
A variety of supernova events, including Type IIn supernovae and ultraluminous supernovae, appear to have lost up to solar masses of their envelopes in 10's to 100's of years leading up to the explosion. In order to explain the close timing of the mass loss and supernova events, we explore the possibility that the mass loss is driven by common envelope evolution of a compact object (neutron star or black hole) in the envelope of a massive star and the supernova is triggered by the inspiral of the compact object to the central core of the companion star. The expected rate of such events is smaller than the observed rate of Type IIn supernovae but the rates may agree within the uncertainties. The mass loss velocity is related to the escape velocity from the common envelope system and is comparable to the observed velocity of 100's of km s$^{-1}$ in Type IIn events. The mass loss is expected to be denser near the equatorial plane of the binary system and there is good evidence that the circumstellar media in Type IIn supernovae are asymmetric. Some of these supernova types show evidence for energies in excess of the canonical $10^{51}$ ergs, which might be the result of explosions from rapid accretion onto a compact object through a disk.
We study the radio - far-infrared (FIR) correlation in a sample of faint dwarf irregular galaxies using NVSS data for 1.4 GHz radio flux, Spitzer MIPS 70 um data for FIR flux, and GALEX FUV data to estimate the star formation rates (SFR). Since our target galaxies are extremely faint, we stack images of many galaxies together to estimate the average radio and FIR fluxes. We find that for a given SFR both 70 um and 1.4 GHz fluxes are low compared to the calibration for large spirals. Nonetheless, the ratio of 70 um to 1.4 GHz flux agrees within errorbars with that seen for large galaxies. The radio-FIR correlation thus appears to be the result of a 'conspiracy'. We use the SFR to estimate the non-thermal fraction of the 1.4 GHz radio emission and find it to be around 50%, much smaller than the 90% typical for spirals. We also estimate the equipartition magnetic field and find it to be ~ 2 microgauss, about five times smaller than that typical for spirals.
The eclipsing binary system 2M 1938+4603 consists of a pulsating hot subdwarf B star and a cool M dwarf companion in an effectively circular three-hour orbit. The light curve shows both primary and secondary eclipses, along with a strong reflection effect from the cool companion. Here we present constraints on the component masses and eccentricity derived from the R{\o}mer delay of the secondary eclipse. Using six months of publicly-available Kepler photometry obtained in Short Cadence mode, we fit model profiles to the primary and secondary eclipses to measure their centroid values. We find that the secondary eclipse arrives on average 2.06 +/- 0.12 s after the midpoint between primary eclipses. Under the assumption of a circular orbit, we calculate from this time delay a mass ratio of q = 0.2691 +/- 0.0018 and individual masses of M_sd = 0.372 +/- 0.024 Msun and M_c = 0.1002 +/- 0.0065 Msun for the sdB and M dwarf, respectively. These results differ slightly from those of a previously-published light curve modeling solution; this difference, however, may be reconciled with a very small eccentricity, e cos \omega\ ~ 0.00004. We also report an orbital period decrease of P-dot = (-1.23 +/- 0.07) x 10^-10.
Surprisingly little is known about the origin and evolution of the Milky Way's satellite galaxy companions. UV photoionisation, supernova feedback and interactions with the larger host halo are all thought to play a role in shaping the population of satellites that we observe today, but there is still no consensus as to which of these effects, if any, dominates. In this paper, we revisit the issue by re-simulating a Milky Way class dark matter (DM) halo with unprecedented resolution. Our set of cosmological hydrodynamic Adaptive Mesh Refinement (AMR) simulations, called the Nut suite, allows us to investigate the effect of supernova feedback and UV photoionisation at high redshift with sub-parsec resolution. We subsequently follow the effect of interactions with the Milky Way-like halo using a lower spatial resolution (50pc) version of the simulation down to z=0. This latter produces a population of simulated satellites that we compare to the observed satellites of the Milky Way and M31. We find that supernova feedback reduces star formation in the least massive satellites but enhances it in the more massive ones. Photoionisation appears to play a very minor role in suppressing star and galaxy formation in all progenitors of satellite halos. By far the largest effect on the satellite population is found to be the mass of the host and whether gas cooling is included in the simulation or not. Indeed, inclusion of gas cooling dramatically reduces the number of satellites captured at high redshift which survive down to z=0.
The star-forming regions in Chamaeleon are one of the nearest (distance ~165 pc) and youngest (age ~2 Myrs) conglomerates of recently formed stars and the ideal target for population studies of star formation. We investigate a total of 16 Cha targets, which have been suggested, but not confirmed as binaries or multiple systems in previous literature. We used the adaptive optics instrument Naos-Conica (NACO) at the Very Large Telescope Unit Telescope 4 of the Paranal Observatory, at 2-5 different epochs, in order to obtain relative and absolute astrometric measurements, as well as differential photometry in the J, H, and K band. On the basis of known proper motions and these observations, we analyse the astrometric results in our "Proper Motion Diagram" (PMD: angular separation / position angle versus time), to eliminate possible (non-moving) background stars, establish co-moving binaries and multiples, and search for curvature as indications for orbital motion. All previously suggested close components are co-moving and no background stars are found. The angular separations range between 0.07 and 9 arcseconds, corresponding to projected distances between the components of 6-845 AU. Thirteen stars are at least binaries and the remaining three (RX J0919.4-7738, RX J0952.7-7933, VW Cha) are confirmed high-order multiple systems with up to four components. In 13 cases, we found significant slopes in the PMDs, which are compatible with orbital motion whose periods range from 60 to 550 years. However, in only four cases there are indications of a curved orbit, the ultimate proof of a gravitational bond. Massive primary components appear to avoid the simultaneous formation of equal-mass secondary components. (abridged)
We present the growing mode solutions of cosmological perturbations to the second order in the matter dominated era. We also present several gauge-invariant combinations of perturbation variables to the second order in most general fluid context. Based on the solutions we study the Newtonian correspondence of relativistic perturbations to the second order. In addition to the previously known exact relativistic/Newtonian correspondence of density and velocity perturbations to the second order in the comoving gauge, here we show that in the sub-horizon limit we have the correspondences for density, velocity and potential perturbations in the zero-shear gauge and in the uniform-expansion gauge to the second order. Density perturbation in the uniform curvature gauge also shows the correspondence to the second order in the sub-horizon scale. We also identify the relativistic gravitational potential which shows exact correspondence to the Newtonian one to the second order.
What are the origins of the soft X-ray line emission from non-AGN galaxies? XMM-Newton RGS spectra of nearby non-AGN galaxies (including starforming ones: M82, NGC 253, M51, M83, M61, NGC 4631, M94, NGC 2903, and the Antennae galaxies, as well as the inner bulge of M31) have been analyzed. In particular, the K{\alpha} triplet of O VII shows that the resonance line is typically weaker than the forbidden and/or inter-combination lines. This suggests that a substantial fraction of the emission may not arise directly from optically thin thermal plasma, as commonly assumed, and may instead originate at its interface with neutral gas via charge exchange. This latter origin naturally explains the observed spatial correlation of the emission with various tracers of cool gas in some of the galaxies. However, alternative scenarios, such as the resonance scattering by the plasma and the relic photo-ionization by AGNs in the recent past, cannot be ruled out, at least in some cases, and are being examined. Such X-ray spectroscopic studies are important to the understanding of the relationship of the emission to various high-energy feedback processes in galaxies.
We present a spatial analysis of the soft X-ray and H{\alpha} emissions from the outflow of the starburst galaxy M82. We find that the two emissions are tightly correlated on various scales. The O VII triplet of M82, as resolved by X-ray grating observations of XMM-Newton, is dominated by the forbidden line, inconsistent with the thermal prediction. The O VII triplet also shows some spatial variations. We discuss three possible explanations for the observed O VII triplet, including the charge exchange at interfaces between the hot outflow and neutral cool gas, a collisional non-equilibrium-ionization recombining plasma, and resonance scattering.
We examine plasma composition of jets in active galactic nuclei through the comparison of the total pressure ($P$) with partial pressures of electrons and protons in a cocoon. The total pressure is estimated from the analysis of an expanding cocoon dynamics. We determine the average kinetic energy per particle for several representative cases of particle energy distribution such as one- and two-temperature thermal plasmas and non-thermal electrons by evaluating the dissipation of total kinetic energy of the jet into the internal energy of cocoon plasma. The number density of the total electrons/positrons ($n_{\pm}$) in the cocoon is constrained by using the particle supply from hot spots and the absence of thermal bremsstrahlung emission from radio lobes. By inserting $P$, $n_{\pm}$ and the particle energy of each population into the equation of state, the number density ($n_{p}$) and pressure ($P_{p}$) of protons in the cocoon can be constrained. Applying this method to Cygnus A, we find that (i) electron/positron ($e^{\pm}$) pairs always dominate in terms of number density, but that (ii) either an "$e^{\pm}$-supported cocoon (i.e., $P_{\pm} >P_{p}$)" or "proton-supported one (i.e, $P_{\pm} <P_{p}$)" is possible.
A sample of 11 thousand galaxies with radial velocities V_ LG < 3500 km/s is used to study the features of the local distribution of luminous (stellar) and dark matter within a sphere of radius of around 50 Mpc around us. The average density of matter in this volume, Omega_m,loc=0.08+-0.02, turns out to be much lower than the global cosmic density Omega_m,glob=0.28+-0.03. We discuss three possible explanations of this paradox: 1) galaxy groups and clusters are surrounded by extended dark halos, the major part of the mass of which is located outside their virial radii; 2) the considered local volume of the Universe is not representative, being situated inside a giant void; and 3) the bulk of matter in the Universe is not related to clusters and groups, but is rather distributed between them in the form of massive dark clumps. Some arguments in favor of the latter assumption are presented. Besides the two well-known inconsistencies of modern cosmological models with the observational data: the problem of missing satellites of normal galaxies and the problem of missing baryons, there arises another one - the issue of missing dark matter.
By dividing the redshift region under consideration into two bins, we estimate the limitations in determining the equation of state $w_{de}$ of dark energy at high redshift from current and future observational data including supernovae, baryon acoustic oscillation and observational Hubble data. It is found that the constraints of $w_{de}$ from current data are weak (2$\sigma(w_{de})\sim1$) even beyond redshift $z=0.3$. For simulated future observational data, it is shown that $\sim2300$ supernovae data from a SANP-like JDEM survey give $2\sigma(w_{de})\sim1$ beyond $z=0.6$. We consider the effects of the divided point, the number of supernovae data and the error in the distance modulus on constraining $w_{de}$ at high redshift. It is shown that the increase of number of supernovae data seems not efficient on improving the constraints of $w_{de}$ at high redshift, while the improvement of observational error in distance modulus seems to be a better way.
The existence of convective and turbulent motions and the evolution of stellar magnetic fields give rise to existence of temperature fluctuations in stellar atmospheres. We observe the time and surface averaged radiation fluxes from the stars. The usual photosphere models do not take into account the temperature fluctuations and only present the distribution of the mean temperature into surface layers of stars. We investigate how the temperature fluctuations change the stellar spectra in continuum. The degree of fluctuations (the ratio of mean temperature fluctuation to the mean temperature) is supposed to be small. We discuss the procedure of calculation of the star spectrum, which takes into account the temperature fluctuations. As a first step we use the usual model of a photosphere without fluctuations. The observed spectrum is presented as a part depending on mean temperature and the additional part proportional to quadratic value of fluctuation degree. It is shown that the additional part in Wien's region of spectrum can be evaluated directly from wave length dependence of observed spectrum. This part depends on the first and second wavelength derivatives near the observed wavelength. It can be also derived from known models of photospheres. Our estimations show that the temperature dependence of absorption factors is very important by calculation of continuum spectra corrections. As the examples we present these estimations for some stars from Pulkovo spectrophotometric catalog and for the Sun. The influence of temperature fluctuations on color indices is also investigated. The problem how estimate the degree of fluctuations from statistical investigation of weakly variable stars and the stars of the same spectral type with almost equal luminosities is also discussed.
We successfully detected a molecular outflow with a scale of 370-450 pc in the central region of the starburst galaxy NGC 3628 through deep CO(1-0) observations by using the Nobeyama Millimeter Array (NMA). The mass of the outflowing molecular gas is ~2.8x10^7 M_sun, and the outflow velocity is ~90(+/-10) km s^{-1}. The expansion timescale of the outflow is 3.3-6.8 Myr, and the molecular gas mass flow rate is 4.1-8.5 M_sun yr^{-1}. It requires mechanical energy of (1.8-2.8)x10^{54} erg to create this sub-kpc scale molecular outflow. In order to understand the evolution of the molecular outflow, we compare the physical properties between the molecular outflow observed from our NMA CO(1-0) data and the plasma gas from the soft X-ray emission of the Chandra X-ray Observatory (CXO) archival data. We found that the distribution between the molecular outflow and the strong plasma outflow seems to be in a similar region. In this region, the ram pressure and the thermal pressure of the plasma outflow are 10^{-(8-10)} dyne cm^{-2}, and the thermal pressure of molecular outflow is 10^{-(11-13)} dyne cm^{-2}. This implies the molecular outflow is still expanding outward. The molecular gas consumption timescale is estimated as 17-27 Myr, and the total starburst timescale is 20-34 Myr. The evolutionary parameter is 0.11-0.25, suggesting that the starburst activity in NGC 3628 is still in a young stage.
Previous studies have found that the width of gamma-ray burst (GRB) pulse is energy dependent and that it decreases as a power-law function with increasing photon energy. In this work we have investigated the relation between the energy dependence of pulse and the so-called Band spectrum by using a sample including 51 well-separated fast rise and exponential decay long-duration GRB pulses observed by BATSE (Burst and Transient Source Experiment on the Compton Gamma Ray Observatory). We first decompose these pulses into rise, and decay phases and find the rise widths, and the decay widths also behavior as a power-law function with photon energy. Then we investigate statistically the relations between the three power-law indices of the rise, decay and total width of pulse (denoted as $\delta_r$, $\delta_d$ and $\delta_w$, respectively) and the three Band spectral parameters, high-energy index ($\alpha$), low-energy index ($\beta$) and peak energy ($E_p$). It is found that (1)$\alpha$ is strongly correlated with $\delta_w$ and $\delta_d$ but seems uncorrelated with $\delta_r$; (2)$\beta$ is weakly correlated with the three power-law indices and (3)$E_p$ does not show evident correlations with the three power-law indices. We further investigate the origin of $\delta_d-\alpha$ and $\delta_w-\alpha$. We show that the curvature effect and the intrinsic Band spectrum could naturally lead to the energy dependence of GRB pulse width and also the $\delta_d-\alpha$ and $\delta_w-\alpha$ correlations. Our results would hold so long as the shell emitting gamma rays has a curve surface and the intrinsic spectrum is a Band spectrum or broken power law. The strong $\delta_d-\alpha$ correlation and inapparent correlations between $\delta_r$ and three Band spectral parameters also suggest that the rise and decay phases of GRB pulses have different origins.
We present a search for the [CII] 158micron fine structure line (a main cooling line of the interstellar medium) and the underlying far-infrared (FIR) continuum in three high-redshift (6.6<z<8.2) star-forming galaxies using the IRAM Plateau de Bure interferometer. We targeted two Lyman-Alpha-selected galaxies (Lyman-Alpha-Emitters, LAEs) with moderate UV-based star formation rates (SFR~20 M_sun/yr; Himiko at z=6.6 and IOK-1 at z=7.0) and a Gamma Ray Burst (GRB) host galaxy (GRB 090423 at z~8.2). Based on our 3 sigma rest-frame FIR continuum limits, previous (rest-frame) UV continuum measurements and spectral energy distribution (SED) fitting, we rule out SED shapes similar to highly obscured galaxies (e.g. Arp220, M82) and less extreme dust-rich nearby spiral galaxies (e.g. M51) for the LAEs. Conservatively assuming a SED shape typical of local spiral galaxies we derive upper limits for the FIR-based star formation rates (SFRs) of ~70 M_sun/yr, ~50 M_sun/yr and ~40 M_sun/yr for Himiko, IOK-1 and GRB 090423, respectively. For the LAEs these limits are only a factor ~3 higher than the published UV-based SFRs (uncorrected for extinction). This indicates that the dust obscuration in the z>6 LAEs studied here is lower by a factor of a few than what has recently been found in some LAEs at lower redshift (2<z<3.5) with similar UV-based SFRs. A low obscuration in our z>6 LAE sample is consistent with recent rest-frame UV studies of z~7 Lyman-Break-Galaxies (LBGs).
We measure the shape of the velocity ellipsoid in two late-type spiral galaxies (Hubble types Sc and Scd) and combine these results with our previous analyses of six early-type spirals (Sa to Sbc) to probe the relation between galaxy morphology and the ratio of the vertical and radial dispersions. We confirm at much higher significance (99.9 percent) our prior detection of a tight correlation between these quantities. We explore the trends of the magnitude and shape of the velocity ellipsoid axes with galaxy properties (colour, gas surface mass density, and spiral arm structure). The observed relationships allow for an observational identification of the radial and vertical disk heating agents in external disk galaxies.
We characterise the primordial perturbations produced due to both inflaton and curvaton fluctuations in models where the curvaton has a quadratic, cosine or hyperbolic potential, and the inflaton potential is characterised by the usual slow-roll parameters. Isocurvature curvaton field perturbations can produce significant non-Gaussianity in the primordial density field, in contrast with adiabatic inflaton field perturbations which produce negligible non-Gaussianity for canonical scalar fields. A non-self-interacting curvaton with quadratic potential produces a local-type non-Gaussianity that is well described by the non-linearity parameter fNL, which may be scale-dependent when the inflaton perturbations dominate the power spectrum. We show how observational bounds on non-linearity parameters and the tensor-scalar ratio can be used to constrain curvaton and inflaton parameters. We find a consistency relation between the bispectrum and trispectrum parameters in a mixed inflaton-curvaton model for a quadratic curvaton potential. Self-interaction terms in the curvaton potential can lead to both a large trispectrum parameter, gNL, and scale-dependence of the non-linearity parameters.
The properties of the spin-down age are investigated. Based on assumption about a uniform magnetic field decay law we suggest a new method which allows us to shed light on magnetic field decay. This method is applied for following selection: isolated non-millisecond pulsars from the ATNF catalog are chosen. Pulsars in the selection are with the spin-down ages from 4 \cdot 10^4 to 2 \cdot 10^6 years. In order to avoid observational selection we take into account only pulsars which are closer to the Sun than 10 kpc. For this selection we restore the uniform magnetic field decay law. It appears that the magnetic field decays three times from 4 \cdot 10^4 to 3.5 \cdot 10^5 years. This function is approximated by modified power-law. We also estimate the birthrate of pulsars in our Galaxy and find that it should be about 2.9 pulsars per century.
Gliese 569B is a multiple brown dwarf system whose exact nature has been the
subject of several investigations over the past few years. Interpretation has
partially relied on infra-red photometry and spectroscopy of the resolved
components of the system. We present seeing limited Ks photometry over four
nights, searching for variability in this young low mass substellar system. Our
photometry is consistent with other reported photometry, and we report the
tentative detection of several periodic signals consistent with rotational
modulation due to spots on their surfaces. The five significant periods range
from 2.90 hours to 12.8 hours with peak to peak variabilities from 28 mmag to
62 mmag in the Ks band.
If both components are rotating with the shortest periods, then their
rotation axes are not parallel with each other, and the rotation axis of the Bb
component is not perpendicular to the Ba-Bb orbital plane. If Bb has one of the
longer rotational periods, then the Bb rotation axis is consistent with being
parallel to the orbital axis of the Ba-Bb system.
The hyper luminous X-ray source HLX-1 in the galaxy ESO 243-49, currently the best intermediate mass black hole candidate, displays spectral transitions similar to those observed in Galactic black hole binaries, but with a luminosity 100-1000 times higher. We investigated the X-ray properties of this unique source fitting multi-epoch data collected by Swift, XMM-Newton & Chandra with a disk model computing spectra for a wide range of sub- and super-Eddington accretion rates assuming a non-spinning black hole and a face-on disk (i = 0 deg). Under these assumptions we find that the black hole in HLX-1 is in the intermediate mass range (~2 x 10^4 M_odot) and the accretion flow is in the sub-Eddington regime. The disk radiation efficiency is eta = 0.11 +/-0.03. We also show that the source does follow the L_X ~ T^4 relation for our mass estimate. At the outburst peaks, the source radiates near the Eddington limit. The accretion rate then stays constant around 4 x 10^(-4) M_odot yr^(-1) for several days and then decreases exponentially. Such "plateaus" in the accretion rate could be evidence that enhanced mass transfer rate is the driving outburst mechanism in HLX-1. We also report on the new outburst observed in August 2011 by the Swift-X-ray Telescope. The time of this new outburst further strengthens the ~1 year recurrence timescale.
We study the cosmology of quintessence models in an extended theory of gravity in Lyra's geometry. By analyzing the possible interactions between the quintessence scalar and the intrinsic displacement field in Lyra's geometry, we obtain the closed form solutions of the modified Friedmann equations for four classes of quintessence models. Due to the presence of the geometrical displacement field, a late-time cosmic acceleration with the phantom divide crossing in a flat Robertson-Walker background is possible even if in these models there is no dynamical ghost mode involved.
Recent X-ray observations of the supernova remnant IC443 interacting with molecular clouds have shown the presence of a new population of hard X-ray sources related to the remnant itself, which has been interpreted in terms of fast ejecta fragment propagating inside the dense environment. Prompted by these studies, we have obtained a deep {\sl XMM-Newton} observation of the supernova remnant (SNR) Kes 69, which also shows signs of shock-cloud interaction. We report on the detection of 18 hard X-ray sources in the field of Kes 69, a significant excess of the expected galactic source population in the field, spatially correlated with CO emission from the cloud in the remnant environment. The spectra of 3 of the 18 sources can be described as hard power laws with photon index <2 plus line emission associated to K-shell transitions. We discuss the two most promising scenarios for the interpretation of the sources, namely fast ejecta fragments (as in IC443) and cataclysmic variables. While most of the observational evidences are consistent with the former interpretation, we cannot rule out the latter.
The NGC 1023 group is one of the most studied nearby groups. We want to give an insight into the evolution of its innermost region by means of ultraviolet observations and proper models. We used the FUV and NUV GALEX archival data as well as a large set of SPH simulations with chemo-photometric implementation. From the UV observations we found that several, already known, dwarf galaxies very close to NGC 1023 are also detected in UV and two more objects (with no optical counterpart) can be added to the group. Using these data we construct exhaustive models to account for their formation. We find that the whole SED of NGC 1023 and its global properties are well matched by a simulation which provides a minor merger with a companion system 5 times less massive. The strong interaction phase started 7.7 Gyr ago and the final merger 1.8 Gyr ago.
Optical and near-infrared variability is a well-known property of young stellar objects. However, a growing number of recent studies claim that a considerable fraction of them also exhibit mid-infrared flux changes. With the aim of studying and interpreting variability on a decadal timescale, here we present a mid-infrared spectral atlas containing observations of 68 low- and intermediate mass young stellar objects. The atlas consists of 2.5-11.6 um low-resolution spectra obtained with the ISOPHOT-S instrument on-board the Infrared Space Observatory (ISO) between 1996 and 1998, as well as 5.2-14.5 um low-resolution spectra obtained with the IRS instrument on-board the Spitzer Space Telescope between 2004 and 2007. The observations were retrieved from the ISO and Spitzer archives and were post-processed interactively by our own routines. For those 47 objects where multi-epoch spectra were available, we analyze mid-infrared spectral variability on annual and/or decadal timescales. We identify 37 variable candidate sources. Many stars show wavelength-independent flux changes, possibly due to variable accretion rate. In several systems, all exhibiting 10 um silicate emission, the variability of the 6-8 um continuum and the silicate feature exhibit different amplitudes. A possible explanation is variable shadowing of the silicate emitting region by an inner disk structure of changing height or extra silicate emission from dust clouds in the disk atmosphere. Our results suggest that mid-infrared variability, in particular the wavelength-dependent changes, are more ubiquitous than was known before. Interpreting this variability is a new possibility to explore the structure of the disk and its dynamical processes.
Wolf-Rayet (WR) stars are the evolved descendants of massive O-type stars and are considered to be progenitor candidates for Type Ib/c core-collapse supernovae (SNe). Recent results of our HST/WFC3 survey of Wolf-Rayet stars in M101 are summarised based on the detection efficiency of narrow-band optical imaging compared to broad-band methods. Weshow that on average of 42% WR stars, increasing to ~85% in central regions, are only detected in the narrow-band imaging. Hence, the non-detection of a WR star at the location of ~10 Type Ib/c SNe in broad-band imaging is no longer strong evidence for a non-WR progenitor channel.
We analyzed all archival data of the low-mass X-ray binary system 4U 1636--53 with the Rossi X-ray Timing Explorer (1490 observations). We found a total of 336 type-I X-ray bursts from this source. From fits to the time-resolved spectra, we classified 69 of these bursts as photospheric radius-expansion (PRE) bursts. PRE bursts show a characteristic time profile in which the fitted blackbody radius increases rapidly at the beginning of the burst, and then drops abruptly close to the peak of the burst. The lowest value of the radius after the expansion phase defines the so-called touchdown point. We found that in 17 of the PRE bursts, after the touchdown point, the blackbody radius increases again quickly after about 1 second, and from then on the radius decreases slightly or it remains more or less constant. In the other 52 PRE bursts, after touchdown, the radius of the blackbody stays more or less constant for $\sim 2 - 8$ seconds, and after that it increases slowly. Interestingly, those PRE bursts in which the blackbody radius remains more or less constant for $\simmore 2$ seconds show coherent oscillations in the tail of the burst, whereas those PRE in which the blackbody radius changes rapidly after touchdown show no coherent oscillations in the tail of the burst. From a Kolmogorov-Smirnov test we find that the difference between the two groups of PRE bursts is significant at a 5-$\sigma$ level. This is the first time that the presence of burst oscillations in the tail of X-ray bursts is associated with a systematic behaviour of the spectral parameters in that phase of the bursts. This result is consistent with predictions of models that associate the oscillations in the tail of X-ray bursts with the propagation of a cooling wake in the material on the neutron-star surface during the decay of the bursts.
We investigate the clustering of halos in cosmological models starting with general local-type non-Gaussian primordial fluctuations. We employ multiple Gaussian fields and add local-type non-Gaussian corrections at arbitrary order to cover a class of models described by frequently-discussed f_nl, g_nl and tau_nl parameterization. We derive a general formula for the halo power spectrum based on the peak-background split formalism. The resultant spectrum is characterized by only two parameters responsible for the scale-dependent bias at large scale arising from the primordial non-Gaussianities in addition to the Gaussian bias factor. We introduce a new inequality for testing non-Gaussianities originating from multi fields, which is directly accessible from the observed power spectrum. We show that this inequality is a generalization of the Yamaguchi-Suyama inequality between f_nl and tau_nl to the primordial non-Gaussianities at arbitrary order. We also show that the amplitude of the scale-dependent bias is useful to distinguish the simplest quadratic non-Gaussianities (i.e., f_nl-type) from higher-order ones (g_nl and higher), if one measures it from multiple species of galaxies or clusters of galaxies. We discuss the validity and limitations of our analytic results by comparison with numerical simulations in an accompanying paper.
Aiming at obtaining detailed information of surface environment of Earth-analogs, Kawahara & Fujii 2011 proposed an inversion technique of annual scattered light curves named the spin-orbit tomography (SOT), which enables one to sketch a 2-dimensional albedo map from annual variation of the disk-integrated scattered light, and demonstrated the method with a planet in a face-on orbit. We extend it to be applicable to general geometric configurations, including low-obliquity planets like the Earth in inclined orbits. We simulate light curves of the Earth in an inclined orbit in three photometric bands (0.4-0.5um, 0.6-0.7um, and 0.8-0.9um) and show that the distribution of clouds, snow, and continents are retrieved with the aid of the SOT. We also demonstrate the SOT by applying it to an upright Earth, a tidally-locked Earth, and Earth-analogs with ancient continental configurations. The inversion is model-independent in the sense that we do not assume specific albedo models when mapping the surface, and hence applicable in principle to any kind of inhomogeneity. This method can potentially serve as a unique tool to investigate the exohabitats/exoclimes of Earth-analogs.
We present a study of the large-scale spatial distribution of 6482 RASS X-ray sources in approximately 5000 deg^2 in the direction of Orion. We examine the astrophysical properties of a sub-sample of ~100 optical counterparts, using optical spectroscopy. This sub-sample is used to investigate the space density of the RASS young star candidates by comparing X-ray number counts with Galactic model predictions. We characterize the observed sub-sample in terms of spectral type, lithium content, radial and rotational velocities, as well as iron abundance. A population synthesis model is then applied to analyze the stellar content of the RASS in the studied area. We find that stars associated with the Orion star-forming region do show a high lithium content. A population of late-type stars with lithium equivalent widths larger than Pleiades stars of the same spectral type (hence younger than ~70-100 Myr) is found widely spread over the studied area. Two new young stellar aggregates, namely "X-ray Clump 0534+22" (age~2-10 Myr) and "X-ray Clump 0430-08" (age~2-20 Myr), are also identified. The spectroscopic follow-up and comparison with Galactic model predictions reveal that the X-ray selected stellar population in the direction of Orion is characterized by three distinct components, namely the clustered, the young dispersed, and the widespread field populations. The clustered population is mainly associated with regions of recent or ongoing star formation and correlates spatially with molecular clouds. The dispersed young population follows a broad lane apparently coinciding spatially with the Gould Belt, while the widespread population consists primarily of active field stars older than 100 Myr. We expect the "bi-dimensional" picture emerging from this study to grow in depth as soon as the distance and the kinematics of the studied sources will become available from the future Gaia mission.
Using the High Resolution Camera (HRC) aboard the Chandra X-ray Observatory, we have re-examined the proper motion of the central compact object RX J0822-4300 in the supernova remnant Puppis A. New data from 2010 August, combined with three archival data sets from as early as 1999 December, provide a baseline of 3886 days (more than 10 1/2 years) to perform the measurement. Correlating the four positions of RX J0822-4300 measured in each data set implies a projected proper motion of mu 71 \pm 12 masy. For a distance of 2 kpc this proper motion is equivalent to a recoil velocity of 672 \pm 115 km/s. The position angle is found to be 244 \pm 11 degrees. Both the magnitude and direction of the proper motion are in agreement with RX J0822-4300 originating near the optical expansion center of the supernova remnant. For a displacement of 371 \pm 31 arcsec between its birth place and today's position we deduce an age of (5.2 \pm 1.0) 10^3 yrs for RX J0822-4300. The age inferred from the neutron star proper motion and filament motions can be considered as two independent measurements of the same quantity. They average to 4450 \pm 750 yrs for the age of the supernova remnant Puppis A.
We report the results of the first X-ray observation of the luminous and helium-rich O-type subdwarf BD+37 442, carried out with the XMM-Newton satellite in August 2011. X-ray emission is detected with a flux of about 3x10^(-14) erg/cm2/s (0.2-1 keV) and a very soft spectrum, well fit by the sum of a blackbody with temperature kT_BB = 45^(+11)_(-9) eV and a power law with a poorly constrained photon index. Significant pulsations with a period of 19.2 s are detected, indicating that the X-ray emission originates in a white dwarf or neutron star companion, most likely powered by accretion from the wind of BD+37 442.
We study the non-linear gravitational collapse of dark matter into halos through numerical N-body simulations of Lemaitre-Tolman-Bondi void models. We extend the halo mass function formalism to these models in a consistent way. This extension not only compares well with the simulated data at all times and radii, but it also gives interesting clues about the impact of the background shear on the growth of perturbations. Our results give hints about the possibility of constraining the background shear via cluster number counts, which could then give rise to strong constraints on general inhomogeneous models, of any scale.
Using optical long baseline interferometry, we resolved for the first time the two wide components of HD167971, a candidate hierarchical triple system known to efficiently accelerate particles. Our multi-epoch VLTI observations provide direct evidence for a gravitational link between the O8 supergiant and the close eclipsing O + O binary. The separation varies from 8 to 15 mas over the three-year baseline of our observations, suggesting that the components evolve on a wide and very eccentric orbit (most probably e>0.5). These results provide evidence that the wide orbit revealed by our study is not coplanar with the orbit of the inner eclipsing binary. From our measurements of the near-infrared luminosity ratio, we constrain the spectral classification of the components in the close binary to be O6-O7, and confirm that these stars are likely main-sequence objects. Our results are discussed in the context of the bright non-thermal radio emission already reported for this system, and we provide arguments in favour of a maximum radio emission coincident with periastron passage. HD167971 turns out to be an efficient O-type particle accelerator that constitutes a valuable target for future high angular resolution radio imaging using VLBI facilities.
Simple scalings suggest that super-Earths are more likely than an equivalent Earth-sized planet to be undergoing plate tectonics. Generally, viscosity and thermal conductivity increase with pressure while thermal expansivity decreases, resulting in lower convective vigor in the deep mantle. According to conventional thinking, this might result in no convection in a super-Earth's deep mantle. Here we evaluate this. First, we here extend the density functional theory (DFT) calculations of post-perovskite activation enthalpy of to a pressure of 1 TPa. The activation volume for diffusion creep becomes very low at very high pressure, but nevertheless for the largest super-Earths the viscosity along an adiabat may approach 1030 Pa s in the deep mantle. Second, we use these calculated values in numerical simulations of mantle convection and lithosphere dynamics of planets with up to ten Earth masses. The models assume a compressible mantle including depth-dependence of material properties and plastic yielding induced plate tectonics. Results confirm the likelihood of plate tectonics and show a novel self-regulation of deep mantle temperature. The deep mantle is not adiabatic; instead internal heating raises the temperature until the viscosity is low enough to facilitate convective loss of the radiogenic heat, which results in a super-adiabatic temperature profile and a viscosity increase with depth of no more than ~3 orders of magnitude, regardless of the viscosity increase that is calculated for an adiabat. Convection in large super-Earths is characterised by large upwellings and small, time-dependent downwellings. If a super-Earth was extremely hot/molten after its formation, it is thus likely that even after billions of years its deep interior is still extremely hot and possibly substantially molten with a "super basal magma ocean" - a larger version of (Labrosse et al., 2007).
Radio and infrared interferometry of SiO maser stars provide complementary information on the atmosphere and circumstellar environment at comparable spatial resolution. Here, we present the latest results on the atmospheric structure and the dust condensation region of AGB stars based on our recent infrared spectro-interferometric observations, which represent the environment of SiO masers. We discuss, as an example, new results from simultaneous VLTI and VLBA observations of the Mira variable AGB star R Cnc, including VLTI near- and mid-infrared interferometry, as well as VLBA observations of the SiO maser emission toward this source. We present preliminary results from a monitoring campaign of high-frequency SiO maser emission toward evolved stars obtained with the APEX telescope, which also serves as a precursor of ALMA images of the SiO emitting region. We speculate that large-scale long-period chaotic motion in the extended molecular atmosphere may be the physical reason for observed deviations from point symmetry of atmospheric molecular layers, and for the observed erratic variability of high-frequency SiO maser emission
We review progress over the past decade in observations of large-scale star formation, with a focus on the interface between extragalactic and Galactic studies. Methods of measuring gas contents and star formation rates are discussed, and updated prescriptions for calculating star formation rates are provided. We review relations between star formation and gas on scales ranging from entire galaxies to individual molecular clouds.
An unbinned maximum likelihood analysis of CDMS low-energy data reveals a strong preference (5.7 sigma C.L.) for a model containing an exponential excess of events in the nuclear recoil band, when compared to the null hypothesis. We comment on the possible origin of such an excess, establishing a comparison with anomalies in other dark matter experiments. A recent annual modulation search in CDMS data is shown to be insufficiently sensitive to test a dark matter origin for this excess.
White dwarfs are almost completely degenerate objects that cannot obtain energy from thermonuclear sources, so their evolution is just a gravothermal cooling process. Recent improvements in the accuracy and precision of the luminosity function and in pulsational data of variable white dwarfs suggest that they are cooling faster than expected from conventional theory. In this contribution we show that the inclusion of an additional cooling term due to axions able to interact with electrons with a coupling constant g_ae ~(2-7)x10^{-13} allows to fit better the observations.
We simulate the multiphase ISM randomly heated and stirred by supernovae, with gravity, differential rotation and other parameters of the solar neighbourhood. Here we describe in detail both numerical and physical aspects of the model, including injection of thermal and kinetic energy by SN explosions, radiative cooling, photoelectric heating and various transport processes. With a three dimensional domain extending 1x1kpc^2 horizontally and 2kpc vertically, the model routinely spans gas number densities 10^-5-10^2cm^-3, temperatures 10-10^8K, local velocities up to 10^3kms^-1 (with Mach numbers to 25). The working numerical resolution of 4pc has been selected via simulations of a single expanding SN remnant, where we closely reproduce, at this resolution, analytical solutions for the adiabatic and snowplough regimes. The thermal structure of the modelled ISM is classified using the altitude variation of the fractional volumes occupied by gas in relatively narrow temperature bands. We confirm that most of the complexity can be captured in terms of just three phases, separated by temperature borderlines at about 10^3K and 5x10^5K. The distribution of gas densities within each phase is approximately lognormal. We clarify the connection between the fractional volume of a phase and its various proxies, and derive an exact relation between the fractional volume and the filling factors defined in terms of the volume and probabilistic averages. These results are discussed in both observational and computational contexts. The correlation scale of the random flows is calculated from the velocity autocorrelation function; it is of order 100pc and tends to grow with distance from the midplane. We use two distinct parameterizations of radiative cooling to show that the multiphase structure of the gas is robust, as it does not depend significantly on this choice.
The Lunar University Network for Astrophysics Research (LUNAR) is a team of researchers and students at leading universities, NASA centers, and federal research laboratories undertaking investigations aimed at using the Moon as a platform for space science. LUNAR research includes Lunar Interior Physics & Gravitation using Lunar Laser Ranging (LLR), Low Frequency Cosmology and Astrophysics (LFCA), Planetary Science and the Lunar Ionosphere, Radio Heliophysics, and Exploration Science. The LUNAR team is exploring technologies that are likely to have a dual purpose, serving both exploration and science. There is a certain degree of commonality in much of LUNAR's research. Specifically, the technology development for a lunar radio telescope involves elements from LFCA, Heliophysics, Exploration Science, and Planetary Science; similarly the drilling technology developed for LLR applies broadly to both Exploration and Lunar Science.
In 2011, the AAVSO conducted a survey of 615 people who are or were recently active in the 101-year old organization. The survey included questions about their demographic background and variable star interests. Data are descriptively analyzed and compared with prior surveys. Results show an organization of very highly educated, largely male amateur and professional astronomers distributed across 108 countries. Participants tend to be loyal, with the average time of involvement in the AAVSO reported as 14 years. Most major demographic factors have not changed much over time. However, the average age of new members is increasing. Also, a significant portion of the respondents report being strictly active in a non-observing capacity, reflecting the growing mission of the organization. Motivations of participants are more aligned with scientific contribution than with that reported by other citizen science projects. This may help explain why a third of all respondents are an author or co-author of a paper in an astronomical journal. Finally, there is some evidence that participation in the AAVSO has a greater impact on the respondents' view of their role in astronomy compared to that expected through increasing amateur astronomy experience alone. Results paint a picture of participants in a modern, advanced citizen science organization.
We present the results of the study of the contact binary system BO CVn. We have obtained physical parameters of the components based on combined analysis of new, multi-color light curves and spectroscopic mass ratio. This is the first time the latter has been determined for this object. We derived the contact configuration for the system with a very high filling factor of about 88 percent. We were able to reproduce the observed light curve, namely the flat bottom of the secondary minimum, only if a third light has been added into the list of free parameters. The resulting third light contribution is significant, about 20-24 percent, while the absolute parameters of components are: M1=1.16, M2=0.39, R1=1.62 and R2=1.00 (in solar units). The O-C diagram shows an upward parabola which, under the conservative mass transfer assumption, would correspond to a mass transfer rate of dM/dt = 6.3 \times 10-8M\odot/yr, matter being transferred from the less massive component to the more massive one. No cyclic, short-period variations have been found in the O-C diagram (but longer-term variations remain a possibility)
We present $^{12}$CO(2-1) line and 1.4 mm continuum archival observations, made with the Submillimeter Array, of the outflow HH 797 located in the IC 348 cluster in Perseus. The continuum emission is associated with a circumstellar disk surrounding the class 0 object IC 348-MMS/SMM2, a very young solar analog. The line emission, on the other hand, delineates a collimated outflow, and reveals velocity asymmetries about the flow axis over the entire length of the flow. The amplitude of velocity differences is of order 2 km s$^{-1}$ over distances of about 1000 AU, and we interpret them as evidence for jet rotation --although we also discuss alternative possibilities. A comparison with theoretical models suggests that the magnetic field lines threading the protostellar jet might be anchored to the disk of a radius of about 20 AU.
The coexistence of Planck and Fermi satellites in orbit has enabled the exploration of the connection between the (sub-)millimeter and gamma-ray emission in a large sample of blazars. We find that the gamma-ray emission and the (sub-)mm luminosities are correlated over five orders of magnitude. However, this correlation is not significant at some frequency bands when simultaneous observations are considered. The most significant statistical correlations, on the other hand, arise when observations are quasi-simultaneous within 2 months. Moreover, we find that sources with an approximate spectral turnover in the middle of the mm-wave regime are more likely to be strong gamma-ray emitters. These results suggest a physical relation between the newly injected plasma components in the jet and the high levels of gamma-ray emission.
We present the stellar population and velocity dispersion gradients for a sample of 24 brightest cluster galaxies (BCGs) in the nearby Universe for which we have obtained high quality long-slit spectra at the Gemini telescopes. With the aim of studying the possible connection between the formation of the BCGs and their host clusters, we explore the relations between the stellar population gradients and properties of the host clusters as well as the possible connections between the stellar population gradients and other properties of the galaxies. We find mean stellar population gradients (negative {\Delta}[Z/H]/log r gradient of -0.285{\pm}0.064; small positive {\Delta}log (age)/log r gradient of 0.069{\pm}0.049; and null {\Delta}[E/Fe]/log r gradient of -0.008{\pm}0.032) that are consistent with those of normal massive elliptical galaxies. However, we find a trend between metallicity gradients and velocity dispersion (with a negative slope of -1.616{\pm}0.539) that is not found for the most massive ellipticals. Furthermore, we find trends between the metallicity gradients and K-band luminosities (with a slope of 0.173{\pm}0.081) as well as the distance from the BCG to the X-ray peak of the host cluster (with a slope of -7.546{\pm}2.752). The latter indicates a possible relation between the formation of the cluster and that of the central galaxy.
We analyze the physical parameters of interstellar filaments that we describe
by an idealized model of isothermal self-gravitating infinite cylinder in
pressure equilibrium with the ambient medium. Their gravitational state is
characterized by the ratio f_cyl of their mass line density to the maximum
possible value for a cylinder in a vacuum. Equilibrium solutions exist only for
f_cyl < 1. This ratio is used in providing analytical expressions for the
central density, the radius, the profile of the column density, the column
density through the cloud centre, and the fwhm. The dependence of the physical
properties on external pressure and temperature is discussed and directly
compared to the case of pressure-confined isothermal self-gravitating spheres.
Comparison with recent observations of the fwhm and the central column
density N_H(0) show good agreement and suggest a filament temperature of ~10 K
and an external pressure p_ext/k in the range 1.5x10^4 K/cm^3 to 5x10^4 K/cm^3.
Stability considerations indicate that interstellar filaments become
increasingly gravitationally unstable with mass line ratio f_cyl approaching
unity. For intermediate f_cyl>0.5 the instabilities should promote core
formation through compression, with a separation of about five times the fwhm.
We discuss the nature of filaments with high mass line densities and their
relevance to gravitational fragmentation and star formation.
We present a clustering analysis of Luminous Red Galaxies (LRGs) in SDSS Stripe 82. We study the angular 2-point correlation function, w(theta), of 130,000 LRG candidates via colour-cut selections in izK with the K band coverage coming from UKIDSS LAS. We have used the cross-correlation technique of Newman (2008) to establish the LRG redshift distribution. Cross-correlating with SDSS QSOs, MegaZ-LRGs and DEEP2 galaxies implies an average LRG redshift of z~1 with space density, n_g~3.2x10^-4 h^3 Mpc^-3. For theta < 10', the LRG w(theta) significantly deviates from a single power-law as noted by previous galaxy clustering studies. A double power-law with a break at r_b~2.4 h^-1 Mpc fits the data better, with scale length, r_0,1=7.63+/-0.27 h^-1Mpc and slope gamma_1=2.01 +/-0.02 at small scales and r_0,2=9.92 +/-0.40 h^-1 Mpc and gamma_2=1.64 +/-0.04 at large scales. Due to the flat slope at large scales, we find that a standard LCDM linear model is accepted only at 2-3sigma, with the best-fit bias factor, b=2.74+/-0.07. We also fitted HOD models and estimate an effective halo mass of Stripe 82 LRGs of M_eff=3.3 +/-0.6x10^13 h^-1 M_sun. But at large scales, the current HOD models did not help explain the power excess in the clustering signal. We then compare the w(theta) results to those of Sawangwit et al. (2011) from 3 samples of photometrically selected LRGs at lower redshifts to measure clustering evolution. We find that a long-lived model may be a poorer fit than at lower redshifts, although this assumes that the Stripe 82 LRGs are luminosity-matched to the AAOmega LRGs. We find stronger evidence for evolution in the form of the z~1 LRG correlation function, with the above flat 2-halo slope maintaining to r>50 h^-1 Mpc. If this result is not caused by systematics, then it may provide evidence for primordial non-Gaussianity in the matter distribution, with f^local_NL=90+/-30.
The Cisco router in Low Earth Orbit (CLEO) was launched into space as an experimental secondary payload onboard the UK Disaster Monitoring Constellation (UK-DMC) satellite in September 2003. The UK-DMC satellite is one of an increasing number of DMC satellites in orbit that rely on the Internet Protocol (IP) for command and control and for delivery of data from payloads. The DMC satellites, built by Surrey Satellite Technology Ltd (SSTL), have imaged the effects of Hurricane Katrina, the Indian Ocean Tsunami, and other events for disaster relief under the International Space and Major Disasters Charter. It was possible to integrate the Cisco mobile access router into the UK-DMC satellite as a result of the DMC satellites' adoption of existing commercial networking standards, using IP over Frame Relay over standard High-Level Data Link Control, or HDLC (ISO 13239) on standard serial interfaces. This approach came from work onboard SSTL's earlier UoSAT-12 satellite
A networking transport protocol, named Saratoga, has been developed at the University of Surrey for efficient delivery of imagery from Internet-Protocol-based remote-sensing satellites. Saratoga is now being implemented and evaluated for use for the high-end data-delivery needs of astronomers using large, advanced, radio telescopes. These telescopes are expected to take advantage of Internet technologies. This brief paper outlines the reasons for the creation and adoption of this protocol, discusses how it differs from and complements other protocols, and summarises the worldwide collaboration that is making this development possible.
In this paper we propose a mechanism that protects theories violating a holographic bound suggested in arXiv:1203.5467 from developing accelerated expansion. The mechanism builts on work on transplanckian physics, and a non-trivial choice of vacuum states. If correct, it lends further support for detectable signatures in the CMBR signalling new physics.
We find a solution to Einstein field equations for a regular toroidal lattice of size L with equal masses M at the centre of each cell; this solution is exact at order M/L. Such a solution is convenient to study the dynamics of an assembly of galaxy-like objects. We find that the solution is expanding (or contracting) in exactly the same way as the solution of a Friedman-Lema\^itre-Robertson-Walker Universe with dust having the same average density as our model. This points towards the absence of backreaction in a Universe filled with an infinite number of objects, and this validates the fluid approximation, as far as dynamics is concerned.
It has recently been pointed out that a substantial amount of e-folds can occur during the waterfall regime of hybrid inflation. Moreover, Kodama et.al. have derived analytic approximations for the trajectories of the inflaton and of the waterfall fields. Based on these, we derive here the consequences for F- and D-term SUSY hybrid inflation: A substantial amount of e-folds may occur in the waterfall regime, provided kappa << M^2/M_P^2, where kappa is the superpotential coupling, M the scale of symmetry breaking and M_P the reduced Planck mass. When this condition is amply fulfilled, a number of e-folds much larger than N_e\approx60 can occur in the waterfall regime and the scalar spectral index is then given by the expression found by Kodama et.al. n_s=1-4/N_e. This value may be increased up to unity, if only about N_e e-folds occur during the waterfall regime, such that the largest observable scale leaves the horizon close to the critical point of hybrid inflation, what can be achieved for kappa\approx10^(-13) and M\approx5x10^(12) GeV in F-term inflation. Imposing the normalization of the power spectrum leads to a lower bound on the scale of symmetry breaking.
We examine the impact of electromagnetic properties of neutrinos on the annihilation of relic neutrinos with ultra high energy cosmic neutrinos for the $\nu \bar{\nu}\to \gamma\gamma$ process. For this process, photon-neutrino decoupling temperature is calculated via effective lagrangian model beyond the standard model. We find that photon-neutrino decoupling temperature can be importantly reduced below the QCD phase transition with the model independent analysis defining electromagnetic properties of neutrinos.
In thermal equilibrium the ground state of the plasma of Standard Model particles is determined by temperature and exactly conserved combinations of baryon and lepton numbers. We show that at non-zero values of the global charges a translation invariant and homogeneous state of the plasma becomes unstable and the system transits into a new state, containing a large-scale magnetic field. The origin of this effect is the parity-breaking character of weak interactions and chiral anomaly. This situation can occur in the early Universe and may play an important role in its subsequent evolution.
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We present a comprehensive catalog of ultraviolet HST/STIS and FUSE absorbers in the low-redshift IGM at z<0.4. The catalog draws from the extensive literature on IGM absorption, and it reconciles discrepancies among previous catalogs through a critical evaluation of all reported absorption features in light of new HST/COS data. We report on 746 HI absorbers down to a rest-frame equivalent width of 12 milliAngstroms over a maximum redshift path length Deltaz=5.38. We also confirm 111 OVI absorbers, 29 CIV absorbers, and numerous absorption features due to other metal ions. We characterize the distribution of absorber line frequency as a function of column density as a power law, dN/dz \propto N^{-beta}, where beta=2.08+-0.12 for OVI and beta=1.68+-0.03 for HI. Utilizing a more sophisticated accounting technique than past work, the catalog accounts for ~43% of the baryons: 24+-2% in the photoionized Ly-alpha forest and 19+-2% in the WHIM as traced by OVI. We discuss the large systematic effects of various assumed metallicities and ionization states on these calculations, and we implement recent simulation results in our estimates.
With its unprecedented light-collecting area for night-sky observations, the Cherenkov Telescope Array (CTA) holds great potential for also optical stellar astronomy, in particular as a multi-element intensity interferometer for realizing imaging with sub-milliarcsecond angular resolution. Such an order-of-magnitude increase of the spatial resolution achieved in optical astronomy will reveal the surfaces of rotationally flattened stars with structures in their circumstellar disks and winds, or the gas flows between close binaries. Image reconstruction is feasible from the second-order coherence of light, measured as the temporal correlations of arrival times between photons recorded in different telescopes. This technique (once pioneered by Hanbury Brown and Twiss) connects telescopes only with electronic signals and is practically insensitive to atmospheric turbulence and to imperfections in telescope optics. Detector and telescope requirements are very similar to those for imaging air Cherenkov observatories, the main difference being the signal processing (calculating cross correlations between single camera pixels in pairs of telescopes). Observations of brighter stars are not limited by sky brightness, permitting efficient CTA use during also bright-Moon periods. While other concepts have been proposed to realize kilometer-scale optical interferometers of conventional amplitude (phase-) type, both in space and on the ground, their complexity places them much further into the future than CTA, which thus could become the first kilometer-scale optical imager in astronomy.
We derive general covariant expressions for the six independent observable modes of distortion of ideal standard rulers in a perturbed Friedmann-Robertson-Walker spacetime. Our expressions are gauge-invariant and valid on the full sky. These six modes are most natually classified in terms of their rotational properties on the sphere, yielding two scalars, two vector (spin-1), and two tensor (spin-2) components. One scalar corresponds to the magnification, while the spin-2 components correspond to the shear. The vector components allow for a polar/axial decomposition analogous to the E/B-decomposition for the shear. Scalar modes do not contribute to the axial (B-)vector, opening a new avenue to probing tensor modes. Our results apply, but are not limited to, the distortion of correlation functions (of the CMB, 21cm emission, or galaxies) as well as to weak lensing shear and magnification, all of which can be seen as methods relying on "standard rulers".
We combine recent estimates of dust extinction at z~4-7 with UV luminosity function (LF) determinations to derive star formation rate (SFR) functions at z~4, 5, 6 and 7. SFR functions provide a more physical description of galaxy build-up at high redshift and allow for direct comparisons to other techniques for determining the SFRs at lower redshifts. The present SFR functions are based on well-established z~4-7 UV LFs, UV-continuum slope trends with redshift and luminosity, and IRX-beta relations, and are well-described by Schechter relations. We extend the comparison baseline to z~2 by considering recent determinations of the H{\alpha} and mid-IR luminosity functions. We find that the high-end turnover of the SFR function, log SFR*, increases linearly with cosmic time from ~5 M_sun/yr at z~8, 650 Myr after the Big Bang, to ~100 M_sun/yr at z~2, ~2.5 Gyr later. Recent results at z~10, close to the onset of galaxy formation, are consistent with this trend. These results provide strong evidence that galaxies build up uniformly over the first 3 Gyr of cosmic time. The uniformity of this evolution is even greater than seen in the UV LF over the redshift range z~2-8, providing validation for our dust corrections. The low-end slopes of the SFR functions are flatter than for the UV LFs, \Delta\alpha\sim+0.13, and show no clear evolution with cosmic time (z~0-7).
The Rapid Burster (MXB 1730-335) is a unique object, showing both type I and type II X-ray bursts. A type I burst of the Rapid Burster was observed with Swift/XRT on 2009 March 5, showing photospheric radius expansion for the first time in this source. We report here on the mass and radius determination from this photospheric radius expansion burst using a Bayesian approach. After marginalization over the likely distance of the system (5.8-10 kpc) we obtain M=1.1+/-0.3 M_sun and R=9.6+/-1.5 km (1-sigma uncertainties) for the compact object, ruling out the stiffest equations of state for the neutron star. We study the sensitivity of the results to the distance, the color correction factor, and the hydrogen mass fraction in the envelope. We find that only the distance plays a crucial role.
Whether massive stars can occasionally form in relative isolation or if they require a large cluster of lower-mass stars around them is a key test in the differentiation of star formation theories as well as how the initial mass function of stars is sampled. Previous attempts to find O-type stars that formed in isolation were hindered by the possibility that such stars are merely runaways from clusters, i.e., their current isolation does not reflect their birth conditions. We introduce a new method to find O-type stars that are not affected by such a degeneracy. Using the VLT-FLAMES Tarantula Survey and additional high resolution imaging we have identified stars that satisfy the following constraints: 1) they are O-type stars that are not detected to be part of a binary system based on RV time series analysis; 2) they are designated spectral type O7 or earlier ; 3) their velocities are within 1\sigma of the mean of OB-type stars in the 30 Doradus region, i.e. they are not runaways along our line-of-sight; 4) the projected surface density of stars does not increase within 3 pc towards the O-star (no evidence for clusters); 5) their sight lines are associated with gaseous and/or dusty filaments in the ISM, and 6) if a second candidate is found in the direction of the same filament with which the target is associated, both are required to have similar velocities. With these criteria, we have identified 15 stars in the 30 Doradus region, which are strong candidates for being high-mass stars that have formed in isolation. Additionally, we employed extensive MC stellar cluster simulations to confirm that our results rule out the presence of clusters around the candidates. Eleven of these are classified as Vz stars, possibly associated with the zero-age main sequence. We include a newly discovered W-R star as a candidate, although it does not meet all of the above criteria.
We study the time variability of five Fe Low ionization Broad Absorption Line (FeLoBAL) QSOs using repeated spectroscopic observations with the 2m telescope at IUCAA Girawali observatory (IGO) spanning an interval of upto 10 years. We report a dramatic variation in Al III and Fe III fine-structure lines in the spectra of SDSS J221511.93-004549.9 (z_em ~ 1.478). However, there is no such strong variability shown by the C IV absorption. This source is known to be unusual with (i) the continuum emission dominated by Fe emission lines, (ii) Fe III absorption being stronger than Fe II and (iii) the apparent ratio of Fe III UV 48 to Fe III UV 34 absorption suggesting an inverted population ratio. This is the first reported detection of time variability in the Fe III fine-structure lines in QSO spectra. There is a strong reduction in the absorption strength of these lines between year 2000 and 2008. Using the template fitting techniques, we show that the apparent inversion of strength of UV lines could be related to the complex spectral energy distribution of this QSO. The observed variability can be related to change in the ionization state of the gas or due to transverse motion of this absorbing gas. The shortest variability timescale of Al III line gives a lower limit on the electron density of the absorbing gas as n_e >= 1.1 x 10^4 cm^-3. The remaining 4 FeLoBALs do not show any changes beyond the measurement uncertainties either in optical depth or in the velocity structure. We present the long-term photometric light curve for all of our sources. Among them only SDSS J221511.93-004549.9 shows significant (>= 0.2 mag) variability.
We derive an accurate mass distribution of the galaxy cluster MACS J1206.2-0847 (z=0.439) from a combined weak-lensing distortion, magnification, and strong-lensing analysis of wide-field Subaru BVRIz' imaging and our recent 16-band Hubble Space Telescope observations taken as part of the Cluster Lensing And Supernova survey with Hubble (CLASH) program. We find good agreement in the regions of overlap between several weak and strong lensing mass reconstructions using a wide variety of modeling methods, ensuring consistency. The Subaru data reveal the presence of a surrounding large scale structure with the major axis running approximately north-west south-east (NW-SE), aligned with the cluster and its brightest galaxy shapes, showing elongation with a \sim 2:1 axis ratio in the plane of the sky. Our full-lensing mass profile exhibits a shallow profile slope dln\Sigma/dlnR\sim -1 at cluster outskirts (R>1Mpc/h), whereas the mass distribution excluding the NW-SE excess regions steepens further out, well described by the Navarro-Frenk-White form. Assuming a spherical halo, we obtain a virial mass M_{vir}=(1.1\pm 0.2\pm 0.1)\times 10^{15} M_{sun}/h and a halo concentration c_{vir} = 6.9\pm 1.0\pm 1.2 (\sim 5.7 when the central 50kpc/h is excluded), which falls in the range 4< <c> <7 of average c(M,z) predictions for relaxed clusters from recent Lambda cold dark matter simulations. Our full lensing results are found to be in agreement with X-ray mass measurements where the data overlap, and when combined with Chandra gas mass measurements, yield a cumulative gas mass fraction of 13.7^{+4.5}_{-3.0}% at 0.7Mpc/h (\approx 1.7r_{2500}), a typical value observed for high mass clusters.
We present constraints on core-collapse supernova progenitors through observations of their environments within host galaxies. This is achieved through 2 routes. Firstly, we investigate the spatial correlation of supernovae with host galaxy star formation using pixel statistics. We find that the main supernova types form a sequence of increasing association to star formation. The most logical interpretation is that this implies an increasing progenitor mass sequence going from the supernova type Ia arising from the lowest mass, through the type II, type Ib, and the supernova type Ic arising from the highest mass progenitors. We find the surprising result that the supernova type IIn show a lower association to star formation than type IIPs, implying lower mass progenitors. Secondly, we use host HII region spectroscopy to investigate differences in environment metallicity between different core-collapse types. We find that supernovae of types Ibc arise in slightly higher metallicity environments than type II events. However, this difference is not significant, implying that progenitor metallicity does not play a dominant role in deciding supernova type.
We present a survey of 2,148 galaxy redshifts from the VLT LBG Redshift Survey (VLRS), a spectroscopic survey of z ~ 3 galaxies in wide fields centred on background QSOs made using the VLT VIMOS instrument. To make a definitive LBG clustering analysis, we have combined the VLRS redshifts with the 813 Keck LBG redshifts of Steidel et al, with the statistical power of VLRS at large scales complementing the accuracy of the Keck sample at small scales. From the semi-projected correlation function for the VLRS and combined surveys, we find that the results are well fit with a single power law model for the real space correlation function with clustering scale lengths of respectively r0 = 3.32 \pm 0.41 and 3.75 \pm 0.24 Mpc/h. We note that the corresponding combined slope is flatter than for local galaxies at {\gamma} = 1.55 \pm 0.09. This flat slope is confirmed by the z-space correlation function and in the range 10 < s < 100 Mpc/h the VLRS shows a 2.5{\sigma} excess over the {\Lambda}CDM linear prediction. This excess may be consistent with recent evidence for non-Gaussianity in clustering results at z \approx 1. We then analyse the LBG z-space distortions using the 2-D correlation function finding for the combined sample a large scale infall parameter of {\beta} = 0.32 \pm 0.20 and a velocity dispersion of 540 \pm 200 km/s. Fixing this velocity dispersion, we fit the 2D clustering for the matter density and infall parameter and break their degeneracy using low-redshift data to find {\Omega}m(z = 0) = 0.30+0.32-0.18. Finally, based on our measured {\beta}, we are able to determine the gravitational growth rate, finding a value of f(z = 3) = 0.83 \pm 0.46, which is the highest redshift measurement of the growth rate via galaxy clustering and is consistent with {\Lambda}CDM.
We present an analysis of the galaxy distribution surrounding 15 of the most luminous (>10^{14} L_sun; M_1450 ~ -30) QSOs in the sky with z~2.7. Our data are drawn from the Keck Baryonic Structure Survey (KBSS). In this work, we use the positions and spectroscopic redshifts of 1558 galaxies that lie within ~3', (4.2 h^{-1} comoving Mpc; cMpc) of the hyperluminous QSO (HLQSO) sightline in one of 15 independent survey fields, together with new measurements of the HLQSO systemic redshifts. We measure the galaxy-HLQSO cross-correlation function, the galaxy-galaxy autocorrelation function, and the characteristic scale of galaxy overdensities surrounding the sites of exceedingly rare, extremely rapid, black hole accretion. On average, the HLQSOs lie within significant galaxy overdensities, characterized by a velocity dispersion sigma_v ~ 200 km s^{-1} and a transverse angular scale of ~25", (~200 physical kpc). We argue that such scales are expected for small groups with log(M_h/M_sun)~13. The galaxy-HLQSO cross-correlation function has a best-fit correlation length r_0_GQ = (7.3 \pm 1.3) h^{-1} cMpc, while the galaxy autocorrelation measured from the spectroscopic galaxy sample in the same fields has r_0_GG = (6.0 \pm 0.5) h^{-1} cMpc. Based on a comparison with simulations evaluated at z ~ 2.6, these values imply that a typical galaxy lives in a host halo with log(M_h/M_sun) = 11.9\pm0.1, while HLQSOs inhabit host halos of log(M_h/M_sun) = 12.3\pm0.5. In spite of the extremely large black hole masses implied by their observed luminosities [log(M_BH/M_sun) > 9.7], it appears that HLQSOs do not require environments very different from their much less luminous QSO counterparts. Evidently, the exceedingly low space density of HLQSOs (< 10^{-9} cMpc^{-3}) results from a one-in-a-million event on scales << 1 Mpc, and not from being hosted by rare dark matter halos.
We examine a large collection of low resolution near-infrared spectra of Kuiper belt objects and centaurs in an attempt to understand the presence of water ice in the Kuiper belt. We find that water ice on the surface of these objects occurs in three separate manners: (1) Haumea family members uniquely show surfaces of nearly pure water ice, presumably a consequence of the fragmentation of the icy mantle of a larger differentiated proto-Haumea; (2) large objects with absolute magnitudes of $H<3$ (and a limited number to H=4.5) have surface coverings of water ice - perhaps mixed with ammonia - that appears to be related to possibly ancient cryovolcanism on these large objects; and (3) smaller KBOs and centaurs which are neither Haumea family members nor cold-classical KBOs appear to divide into two families (which we refer to as "neutral" and "red"), each of which is a mixture of a common nearly-neutral component and either a slightly red or very red component that also includes water ice. A model suggesting that the difference between neutral and red objects is due to formation in an early compact solar system either inside or outside, respectively, of the ~20 AU methanol evaporation line is supported by the observation that methanol is only detected on the reddest objects, which are those which would be expected to have the most of the methanol containing mixture.
We report the discovery of 33 Lyman break galaxy (LBG) candidates at z~8 detected in Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) imaging as part of the Brightest of Reionizing Galaxies (BoRG) pure-parallel survey. The ongoing BoRG survey currently has the largest area (274 arcmin^2) with Y_098 (or Y_105), J_125, and H_160 band coverage needed to search for z~8 galaxies, about three times the current CANDELS area, and slightly larger than what will be the final CANDELS wide component with Y_105 data. Our sample of 33 relatively bright Y_098-dropout galaxies have J_125 band magnitudes between 25.5 and 27.4 mag. This is the largest sample of bright (J_125 <~ 27.4) z~8 galaxy candidates presented to date. Combining our dataset with the Hubble Ultra-Deep Field (HUDF09) dataset, we constrain the rest-frame ultraviolet galaxy luminosity function at z~8 over the widest dynamic range currently available. The combined datasets are well fitted by a Schechter function, i.e. \phi(L) = \phi_* (L/L_*)^{\alpha}\ e^{-(L/L_*)}, without evidence for an excess of sources at the bright end. At 68% confidence, we derive \phi_* = (4.3^{+3.5}_{-2.1}) \times 10^{-4} Mpc^{-3}, M_* = -20.26^{+0.29}_{-0.34}, and a very steep faint-end slope \alpha = -1.98^{+0.23}_{-0.22}. While the best-fit parameters still have a strong degeneracy, especially between \phi_* and M_*, our improved coverage at the bright end has reduced the uncertainty of the faint-end power-law slope at z~8 compared to the best previous determination at +/-0.4. With a future expansion of the BoRG survey, combined with planned ultradeep WFC3/IR observations, it will be possible to further reduce this uncertainty and clearly demonstrate the steepening of the faint-end slope compared to measurements at lower redshift, thereby confirming the key role played by small galaxies in the reionization of the universe.
Electromagnetic radiation from superconducting cosmic string loops can reionize neutral hydrogen in the universe at very early epochs, and affect the cosmic microwave background (CMB) temperature and polarization correlation functions at large angular scales. We constrain the string tension and current using WMAP7 data, and compare with earlier constraints that employed CMB spectral distortions. Over a wide range of string tensions, the current on the string has to be less than 10^7 GeV.
Results are presented for XMM-Newton observations of five hard X-ray sources discovered by INTEGRAL in the direction of the Scutum Arm. Each source received >20 ks of effective exposure time. We provide refined X-ray positions for all five targets enabling us to pinpoint the most likely counterpart in optical/infrared archives. Spectral and timing information (much of which are provided for the first time) allow us to give a firm classification for IGR J18462-0223 and to offer tentative classifications for the others. For IGR J18462-0223, we discovered a coherent pulsation period of 997+-1 s which we attribute to the spin of a neutron star in a highly-obscured (nH = 2e23 /cm2) high-mass X-ray binary (HMXB). This makes IGR J18462-0223 the seventh supergiant fast X-ray transient (SFXT) candidate with a confirmed pulsation period. IGR J18457+0244} is a highly-absorbed (nH = 8e23 /cm2) source in which the possible detection of an iron line suggests an active galactic nucleus (AGN) of type Sey-2 situated at z = 0.07(1). A periodic signal at 4.4 ks could be a quasi-periodic oscillation which would make IGR J18457+0244 one of a handful of AGN in which such features have been claimed, but a slowly-rotating neutron star in an HMXB can not be ruled out. IGR J18482+0049 represents a new obscured HMXB candidate with nH = 4e23 /cm2. We tentatively propose that IGR J18532+0416 is either an AGN or a pulsar in an HMXB system, while IGR J18538-0102 is a soft X-ray source which could be a low-mass X-ray binary or a cataclysmic variable.
We review progress in the development of physically realistic three dimensional simulated models of the galaxy.We consider the scales from star forming molecular clouds to the full spiral disc. Models are computed using hydrodynamic (HD) or magnetohydrodynamic (MHD) equations and may include cosmic ray or tracer particles. The range of dynamical scales between the full galaxy structure and the turbulent scales of supernova (SN) explosions and even cloud collapse to form stars, make it impossible with current computing tools and resources to resolve all of these in one model. We therefore consider a hierarchy of models and how they can be related to enhance our understanding of the complete galaxy.
We study the PAH emission from protoplanetary disks. First, we discuss the dependence of the PAH band ratios on the hardness of the absorbed photons and the temperature of the stars. We show that the photon energy together with a varying degree of the PAH hydrogenation accounts for most of the observed PAH band ratios without the need to change the ionization degree of the molecules. We present an accurate treatment of stochastic heated grains in a vectorized three dimensional Monte Carlo dust radiative transfer code. The program is verified against results using ray tracing techniques. Disk models are presented for T Tauri and Herbig Ae stars. Particular attention is given to the photo-dissociation of the molecules. We consider beside PAH destruction also the survival of the molecules by vertical mixing within the disk. By applying typical X-ray luminosities the model accounts for the low PAH detection probability observed in T Tauri and the high PAH detection statistics found in Herbig Ae disks. Spherical halos above the disks are considered. We show that halos reduce the observed PAH band-to-continuum ratios when observed at high inclination. Finally, mid-IR images of disks around Herbig Ae disks are presented. We show that they are easier to resolve when PAH emission dominate.
We present 3D models of the Galactic magnetic field including regular and turbulent components, and of the distribution of matter in the Galaxy including relativistic electrons and dust grains. By integrating along the line of sight, we construct maps of the polarized Galactic synchrotron and thermal dust emissions for each of these models. We perform a likelihood analysis to compare the maps of the Ka, Q, V and W bands of the Wilkinson Microwave Anisotropy Probe (Wmap) and the 353 GHz Archeops data to the models obtained by varying the pitch angle of the regular magnetic field, the relative amplitude of the turbulent magnetic field and the extrapolation spectral indices of the synchrotron and thermal dust emissions. The best-fit parameters obtained for the different frequency bands are very similar and globally the data seem to favor a negligible isotropic turbulent magnetic field component at large angular scales (an anisotropic line-of-sight ordered component can not be studied using these data). From this study, we conclude that we are able to propose a consistent model of the polarized diffuse Galac- tic synchrotron and thermal dust emissions in the frequency range from 33 to 353 GHz, where most of the CMB studies are performed and where we expect a mixture of these two main foreground emissions. This model can be very helpful to estimate the contamination by foregrounds of the polarized CMB anisotropies, for experiments like the Planck satellite.
A new, much improved model of the Galactic Magnetic Field (GMF) is presented. We use the WMAP7 Galactic Synchrotron Emission map and more than forty thousand extragalactic rotation measures to constrain the parameters of the GMF model, which is substantially generalized compared to earlier work to now include an out-of-plane component (as suggested by observations of external galaxies) and striated-random fields (motivated by theoretical considerations). The new model provides a greatly improved fit to observations. Consistent with our earlier analyses, the best-fit model has a disk field and an extended halo field. Our new analysis reveals the presence of a large, out-of-plane component of the GMF; as a result, the polarized synchrotron emission of our Galaxy seen by an edge-on observer is predicted to look intriguingly similar to what has been observed in external edge-on galaxies. We find evidence that the cosmic ray electron density is significantly larger than given by GALPROP, or else that there is a widespread striated component to the GMF.
Magnetic fields appear wherever plasma and currents can be found. As such, they thread through all scales in Nature. It is natural, therefore, to suppose that magnetic fields might have been formed within the high temperature environments of the big bang. Such a primordial magnetic field (PMF) would be expected to arise from and/or influence a variety of cosmological phenomena such as inflation, cosmic phase transitions, big bang nucleosynthesis, the cosmic microwave background (CMB) temperature and polarization anisotropies, the cosmic gravity wave background, and the formation of large-scale structure. In this review, we summarize the development of theoretical models for analyzing the observational consequences of a PMF. We also summarize the current state of the art in the search for observational evidence of a PMF. In particular we review the framework needed to calculate the effects of a PMF power spectrum on the CMB and the development of large scale structure. We summarize the current constraints on the PMF amplitude $B_\lambda$ and the power spectral index $n_B$ and discuss prospects for better determining these quantities in the near future.
We perform a joint determination of the distance-redshift relation and cosmic expansion rate at redshifts z = 0.44, 0.6 and 0.73 by combining measurements of the baryon acoustic peak and Alcock-Paczynski distortion from galaxy clustering in the WiggleZ Dark Energy Survey, using a large ensemble of mock catalogues to calculate the covariance between the measurements. Further combining our results with other baryon acoustic oscillation and distant supernovae datasets, we use a Monte Carlo Markov Chain technique to determine the evolution of the Hubble parameter H(z) as a stepwise function in 9 redshift bins of width dz = 0.1, also marginalizing over the spatial curvature. Our measurements of H(z), which have precision better than 7% in most redshift bins, are consistent with the expansion history predicted by a cosmological-constant dark-energy model, in which the expansion accelerates at redshift z < 0.7. We also measure the normalized cosmic growth rate at z = 0.44, 0.6 and 0.73, together with its covariance with the expansion history, using redshift-space distortions in the WiggleZ Survey dataset. The measured growth rate is consistent with the same cosmological-constant model that describes the expansion history.
We examine stochastic variability in the dynamics of X-ray emission from the black hole system GRS 1915+105, a strongly variable microquasar commonly used for studying relativistic jets and the physics of black hole accretion. The analysis of sample observations for 13 different states in both soft (low) and hard (high) energy bands is performed by flicker-noise spectroscopy (FNS), a phenomenological time series analysis method operating on structure functions and power spectrum estimates. We find the values of FNS parameters, including the Hurst exponent, flicker-noise parameter, and characteristic time scales, for each observation based on multiple 2,500-second continuous data segments. We identify four modes of stochastic variability driven by dissipative processes that may be related to viscosity fluctuations in the accretion disk around the black hole: random (RN), power-law (1F), one-scale (1S), and two-scale (2S). The variability modes are generally the same in soft and hard energy bands of the same observation. We discuss the potential for future FNS studies of accreting black holes.
We investigate the value of horizontal turbulent diffusivity {\eta} by numerical calculation of thermal convection. In this study, we introduce a new method whereby the turbulent diffusivity is estimated by monitoring the time devel- opment of the passive scalar, which is initially distributed in a given Gaussian function with a spatial scale d0. Our conclusions are as follows: (1) Assuming the relation {\eta} = Lcvrms/3 where vrms is the RMS velocity, the characteristic length Lc is restricted by the shortest one among the pressure (density) scale height and the region depth. (2) The value of turbulent diffusivity becomes greater with the larger initial distribution scale d0. (3) The approximation of turbulent diffusion holds better when the ratio of the initial distribution scale d0 to the characteristic length Lc is larger.
We present results from an optical photometric and spectroscopic survey of
the young stellar population in L1641, the low-density star-forming region of
the Orion A cloud south of the Orion Nebula Cluster (ONC). Our goal is to
determine whether L1641 has a large enough low-mass population to make the
known lack of high-mass stars a statistically-significant demonstration of
environmental dependence of the upper mass stellar initial mass function (IMF).
Our spectroscopic sample consists of IR-excess objects selected from the
Spitzer/IRAC survey and non-excess objects selected from optical photometry. We
have spectral confirmation of 864 members, with another 98 probable members; of
the confirmed members, 406 have infrared excesses and 458 do not. Assuming the
same ratio of stars with and without IR excesses in the highly-extincted
regions, L1641 may contain as many as ~1600 stars down to ~0.1 solar mass,
comparable within a factor of two to the the ONC. Compared to the standard
models of the IMF, L1641 is deficient in O and early B stars to a 3-4 sigma
significance level, assuming that we know of all the massive stars in L1641.
With a forthcoming survey of the intermediate-mass stars, we will be in a
better position to make a direct comparison with the neighboring, dense ONC,
which should yield a stronger test of the dependence of the high-mass end of
the stellar initial mass function upon environment.
We explore the sensitivity and completeness of long baseline interferometric observations for detecting unknown, faint companions around bright unresolved stars. We derive a linear expression for the closure phase signature of a faint companion in the high contrast regime (<0.1), and provide a quantitative estimation of the detection efficiency for the currently offered four-telescope configurations at the Very Large Telescope Interferometer. The results are compared to the performances provided by linear and Y-shaped interferometric configurations in order to identify the ideal array. We find that all configurations have a similar efficiency in discovering companions wider than 10mas. Assuming a closure phase accuracy of 0.25deg, that is typical of state-of-the-art instruments, we predict a median dynamic range of up to six magnitudes when stacking observations obtained at five different hour angles. Surveying bright stars to search for faint companions can be considered as an ideal filler programme for modern interferometric facilities because that places few constraints on the choice of the interferometric configuration.
We provide a dynamical mechanism to generate localized features during inflation. The local feature is due to a sharp waterfall phase transition which is coupled to the inflaton field. The key effect is the contributions of waterfall quantum fluctuations which induce a sharp peak on the curvature perturbation which can be as large as the background curvature perturbation from inflaton field. Due to non-Gaussian nature of waterfall quantum fluctuations a large spike non-Gaussianity is produced which is narrowly peaked at modes which leave the Hubble radius at the time of phase transition. The large localized peaks in power spectrum and bispectrum can have interesting consequences on CMB anisotropies.
OH(1720 MHz) masers are created by the interaction of supernova remnants with
molecular clouds. These masers are pumped by collisions in warm, shocked
molecular gas with OH column densities in the range 10^{16}--10^{17} cm^{-2}.
Excitation calculations suggest that inversion of the 6049 MHz OH line may
occur at the higher column densities that have been inferred from main-line
absorption studies of supernova remnants with the Green Bank Telescope. OH(6049
MHz) masers have therefore been proposed as a complementary indicator of
remnant-cloud interaction.
This motivated searches for 6049 MHz maser emission from supernova remnants
using the Parkes 63 m and Effelsberg 100 m telescopes, and the Australia
Telescope Compact Array. A total of forty-one remnants have been examined by
one or more of these surveys, but without success. To check the accuracy of the
OH column densities inferred from the single-dish observations we modelled OH
absorption at 1667 MHz observed with the Very Large Array towards three
supernova remnants, IC 443, W44 and 3C 391. The results are mixed -- the OH
column is revised upwards in IC443, downwards in 3C391, and is somewhat reduced
in W44. We conclude that OH columns exceeding 10^{17} cm^{-2} are indeed
present in some supernova remnants and so the lack of any detections is not
explained by low OH column density. We discuss the possibility that non-local
line overlap is responsible for suppressing the inversion of the 6049 MHz line.
Several examples of thin, Keplerian, sub-parsec megamaser disks have been discovered in the nuclei of active galaxies and used to precisely determine the mass of their host black holes. We show that there is an empirical linear correlation between the disk radius and black hole mass and that such disks are naturally formed as molecular clouds pass through the galactic nucleus and temporarily engulf the central supermassive black hole. For initial cloud column densities below about 10^{23.5} cm^{-2} the disk is non-self gravitating, but for higher cloud columns the disk would fragment and produce a compact stellar disk similar to that observed around Sgr A* at the galactic centre.
Magnetic flux tubes reaching from the solar convective zone into the chromosphere have to pass through the relatively cool, and therefore non-ideal (i.e. resistive) photospheric region enclosed between the highly ideal sub-photospheric and chromospheric plasma. It is shown that stationary MHD equilibria of magnetic flux tubes which pass through this region require an inflow of photospheric material into the flux tube and a deviation from iso-rotation along the tube axis. This means that there is a difference in angular velocity of the plasma flow inside the tube below and above the non-ideal region. Both effects increase with decreasing cross section of the tube. Although for characteristic parameters of thick flux tubes the effect is negligible, a scaling law indicates its importance for small-scale structures. The relevance of this "inflow effect" for the expansion of flux tubes above the photosphere is discussed.
We aim at characterizing a sample of 9 new hard X-ray selected Cataclysmic Variable (CVs), to unambiguously identify them as magnetic systems of the Intermediate Polar (IP) type. We performed timing and spectral analysis by using X-ray, and simultaneous UV and optical data collected by XMM-Newton, complemented with hard X-ray data provided by INTEGRAL and Swift. The pulse arrival time were used to estimate the orbital periods. The X-ray spectra were fitted using composite models consisting of different absorbing columns and emission components. Strong X-ray pulses at the White Dwarf (WD) spin period are detected and found to decrease with energy. Most sources are spin-dominated systems in the X-rays, though four are beat dominated at optical wavelengths. We estimated the orbital period in all system (except for IGR J16500-3307), providing the first estimate for IGR J08390-4833, IGR J18308-1232, and IGR J18173-2509. All X-ray spectra are multi-temperature. V2069 Cyg and RX J0636+3535 posses a soft X-ray optically thick component at kT 80 eV. An intense K_alpha Fe line at 6.4 keV is detected in all sources. An absorption edge at 0.76 keV from OVII is detected in IGR J08390-4833. The WD masses and lower limits to the accretion rates are estimated. We found all sources to be IPs. IGR J08390-4833, V2069 Cyg, and IGR J16500-3307 are pure disc accretors, while IGR J18308-1232, IGR J1509-6649, IGR J17195-4100, and RX J0636+3535 display a disc-overflow accretion mode. All sources show a temperature gradient in the post-shock regions and a highly absorbed emission from material located in the pre-shock flow which is also responsible for the X-ray pulsations. Reflection at the WD surface is likely the origin of the fluorescent iron line. There is an increasing evidence for the presence of a warm absorber in IPs. The addition of 2 systems to the subgroup of soft X-ray IPs confirms a \sim 30% incidence.
A recent third-order, essentially non-oscillatory central scheme to advance the equations of single-fluid magnetohydrodynamics (MHD) in time has been implemented into a new numerical code. This code operates on a 3-D Cartesian, non-staggered grid, and is able to handle shock-like gradients without producing spurious oscillations. To demonstrate the suitability of our code for the simulation of coronal mass ejections (CMEs) and similar heliospheric transients, we present selected results from test cases and perform studies of the solar wind expansion during phases of minimum solar activity. We can demonstrate convergence of the system into a stable Parker-like steady state for both hydrodynamic and MHD winds. The model is subsequently applied to expansion studies of CME-like plasma bubbles, and their evolution is monitored until a stationary state similar to the initial one is achieved. In spite of the model's (current) simplicity, we can confirm the CME's nearly self-similar evolution close to the Sun, thus highlighting the importance of detailed modelling especially at small heliospheric radii. Additionally, alternative methods to implement boundary conditions at the coronal base, as well as strategies to ensure a solenoidal magnetic field, are discussed and evaluated.
Neutron stars may harbour the true ground state of matter in the form of strange quark matter. If present, this type of matter is expected to be a color superconductor, a consequence of quark pairing with respect to the color/flavor degrees of freedom. The stellar magnetic field threading the quark core becomes a color-magnetic admixture and, in the event that superconductivity is of type II, leads to the formation of color-magnetic vortices. In this Letter we show that the volume-averaged color-magnetic vortex tension force should naturally lead to a significant degree of non-axisymmetry in systems like radio pulsars. We show that gravitational radiation from such color-magnetic `mountains' in young pulsars like the Crab and Vela could be observable by the future Einstein Telescope, thus becoming a probe of paired quark matter in neutron stars. The detectability threshold can be pushed up toward the sensitivity level of Advanced LIGO if we invoke an interior magnetic field about a factor ten stronger than the surface polar field.
Filament longitudinal oscillations have been observed on the solar disk in H$\alpha$. We intend to find an example of the longitudinal oscillations of a prominence, where the magnetic dip can be seen directly, and examine what is the restoring force of such kind of oscillations. We carry out a multiwavelength data analysis of the active region prominence oscillations above the western limb on 2007 February 8. Besides, we perform a one-dimensional hydrodynamic simulation of the longitudinal oscillations. The high-resolution observations by Hinode/SOT indicate that the prominence, seen as a concave-inward shape in lower-resolution Extreme Ultraviolet (EUV) images, actually consists of many concave-outward threads, which is indicative of the existence of magnetic dips. After being injected into the dip region, a bulk of prominence material started to oscillate for more than 3.5 hours, with the period being 52 min. The oscillation decayed with time, with the decay timescale being 133 min. Our hydrodynamic simulation can well reproduce the oscillation period, but the damping timescale in the simulation is 1.5 times as long as the observations. The results clearly show the prominence longitudinal oscillations around the dip of the prominence and our study suggests that the restoring force of the longitudinal oscillations might be the gravity. Radiation and heat conduction are insufficient to explain the decay of the oscillations. Other mechanisms, such as wave leakage and mass accretion, have to be considered. The possible relation between the longitudinal oscillations and the later eruption of a prominence thread, as well as a coronal mass ejection (CME), is also discussed.
The bispectrum of the cosmic microwave background (CMB) generated by a correlation between a time-dependent gravitational potential and the weak gravitational lensing effect provides a direct measurement of the influence of dark energy on CMB. This bispectrum is also known to yield the most important contamination of the so-called "local-form" primordial bispectrum, which can be used to rule out all single-field inflation models. In this paper, we reexamine the effect of non-linear matter clustering on this bispectrum. We compare three different approaches: the 3rd-order perturbation theory (3PT), and two empirical fitting formulae available in the literature, finding that detailed modeling of non-linearity appears to be not very important, as most of the signal-to-noise comes from the squeezed triangle, for which the correlation in the linear regime dominates. The expected signal-to-noise ratio for an experiment dominated by the cosmic variance up to $l_{\rm max}=1500$ is about 5, which is much smaller than the previous estimates including non-linearity, but agrees with the estimates based on the linear calculation. We find that the difference between the linear and non-linear predictions is undetectable, and does not alter the contamination of the local-form primordial non-Gaussianity.
Narrow absorption line (NAL) outflows are an important yet poorly understood part of the quasar outflow phenomenon. We discuss one particular NAL outflow that has high speeds, time variability, and moderate ionizations like typical BAL flows, at an estimated location just ~5 pc from the quasar. It also has a total column density and line widths (internal velocity dispersions) ~100 times smaller than BALs, with no substantial X-ray absorption. We argue that radiative shielding (in the form of an X-ray/warm absorber) is not critical for the outflow acceleration and that the moderate ionizations occur in dense substructures that have an overall small volume filling factor in the flow. We also present new estimates of the overall incidence of quasar outflow lines; e.g., ~43% of bright quasars have a C IV NAL outflow while ~68% have a C IV outflow line of any variety (NAL, BAL, or mini-BAL).
VLBI multi-epoch water maser observations are a powerful tool to study the dense, warm shocked gas very close to massive protostars. The very high-angular resolution of these observations allow us to measure the proper motions of the masers in a few weeks, and together with the radial velocity, to determine their full kinematics. In this paper we present a summary of the main observational results obtained toward the massive star-forming regions of Cepheus A and W75N, among them: (i) the identification of different centers of high-mass star formation activity at scales of 100 AU; (ii) the discovery of new phenomena associated with the early stages of high-mass protostellar evolution (e.g., isotropic gas ejections); and (iii) the identification of the simultaneous presence of a wide-angle outflow and a highly collimated jet in the massive object Cep A HW2, similar to what is observed in some low-mass protostars. Some of the implications of these results in the study of high-mass star formation are discussed.
VLBI multi-epoch water maser observations are a powerful tool to study the gas very close to the central engine responsible for the phenomena associated with the early evolution of massive protostars. In this paper we present a summary of the main observational results obtained toward the massive star-forming regions of Cepheus A and W75N. These observations revealed unexpected phenomena in the earliest stages of evolution of massive objects (e.g., non-collimated "short-lived" pulsed ejections in different massive protostars), and provided new insights in the study of the dynamic scenario of the formation of high-mass stars (e.g., simul- taneous presence of a jet and wide-angle outflow in the massive object Cep A HW2, similar to what is observed in low-mass protostars). In addition, with these observations it has been possible to identify new, previously unseen centers of high-mass star formation through outflow activity.
The Fixed-\Phi (F\Phi) and Harmonic Mean (HM) fitting methods are two methods to determine the average direction and velocity of coronal mass ejections (CMEs) from time-elongation tracks produced by Heliospheric Imagers (HIs), such as the HIs onboard the STEREO spacecraft. Both methods assume a constant velocity in their descriptions of the time-elongation profiles of CMEs, which are used to fit the observed time-elongation data. Here, we analyze the effect of aerodynamic drag on CMEs propagating through interplanetary space, and how this drag affects the result of the F\Phi and HM fitting methods. A simple drag model is used to analytically construct time-elongation profiles which are then fitted with the two methods. It is found that higher angles and velocities give rise to greater error in both methods, reaching errors in the direction of propagation of up to 15 deg and 30 deg for the F\Phi and HM fitting methods, respectively. This is due to the physical accelerations of the CMEs being interpreted as geometrical accelerations by the fitting methods. Because of the geometrical definition of the HM fitting method, it is affected by the acceleration more greatly than the F\Phi fitting method. Overall, we find that both techniques overestimate the initial (and final) velocity and direction for fast CMEs propagating beyond 90 deg from the Sun-spacecraft line, meaning that arrival times at 1 AU would be predicted early (by up to 12 hours). We also find that the direction and arrival time of a wide and decelerating CME can be better reproduced by the F\Phi due to the cancellation of two errors: neglecting the CME width and neglecting the CME deceleration. Overall, the inaccuracies of the two fitting methods are expected to play an important role in the prediction of CME hit and arrival times as we head towards solar maximum and the STEREO spacecraft further move behind the Sun.
We measure equivalent widths (EW) - focussing on two unique features (NaI and TiO2) of low-mass stars (\leq 0.3 M\odot) - for luminous red galaxy spectra from the the Sloan Digital Sky Survey (SDSS) and X-Shooter Lens Survey (XLENS) in order to study the low-mass end of the IMF. We compare these EWs to those derived from simple stellar population models computed with different IMFs, ages,[{\alpha}/Fe], and elemental abundances. We find that models are able to simultaneously reproduce the observed NaD {\lambda}5895 and NaI {\lambda}8190 features for the lower-mass (~{\sigma}*) ETGs but deviate increasingly for more massive ETGs, due do strongly mismatching NaD EWs. The TiO2 {\lambda}6230 feature and the NaI {\lambda}8190 feature, may be a powerful IMF diagnostic, with age and metallicity effects orthogonal to the effect of IMF on the feature's strength. We find that both features correlate strongly with galaxy velocity dispersion. The XLENS ETG (SDSSJ0912+0029) and one SDSS ETG (SDSSJ0041-0914) appear to require both an extreme dwarf-rich IMFs and a high sodium enhancement ([Na/Fe]=+0.4). However, lensing constraints on the total mass of the XLENS system within its Einstein radius limit a bottom-heavy IMF with a power-law slope to x \leq 3.0 at the 90% C.L. We conclude that NaI and TiO features, in comparison with state-of-the-art SSP models, suggest a mildly steepening IMF from Salpeter to x~3.0 for ETGs in the range {\sigma}=200-335 km/s.
Photometric data from the ASAS - South (declination less than 29 deg) survey
have been used for identification of bright stars located near the sources from
the ROSAT All Sky Survey Bright Source Catalog (RBSC). In total 6028 stars
brighter than 12.5 mag in I- or V -bands have been selected and analyzed for
periodicity. Altogether 2302 variable stars have been found with periods
ranging from 0.137 d to 193 d. Most of these stars have X-ray emission of
coronal origin with a few cataclysmic binaries and early type stars with
colliding winds. Whenever it was possible we collected data available in the
literature to verify periods and to classify variable objects.
The catalog includes 1936 stars (1233 new) considered to be variable due to
presence of spots (rotationally variable), 127 detached eclipsing binary stars
(33 new), 124 contact binaries (11 new), 96 eclipsing stars with deformed
components (19 new), 13 ellipsoidal variables (4 new), 5 miscellaneous
variables and one pulsating RR Lyr type star (blended with an eclipsing
binary). More than 70% of new variable stars have amplitudes smaller than 0.1
mag, but for ASAS 063656-0521.0 we have found the largest known amplitude of
brightness variations due to the presence of spots (up to Delta V=0.8 mag). The
table with the compiled data and figures with light curves can be downloaded
from the Acta Astronomica Archive.
In this paper we describe the state-of-the art status of multi-frequency detection techniques for compact sources in microwave astronomy. From the simplest cases where the spectral behaviour is well-known (i.e. thermal SZ clusters) to the more complex cases where there is little a priori information (i.e. polarized radio sources) we will review the main advances and the most recent results in the detection problem.
The Light-Time Effect (LTE) is observed whenever the distance between the observer and any kind of periodic event changes in time. The usual cause of this distance change is the reflex motion about the system's barycenter due to the gravitational influence of one or more additional bodies. We analyze 5032 eclipsing contact (EC) and detached (ED) binaries from the All Sky Automated Survey (ASAS) catalogue to detect variations in the times of eclipses which possible can be due to the LTE effect. To this end we use an approach known from the radio pulsar timing where a template radio pulse of a pulsar is used as a reference to measure the times of arrivals of the collected pulses. In our analysis as a template for a photometric time series from ASAS, we use a best-fitting trigonometric series representing the light curve of a given EC or ED. Subsequently, an O-C diagram is built by comparing the template light curve with light curves obtained from subsets of a given time series. Most of the variations we detected in O-Cs correspond to a linear period change. Three show evidence of more than one complete LTE-orbit. For these objects we obtained preliminary orbital solutions. Our results demonstrate that the timing analysis employed in radio pulsar timing can be effectively used to study large data sets from photometric surveys.
Tau Boo is an intriguing planet-host star that is believed to undergo magnetic cycles similar to the Sun, but with a duration that is about one order of magnitude smaller than that of the solar cycle. With the use of observationally derived surface magnetic field maps, we simulate the magnetic stellar wind of Tau Boo by means of three-dimensional MHD numerical simulations. As the properties of the stellar wind depend on the particular characteristics of the stellar magnetic field, we show that the wind varies during the observed epochs of the cycle. Although the mass loss-rates we find (~2.7e-12 Msun/yr) vary less than 3 per cent during the observed epochs of the cycle, our derived angular momentum loss-rates vary from 1.1 to 2.2e32erg. The spin-down times associated to magnetic braking range between 39 and 78Gyr. We also compute the emission measure from the (quiescent) closed corona and show that it remains approximately constant through these epochs at a value of ~10^{50.6} cm^{-3}. This suggests that a magnetic cycle of Tau Boo may not be detected by X-ray observations. We further investigate the interaction between the stellar wind and the planet by estimating radio emission from the hot-Jupiter that orbits at 0.0462 au from Tau Boo. By adopting reasonable hypotheses, we show that, for a planet with a magnetic field similar to Jupiter (~14G at the pole), the radio flux is estimated to be about 0.5-1 mJy, occurring at a frequency of 34MHz. If the planet is less magnetised (field strengths roughly <4G), detection of radio emission from the ground is unfeasible due to the Earth's ionospheric cutoff. According to our estimates, if the planet is more magnetised than that and provided the emission beam crosses the observer line-of-sight, detection of radio emission from Tau Boo b is only possible by ground-based instruments with a noise level of < 1 mJy, operating at low frequencies.
Starlight in the Universe impedes the passage of high energy (e.g. TeV) gamma rays due to positron-electron pair production. The history of this stellar radiation field depends upon observations of star formation rate which themselves can only be interpreted in the context of a particular cosmology. For different equations of state of dark energy, the star formation rate data suggests a different density of stellar photons at a particular redshift and a different probability of arrival of gamma rays from distant sources. In this work we aim to show that this effect can be used to constrain the equation of state of dark energy. The current work is a proof of concept and we outline the steps that would have to be taken to place the method in a rigorous statistical framework which could then be combined with other more mature methods such as fitting supernova luminosity distances.
We present the first interferometric polarization map of the W3(OH) massive star-forming region observed with the Submillimeter Array (SMA) at 878 mum with an angular resolution of 1.5 (about 3 \times 10 AU). Polarization is detected in the W3(H2O) hot core, an extended emission structure in the north-west of W3(H2O), and part of the W3(OH) ultracompact HII region. The W3(H2O) hot core is known to be associated with a synchrotron jet along the east-west direction. In this core, the inferred magnetic field orientation is well aligned with the synchrotron jet and close to the plane of sky. Using the Chandrasekhar-Fermi method with the observed dispersion in polarization angle, we estimate a plane-of-sky magnetic field strength of 17.0 mG. Combined with water maser Zeeman measurements, the total magnetic field strength is estimated to be 17.1 mG, comparable to the field strength estimated from the synchrotron model. The magnetic field energy dominates over turbulence in this core. In addition, the depolarization effect is discerned in both SMA and JCMT measurements. Despite the great difference in angular resolutions and map extents, the polarization percentage shows a similar power-law dependence with the beam averaged column density. We suggest that the column density may be an important factor to consider when interpreting the depolarization effect.
The results of Monte-Carlo simulations of Extensive Air Shower are presented to show the difference of hadronic component content at various altitudes with the aim to choose an optimal altitude for the PRISMA-like experiment. CORSIKA program for EAS simulations with QGSJET and GHEISHA models was used to calculate the number of hadrons reaching the observational level inside a ring of 50 m radius around the EAS axis. Then the number of neutrons produced by the hadronic component was calculated using an empirical relationship between the two components. We have tested the results with the ProtoPRISMA array at sea level, and recorded neutrons are close to the simulation results.
Dispersion in the interstellar medium is a well known phenomenon that follows a simple relationship, which has been used to predict the time delay of dispersed radio pulses since the late 1960s. We performed wide-band simultaneous observations of four pulsars with LOFAR (at 40-190 MHz), the 76-m Lovell Telescope (at 1400 MHz) and the Effelsberg 100-m Telescope (at 8000 MHz) to test the accuracy of the dispersion law over a broad frequency range. In this paper we present the results of these observations which show that the dispersion law is accurate to better than 1 part in 100000 across our observing band. We use this fact to constrain some of the properties of the ISM along the line-of-sight and use the lack of any aberration or retardation effects to determine upper limits on emission heights in the pulsar magnetosphere. We also discuss the effect of pulse profile evolution on our observations, and the 1 implications that it could have for precision pulsar timing projects such as the detection of gravitational waves with pulsar timing arrays.
We show the conclusions claimed in the manuscript arXiv:1202.5309v1 by Cuoco, Komatsu and Siegal-Gaskins (CKS) are not generally valid. The results in CKS are based on a number of simplifying assumptions regarding the source population below the detection threshold and the threshold flux itself, and do not apply to many physical models of the blazar population. Physical blazar population models that match the measured source counts above the observational threshold can account for 60% of the diffuse gamma-ray background intensity between 1-10 GeV, while the assumptions in CKS limit the intensity to <30%. The shortcomings of the model considered in CKS arise from an over-simplified blazar source model. A number of the simplifying assumptions are unjustified, including: first, the adoption of an assumed power-law source-count distribution, dN/dS, to arbitrary low source fluxes, which is not exhibited in physical models of the blazar population; and, second, the lack of blazar spectral information in calculating the anisotropy of unresolved gamma-ray blazar emission. We also show that the calculation of the unresolved blazars' anisotropy is very sensitive to the spectral distribution of the unresolved blazars through the adopted source resolution threshold value, and must be taken into account in an accurate anisotropy calculation.
Tidal debris around galaxies can yield important clues on their evolution. We have identified tidal debris in 11 early type galaxies (T \leq 0) from a sample of 65 early types drawn from the Spitzer Survey of Stellar Structure in Galaxies (S4G). The tidal debris includes features such as shells, ripples and tidal tails. A variety of techniques, including two-dimensional decomposition of galactic structures, was used to quantify the residual tidal features. The tidal debris contributes ~3 - 10% to the total 3.6 {\mu}m luminosity of the host galaxy. Structural parameters of the galaxies were estimated using two-dimensional profile fitting. We investigate the locations of galaxies with tidal debris in the Fundamental Plane and Kormendy relation. We find that galaxies with tidal debris lie within the scatter of early type galaxies without tidal features. Assuming that the tidal debris is indicative of recent gravitational interaction or merger, this suggests that these galaxies have either undergone minor merging events so that the overall structural properties of the galaxies are not significantly altered, or they have undergone a major merging events but already have experienced sufficient relaxation and phase-mixing so that their structural properties become similar to those of the non-interacting early type galaxies.
The measurement of electron temperatures and metallicities in H ii regions and Planetary Nebulae (PNe) has-for several decades-presented a problem: results obtained using different techniques disagree. What it worse, they disagree consistently. There have been numerous attempts to explain these discrepancies, but none has provided a satisfactory solution to the problem. In this paper, we explore the possibility that electrons in H ii regions and PNe depart from a Maxwell-Boltzmann equilibrium energy distribution. We adopt a "kappa-distribution" for the electron energies. Such distributions are widely found in Solar System plasmas, where they can be directly measured. This simple assumption is able to explain the temperature and metallicity discrepancies in H ii regions and PNe arising from the different measurement techniques. We find that the energy distribution does not need to depart dramatically from an equilibrium distribution. From an examination of data from Hii regions and PNe it appears that kappa ~ 10 is sufficient to encompass nearly all objects. We argue that the kappa-distribution offers an important new insight into the physics of gaseous nebulae, both in the Milky Way and elsewhere, and one that promises significantly more accurate estimates of temperature and metallicity in these regions.
Motivated by recent spectroscopic observations suggesting that atmospheres of some extrasolar giant-planets are carbon-rich, i.e. carbon/oxygen ratio (C/O) $\ge$ 1, we find that the whole set of compositional data for Jupiter is consistent with the hypothesis that it be a carbon-rich giant planet. We show that the formation of Jupiter in the cold outer part of an oxygen-depleted disk (C/O $\sim$1) reproduces the measured Jovian elemental abundances at least as well as the hitherto canonical model of Jupiter formed in a disk of solar composition (C/O = 0.54). The resulting O abundance in Jupiter's envelope is then moderately enriched by a factor of $\sim$2 $\times$ solar (instead of $\sim$7 $\times$ solar) and is found to be consistent with values predicted by thermochemical models of the atmosphere. That Jupiter formed in a disk with C/O $\sim$1 implies that water ice was heterogeneously distributed over several AU beyond the snow line in the primordial nebula and that the fraction of water contained in icy planetesimals was a strong function of their formation location and time. The Jovian oxygen abundance to be measured by NASA's Juno mission en route to Jupiter will provide a direct and strict test of our predictions.
We explore the implications of a 124-126 GeV CP-even Higgs boson on the fundamental parameter space and sparticle spectroscopy of the minimal gauge mediated supersymmetry breaking (mGMSB) scenario. The above mass for the Higgs boson yields stringent lower bounds on the sparticle masses in this class of models. The lightest neutralino and stau masses lie close to 1.5 TeV and 800 GeV respectively, while the majority of the sparticle masses are in the several to multi-TeV range. We show that with a single pair of 5+\bar{5} SU(5) messenger multiplets, the lower limit on the gravitino mass is \sim 360 eV. This is reduced to about 60 eV if five pairs of 5+\bar{5} messenger fields are introduced. Non-standard cosmology and non-standard gravitino production mechanisms are required in order to satisfy cosmological observations.
If dark matter (DM) is a weakly interacting massive particle (WIMP) that is a thermal relic of the early Universe, then its total self-annihilation cross section is revealed by its present-day mass density. The canonical thermally averaged cross section for a generic WIMP is usually stated as 3*10^-26 cm^3s^-1, with unspecified uncertainty, and taken to be independent of WIMP mass. Recent searches for annihilation products of DM annihilation have just reached the sensitivity to exclude this canonical cross section for 100% branching ratio to certain final states and small WIMP masses. The ultimate goal is to probe all kinematically allowed final states as a function of mass and, if all states are adequately excluded, set a lower limit to the WIMP mass. Probing the low-mass region is further motivated due to recent hints for a light WIMP in direct and indirect searches. We revisit the thermal relic abundance calculation for a generic WIMP and show that the required cross section can calculated precisely. It varies significantly with mass at masses below 10 GeV, reaching a maximum of 5.2*10^-26 cm^3s^-1 at masses around 0.3 GeV, and is 2.2*10^-26 cm^3s^-1 with feeble mass-dependence for masses above 10 GeV. These results, which differ significantly from the canonical value and have not been taken into account in searches for annihilation products from generic WIMPs, have a noticeable impact on the interpretation of present limits from Fermi-LAT and WMAP+ACT.
We analyze the dynamical system defined by a universe filled with a barotropic fluid plus a scalar field with modified kinetic term of the form L = F (X) - V (phi). After a suitable choice of variables that allows us to study the phase space of the system we obtain the critical points and their stability. We find that they reduce to the ones defined for the canonical case when F (X) = X. We also study the field energy conditions to have a nonsingular bounce.
Dense enough compact objects were recently shown to lead to an exponentially fast increase of the vacuum energy density for free scalar fields properly coupled to the spacetime curvature: the vacuum awakening effect. This exponential increase may be alternatively seen as a sort of tachyonic instability which also plays an important role in inflationary cosmology. After the instability is triggered, the star energy density would be overwhelmed by the vacuum energy in a few milliseconds. This demands that at some point backreaction takes over to bring the vacuum back to a stationary regime. Here we show that the vacuum energy density built up during the unstable epoch when the vacuum is awake leads to a burst of particles in the final stationary state when the vacuum "falls asleep". We emphasize that this phenomenon occurs even in the adiabatic limit, where the spacetime geometry changes arbitrarily slowly. Therefore, the burst of particles at the end of the awaken phase differs drastically from the usual particle creation due to the change in the background geometry.
We will investigate the influence of the inhomogeneity of the universe, especially that of the Lema{\^i}tre--Tolman--Bondi (LTB) model, on a gravitationally bound local system such as the solar system. We concentrate on the dynamical perturbation to the planetary motion and derive the leading order effect generated from the LTB model. It will be shown that there appear not only a well-known cosmological effect arisen from the homogeneous and isotropic model, such as the Robertson--Walker (RW) model, but also the additional terms due to the radial inhomogeneity of the LTB model. We will also apply the obtained results to the problem of secular increase in the astronomical unit, reported by Krasinsky and Brumberg (2004), and imply that the inhomogeneity of the universe cannot have a significant effect for explaining the observed $d{\rm AU}/dt = 15 \pm 4 ~{\rm [m/century]}$.
The geometrical structure of a real four-dimensional space-time has been extended via the Conservation group with basic field variable being the orthonormal tetrad. Field equations were obtained from a variational principle which is invariant under the conservation group. Recently, symmetric solutions of the field equations have been developed. In this note, the free-field solution is investigated in terms of the value of the scalar curvature and an expression for the cosmological term is developed. This term, while not a constant, has asymptotic values in the range that match nicely with the current value of $\Lambda$. This may add further support to the conclusion that the theory developed by Pandres unifies the fields.
We reexamine the light deflection by an Ellis wormhole. The bending angle as a function of the ratio between the impact parameter and the throat radius of the wormhole is obtained in terms of a complete elliptic integral of the first kind. This result immediately yields asymptotic expressions in the weak field approximation. It is shown that an expression for the deflection angle derived (and used) in recent papers is valid at the leading order but it breaks down at the next order because of the nontrivial spacetime topology.
Investigation of the cosmic microwave background formation processes is one of the most actual problem at present time. In this paper we analyze the response of the hydrogen atom to the external photon fields. Field characteristics are defined via conditions corresponding to the recombination era of universe. Approximation of three-level atom is used to describe the "atom - fields" interaction. It is found that the phenomena of the electromagnetically induced transparancy takes place in this case. Consideration of EIT phenomena makes it necessary to update astrophysical description of the processes of the cosmic microwave background formation and, in particular, Sobolev escape probability. Additional terms to the optical depth in definition of Sobolev escape probability on the level about 1% are found.
We show that the improper ferroelectric phase transition in the multiferroic hexagonal manganites displays the same symmetry-breaking characteristics as those proposed in early-universe theories. We present an analysis of the Kibble-Zurek theory of topological defect formation applied to the hexagonal manganites, discuss the conditions determining the range of cooling rates in which Kibble-Zurek behavior is expected, and show that recent literature data are consistent with our predictions. We explore experimentally for the first time to our knowledge the cross-over out of the Kibble-Zurek regime and find a surprising "anti-Kibble-Zurek" behavior.
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We have identified and studied a sample of 151 FR IIs found in brightest cluster galaxies (BCGs) in the MaxBCG cluster catalog with data from FIRST and NVSS. We have compared the radio luminosities and projected lengths of these FR IIs to the projected length distribution of a range of mock catalogs generated by an FR II model and estimate the FR II lifetime to be 1.9 x 10^8 yr. The uncertainty in the lifetime calculation is a factor of two, due primarily to uncertainties in the ICM density and the FR II axial ratio. We furthermore measure the jet power distribution of FR IIs in BCGs and find that it is well described by a log-normal distribution with a median power of 1.1 x 10^37 W and a coefficient of variation of 2.2. These jet powers are nearly linearly related to the observed luminosities, and this relation is steeper than many other estimates, although it is dependent on the jet model. We investigate correlations between FR II and cluster properties and find that galaxy luminosity is correlated with jet power. This implies that jet power is also correlated with black hole mass, as the stellar luminosity of a BCG should be a good proxy for its spheroid mass and therefore the black hole mass. Jet power, however, is not correlated with cluster richness, nor is FR II lifetime strongly correlated with any cluster properties. We calculate the enthalpy of the lobes to examine the impact of the FR IIs on the ICM and find that heating due to adiabatic expansion is too small to offset radiative cooling by a factor of at least six. In contrast, the jet power is approximately an order of magnitude larger than required to counteract cooling. We conclude that if feedback from FR IIs offsets cooling of the ICM, then heating must be primarily due to another mechanism associated with FR II expansion.
We present observations of CO J=2-1 line emission in infrared-luminous cluster galaxies at z~1 using the IRAM Plateau de Bure Interferometer. Our two primary targets are optically faint, dust-obscured galaxies (DOGs) found to lie within 2 Mpc of the centers of two massive (>10^14 Msun) galaxy clusters. CO line emission is not detected in either DOG. We calculate 3-sigma upper limits to the CO J=2-1 line luminosities, L'_CO < 6.08x10^9 and < 6.63x10^9 K km/s pc^2. Assuming a CO-to-H_2 conversion factor derived for ultraluminous infrared galaxies in the local Universe, this translates to limits on the cold molecular gas mass of M_H_2 < 4.86x10^9 Msun and M_H_2 < 5.30x10^9 Msun. Both DOGs exhibit mid-infrared continuum emission that follows a power-law, suggesting that an AGN contributes to the dust heating. As such, estimates of the star formation efficiencies in these DOGs are uncertain. A third cluster member with an infrared luminosity, L_IR < 7.4x10^11 Lsun, is serendipitously detected in CO J=2-1 line emission in the field of one of the DOGs located roughly two virial radii away from the cluster center. The optical spectrum of this object suggests that it is likely an obscured AGN, and the measured CO line luminosity is L'_CO = (1.94 +/- 0.35)x10^10 K km/s pc^2, which leads to an estimated cold molecular gas mass M_H_2 = (1.55+/-0.28)x10^10 Msun. A significant reservoir of molecular gas in a z~1 galaxy located away from the cluster center demonstrates that the fuel can exist to drive an increase in star-formation and AGN activity at the outskirts of high-redshift clusters.
We report the first detection of elements at all three r-process peaks in the metal-poor halo star HD 160617. These elements include arsenic and selenium, which have not been detected previously in halo stars, and the elements tellurium, osmium, iridium, and platinum, which have been detected previously. Absorption lines of these elements are found in archive observations made with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. We present up-to-date absolute atomic transition probabilities and complete line component patterns for these elements. Additional archival spectra of this star from several ground-based instruments allow us to derive abundances or upper limits of 45 elements in HD 160617, including 27 elements produced by neutron-capture reactions. The average abundances of the elements at the three r-process peaks are similar to the predicted solar system r-process residuals when scaled to the abundances in the rare earth element domain. This result for arsenic and selenium may be surprising in light of predictions that the production of the lightest r-process elements generally should be decoupled from the heavier r-process elements.
We present a new empirical calibration of equilibrium tidal theory for
extrasolar planet systems, extending a prior study by incorporating detailed
physical models for the internal structure of planets and host stars. The
resulting strength of the stellar tide produces a coupling that is strong
enough to reorient the spins of some host stars without causing catastrophic
orbital evolution, thereby potentially explaining the observed trend in
alignment between stellar spin and planetary orbital angular momentum. By
isolating the sample whose spins should not have been altered in this model, we
also show evidence for two different processes that contribute to the
population of planets with short orbital periods.
We apply our results to estimate the remaining lifetimes for short period
planets, examine the survival of planets around evolving stars, and determine
the limits for circularisation of planets with highly eccentric orbits. Our
analysis suggests that the survival of circularised planets is strongly
affected by the amount of heat dissipated, which is often large enough to lead
to runaway orbital inflation and Roche lobe overflow.
This work aims at investigating the characteristics of the molecular gas
associated with the nebula G18.8+1.8, linked to the Wolf-Rayet star HD168206
(WR 113), and its relation to other components of its local interstellar
medium.
We carried out molecular observations of the 12CO(J=1-0) and (J=2-1) lines
with angular resolution of 44 arcsec and 22 arcsec using the SEST telescope.
Complementary NANTEN data of the 12CO(1-0) line were also used. The dust
emission was analyzed using Spitzer-IRAC images at 8.0 microns, and WISE data
at 3.4, 4.6, and 12.0 microns.
The SEST data allowed us to identify a molecular component (Cloud 3) having
velocities in the interval from ~ +30 to +36 km/s which is most probably linked
to the nebula. Morphological and kinematical properties suggest that Cloud 3
constitute a wind-blown molecular half-shell, which expands around WR113. The
ratio R_(2-1/1-0) and excitation temperatures indicate that the molecular gas
is being irradiated by strong UV radiation. The location of the inner optical
ring in the outer edge of Cloud 3 suggests that the stars SerOB2-1, -2, -3,
-63, and -64 are responsables for the ionization of Cloud 3 and the inner ring
nebula. A comparison between the spatial distribution of the molecular gas and
the PAH emission at 8 $\mu$m indicates the existence of a PDR between the
ionized and the molecular gas.
A search for candidate young stellar objects (YSOs) in the region around
G18.8+1.8 based on available 2MASS, MSX, IRAS, and Spitzer-IRAC catalogs
resulted in the detection of about sixty sources, some of them projected onto
Cloud 3. Two small spots of clustered candidates YSOs are projected near the
outer border of Cloud 3, although a triggered stellar formation scenario is
doubtful.
The ionizing fluxes from quasars and other active galactic nuclei (AGN) are critical for interpreting the emission-line spectra of AGN and for photoionization and heating of the intergalactic medium (IGM). Using ultraviolet spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), we have directly measured the rest-frame ionizing continua and emission lines for 22 AGN. Over the redshift range 0.026 < z < 1.44, COS samples the Lyman continuum and many far-UV emission lines (Lya 1216, C IV 1549, Si IV/OIV] 1400, N V 1240, O VI 1035). Strong EUV emission lines with 14-22 eV excitation energies (Ne VIII 770,780, Ne V 569, O II 834, O III 833, 702, O IV 788,608,554, O V 630, N III 685) suggest the presence of hot gas in the broad emission-line region. The rest-frame continuum, F_nu \sim nu^{alpha_nu}, shows a break at wavelengths below 1000 A, with spectral index alpha_nu = -0.68 +/- 0.14 in the FUV (1200-2000 A) steepening to alpha_nu = -1.41 +/- 0.21 in the EUV (500-1000 A). The COS EUV index is similar to that of radio-quiet AGN in the 2002 HST/FOS survey (alpha_nu = -1.57 +/- 0.17). We see no Lyman edge (tau_HI < 0.03) or He I 584 emission in the AGN composite. Our 22 AGN exhibit a substantial range of FUV/EUV spectral indices and a correlation with AGN luminosity and redshift, likely due to observing below the 1000 A spectral break.
There is ample observational evidence that the star formation rate (SFR) surface density, Sigma_SFR, is closely correlated with the surface density of molecular hydrogen, Sigma_H2. This empirical relation holds both for galaxy-wide averages and for individual >=kpc sized patches of the interstellar medium (ISM), but appears to degrade substantially at a sub-kpc scale. Identifying the physical mechanisms that determine the scale-dependent properties of the observed Sigma_H2-Sigma_SFR relation remains a challenge from a theoretical perspective. To address this question, we analyze the slope and scatter of the Sigma_H2-Sigma_SFR relation using a set of cosmological, galaxy formation simulations with a peak resolution of ~100 pc. These simulations include a chemical network for molecular hydrogen, a model for the CO emission, and a simple, stochastic prescription for star formation that operates on ~100 pc scales. Specifically, star formation is modeled as a Poisson process in which the average SFR is directly proportional to the present mass of H2. The predictions of our numerical model are in good agreement with the observed Kennicutt-Schmidt and Sigma_H2-Sigma_SFR relations. We show that observations based on CO emission are ill suited to reliably measure the slope of the latter relation at low (<20 M_sun pc^-2) H2 surface densities on sub-kpc scales. Our models also predict that the inferred Sigma_H2-Sigma_SFR relation steepens at high H2 surface densities as a result of the surface density dependence of the CO/H2 conversion factor. Finally, we show that on sub-kpc scales most of the scatter in the relation is a consequence of discreteness effects in the star formation process. In contrast, variations of the CO/H2 conversion factor are responsible for most of the scatter measured on super-kpc scales.
The model for pulsar wind nebulae (PWNe) as the result of the magnetohydrodynamic (MHD) downstream flow from a shocked, relativistic pulsar wind has been successful in reproducing many features of the nebulae observed close to the central pulsars. However, observations of well-studied young nebulae like the Crab Nebula, 3C 58, and G21.5--0.9 do not show the toroidal magnetic field on a larger scale that might be expected in the MHD flow model; in addition, the radial variation of spectral index due to synchrotron losses is smoother than expected in the MHD flow model. We find that pure diffusion models can reproduce the basic data on nebular size and spectral index variation for the Crab, 3C 58, and G21.5--0.9. Most of our models use an energy independent diffusion coefficient; power law variations of the coefficient with energy are degenerate with variation in the input particle energy distribution index in the steady state, reflecting boundary case. Energy dependent diffusion is a possible reason for the smaller diffusion coefficient inferred for the Crab. Monte Carlo simulations of the particle transport allowing for advection and diffusion of particles suggest that diffusion dominates over much of the total nebular volume of the Crab. Advection dominates close to the pulsar and is likely to play a role in the X-ray half-light radius. The source of diffusion and mixing of particles is uncertain, but may be related to the Rayleigh-Taylor instability at the outer boundary of a young PWN or to instabilities in the toroidal magnetic field structure.
The NEAs (Near-Earth Asteroids) are good targets for spatial missions, since they periodically approach the orbit of the Earth. Recently, the NEA (153591) 2001 SN263 was chosen as the target of the ASTER MISSION- First Brazilian Deep Space Mission, planned to be launched in 2015. In February 2008, the radio astronomers from Arecibo-Puerto Rico concluded that (153591) 2001 SN263 is actually a triple system (Nolan et al., 2008). The announcement of the ASTER MISSION has motivated the development of the present work, whose goal is to characterize regions of stability and instability of the triple system (153591) 2001 SN263. The method adopted consisted in dividing the region around the system into four distinct regions. We have performed numerical integrations of systems composed by seven bodies: Sun, Earth, Mars, Jupiter and the three components of the system, and by thousands of particles randomly distributed within the demarcated regions, for the planar and inclined prograde cases. The results are diagrams of semi-major axis versus eccentricity, where it is shown the percentage of particles that survive for each set of initial conditions. The regions where 100% of the particles survive is defined as stable regions. We found that the stable regions are in the neighborhood of Alpha and Beta, and in the external region. It was identified resonant motion of the particles with Beta and Gamma in the internal regions, which lead to instability. For particles with I>45{\deg} in the internal region, where I is the inclination with respect to Alpha's equator, there is no stable region, except for the particles placed really close to Alpha. The stability in the external region is not affected by the variation of inclination. We also present a discussion on the long-term stability in the internal region, for the planar and circular cases, with comparisons with the short-term stability.
We present the results of a cross-correlation of the Planck Early Release Compact Source Catalog (ERCSC) with the catalog of Herschel-ATLAS sources detected in the Phase 1 fields, covering 134.55 deg2. There are 28 ERCSC sources detected by Planck at 857 GHz in this area. As many as 16 of them are probably high Galactic latitude cirrus; 10 additional sources can be clearly identified as bright, low-z galaxies; one further source is resolved by Herschel as two relatively bright sources; and the last is resolved into an unusual condensation of low-flux, probably high-redshift point sources, around a strongly lensed Herschel-ATLAS source at z = 3.26. Our results demonstrate that the higher sensitivity and higher angular resolution H-ATLAS maps provide essential information for the interpretation of candidate sources extracted from Planck sub-mm maps.
We measured the surface mass density of the Galactic disk at the solar position, up to 4 kpc from the plane,by means of the kinematics of ~400 thick disk stars. The results match the expectations for the visible mass only, and no dark matter is detected in the volume under analysis. The current models of dark matter halo are excluded with a significance higher than 5sigma, unless a highly prolate halo is assumed, very atypical in cold dark matter simulations. The resulting lack of dark matter at the solar position challenges the current models.
Hubble Space Telescope observations between 2001 and 2010 resolved the binary components of the Cold Classical transneptunian object (79360) Sila-Nunam (provisionally designated 1997 CS29). From these observations we have determined the circular, retrograde mutual orbit of Nunam relative to Sila with a period of 12.50995 \pm 0.00036 days and a semimajor axis of 2777 \pm 19 km. A multi-year season of mutual events, in which the two near-equal brightness bodies alternate in passing in front of one another as seen from Earth, is in progress right now, and on 2011 Feb. 1 UT, one such event was observed from two different telescopes. The mutual event season offers a rich opportunity to learn much more about this barely-resolvable binary system, potentially including component sizes, colors, shapes, and albedo patterns. The low eccentricity of the orbit and a photometric lightcurve that appears to coincide with the orbital period are consistent with a system that is tidally locked and synchronized, like the Pluto-Charon system. The orbital period and semimajor axis imply a system mass of (10.84 \pm 0.22) \times 10^18 kg, which can be combined with a size estimate based on Spitzer and Herschel thermal infrared observations to infer an average bulk density of 0.72 +0.37 -0.23 g cm^-3, comparable to the very low bulk densities estimated for small transneptunian binaries of other dynamical classes.
We estimated the dynamical surface mass density Sigma at the solar position between Z=1.5 and 4 kpc from the Galactic plane, as inferred from the kinematics of thick disk stars. The formulation is exact within the limit of validity of a few basic assumptions. The resulting trend of Sigma(Z) matches the expectations of visible mass alone, and no dark component is required to account for the observations. We extrapolate a dark matter (DM) density in the solar neighborhood of 0+-1 mM_sun pc^-3, and all the current models of a spherical DM halo are excluded at a confidence level higher than 4sigma. A detailed analysis reveals that a small amount of DM is allowed in the volume under study by the change of some input parameter or hypothesis, but not enough to match the expectations of the models, except under an exotic combination of non-standard assumptions. Identical results are obtained when repeating the calculation with kinematical measurements available in the literature. We demonstrate that a DM halo would be detected by our method, and therefore the results have no straightforward interpretation. Only the presence of a highly prolate (flattening q>2) DM halo can be reconciled with the observations, but this is highly unlikely in LambdaCDM models. The results challenge the current understanding of the spatial distribution and nature of the Galactic DM. In particular, our results may indicate that any direct DM detection experiment is doomed to fail, if the local density of the target particles is negligible.
A significant fraction of massive stars are moving supersonically through the interstellar medium (ISM), either due to disruption of a binary system or ejection from their parent star cluster. The interaction of their wind with the ISM produces a bow shock. In late evolutionary stages these stars may undergo rapid transitions from red to blue and vice versa on the Hertzsprung-Russell diagram, with accompanying rapid changes to their stellar winds and bow shocks. Recent 3D simulations of the bow shock produced by the nearby runaway red supergiant (RSG) Betelgeuse, under the assumption of a constant wind, indicate that the bow shock is very young (<30000 years old), hence Betelgeuse may have only recently become a RSG. To test this possibility, we have calculated stellar evolution models for single stars which match the observed properties of Betelgeuse in the RSG phase. The resulting evolving stellar wind is incorporated into 2D hydrodynamic simulations in which we model a runaway blue supergiant (BSG) as it undergoes the transition to a RSG near the end of its life. We find that the collapsing BSG wind bubble induces a bow shock-shaped inner shell around the RSG wind that resembles Betelgeuse's bow shock, and has a similar mass. Surrounding this is the larger-scale retreating bow shock generated by the now defunct BSG wind's interaction with the ISM. We suggest that this outer shell could explain the bar feature located (at least in projection) just in front of Betelgeuse's bow shock.
The literature is rich in analysis and results related to thermally
pulsing-asymptotic giant branch (TP-AGB) stars, but the problem of the
instabilities that arise and cause the divergence of models during the late
stages of their evolution is rarely addressed. We investigate the physical
conditions, causes and consequences of the interruption in the calculations of
massive AGB stars in the late thermally-pulsing AGB phase. We have thoroughly
analysed the physical structure of a solar metallicity 8.5 solar mass star and
described the physical conditions at the base of the convective envelope (BCE)
just prior to divergence.
We find that the local opacity maximum caused by M-shell electrons of
Fe-group elements lead to the accumulation of an energy excess, to the
departure of thermal equilibrium conditions at the base of the convective
envelope and, eventually, to the divergence of the computed models. For the 8.5
solar mass case we present in this work the divergence occurs when the envelope
mass is about 2 solar mass. The remaining envelope masses range between
somewhat less than 1 and more than 2 solar mass for stars with initial masses
between 7 and 10 solar mass and, therefore, our results are relevant for the
evolution and yields of super-AGB stars. If the envelope is ejected as a
consequence of the instability we are considering, the occurrence of
electron-capture supernovae would be avoided at solar metallicity.
We develop a numerical hydrodynamics code using a pseudo-Newtonian formulation that uses the weak field approximation for the geometry, and a generalized source term for the Poisson equation that takes into account relativistic effects. The code was designed to treat moderately relativistic systems such as rapidly rotating neutron stars. The hydrodynamic equations are solved using a finite volume method with High Resolution Shock Capturing (HRSC) techniques. We implement several different slope limiters for second order reconstruction schemes and also investigate higher order reconstructions. We use the method of lines (MoL) to convert the mixed spatial-time partial differential equations into ordinary differential equations (ODEs) that depend only on time. These ODEs are solved using 2nd and 3rd order Runge-Kutta methods. The Poisson equation for the gravitational potential is solved with a multigrid method. In order to confirm the validity of our code, we carry out four different tests including one and two dimensional shock tube tests, stationary star tests of both non-rotating and rotating models and radial oscillation mode tests for spherical stars. In the shock tube tests, the code shows good agreement with analytic solutions which include shocks, rarefaction waves and contact discontinuities. The code is found to be stable and accurate: for example, when solving a stationary stellar model the fractional changes in the maximum density, total mass, and total angular momentum per dynamical time are found to be $3 \times 10^{-6}$, $5 \times 10^{-7}$ and $2 \times 10^{-6}$, respectively. We also find that the frequencies of the radial modes obtained by the numerical simulation of the steady state star agree very well with those obtained by linear analysis.
PSR J1738+0333 is one of the four millisecond pulsars known to be orbited by a white dwarf companion bright enough for optical spectroscopy. Of these, it has the shortest orbital period, making it especially interesting for a range of astrophysical and gravity related questions. We present a spectroscopic and photometric study of the white dwarf companion and infer its radial velocity curve, effective temperature, surface gravity and luminosity. We find that the white dwarf has properties consistent with those of low-mass white dwarfs with thick hydrogen envelopes, and use the corresponding mass-radius relation to infer its mass; M_WD = 0.181 +/- +0.007/-0.005 solar masses. Combined with the mass ratio q=8.1 +/- 0.2 inferred from the radial velocities and the precise pulsar timing ephemeris, the neutron star mass is constrained to M_PSR = 1.47 +/- +0.07/-0.06 solar masses. Contrary to expectations, the latter is only slightly above the Chandrasekhar limit. We find that, even if the birth mass of the neutron star was only 1.20 solar masses, more than 60% of the matter that left the surface of the white dwarf progenitor escaped the system. The accurate determination of the component masses transforms this system in a laboratory for fundamental physics by constraining the orbital decay predicted by general relativity. Currently, the agreement is within 1 sigma of the observed decay. Further radio timing observations will allow precise tests of white dwarf models, assuming the validity of general relativity.
Because of proximity to the Galactic plane, reliable identification of members of the alpha Persei cluster is often problematic. Based primarily on membership evaluations contained in six published papers, we constructed a mostly complete list of high-fidelity members of spectral type G and earlier that lie within 3 arc degrees of the cluster center. Alpha Persei was the one nearby, rich, young open cluster not surveyed with the Spitzer Space Telescope. We examined the first and final data releases of the Wide Field Infrared Survey Explorer (WISE) and found 11, or perhaps 12, alpha Per cluster members that have excess mid-infrared emission above the stellar photosphere attributable to an orbiting dusty debris disk. The most unusual of these is V488 Per, a K-type star with an excess IR luminosity 16% (or more) of the stellar luminosity; this is a larger excess fraction than that of any other known dusty main sequence star. Much of the dust that orbits V488 Per is at a temperature of ~800 K; if these grains radiate like blackbodies, then they lie only ~0.06 AU from the star. The dust is probably the aftermath of a collision of two planetary embryos or planets with small semimajor axes; such orbital radii are similar to those of many of the transiting planets discovered by the Kepler satellite.
We present HST/COS high S/N observations of the z = 0.32566 multi-phase absorber towards 3C263. The COS data shows absorption from H I, O VI, C III, N III, Si III and C II. The Ne VIII in this absorber is detected in the FUSE spectrum. The low and intermediate ions are kinematically aligned with each other and H I and display narrow line widths of 6 km/s. The O VI lines are kinematically offset by 12 km/s from the low ions and are a factor of four broader. All metal ions except O VI and Ne VIII are consistent with an origin in gas photoionized by the extragalactic background radiation. The bulk of the observed H I is also traced by this photoionized medium. The carbon abundance in this gas phase is near-solar. The O VI and Ne VIII favor an origin in collisionally ionized gas at T = 5.2 x 10^5 K. The H I absorption associated with this warm absorber is a BLA marginally detected in the COS spectrum. This warm gas phase has total hydrogen column density of N(H) ~ 3 x 10^19 which is 2 dex higher than what is traced by the photoionized gas. Simultaneous detection of O VI, Ne VIII and BLAs in an absorber can be a strong diagnostic of gas with temperature in the range of 10^5 - 10^6 K corresponding to the warm phase of the WHIM or shock-heated gas in the extended halos of galaxies.
The Li abundances of the two components of the very metal-poor ([Fe/H]=-2.5) double-lined spectroscopic binary G166-45 (BD+26 2606) are determined separately based on high resolution spectra obtained with the Subaru Telescope High Dispersion Spectrograph and its image slicer. From the photometric colors and the mass ratio the effective temperatures of the primary and secondary components are estimated to be 6350+/-100K and 5830+/-170K, respectively. The Li abundance of the primary (A(Li)=2.23) agrees well with the Spite plateau value, while that of the secondary is slightly lower (A(Li)=2.11). Such a discrepancy of the Li abundances between the two components is previously found in the extremely metal-poor, double-lined spectroscopic binary CS22876-032, however, the discrepancy in G166-45 is much smaller. The results agree with the trends found for Li abundance as a function of effective temperature (and of stellar mass) of main-sequence stars with -3.0<[Fe/H]<-2.0, suggesting that the depletion of Li at Teff ~ 5800K is not particularly large in this metallicity range. The significant Li depletion found in CS22876-032B is a phenomenon only found in the lowest metallicity range ([Fe/H]<-3).
Most Sun-like stars in the Galaxy reside in gravitationally-bound pairs of stars called "binary stars". While long anticipated, the existence of a "circumbinary planet" orbiting such a pair of normal stars was not definitively established until the discovery of Kepler-16. Incontrovertible evidence was provided by the miniature eclipses ("transits") of the stars by the planet. However, questions remain about the prevalence of circumbinary planets and their range of orbital and physical properties. Here we present two additional transiting circumbinary planets, Kepler-34 and Kepler-35. Each is a low-density gas giant planet on an orbit closely aligned with that of its parent stars. Kepler-34 orbits two Sun-like stars every 289 days, while Kepler-35 orbits a pair of smaller stars (89% and 81% of the Sun's mass) every 131 days. Due to the orbital motion of the stars, the planets experience large multi-periodic variations in incident stellar radiation. The observed rate of circumbinary planets implies > ~1% of close binary stars have giant planets in nearly coplanar orbits, yielding a Galactic population of at least several million.
New theory of the dynamical tides of celestial bodies founded on a Newtonian creep instead of the classical delaying approach of the standard viscoelastic theories. The results of the theory derive mainly from the solution of a non-homogeneous ordinary differential equation. Lags appear in the solution, but as quantities determined from the solution of the equation and are not arbitrary external quantities plugged on an elastic model. The resulting lag of each tide component is an increasing function of its frequency (as in Darwin's theory), and are not small quantities. The amplitudes of the tide components depend on the viscosity of the body and on their frequencies; they are not constants. The resulting stationary rotations (often called pseudo-synchronous) have an excess velocity roughly proportional to 6ne^2/(\chi^2+1/\chi^2) (\chi\ is the mean-motion in units of one relaxation factor inversely proportional to the viscosity) instead of the exact 6ne^2 of standard theories. The dissipation in the pseudo-synchronous solution is inversely proportional to (\chi+1/\chi); thus, in the inviscid limit it is roughly proportional to the frequency (as in standard theories), but that behavior is inverted when the viscosity is high and the relaxation factor much smaller than the tide frequency. For free rotating bodies, the dissipation is given by the same law, but now \chi\ is the frequency of the semidiurnal tide in units of the relaxation factor. This approach fails, however, to reproduce the actual tidal lags on Earth and on natural satellites. To reconcile theory and observations, in this case, we had to assume the coexistence of a small elastic tide superposed to the creeping tide. The theory is applied to several Solar System and extrasolar bodies and values of the relaxation factor \gamma\ are derived for these bodies on the basis of currently available data.
There is an observational indication of extragalactic magnetic fields. No known astrophysical process can explain the origin of such large scale magnetic fields, which motivates us to look for their origin in primordial inflation. By solving the linearized Einstein equations, we study metric perturbations sourced by magnetic fields that are produced during inflation. This leads to a simple but robust bound on the inflation models by requiring that the induced metric perturbation should not exceed the observed value 10^-5. In case of the standard single field inflation model, the bound can be converted into a lower bound on the Hubble parameter during inflation.
We present optical observations and Monte Carlo models of the dust coma,
tail, and trail structures of comet 22P/Kopff during the 2002 and 2009
apparitions. Dust loss rates, ejection velocities, and power-law size
distribution functions are derived as functions of the heliocentric distance
using pre- and post-perihelion imaging observations during both apparitions.
The 2009 post-perihelion images can be accurately fitted by an isotropic
ejection model. On the other hand, strong dust ejection anisotropies are
required to fit the near-coma regions at large heliocentric distances (both
inbound at $r_h$=2.5 AU and outbound at $r_h$=2.6 AU) for the 2002 apparition.
These asymmetries are compatible with a scenario where dust ejection is mostly
seasonally-driven, coming mainly from regions near subsolar latitudes at far
heliocentric distances inbound and outbound. At intermediate to near-perihelion
heliocentric distances, the outgassing would affect much more extended latitude
regions, the emission becoming almost isotropic near perihelion. We derived a
maximum dust production rate of 260 kg s$^{-1}$ at perihelion, and an averaged
production rate over one orbit of 40 kg s$^{-1}$. An enhanced emission rate,
accompanied also by a large ejection velocity, is predicted at $r_h>$2.5
pre-perihelion.
The model has also been extended to the thermal infrared in order to be
applied to available trail observations with IRAS and ISO spacecrafts of this
comet. The modeled trail intensities are in good agreement with those
observations, which is remarkable taking into account that those data are
sensitive to dust ejection patterns corresponding to several orbits before the
2002 and 2009 apparitions.
We use the Vista Variables in the Via Lactea (VVV) ESO public survey data to measure extinction values in the complete area of the Galactic bulge covered by the survey at high resolution. We derive reddening values using the method described in Paper I. This is based on measuring the mean (J-Ks) color of red clump giants in small subfields of 2' to 6' in the following bulge area: -10.3<b<+5.1 and -10<l<+10.4. To determine the reddening values E(J-Ks) for each region, we measure the RC color and compare it to the (J-Ks) color of RC stars measured in Baade's window, for which we adopt E(B-V)=0.55. This allows us to construct a reddening map sensitive to small scale variations minimizing the problems arising from differential extinction. The significant reddening variations are clearly observed on spatial scales as small as 2'. We find a good agreement between our extinction measurements and Schlegel maps in the outer bulge, but, as already stated in the literature the Schlegel maps are not reliable for regions within |b| < 6. In the inner regions we compare our results with maps derived from DENIS and Spitzer surveys. While we find good agreement with other studies in the corresponding overlapping regions, our extinction map has better quality due to both higher resolution and a more complete spatial coverage in the Bulge. We investigate the importance of differential reddening and demonstrate the need for high resolution extinction maps for detailed studies of Bulge stellar populations and structure. The extinction variations on scales of up to 2'-6', must be taken into account when analysing the stellar populations of the Bulge.
We investigate the teleparallel dark energy model with purely non-minimal coupling and without potential. We find the analytic solutions of the scalar field in the radiation, matter, and scalar field (or dark energy) dominated eras, respectively. These solutions indicate the tracker behavior in the radiation and matter dominated eras, while the equation of state $w_{\phi}$ of the teleparallel dark energy is determined by the non-minimal coupling constant $\xi$ but insensitive to the initial condition. In the scalar field dominated era, $w_{\phi}$ monotonically decreases and goes to negative infinity at some finite time when $H$ goes to positive infinity, resulting in a future singularity. We also present the possible evolution patterns and the data fittings in this model.
In this paper, we shall study the dynamical behavior of the universe accelerated by the so called Veneziano ghost dark energy component locally and globally by using the linearization and nullcline method developed in this paper. The energy density is generalized to be proportional to the Hawking temperature defined on the trapping horizon instead of Hubble horizon of the Friedmann-Robertson-Walker (FRW) universe. We also give a prediction of the fate of the universe and present the bifurcation phenomenon of the dynamical system of the universe. It seems that the universe could be dominated by dark energy at present in some region of the parameter space.
We present far-red, intermediate resolution spectroscopy of 572 photometrically selected, low-mass stars (0.2<M/M_sun<0.7) in the young open cluster NGC 2516, using the FLAMES spectrograph at the Very Large Telescope. Precise radial velocities confirm membership for 210 stars that have published rotation periods from spot-modulated light curves and for another 144 stars in which periodic modulation could not be found. The two sub-samples are compared and no significant differences are found between their positions in colour-magnitude diagrams, the distribution of their projected equatorial velocities or their levels of chromospheric activity. We rule out differing observational sensitivity as an explanation and conclude that otherwise similar objects, with equally high levels of chromospheric activity, do not exhibit spot-induced light curve modulation because their significant spot coverage is highly axisymmetric. We propose that the spot coverage consists of large numbers of small, dark spots with diameters of about 2 degrees. This explains why about half of cluster members do not exhibit rotationally modulated light curves and why the light curve amplitudes of those that do have mean values of only 0.01-0.02 mag.
Globular clusters are an excellent laboratory for stellar population and dynamical research. Recent studies have shown that these stellar systems are not as simple as previously assumed. With multiple stellar populations as well as outer rotation and mass segregation they turn out to exhibit high complexity. This includes intermediate-mass black holes which are proposed to sit at the centers of some massive globular clusters. Today's high angular resolution ground based spectrographs allow velocity-dispersion measurements at a spatial resolution comparable to the radius of influence for plausible IMBH masses, and to detect changes in the inner velocity-dispersion profile. Together with high quality photometric data from HST, it is possible to constrain black-hole masses by their kinematic signatures. We determine the central velocity-dispersion profile of the globular cluster NGC 2808 using VLT/FLAMES spectroscopy. In combination with HST/ACS data our goal is to probe whether this massive cluster hosts an intermediate-mass black hole at its center and constrain the cluster mass to light ratio as well as its total mass. We derive a velocity-dispersion profile from integral field spectroscopy in the center and Fabry Perot data for larger radii. High resolution HST data are used to obtain the surface brightness profile. Together, these data sets are compared to dynamical models with varying parameters such as mass to light ratio profiles and black-hole masses. Using analytical Jeans models in combination with variable M/L profiles from N-body simulations we find that the best fit model is a no black hole solution. After applying various Monte Carlo simulations to estimate the uncertainties, we derive an upper limit of the back hole mass of M_BH < 1 x 10^4 M_SUN (with 95 % confidence limits) and a global mass-to-light ratio of M/L_V = (2.1 +- 0.2) M_SUN/L_SUN.
The metallic gas associated with the Beta Pic debris disk is believed to not be primordial, but arise during the destruction of dust grains. Recent observations have shown that carbon and oxygen in this gas are exceptionally overabundant compared to other elements, by some 400 times. We study the origin of this enrichment under two opposing hypothesis, preferential production, where the gas is produced with the observed unusual abundance, and preferential depletion, where the gas evolves to the observed state from an original solar abundance under a number of dynamical processes. We include in our study the following processes: radiative blow-out of metallic elements, dynamical coupling between different species, and viscous accretion onto the star. We find that, if gas viscosity is sufficiently low (the conventional alpha parameter <1e-3), differential blow-out dominates. While gas accumulates gradually in the disks, metallic elements subject to strong radiation forces, such as Na and Fe, deplete more quickly than C and O, naturally leading to the observed overabundance of C and O. On the other hand, if gas viscosity is high (alpha>1e-1, as expected for this largely ionized disk), gas is continuously produced and viscously accreted toward the star. This removal process does not discriminate between elements so the observed overabundance of C and O has to be explained by a preferential production that strongly favors C and O to other metallic elements. One such candidate is photo-desorption off the grains. We compare our calculation against all observed elements (~10) in the gas disk and find a mild preference for the second scenario, based on the abundance of Si alone. If true, Beta Pic should still be accreting at an observable rate, well after its primordial disk has disappeared.
High resolution blue continuum filtergrams from Hinode are employed to study the umbral fine structure of a regular unipolar sunspot. The removal of scattered light from the images increases the rms contrast by a factor of 1.45 on average. Improvement in image contrast renders identification of short filamentary structures resembling penumbrae that are well separated from the umbra-penumbra boundary and comprise bright filaments/grains flanking dark filaments. Such fine structures were recently detected from ground based telescopes and have now been observed with Hinode. A multi-level tracking algorithm was used to identify umbral dots in both the uncorrected and corrected images and to track them in time. The distribution of the values describing the photometric and geometric properties of umbral dots are more easily affected by the presence of stray light while it is less severe in the case of kinematic properties. Statistically, umbral dots exhibit a peak intensity, effective diameter, lifetime, horizontal speed and a trajectory length of 0.29 I_QS, 272 km, 8.4 min, 0.45 km/s and 221 km respectively. The 2 hr 20 min time sequence depicts several locations where umbral dots tend to appear and disappear repeatedly with various time intervals. The correction for scattered light in the Hinode filtergrams facilitates photometry of umbral fine structure which can be related to results obtained from larger telescopes and numerical simulations.
In this paper we present results from the Mapping Dark Matter competition that expressed the weak lensing shape measurement task in its simplest form and as a result attracted over 700 submissions in 2 months and a factor of 3 improvement in shape measurement accuracy on high signal to noise galaxies, over previously published results, and a factor 10 improvement over methods tested on constant shear blind simulations. We also review weak lensing shape measurement challenges, including the Shear TEsting Programmes (STEP1 and STEP2) and the GRavitational lEnsing Accuracy Testing competitions (GREAT08 and GREAT10).
We present a detailed single pulse study of PSR B1055-52 based on observations at the Parkes radio telescope. The radio emission is found to have a complex modulation dominated by a periodicity of ~20 times its rotational period P (0.197s), whose phase and strength depends on pulse longitude. This periodicity exhibits a phase-locked delay of about 2.5P between the main pulse (MP) and interpulse (IP), presumed to be the opposite poles of the pulsar. This delay corresponds to a light travel distance of many times the light cylinder radius. More complex modulations are found within the MP on timescales down to about 9P, and both these and the principal modulation vary strongly across the (at least) 7 components which the MP and IP exhibit. The nature of the single pulse emission, which ranges from smooth and longitudinally extended to `spiky', is also component-dependent. Despite these disparities, the total pulse intensity distributions at the MP and IP are virtually identical in shape, suggesting a common emission mechanism. In an attempt to account for the complex modulations we examine a number of physical models, both intrinsic (which presuppose the pulsar to be an isolated neutron star) and extrinsic (appealing to the presence of circumstellar material to modulate the emission). Significant objections can be made to each model, so this pulsar's behaviour patterns remain a crucial challenge to theorists.
We present an observational program we started in 1999, to systematically obtain mid-resolution spectra of late-type stars, to study in particular chromospheric activity. In particular, we found cyclic activity in four dM stars, including Prox-Cen. We directly derived the conversion factor that translates the known S index to flux in the Ca II cores, and extend its calibration to a wider spectral range. We investigated the relation between the activity measurements in the calcium and hydrogen lines, and found that the usual correlation observed is the product of the dependence of each flux on stellar color, and it is not always preserved when simultaneous observations of a particular star are considered. We also used our observations to model the chromospheres of stars of different spectral types and activity levels, and found that the integrated chromospheric radiative losses, normalized to the surface luminosity, show a unique trend for G and K dwarfs when plotted against the S index.
Gamma-Ray Bursts are likely associated with a catastrophic energy release in stellar mass objects. Electromagnetic observations provide important, but indirect information on the progenitor. On the other hand, gravitational waves emitted from the central source, carry direct information on its nature. In this context, I give an overview of the multi-messenger study of gamma-ray bursts that can be carried out by using electromagnetic and gravitational wave observations. I also underline the importance of joint optical and gravitational wave searches, in the absence of a gamma-ray trigger. Finally, I discuss how multi-messenger observations may probe alternative gamma-ray burst progenitor models, such as the magnetar scenario.
Process of preheating for supersymmetric hybrid model of inflation is generally analyzed in two different ways known as parametric resonance and tachyonic preheating. In a common frame-work, we study both the processes from the decay or growth of homogeneous inflaton field and inhomogeneous waterfall field. We find that these two processes in SUSY hybrid F-term inflation are not parameter independent; rather one process will be more preferable than the other depending on the values of parameters and Fourier mode of the waterfall field. Parameters of the inflationary potential are constrained from the observed CMB data and these constrains help us to identify the process of preheating responsible for this model.
Radiation, winds and jets from the active nucleus of a massive galaxy can interact with its interstellar medium leading to ejection or heating of the gas. This can terminate star formation in the galaxy and stifle accretion onto the black hole. Such Active Galactic Nucleus (AGN) feedback can account for the observed proportionality between central black hole and host galaxy mass. Direct observational evidence for the radiative or quasar mode of feedback, which occurs when the AGN is very luminous, has been difficult to obtain but is accumulating from a few exceptional objects. Feedback from the kinetic or radio mode, which uses the mechanical energy of radio-emitting jets often seen when the AGN is operating at a lower level, is common in massive elliptical galaxies. This mode is well observed directly through X-ray observations of the central galaxies of cool core clusters in the form of bubbles in the hot surrounding medium. The energy flow, which is roughly continuous, heats the hot intracluster gas and reduces radiative cooling and subsequent star formation by an order of magnitude. Feedback appears to maintain a long-lived heating/cooling balance. Powerful, jetted radio outbursts may represent a further mode of energy feedback which affect the cores of groups and subclusters. New telescopes and instruments from the radio to X-ray bands will come into operation over the next few years and lead to a rapid expansion in observational data on all modes of AGN feedback.
The oxygen 7771-4 A triplet is a good indicator of luminosity in A-G supergiants. However, its strength also depends on other atmospheric parameters. In this study, we present the luminosity calibrations, where, for the first time, the effects of the effective temperature, microturbulent velocity, surface gravity, and the abundance have been disentangled. The calibrations are derived on the basis of a dataset of high-dispersion spectra of 60 yellow supergiants with highly reliable luminosities and accurate atmospheric parameters. This allowed to bring the uncertainty of the triplet-based absolute magnitudes down to 0.26 mag. The calibrations are suitable for spectral types F0-K0 and luminosity classes I-II, covering absolute magnitudes Mv from -1.0 to -10 mag.
While dark matter (DM) is the key ingredient for a successful theory of structure formation, its microscopic nature remains elusive. Indirect detection may provide a powerful test for some strongly motivated DM particle models. Nevertheless, astrophysical backgrounds are usually expected with amplitudes and spectral features similar to the chased signals. On galactic scales, these backgrounds arise from interactions of cosmic rays (CRs) with the interstellar gas, both being difficult to infer and model in detail from observations. Moreover, the associated predictions unavoidably come with theoretical errors, which are known to be significant. We show that a trustworthy guide for such challenging searches can be obtained by exploiting the full information contained in cosmological simulations of galaxies, which now include baryonic gas dynamics and star formation. We further insert CR production and transport from the identified supernova events and fully calculate the CR distribution in a simulated galaxy. We focus on diffuse gamma-rays, and self-consistently calculate both the astrophysical galactic emission and the dark matter signal. We notably show that adiabatic contraction does not necessarily induce large signal-to-noise ratios in galactic centers, and could anyway be traced from the astrophysical background itself. We finally discuss how all this may be used as a generic diagnostic tool for galaxy formation.
PKS 1749+096 is a BL Lac object showing weak extended jet emission to the northeast of the compact VLBI core on parsec scales. We aim at better understanding the jet kinematics and variability of this source and finding clues that may applicable to other BL Lac objects. The jet was studied with multi-epoch multi-frequency high-resolution VLBI observations. The jet is characterized by a one-sided curved morphology at all epochs and all frequencies. The VLBI core, located at the southern end of the jet, was identified based on its spectral properties. The equipartition magnetic field of the core was investigated, through which we derived a Doppler factor of 5, largely consistent with that derived from kinematics (component C5). The study of the detailed jet kinematics at 22 and 15 GHz, spanning a period of more than 10 years, indicates the possible existence of a bimodal distribution of the jet apparent speed. Ballistic and non-ballistic components are found to coexist in the jet. Superluminal motions in the range of 5--21 c were measured in 11 distinct components. We estimated the physical jet parameters with the minimum Lorentz factor of 10.2 and Doppler factors in the range of 10.2--20.4 (component C5). The coincidence in time of the component's ejection and flares supports the idea that, at least in PKS 1749+096, ejection of new jet components is connected with major outbursts in flux density. For the best-traced component (C5) we found that the flux density decays rapidly as it travels downstream the jet, accompanied by a steepening of its spectra, which argues in favor of a contribution of inverse Compton cooling. These properties make PKS 1749+096 a suitable target for an intensive monitoring to decipher the variability phenomenon of BL Lac objects.
This paper is concerned with string cosmology and the dynamics of multiple scalar fields in potentials that can become negative, and their features as (Early) Dark Energy models. Our point of departure is the "String Axiverse", a scenario that motivates the existence of cosmologically light axion fields as a generic consequence of string theory. We couple such an axion to its corresponding modulus. We give a detailed presentation of the rich cosmology of such a model, ranging from the setting of initial conditions on the fields during inflation, to the asymptotic future. We present some simplifying assumptions based on the fixing of the axion decay constant $f_a$, and on the effective field theory when the modulus trajectory is adiabatic, and find the conditions under which these assumptions break down. As a by-product of our analysis, we find that relaxing the assumption of fixed $f_a$ leads to the appearance of a new meta-stable de-Sitter region for the modulus without the need for uplifting by an additional constant. A dynamical systems analysis reveals the existence of many fixed point attractors, repellers and saddle points, which we analyse in detail. We also provide geometric interpretations of the phase space. The fixed points can be used to bound the couplings in the model. A systematic scan of certain regions of parameter space reveals that the future evolution of the universe in this model can be rich, containing multiple epochs of accelerated expansion.
We review the current status of studies of the coalescence of binary neutron star systems. We begin with a discussion of the formation channels of merging binaries and we discuss the most recent theoretical predictions for merger rates. Next, we turn to the quasi-equilibrium formalisms that are used to study binaries prior to the merger phase and to generate initial data for fully dynamical simulations. The quasi-equilibrium approximation has played a key role in developing our understanding of the physics of binary coalescence and, in particular, of the orbital instability processes that can drive binaries to merger at the end of their lifetimes. We then turn to the numerical techniques used in dynamical simulations, including relativistic formalisms, (magneto-)hydrodynamics, gravitational-wave extraction techniques, and nuclear microphysics treatments. This is followed by a summary of the simulations performed across the field to date, including the most recent results from both fully relativistic and microphysically detailed simulations. Finally, we discuss the likely directions for the field as we transition from the first to the second generation of gravitational-wave interferometers and while supercomputers reach the petascale frontier.
We demonstrate that three sterile neutrinos can simultaneously explain neutrino oscillations, the observed dark matter and baryon asymmetry of the Universe. We perform the first complete study to identify the range of sterile neutrino properties consistent with these requirements, combining the study of neutrino abundances and lepton asymmetries in the early universe with bounds from nucleosynthesis and direct searches. We find that there is a domain of parameters where all these particles can be found with present day experimental techniques, using upgrades to existing experimental facilities.
In the present work, we reconsider the idea of holographic dark energy. One of its key points is the formation of black hole. And then, we propose the so-called "pilgrim dark energy" based on the speculation that the repulsive force contributed by the phantom-like dark energy ($w<-1$) is strong enough to prevent the formation of black hole. We also consider the cosmological constraints on pilgrim dark energy by using the latest observational data. Of course, one can instead regard pilgrim dark energy as a purely phenomenological model without any physical motivation. We also briefly discuss this issue.
We consider a Hubble expansion law modified in the infra-red by distance-dependent terms, and attempt to enforce homogeneity upon it. As a warm-up, we re-derive the basic kinematics of a Friedman Robertson Walker universe without using standard general relativistic tools: we describe the expansion with a `Hubble velocity field' rather than with a four dimensional metric. Then we extend this analysis to the modified Hubble expansion and impose a transformation for velocities that makes it identical for all comoving observers, and therefore homogeneous. We derive the modified equation for light ray trajectories and other geometrical properties that are incompatible with the general relativistic description. We speculate that this extended framework could help addressing cosmological problems which are normally explained with accelerating expansions.
We have recently suggested [1,2] that Inflation could have started in a local minimum of the Higgs potential at field values of about $10^{15}-10^{17}$ GeV, which exists for a narrow band of values of the top quark and Higgs masses and thus gives rise to a prediction on the Higgs mass to be in the range 123-129 GeV, together with a prediction on the the top mass and the cosmological tensor-to-scalar ratio $r$. Inflation can be achieved provided there is an additional degree of freedom which allows the transition to a radiation era. In [1] we had proposed such field to be a Brans-Dicke scalar. Here we present an alternative possibility with an additional subdominant scalar very weakly coupled to the Higgs, realizing an (inverted) hybrid Inflation scenario. Interestingly, we show that such model has an additional constraint $m_H<125.3 \pm 3_{th}$, where $3_{th}$ is the present theoretical uncertainty on the Standard Model RGEs. The tensor-to-scalar ratio has to be within the narrow range $10^{-4}\lesssim r<0.007$, and values of the scalar spectral index compatible with the observed range can be obtained. Moreover, if we impose the model to have subplanckian field excursion, this selects a narrower range $10^{-4} \lesssim r<0.001$ and an upper bound on the Higgs mass of about $m_H <124 \pm 3_{th}$.
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With growing data volumes from synoptic surveys, astronomers must become more abstracted from the discovery and introspection processes. Given the scarcity of follow-up resources, there is a particularly sharp onus on the frameworks that replace these human roles to provide accurate and well-calibrated probabilistic classification catalogs. Such catalogs inform the subsequent follow-up, allowing consumers to optimize the selection of specific sources for further study and permitting rigorous treatment of purities and efficiencies for population studies. Here, we describe a process to produce a probabilistic classification catalog of variability with machine learning from a multi-epoch photometric survey. In addition to producing accurate classifications, we show how to estimate calibrated class probabilities, and motivate the importance of probability calibration. We also introduce a methodology for feature-based anomaly detection, which allows discovery of objects in the survey that do not fit within the predefined class taxonomy. Finally, we apply these methods to sources observed by the All Sky Automated Survey (ASAS), and unveil the Machine-learned ASAS Classification Catalog (MACC), which is a 28-class probabilistic classification catalog of 50,124 ASAS sources. We estimate that MACC achieves a sub-20% classification error rate, and demonstrate that the class posterior probabilities are reasonably calibrated. MACC classifications compare favorably to the classifications of several previous domain-specific ASAS papers and to the ASAS Catalog of Variable Stars, which had classified only 24% of those sources into one of 11 science classes. The MACC is publicly available at this http URL
We present the results of a machine-learning (ML) based search for new R Coronae Borealis (RCB) stars and DY Persei-like stars (DYPers) in the Galaxy using cataloged light curves obtained by the All-Sky Automated Survey (ASAS). RCB stars - a rare class of hydrogen-deficient carbon-rich supergiants - are of great interest owing to the insights they can provide on the late stages of stellar evolution. DYPers are possibly the low-temperature, low-luminosity analogs to the RCB phenomenon, though additional examples are needed to fully establish this connection. While RCB stars and DYPers are traditionally identified by epochs of extreme dimming that occur without regularity, the ML search framework more fully captures the richness and diversity of their photometric behavior. We demonstrate that our ML method recovers ASAS candidates that would have been missed by traditional search methods employing hard cuts on amplitude and periodicity. Our search yields 13 candidates that we consider likely RCB stars/DYPers: new and archival spectroscopic observations confirm that four of these candidates are RCB stars and four are DYPers. Our discovery of four new DYPers increases the number of known Galactic DYPers from two to six; noteworthy is that one of the new DYPers has a measured parallax and is m ~ 7 mag, making it the brightest known DYPer to date. Future observations of these new DYPers should prove instrumental in establishing the RCB connection. We consider these results, derived from a machine-learned probabilistic classification catalog, as an important proof-of-concept for the efficient discovery of rare sources with time-domain surveys.
It is very difficult to find archival images of solar system objects. While regular archive searches can find images at a fixed location, they cannot find images of moving targets. Archival images have become increasingly useful to galactic and stellar astronomers the last few years but, until now, solar system researchers have been at a disadvantage in this respect. The Solar System Object Search (SSOS) at the Canadian Astronomy Data Centre allows users to search for images of moving objects. SSOS accepts as input either a list of observations, an object designation, a set of orbital elements, or a user-generated ephemeris for an object. It then searches for images containing that object over a range of dates. The user is then presented with a list of images containing that object from a variety of archives. Initially created to search the CFHT MegaCam archive, SSOS has been extended to other telescope archives including Gemini, Subaru/SuprimeCam, HST, and several ESO instruments for a total of 1.6 million images. The SSOS tool is located on the web at: this http URL
Recent studies have found a dramatic difference between the observed number density evolution of low mass galaxies and that predicted by semi-analytic models. Whilst models accurately predict the z=0 number density, they require that the evolution occurs rapidly at early times, which is incompatible with the strong late evolution found in observational results. We report here the same discrepancy in two state-of-the-art cosmological hydrodynamical simulations, which is evidence that the problem is fundamental. We search for the underlying cause of this problem using two complementary methods. Firstly, we try to find evidence for the evolutionary history of today's low mass galaxies being different in models and observations. We find that the exclusion of satellite galaxies from the analysis brings the median ages and star formation rates of galaxies into good agreement. However, the models yield too few young, strongly star-forming galaxies. Secondly, we construct a toy model to link the observed evolution of specific star formation rates and the galaxy stellar mass function. We infer from this model that a key cause of the discrepancy is the presence of a positive correlation between specific star formation rate and stellar mass in both semi-analytical and hydrodynamical models. A similar positive correlation is found between the specific dark matter accretion rate and the halo mass, indicating that model galaxies are growing in a way that follows the growth of their host haloes too closely. It therefore appears necessary to find a mechanism that decouples the growth of low mass galaxies, which occurs at late times, from the growth of their host haloes, which occurs at early times. We argue that the current form of star-formation driven feedback implemented in most galaxy formation models is unlikely to achieve this goal, owing to its fundamental dependence on host halo mass and time.
In general, when gas accretes on to a supermassive black hole binary it is likely to have no prior knowledge of the binary angular momentum. Therefore a circumbinary disc forms with a random inclination angle, theta, to the binary. It is known that for theta < 90 degrees the disc will coalign wrt the binary. If theta > 90 degrees the disc wholly counteraligns if it satisfies cos(theta) < -J_d/2J_b, where J_d and J_b are the magnitudes of the disc and binary angular momentum vectors respectively. If however theta > 90 degrees and this criterion is not satisfied the same disc may counteralign its inner regions and, on longer timescales, coalign its outer regions. I show that for typical disc parameters, describing an accretion event on to a supermassive black hole binary, a misaligned circumbinary disc is likely to wholly co-- or counter--align with the binary plane. This is because the binary angular momentum dominates the disc angular momentum. However with extreme parameters (binary mass ratio M_2/M_1 << 1 or binary eccentricity e ~ 1) the same disc may simultaneously co- and counter-align. It is known that coplanar prograde circumbinary discs are stable. I show that coplanar retrograde circumbinary discs are also stable. A chaotic accretion event on to an SMBH binary will therefore result in a coplanar circumbinary disc that is either prograde or retrograde with respect to the binary plane.
We analyze Spitzer GLIMPSE, MSX, and WMAP images of the Milky Way to identify 8 micron and free-free sources in the Galaxy. Seventy-two of the eighty-eight WMAP sources have coverage in the GLIMPSE and MSX surveys suitable for identifying massive star forming complexes (SFC). We measure the ionizing luminosity functions of the SFCs and study their role in the turbulent motion of the Galaxy's molecular gas. We find a total Galactic free-free flux f_{\nu} = 46177.6 Jy; the 72 WMAP sources with full 8 micron coverage account for 34263.5 Jy (~75%), with both measurements made at \nu=94GHz (W band). We find a total of 280 SFCs, of which 168 have unique kinematic distances and free-free luminosities. We use a simple model for the radial distribution of star formation to estimate the free-free and ionizing luminosity for the sources lacking distance determinations. The total dust-corrected ionizing luminosity is Q = 2.9 \pm 0.5 x 10^53 photons s^-1, which implies a galactic star formation rate of 1.2 \pm 0.2 M_{\sun} yr^-1. We present the (ionizing) luminosity function of the SFCs, and show that 24 sources emit half the ionizing luminosity of the Galaxy. The SFCs appear as bubbles in GLIMPSE or MSX images; the radial velocities associated with the bubble walls allow us to infer the expansion velocity of the bubbles. We calculate the kinetic luminosity of the bubble expansion and compare it to the turbulent luminosity of the inner molecular disk. SFCs emitting 80% of the total galactic free-free luminosity produce a kinetic luminosity equal to 65% of the turbulent luminosity in the inner molecular disk. This suggests that the expansion of the bubbles is a major driver of the turbulent motion of the inner Milky Way molecular gas.
We present a study on Spectral Energy Distributions, Morphologies, and star formation for an IRAC-selected extremely red object sample in the GOODS Chandra Deep Field-South. This work was enabled by new HST/WFC3 near-IR imaging from the CANDELS survey as well as the deepest available X-ray data from Chandra 4 Ms observations. This sample consists of 133 objects with the 3.6um limiting magnitude of [3.6] = 21.5, and is approximately complete for galaxies with M >10^{11}M_sun at 1.5 < z < 2.5. We classify this sample into two types, quiescent and star-forming galaxies, in the observed infrared color-color ([3.6]-[24] vs K-[3.6]) diagram. The further morphological study of this sample show a consistent result with the observed color classification. The classified quiescent galaxies are bulge dominated and star-forming galaxies in the sample have disk or irregular morphologies. Our observed infrared color classification is also consistent with the rest-frame color (U-V vs V-J) classification. We also found that quiescent and star-forming galaxies are well separated in the nonparametric morphology parameter (Gini vs M_{20}) diagram measuring their concentration and clumpiness: quiescent galaxies have Gini coefficient higher than 0.58 and star forming galaxies have Gini coefficient lower that 0.58. We argue that the star formation quenching process must lead to or be accompanied by the increasing galaxy concentration. One prominent morphological feature of this sample is that disks are commonly seen in this massive galaxy sample at 1.5 < z < 2.5: 30% of quiescent galaxies and 70% of star forming galaxies with M >10^{11}M_sun have disks in their rest-frame optical morphologies. The prevalence of these extended, relatively undisturbed disks challenges the merging scenario as the main mode of massive galaxy formation.
We present an exhaustive methodology for fitting Compton-thick X-ray reprocessor models to obscured AGNs and for interpreting the results. We focus on the MYTORUS model but also utilize other models. We apply the techniques to Suzaku, BeppoSAX, and Swift BAT spectra of the Sy 2 galaxy NGC 4945, but the methods are applicable to other AGNs including Compton-thin sources. The models overcome a major restriction of disk-reflection models, namely the assumption of an infinite column density. Finite column-density models produce a richer variety of spectral shapes and characteristics, even for Compton-thin AGNs. Although NGC 4945 is one of the brightest AGNs above 10 keV, the models span nearly a factor of 3 in column density (~2 to 6 x 10^{24} cm^{-2}) and 2 orders of magnitude in the intrinsic 2-195 keV luminosity. Models in which the continuum above 10 keV is dominated by the direct (unscattered) continuum or Compton-scattered continuum give the highest and lowest intrinsic luminosities respectively. Variability properties favor solutions in which the unscattered continuum dominates above 10 keV. The data require that the Compton-scattered continuum and Fe Kalpha line emission come predominantly from the illuminated surfaces of the X-ray reprocessor, implying a clumpy medium with a global covering factor that is small enough that the Compton-scattered continuum does not dominate the spectrum above 10 keV. This can be identified with the ~30 pc region spatially resolved by Chandra. The implied intrinsic bolometric luminosity is close to, or greater than, the Eddington luminosity. However, a strongly beamed AGN embedded in a shell of Compton-thick (but clumpy) matter requires less fine-tuning of the covering factor. Beaming is consistent with recent radio and Fermi results. Such beamed Compton-thick AGNs would be preferentially selected in surveys over unbeamed Compton-thick AGNs.
There is increasingly strong observational evidence that slow magnetoacoustic modes arise in the solar atmosphere. Solar magneto-seismology is a novel tool to derive otherwise directly un-measurable properties of the solar atmosphere when magnetohydrodynamic (MHD) wave theory is compared to wave observations. Here, MHD wave theory is further developed illustrating how information about the magnetic and density structure along coronal loops can be determined by measuring the frequencies of the slow MHD oscillations. The application to observations of slow magnetoacoustic waves in coronal loops is discused.
Waves and oscillations can provide vital information about the internal structure of waveguides they propagate in. Here, we analytically investigate the effects of density and magnetic stratification on linear longitudinal magnetohydrodynamic (MHD) waves. The focus of this paper is to study the eigenmodes of these oscillations. It is our specific aim is to understand what happens to these MHD waves generated in flux tubes with non-constant (e.g., expanding or magnetic bottle) cross-sectional area and density variations. The governing equation of the longitudinal mode is derived and solved analytically and numerically. In particular, the limit of the thin flux tube approximation is examined. The general solution describing the slow longitudinal MHD waves in an expanding magnetic flux tube with constant density is found. Longitudinal MHD waves in density stratified loops with constant magnetic field are also analyzed. From analytical solutions, the frequency ratio of the first overtone and fundamental mode is investigated in stratified waveguides. For small expansion, a linear dependence between the frequency ratio and the expansion factor is found. From numerical calculations it was found that the frequency ratio strongly depends on the density profile chosen and, in general, the numerical results are in agreement with the analytical results. The relevance of these results for solar magneto-seismology is discussed.
A subset of 51 Hipparcos astrometric binaries among FG dwarfs within 67pc has been surveyed with the NICI adaptive optics system at Gemini-S, directly resolving for the first time 17 sub-arcsecond companions and 7 wider ones. Using these data together with published speckle interferometry of 57 stars, we compare the statistics of resolved astrometric companions with those of a simulated binary population. The fraction of resolved companions is slightly lower than expected from binary statistics. About 10% of astrometric companions could be "dark" (white dwarfs and close pairs of late M-dwarfs). To our surprise, several binaries are found with companions too wide to explain the acceleration. Re-analysis of selected intermediate astrometric data shows that some acceleration solutions in the original Hipparcos catalog are spurious.
The discovery of a relationship between supermassive black hole (SMBH) mass and spiral arm pitch angle (P) is evidence that SMBHs are tied to the overall secular evolution of a galaxy. The discovery of SMBHs in late-type galaxies with little or no bulge suggests that an underlying correlation between the dark matter halo concentration and SMBH mass (MBH) exists, rather than between the bulge mass and MBH. In this paper we measure P using a two-dimensional fast fourier transform and estimate the bar pattern speeds of 40 barred spiral galaxies from the Carnegie-Irvine Galaxy Survey. The pattern speeds were derived by estimating the gravitational potentials of our galaxies from Ks-band images and using them to produce dynamical simulation models. The pattern speeds allow us to identify those galaxies with low central dark halo densities, or fast rotating bars, while P provides an estimate of MBH. We find that a wide range of MBH exists in galaxies with low central dark matter halo densities, which appears to support other theoretical results. We also find that galaxies with low central dark halo densities appear to follow more predictable trends in P versus de Vaucouleurs morphological type (T) and bar strength versus T than barred galaxies in general. The empirical relationship between MBH and total gravitational mass of a galaxy (Mtot) allows us to predict the minimum Mtot that will be observationally measured of our fast bar galaxies. These predictions will be investigated in a subsequent paper.
Recent spectroscopic observations of globular clusters (GCs) in the Large Magellanic Cloud (LMC) have discovered that one of the intermediate-age GC, NGC 1718 with [Fe/H]=-0.7 has an extremely low [Mg/Fe] ratio of ~-0.9. We propose that NGC 1718 was formed from the ejecta of type Ia supernovae (SNe Ia) mixed with very metal-poor ([Fe/H] <-1.3) gas about ~ 2 Gyr ago. The proposed scenario is shown to be consistent with the observed abundances of Fe-group elements such as Cr, Mn, and Ni. In addition, compelling evidence for asymptotic giant branch stars playing a role in chemical enrichment during this GC formation is found. We suggest that the origin of the metal-poor gas is closely associated with the efficient gas-transfer from the outer gas disk of the Small Magellanic Cloud to the LMC disk. We anticipate that the outer part of the LMC disk contains field stars exhibiting significantly low [Mg/Fe] ratios, formed through the same process as NGC 1718.
Supermassive black hole binaries (SMBHBs) are expected to emit continuous gravitational waves in the pulsar timing array (PTA) frequency band ($10^{-9}$--$10^{-7}$ Hz). The development of data analysis techniques aimed at efficient detection and characterization of these signals is critical to the gravitational wave detection effort. In this paper we leverage methods developed for LIGO continuous wave gravitational searches, and explore the use of the $\mathcal{F}$-statistic for such searches in pulsar timing data. Babak & Sesana 2012 have already used this approach in the context of PTAs to show that one can resolve multiple SMBHB sources in the sky. Our work improves on several aspects of prior continuous wave search methods developed for PTA data analysis. The algorithm is implemented fully in the time domain, which naturally deals with the irregular sampling typical of PTA data and avoids spectral leakage problems associated with frequency domain methods. We take into account the fitting of the timing model, and have generalized our approach to deal with both correlated and uncorrelated colored noise sources. We also develop an incoherent detection statistic that maximizes over all pulsar dependent contributions to the likelihood. To test the effectiveness and sensitivity of our detection statistics, we perform a number of monte-carlo simulations. We produce sensitivity curves for PTAs of various configurations, and outline an implementation of a fully functional data analysis pipeline. Finally, we present a derivation of the likelihood maximized over the gravitational wave phases at the pulsar locations, which results in a vast reduction of the search parameter space.
Gamma-Ray Bursts (GRBs) have been proposed as a leading candidate for acceleration of ultra high-energy cosmic rays, which would be accompanied by emission of TeV neutrinos produced in proton-photon interactions during acceleration in the GRB fireball. Two analyses using data from two years of the IceCube detector produced no evidence for this neutrino emission, placing strong constraints on models of neutrino and cosmic-ray production in these sources.
We study large trans-neptunian objects (TNOs) using stellar occultations. We derive precise astrometric predictions for stellar occultations by Eris, Haumea, Ixion, Makemake, Orcus, Quaoar, Sedna, Varuna, 2002 TX300, and 2003 AZ84 for 2011-2015. We construct local astrometric catalogs of stars in the UCAC2 (Second US Naval Observatory CCD Astrograph Catalog) frame covering the sky path of these objects. For that purpose, during 2007-2009, we carried out an observational program at the ESO2p2/WFI (2.2 m Max-Planck ESO telescope with the Wide Field Imager) instrument. Astrometric catalogs with proper motions were produced for each TNO, containing more than 5.35 million stars covering the sky paths with 30' width in declination. The magnitude completeness is about R = 19 with a limit of about R = 21. We predicted 2717 stellar occultation candidates for all targets. Ephemeris offsets with about from 50 mas to 100 mas precision were applied to each TNO orbit to improve the predictions. They were obtained during 2007-2010 from a parallel observational campaign carried out with from 0.6 m to 2.2 m in size telescopes. This extends our previous work for the Pluto system to large TNOs, using the same observational and astrometric procedures. The obtained astrometric catalogs are useful for follow-up programs at small to large telescopes used to improve the candidate star positions and TNO ephemeris. They also furnish valuable photometric information for the field stars. For each TNO, updates on the ephemeris offsets and candidate star positions (geometric conditions of predictions and finding charts) are made available in the web by the group.
We study the evolution of the galactic spin using data of high redshift galaxies in the fields of the Great Observatories Origins Deep Survey (GOODS). Through simple dynamical considerations we estimate the spin for the disc galaxies in our sample and find that its distribution is consistent with that found for nearby galaxies. Defining a dimensionless angular momentum parameter for the disc component of the galaxies ($\lambda_{d}$), we do not find signs of evolution in the redshift range $0.4 \leq z \leq 1.2$. We find that the mass and environmental dependence of the spin of our high redshift galaxies are similar to that of low-$z$ galaxies; showing a strong dependence on mass, in the sense that low-mass systems present higher $\lambda_{d}$ values than high-mass galaxies, with no significant dependence on the environmental density. These results lead us to conclude that, although individual disc galaxies might occasionally suffer from strong evolution, they evolve in such a way that the overall spin distribution of the galactic population remains constant from $z\sim1$ to the present epoch.
We consider the rate of ionization of diffuse and molecular clouds in the interstellar medium by Galactic cosmic rays (GCR) in order to constrain its low energy spectrum. We extrapolate the GCR spectrum obtained from PAMELA at high energies ($\ge 200$ GeV/ nucleon) and a recently derived GCR proton flux at $1\hbox{--}200$ GeV from observations of gamma rays from molecular clouds, and find that the observed average Galactic ionization rate can be reconciled with this GCR spectrum if there is a low energy cutoff for protons at $10\hbox{--}50$ MeV. We also identify the flattening below a few GeV as being due to (a) decrease of the diffusion coefficient and dominance of convective loss at low energy and (b) the expected break in energy spectrum for a constant spectral index in momentum. We show that the inferred CR proton spectrum of $\Phi \propto E_{kin}^{-1.7\pm0.2}$ for $E_{kin} \le$ few GeV, is consistent with a power-law spectrum in momentum $p^{-2.45\pm0.4}$, which we identify as the spectrum at source. Diffusion loss at higher energies then introduces a steepening by $E^{-\alpha}$ with $\alpha \sim 1/3$, making it consistent with high energy measurements.
(Abridged) We investigate the phenomenological consequences of a modification of the initial state of a single inflationary field. While single-field inflation with the standard Bunch-Davies initial vacuum state does not generally produce a measurable three-point function (bispectrum) in the squeezed configuration, allowing for a non-standard initial state produces an exception. Here, we calculate the signature of an initial state modification in single-field slow-roll inflation in both the scale-dependent bias of the large-scale structure (LSS) and mu-type distortion in the black-body spectrum of the cosmic microwave background (CMB). We parametrize the initial state modifications and identify certain choices of parameters as natural, though we also note some fine-tuned choices that can yield a larger bispectrum. In both cases, we observe a distinctive k^-3 signature in LSS (as opposed to k^-2 for the local-form). As a non-zero bispectrum in the squeezed configuration correlates a long-wavelength mode with two short-wavelength modes, it induces a correlation between the CMB temperature anisotropy on large scales with the temperature-anisotropy-squared on very small scales; this correlation persists as the small-scale anisotropy-squared is processed into mu-type distortions. While the local-form mu-distortion turns out to be too small to detect in the near future, a modified initial vacuum state enhances the signal by a large factor owing to an extra factor of k_1/k. For example, a proposed absolutely-calibrated experiment, PIXIE, is expected to detect this correlation with a signal-to-noise ratio greater than 10, for an occupation number of about 0.5 in the observable modes. Relatively calibrated experiments such as Planck and LiteBIRD should also be able to measure this effect, provided that the relative calibration between different frequencies meets the required precision.
We show that an alpha effect is driven by the cosmic ray Bell instability
exciting left-right asymmetric turbulence. Alfven waves of a preferred
polarization have maximally helical motion, because the transverse motion of
each mode is parallel to its curl. We show how large-scale Alfven modes, when
rendered unstable by cosmic ray streaming, can create new net flux over any
finite region, in the direction of the original large-scale field. We perform
direct numerical simulations (DNS) of an MHD fluid with a forced cosmic ray
current and use the test-field method to determine the alpha effect and the
turbulent magnetic diffusivity. As follows from DNS, the dynamics of the
instability has the following stages: (i) in the early stage, the small-scale
Bell instability that results in a production of small-scale turbulence is
excited; (ii) in the intermediate stage, there is formation of larger-scale
magnetic structures; (iii) finally, quasi-stationary large-scale turbulence is
formed at a growth rate that is comparable to that expected from the dynamo
instability, but its amplitude over much longer timescales remains unclear. The
results of DNS are in good agreement with the theoretical estimates.
It is suggested that this dynamo is what gives weakly magnetized relativistic
shocks such as those from gamma ray bursts a macroscopic correlation length. It
may also be important for large-scale magnetic field amplification associated
with cosmic ray production and diffusive shock acceleration in supernova
remnants (SNR) and blast waves from gamma ray bursts. Magnetic field
amplification by Bell turbulence in SNR is found to be significant, but it is
limited owing to the finite time available to the super-Alfvenicly expanding
remnant. The effectiveness of the mechanisms is shown to be dependent on the
shock velocity.
Gyrochronology and recent theoretical findings are used to reduce the number of input parameters of differential rotation models. This eventually leads to a theoretical prediction for the surface differential rotation as a function of only two stellar parameters - surface temperature and rotation period - that can be defined observationally. An analytical approximation for this function is suggested. The tendency for the differential rotation to increase with temperature is confirmed. The increase is much steeper for late F-stars compared to G- and K-dwarfs. Slow and fast rotation regimes for internal stellar rotation are identified. A star attains its maximum differential rotation at rotation rates intermediate between these two regimes. The amplitude of the meridional flow increases with surface temperature and rotation rate. The structure of the flow changes considerably between cases of slow and fast rotation. The flow in rapid rotators is concentrated in the boundary layers near the top and bottom of the convection zone with very weak circulation in between.
[Abriged] Supermassive black holes (SMBH) lurk in the nuclei of most massive galaxies, perhaps in all of them. The tight observed scaling relations between SMBH masses and structural properties of their host spheroids likely indicate that the processes fostering the growth of both components are physically linked, despite the many orders of magnitude difference in their physical size. This chapter discusses how we constrain the evolution of SMBH, probed by their actively growing phases, when they shine as active galactic nuclei (AGN) with luminosities often in excess of that of the entire stellar population of their host galaxies. Following loosely the chronological developments of the field, we begin by discussing early evolutionary studies, when AGN represented beacons of light probing the most distant reaches of the universe and were used as tracers of the large scale structure. This early study turned into AGN "Demography", once it was realized that the strong evolution (in luminosity, number density) of the AGN population hindered any attempt to derive cosmological parameters from AGN observations directly. Following a discussion of the state of the art in the study of AGN luminosity functions, we move on to discuss the "modern" view of AGN evolution, one in which a bigger emphasis is given to the physical relationships between the population of growing black holes and their environment. This includes observational and theoretical efforts aimed at constraining and understanding the evolution of scaling relations, as well as the resulting limits on the evolution of the SMBH mass function. Physical models of AGN feedback and the ongoing efforts to isolate them observationally are discussed next. Finally, we touch upon the problem of when and how the first black holes formed and the role of black holes in the high-redshift universe.
X-ray surveys of the Carina nebula have revealed a few hard and luminous sources associated with early-type stars. Such unusual characteristics for the high-energy emission may be related to magnetically-confined winds. To search for the presence of magnetic fields in these objects, we performed a limited spectropolarimetric survey using the FORS instrument. The multi-object mode was used, so that a total of 21 OB stars could be investigated during a one-night-long run. A magnetic field was detected in two objects of the sample, with a 6 sigma significance; Tr16-22 and 13. Such a detection was expected for Tr16-22, as its X-ray emission is too bright, variable and hard, compared to other late-type O or O+OB systems. It is more surprising for Tr16-13, a poorly known star which so far has never shown any peculiar characteristics. Subsequent monitoring is now needed to ascertain the physical properties of these objects and enable a full modelling of their magnetic atmospheres and winds.
For the future development of Chinese Giant Solar Telescope (CGST) in Western China, a new sky brightness monitor (SBM) has been produced for the site survey for CGST. To critically examine the performance and sensitivity of SBM, we used it in the observation of the annular solar eclipse in Dali City, Yunnan, on 15 January 2010. The observation met good weather condition with almost clear sky during the eclipse. The SBM measurement translates into the solar illuminance changes at a level of 2.4 \times 10-4I s-1 during the eclipse. The time of the minimal sky brightness in the field of view (FOV) is found consistent with the time of maximum eclipse. Two local sky regions in the FOV are chosen to make time series of calibrated skylight profiles. The evolution of the sky brightness thus calibrated also shows good consistency with the eclipse, particularly between the second and the third contacts. The minimal sky brightness in each local sky region took place within half a minute from the corresponding predicted contact time. Such small time delays were mainly caused by occasional cirri. The minimal sky brightness measured during the eclipse is a few millionths of I\odot with standard deviation of 0.11 millionths of I\odot. The observation supports that the singlescattering process (optically thin conditions) is the main contributor to the atmospheric scattering. We have demonstrated that many important aerosol optical parameters can be deduced from our data.We conclude that the new SBM is a sensitive sky photometer that can be used for our CGST and coronagraph site surveys.
We present an absolute magnitude calibration for red giants with the colour magnitude diagrams of six Galactic clusters with different metallicities i.e. M92, M13, M5, 47 Tuc, M67, and NGC 6791. The combination of the absolute magnitude offset from the fiducial of giant sequence of the cluster M5 with the corresponding metallicity offset provides calibration for absolute magnitude estimation for red giants for a given (B-V)o colour. The calibration is defined in the colour interval 0.75<=(B-V)o<=1.50 mag and it covers the metallicity interval -2.15<[Fe/H]<=+0.37 dex. 91% of the absolute magnitude residuals obtained by the application of the procedure to another set of Galactic clusters lie in the interval -0.40<\Delta M<=+0.40 mag. The mean and the standard deviation of the residuals are 0.05 and 0.19 mag, respectively. We fitted the absolute magnitude also to metallicity and age for a limited sub-sample of (B-V)o colour, just to test the effect of age in absolute magnitude calibration. Comparison of the mean and the standard deviation of the residuals evaluated by this procedure with the corresponding ones provided by the procedure where the absolute magnitude fitted to a third degree polynomial of metallicity show that the age parameter may be omitted in absolute magnitude estimation of red giants. The derived relations are applicable to stars older than 4 Gyr, the age of the youngest calibrating cluster.
The aperture mass statistic is a common tool used in weak lensing studies. By convolving lensing maps with a filter function of a specific scale, chosen to be larger than the scale on which the noise is dominant, the lensing signal may be boosted with respect to the noise. This allows for detection of structures at increased fidelity. Furthermore, higher-order statistics of the aperture mass (such as its skewness or kurtosis), or counting of the peaks seen in the resulting aperture mass maps, provide a convenient and effective method to constrain the cosmological parameters. In this paper, we more fully explore the formalism underlying the aperture mass statistic. We demonstrate that the aperture mass statistic is formally identical to a wavelet transform at a specific scale. Further, we show that the filter functions most frequently used in aperture mass studies are not ideal, being non-local in both real and Fourier space. In contrast, the wavelet formalism offers a number of wavelet functions that are localized both in real and Fourier space, yet similar to the 'optimal' aperture mass filters commonly adopted. Additionally, for a number of wavelet functions, such as the starlet wavelet, very fast algorithms exist to compute the wavelet transform. This offers significant advantages over the usual aperture mass algorithm when it comes to image processing time, demonstrating speed-up factors of ~ 5 - 1200 for aperture radii in the range 2 to 64 pixels on an image of 1024 x 1024 pixels.
In this paper, we study the influence of solar flares on electron concentration in the terrestrial ionospheric D-region by analyzing the amplitude and phase time variations of very low frequency (VLF) radio waves emitted by DHO transmitter (Germany) and recorded by the AWESOME receiver in Belgrade (Serbia) in real time. The rise of photo-ionization rate in the ionospheric D-region is a typical consequence of solar flare activity as recorded by GOES-15 satellite for the event on March 24, 2011 between 12:01 UT and 12:11 UT. At altitudes around 70 km, the photo-ionization and recombination are the dominant electron gain and electron loss processes, respectively. We analyze the relative contribution of each of these two processes in the resulting electron concentration variation in perturbed ionosphere.
In this paper, we present a model for determination of a weakly time dependent effective recombination coefficient for the perturbed terrestrial ionospheric D-region plasma. We study consequences of a class M1.0 X-ray solar flare, recorded by GOES-15 satellite on February 18, 2011 between 14:00 UT and 14:15 UT, by analyzing the amplitude and phase real time variations of very low frequency (VLF) radio waves emitted by transmitter DHO (located in Germany) at frequency 23.4 kHz and recorded by the AWESOME receiver in Belgrade (Serbia). Our analysis is limited to ionospheric perturbations localized at altitudes around 70 km where the dominant electron gain and electron loss processes are the photo-ionization and recombination respectively.
Galileon gravity offers a robust theoretical alternative to general relativity with a cosmological constant for explaining cosmic acceleration, protected by a shift symmetry and having second order field equations. The predictions for the combination of cosmic expansion and growth history are distinct from \Lambda CDM, and we demonstrate that approaching \Lambda CDM in one causes deviations in the other. This tension allows us to severely disfavor the entire class of minimally coupled standard Galileon gravity through current observational constraints.
An enhanced concentration of 60Fe was found in a deep ocean's crust in 2004 in a layer corresponding to an age of ~2 Myr. The confirmation of this signal in terrestrial archives as supernova-induced and detection of other supernova-produced radionuclides is of great interest. We have identified two suitable marine sediment cores from the South Australian Basin and estimated the intensity of a possible signal of the supernova-produced radionuclides 26Al, 53Mn, 60Fe and the pure r-process element 244Pu in these cores. A finding of these radionuclides in a sediment core might allow to improve the time resolution of the signal and thus to link the signal to a supernova event in the solar vicinity ~2 Myr ago. Furthermore, it gives an insight on nucleosynthesis scenarios in massive stars, the condensation into dust grains and transport mechanisms from the supernova shell into the solar system.
In order to maximize the sensitivity of pulsar timing arrays to a stochastic gravitational wave background, we present computational techniques to optimize observing schedules. The techniques are applicable to both single and multi-telescope experiments. The observing schedule is optimized for each telescope by adjusting the observing time allocated to each pulsar while keeping the total amount of observing time constant. The optimized schedule depends on the timing noise characteristics of each individual pulsar as well as the performance of instrumentation. Several examples are given to illustrate the effects of different types of noise. A method to select the most suitable pulsars to be included in a pulsar timing array project is also presented.
The aim of the project is to improve our knowledge on the low-mass and
low-metallicity population to investigate the influence of metallicity of the
stellar (and substellar) mass function.
We present the results of a photometric and proper motion search aimed at
unearthing ultracool subdwarfs in large-scale surveys. We employed and combined
the UKIDSS LAS DR5 and the SDSS DR7 complemented with ancillary data from
2MASS, DENIS and SuperCOSMOS.
The SDSS DR7 vs UKIDSS LAS DR5 search returned a total of 32 ultracool
subdwarf candidates, only two being recognised as a subdwarf in the literature.
Twenty-seven candidates were followed-up spectroscopically in the optical
between 600 and 1000 nm. We confirmed 20 candidates as subdwarfs, extreme
subdwarfs or ultra-subdwarfs with spectral types later than M5; this represents
a success rate of ~60%. Among those 20 new subdwarfs, we identified 2 early-L
subdwarfs very likely located within 100 pc that we propose as templates for
future searches because they are the first examples of their subclass. Another
7 sources are solar-metallicity M dwarfs with spectral types between M4 and M7
without Halpha emission, suggesting that they are old M dwarfs. The remaining 5
candidates do not have spectroscopic follow-up yet; only 1 remains as a
bona-fide ultracool subdwarf after revision of their proper motions. We
assigned spectral types based on the current classification schemes and, when
possible, we measured their radial velocities. Using the limited number of
subdwarfs with trigonometric parallaxes, we estimated distances between 90 and
600 for the new subdwarfs. We provide mid-infrared photometry from WISE for two
subdwarfs and discuss their colours. Finally, we estimate a lower limit of the
surface density of ultracool subdwarfs of the order of 5000-5700 times lower
than that of solar-metallicity late-M dwarfs (Shortened).
The proper quantum plasma treatment of the electron gas in degenerate stars such as white dwarfs provides an additional quantum contribution to the electron pressure. The additional pressure term modifies the equation for hydrostatic equilibrium, resulting in the quantum modified Lane-Emden equation for polytropic equation of states. The additional pressure term also modifies the expression for the limiting Chandrasekhar mass of white dwarfs. An approximate solution is derived of the quantum modified Lane-Emden equation for general polytropic indices, and it is demonstrated that the quantum corrections reduce the standard Chandrasekhar mass and enhance the white dwarf radius by negligibly small values only.
Despite being all roughly of solar composition, primitive meteorites (chondrites) present a diversity in their chemical, isotopic and petrographic properties, and in particular a first-order dichotomy between carbonaceous and non-carbonaceous chondrites. We investigate here analytically the dynamics of their components (chondrules, refractory inclusions, metal/sulfide and matrix grains) in protoplanetary disks prior to their incorporation in chondrite parent bodies. We find the dynamics of the solids, subject to gas drag, to be essentially controlled by the "gas-solid decoupling parameter" $S\equiv \textrm{St}/\alpha$, the ratio of the dimensionless stopping time to the turbulence parameter. The decoupling of the solid particles relative to the gas is significant when $S$ exceeds unity. $S$ is expected to increase with time and heliocentric distance. On the basis of (i) abundance of refractory inclusions (ii) proportion of matrix (iii) lithophile element abundances and (iv) oxygen isotopic composition of chondrules, we propose that non-matrix chondritic components had $S<1$ when carbonaceous chondrites accreted and $S>1$ when the other chondrites accreted. This suggests that accretion of carbonaceous chondrites predated on average that of the other chondrites and that refractory inclusions are genetically related to their host carbonaceous chondrites.
Mass fluxes J are computed for the extragalactic O stars investigated by
Tramper et al. (2011; TSKK). For one early-type O star, computed and observed
rates agree within errors. However, for two late-type O stars, theoretical
mass-loss rates underpredict observed rates by ~ 1.6 dex, far exceeding
observational errors. A likely cause of the discrepancy is overestimated
observed rates due to the neglect of wind-clumping. A less likely but
intriguing possibility is that, in observing O stars with Z/Z_sun ~ 1/7, TSKK
have serendipitously discovered an additional mass-loss mechanism not evident
in the spectra of Galactic O stars with powerful radiation-driven winds.
Constraints on this unknown mechanism are discussed.
In establishing that the discrepancies, if real, are inescapable for purely
radiation-driven winds, failed searches for high-J solutions are reported and
the importance of a numerical technique that cannot spuriously create or
destroy momentum stressed.
The Z-dependences of the computed rates for Z/Z_sun in the interval (1/30, 2)
show significant departures from a single power law, and these are attributed
to curve-of-growth effects in the differentially-expanding reversing layers.
The best-fitting power-law exponents range from 0.68-0.97.
Using a population number synthesis code with detailed binary evolution, we calculate the distribution of the number of type Ia supernovae as a function of time after starburst. This is done for both main progenitor scenarios (single degenerate and double degenerate), but also with various evolutionary assumptions (such as mass transfer efficiency, angular momentum loss, and common envelope description). The comparison of these theoretically predicted delay time distributions with observations in elliptical galaxies then allows to constrain the evolutionary scenarios and parameters. From the morphological shape of the distributions, we conclude that all supernovae Ia cannot be produced through the single degenerate scenario alone, with the best match being obtained when both scenarios contribute. Within the double degenerate scenario, most systems go through a phase of quasi-conservative, stable Roche lobe overflow. We propose stellar rotation as a possible solution for the underestimation of the observed absolute number of events, as is the case in many theoretical population synthesis studies. A brief comparison with these other studies is made, showing good correspondence under the nontrivial condition of equivalent assumptions. We also investigate the influence of different supernova Ia progenitors and evolutionary parameters on the theoretical distribution of the iron abundance of G-type dwarfs in the Galactic disk. These stars are good indicators of the entire chemical history of the Galaxy, and their predicted metallicity distribution can also be compared to the observational ones. This again limits the number of acceptable combinations of assumptions. Supporting previous results, the best correspondence is found in the case where both the single and double degenerate scenario contribute.
We present a new efficient diagnostic method, based on mid-infrared and X-ray data, to select local (z<0.1) Compton-thick (CT) AGN with the aim of estimating their surface and space density. We define a region in the X-ray/IR vs. HR plane associated to CT AGN, i.e. F(2-12keV)/F25nu25<0.02 and HR>-0.2. We build up a sample of 43 CT AGN candidates using data from IRAS-PSC and 2XMM catalogue. In order to test the efficiency of the proposed method in selecting CT AGN we use the results of the X-ray spectral analysis performed on all the sources of our sample. After taking into account the different selection effects, we have estimated the number of CT in the local Universe and their density down to the IRAS flux limit of F25=0.5Jy. We find that the diagnostic plot proposed here is an efficient method to select Compton-thick AGN in the nearby Universe since ~84% of the sources populating the proposed CT region are actually CT AGN. Twenty percent are newly-discovered CT AGN. We then estimate the surface density of CT AGN down to the IRAS PSC catalogue flux limit (F25=0.5Jy) that turns out to be ~3e-3 src deg-2. After estimating an equivalent IR-hard X-ray limiting flux, we compare our result with those found with SWIFT-BAT. We find that the surface density derived here is a factor 4 above the density computed in the hard X-ray surveys. This difference is ascribed, at least in part, to a significant contribution (~60-90%) of the star-forming activity to the total 25 mic emission for the sources in our sample. By considering only the 25 mic AGN emission, we estimate a surface density of CT AGN which is consistent with the results found by hard X-ray surveys. Finally, we estimated the co-moving space density of CT AGN with intrinsic LX>1e43 erg s-1 (0.004<z<0.06): ~3.5e-6 Mpc-3. The prediction for CT AGN based on the synthesis model of XRB in Gilli et al.(2007) is consistent with this value.
During the process of core-collapse of a massive star, the iron core evolves into an inner central core and an outer envelope, generating a cavity in between. The dynamics of this cavity, filled with plasma and magnetic field by the rapidly rotating pulsar (spun-down magnetar) at the center, is believed to be very relevant to account for supernovae and gamma-ray bursts \citep{uzdensky2007}. The interactions of the pressurized conducting plasma and the magnetic field could generate some spatial distributions of plasma and magnetic field within the cavity. In an effort to better understand the spatial distributions, a set of time-dependent magnetohydrodynamic (MHD) equations is used to model this cavity system. Homologous solutions in Lagrangian representation are obtained to account for the spatial structures. Under this self-similar description, the magnetic flux function is governed by an eigenvalue equation with the eigenvalue being the poloidal plasma $\beta$, which is the ratio of plasma pressure to poloidal magnetic pressure. In terms of the flux function, the magnetic fields are structured in the cavity with a set of axisymmetric lobes (magnetic vortices). Because of a geometric singularity, the magnetic lobe energy tends to collimate onto the polar axis, as a function of increasing plasma pressure in the cavity. Since this model indicates $\beta\gg 1$, plasma pressure stored in the cavity is the primary motor for supernova, not the magnetic field. At very high plasma pressure and high magnetic fields, the collimation is confined to a very small cone along the axis with a sequence of magnetic lobes, generating a configuration appropriate for gamma-ray burst with multiple fireballs.
The sub-arcsec bright points (BP) associated with the small scale magnetic fields in the lower solar atmosphere are advected by the evolution of the photospheric granules. We measure various quantities related to the horizontal motions of the BPs observed in two wavelengths, including the velocity auto-correlation function. A 1 hr time sequence of wideband H$\alpha$ observations conducted at the \textit{Swedish 1-m Solar Telescope} (\textit{SST}), and a 4 hr \textit{Hinode} \textit{G}-band time sequence observed with the Solar Optical telescope are used in this work. We follow 97 \textit{SST} and 212 \textit{Hinode} BPs with 3800 and 1950 individual velocity measurements respectively. For its high cadence of 5 s as compared to 30 s for \textit{Hinode} data, we emphasize more on the results from \textit{SST} data. The BP positional uncertainty achieved by \textit{SST} is as low as 3 km. The position errors contribute 0.75 km$^2$ s$^{-2}$ to the variance of the observed velocities. The \textit{raw} and \textit{corrected} velocity measurements in both directions, i.e., $(v_x,v_y)$, have Gaussian distributions with standard deviations of $(1.32,1.22)$ and $(1.00, 0.86)$ km s$^{-1}$ respectively. The BP motions have correlation times of about $22 - 30$ s. We construct the power spectrum of the horizontal motions as a function of frequency, a quantity that is useful and relevant to the studies of generation of Alfv\'en waves. Photospheric turbulent diffusion at time scales less than 200 s is found to satisfy a power law with an index of 1.59.
The number of publications of aperture-synthesis images based on optical long-baseline interferometry measurements has recently increased due to easier access to visible and infrared interferometers. The interferometry technique has now reached a technical maturity level that opens new avenues for numerous astrophysical topics requiring milli-arcsecond model-independent imaging. In writing this paper our motivation was twofold: 1) review and publicize emblematic excerpts of the impressive corpus accumulated in the field of optical interferometry image reconstruction; 2) discuss future prospects for this technique by selecting four representative astrophysical science cases in order to review the potential benefits of using optical long baseline interferometers. For this second goal we have simulated interferometric data from those selected astrophysical environments and used state-of-the-art codes to provide the reconstructed images that are reachable with current or soon-to-be facilities. The image reconstruction process was "blind" in the sense that reconstructors had no knowledge of the input brightness distributions. We discuss the impact of optical interferometry in those four astrophysical fields. We show that image reconstruction software successfully provides accurate morphological information on a variety of astrophysical topics and review the current strengths and weaknesses of such reconstructions. We investigate how to improve image reconstruction and the quality of the image possibly by upgrading the current facilities. We finally argue that optical interferometers and their corresponding instrumentation, existing or to come, with 6 to 10 telescopes, should be well suited to provide images of complex sceneries.
[Context] Recent detections of disks around young high-mass stars support the idea of massive star formation through accretion rather than coalescence, but the detailed kinematics in the equatorial region of the disk candidates is not well known, which limits our understanding of the accretion process. [Aims] This paper explores the kinematics of the gas around a young massive star with millimeter-wave interferometry to improve our understanding of the formation of massive stars though accretion. [Methods] We use Plateau de Bure interferometric images to probe the environment of the nearby (~1 kpc) and luminous (~20000 Lsun) high-mass (10-16 Msun) young star AFGL 2591-VLA3 in continuum and in lines of HDO, H218O and SO2 in the 115 and 230 GHz bands. Radiative transfer calculations are employed to investigate the kinematics of the source. [Results] At ~0.5" (500 AU) resolution, the line images clearly resolve the velocity field of the central compact source (diameter of ~ 800 AU) and show linear velocity gradients in the northeast-southwest direction. Judging from the disk-outflow geometry, the observed velocity gradient results from rotation and radial expansion in the equatorial region of VLA3. Radiative transfer calculations suggest that the velocity field is consistent with sub-Keplerian rotation plus Hubble-law like expansion. The line profiles of the observed molecules suggest a layered structure, with HDO emission arising from the disk mid-plane, H218O from the warm mid-layer, and SO2 from the upper disk. [Conclusions] We propose AFGL 2591-VLA3 as a new massive disk candidate, with peculiar kinematics. The rotation of this disk is sub-Keplerian, probably due to magnetic braking, while the stellar wind may be responsible for the expansion of the disk. The expansion motion [...]
We present spectro-polarimetric observations of several molecular lines obtained with the Submillimeter Array (SMA) toward the carbon rich AGB star IRC+10216. We have detected and mapped the linear polarization of the CO 3-2, SiS 19-18 and CS 7-6 lines. The polarization arises at a distance of ~450 AU from the star and is blueshifted with respect the Stokes I. The SiS 19-18 polarization pattern appears to be consistent with a locally radial magnetic field configuration. However, the CO 3-2 and CS 7-6 line polarization suggests an overall complex magnetic field morphology within the envelope. This work demonstrates the feasibility of using spectro-polarimetric observations to carry out tomographic imaging of the magnetic field in circumstellar envelopes.
Subluminous B stars come in a variety of flavours including single stars,
close and wide binaries, and pulsating and non-pulsating variables. A majority
have helium-poor surfaces (helium by number nHe<1%), whilst a minority have
extremely helium-rich surfaces (nHe>90%). A small number have an intermediate
surface helium abundance (~ 10 - 30%), accompanied by peculiar abundances of
other elements. The questions posed are i) whether these abundance
peculiarities are associated with radiatively-driven and time-dependent
stratification of elements within the photosphere as the star evolves from an
helium-enriched progenitor to become a normal helium-poor sdB star, and ii)
whether these phenomena occur only in single sdB stars or are also associated
with sdB stars in binaries.
We present a fine analysis of the bright intermediate-helium sdB star CPD-20
1123 (Albus 1) which shows it to be cool, for a hot subdwarf, with Teff~23\,000
K and with a surface helium abundance ~17% by number. Other elements do not
show extraordinary anomalies; in common with majority sdB stars, carbon and
oxygen are substantially depleted, whilst nitrogen is enriched. Magnesium
through sulphur appear to be depleted by ~0.5 dex, but chlorine and argon are
substantially enhanced.
We also present a series of radial-velocity measurements which show the star
to be a close binary with an orbital period of 2.3 d, suggesting it to be a
post-common-envelope system.
The discovery of an intermediate helium-rich sdB star in a close binary in
addition to known and apparently single exemplars supports the view that these
are very young sdB stars in which radiatively-driven stratification of the
photosphere is incomplete.
In the context of planet formation, anticyclonic vortices have recently received lots of attention for the role they can play in planetesimals formation. Radial migration of intermediate size solids toward the central star may prevent their growth to larger solid grains. On the other hand, vortices can trap the dust and accelerate this growth, counteracting fast radial transport. Multiple effects have been shown to affect this scenario, such as vortex migration or decay. The aim of this paper is to study the formation of vortices by the Rossby wave instability and their long term evolution in a full three dimensional protoplanetary disc. We use a robust numerical scheme combined with adaptive mesh refinement in cylindrical coordinates, allowing to affordably compute long term 3D evolutions. We consider a full disc stratified both radially and vertically that is prone to formation of vortices by the Rossby wave instability. We show that the 3D Rossby vortices grow and survive over hundreds of years without migration. The localized overdensity which initiated the instability and vortex formation survives the growth of the Rossby wave instability for very long times. When the vortices are no longer sustained by the Rossby wave instability, their shape changes toward more elliptical vortices. This allows them to survive shear-driven destruction, but they may be prone to elliptical instability and slow decay. When the conditions for growing Rossby wave-related instabilities are maintained in the disc, large-scale vortices can survive over very long timescales and may be able to concentrate solids.
The reported spatial variation in the fine-structure constant at high redshift, if physical, could be due to the presence of dilatonic domains, and one or more domain walls inside our horizon. An absorption spectrum of an object in a different domain from our own would be characterized by a different value of alpha. We show that while a single wall solution is statically comparable to a dipole fit, and is a big improvement over a weighted mean (despite adding 3 parameters), a two-wall solution is a far better fit (despite adding 3 parameters over the single wall solution). We derive a simple model accounting for the two-domain wall solution. The goodness of these fits is however dependent on the extra random error which was argued to account for the large scatter in most of the data. When this error is omitted, all the above solutions are poor fits to the data. When included, the solutions that exhibit a spatial dependence agree with the data much more significantly than the Standard Model; however, the Standard Model itself is not a terrible fit to the data, having a p-value of ~ 20 %.
Several non-threshold reactions which may be used to detect the cosmic neutrino background are presented. The corresponding cross sections are calculated analytically within the Standard Model. These reactions are sensitive not only to the electron neutrinos but also to the muon and tau neutrinos. Some possibilities of experimental observation of the neutrino background are indicated.
We calculate Large Scale Structure observables for non-Gaussianity arising from non-Bunch-Davies initial states in single field inflation. These scenarios can have substantial primordial non-Gaussianity from squeezed (but observable) momentum configurations. They generate a term in the halo bias that may be more strongly scale-dependent than the contribution from the local ansatz. We also discuss theoretical considerations required to generate an observable signature.
We present the results of an extended narrow-band H{\alpha} study of the massive galaxy cluster XMMU J2235.3-2557 at z = 1.39. This paper represents a follow up study to our previous investigation of star-formation in the cluster centre, extending our analysis out to a projected cluster radius of 1.5 Mpc. Using the Near InfraRed Imager and Spectrograph (NIRI) on Gemini North we obtained deep H narrow-band imaging corresponding to the rest-frame wavelength of H{\alpha} at the cluster's redshift. We identify a total of 163 potential cluster members in both pointings, excluding stars based on their near-IR colours derived from VLT/HAWK-I imaging. Of these 163 objects 14 are spectroscopically confirmed cluster members, and 20% are excess line-emitters. We find no evidence of star formation activity within a radius of 200 kpc of the brightest cluster galaxy in the cluster core. Dust-corrected star formation rates (SFR) of excess emitters outside this cluster quenching radius, RQ \sim 200 kpc, are on average <SFR> = 2.7 \pm 1.0 M\odot yr-1, but do not show evidence of increasing star-formation rates toward the extreme 1.5 Mpc radius of the cluster. No individual cluster galaxy exceeds an SFR of 6 M\odot yr-1 . Massive galaxies (log M\ast /M\odot > 10.75) all have low specific SFRs (SSFRs, i.e. SFR per unit stellar mass). At fixed stellar mass, galaxies in the cluster centre have lower SSFRs than the rest of the cluster galaxies, which in turn have lower SSFRs than field galaxies at the same redshift by a factor of a few to 10. For the first time we can demonstrate through measurements of individual SFRs that already at very early epochs (at an age of the Universe of \sim4.5 Gyr) the suppression of star-formation is an effect of the cluster environment which persists at fixed galaxy stellar mass.
The Swift Burst Alert Telescope (BAT) is discovering interesting new objects while monitoring the sky in the 14-195 keV band. Here we present the X-ray properties and spectral energy distributions for two unusual AGN sources. Both NVSS 193013+341047 and IRAS 05218-1212 are absorbed, Compton-thin, but heavily obscured (NH \sim 10^23 cm-2), X-ray sources at redshifts < 0.1. The spectral energy distributions reveal these galaxies to be very red, with high extinction in the optical and UV. A similar SED is seen for the extremely red objects (EROs) detected in the higher redshift universe. This suggests that these unusual BAT-detected sources are a low- redshift (z << 1) analog to EROs, which recent evidence suggests are a class of the elusive type II quasars. Studying the multi-wavelength properties of these sources may reveal the properties of their high redshift counterparts.
We report the abundances of C, Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd, and Sm in 25 solar-type stars in the solar neighbourhood, and their correlations with ages, kinematics, and orbital parameters. The spectroscopic analysis, based high resolution and high S/N ratio data, was differential to the Sun and applied to atomic line EWs and to C and C2 spectral synthesis. We performed a statistical study using a tree clustering analysis, searching for groups of stars sharing similar abundance patterns. We derived Teff, log(g), and [Fe/H] with errors of 30 K, 0.13 dex, and 0.05 dex, respectively. The average error in [X/Fe] is 0.06 dex. Ages were derived from theoretical HR diagrams and memberships in kinematical moving groups. We identified four stellar groups: with over-solar abundances (<[X/H]> = +0.26 dex), under-solar abundances (<[X/H]> = -0.24 dex), and intermediate values (<[X/H]> = -0.06 and +0.06 dex) but with distinct chemical patterns. Stars sharing solar metallicity, age, and Galactic orbit possibly have non-solar abundance, an effect either of chemical heterogeneity in their natal clouds or migration. A trend of [Cu/Fe] with [Ba/Fe] seems to exist, in agreement with previous claims in the literature, and maybe also of [Sm/Fe] with [Ba/Fe]. No such correlation involving C, Na, Mn, and Zn is observed. [Mg/Fe], [Sc/Fe], and [Ti/Fe] increase with age. [Mn/Fe] and [Cu/Fe] first increase towards younger stars up to the solar age, and then decrease, a result we interpret as possibly related to time-varying yields of SN Ia and the weak s-process. [Sr/Fe], [Y/Fe], [Sr/Mg], [Y/Mg], [Sr/Zn], and [Y/Zn] linearly increase towards younger stars. [Zr/Fe], [Ce/Fe], [Nd/Fe], [Ba/Mg], [Ba/Zn], and [Sr,Y,Ba/Sm] increase but only for stars younger than the Sun. The steepest negative age relation is due to [Ba/Fe], but only for stars younger than the Sun.
A list of galaxies with inner regions revealing polar (or strongly inclined to the main galactic plane) disks and rings is compiled from the literature data. The list contains 47 galaxies of all morphological types, from E to Irr. We consider the statistics of the parameters of polar structures known from observations. The radii of the majority of them do not exceed 1.5 kpc. The polar structures are equally common in barred and unbarred galaxies. At the same time, if a galaxy has a bar (or a triaxial bulge), this leads to the polar disk stabilization - its axis of rotation usually coincides with the major axis of the bar. More than two thirds of all considered galaxies reveal one or another sign of recent interaction or merging. This fact indicates a direct relation between the external environment and the presence of an inner polar structure.
The present paper extends to clusters of galaxies the study of Del Popolo (2012), concerning how the baryon-dark matter (DM) interplay shapes the density profile of dwarf galaxies. Cluster density profiles are determined taking into account dynamical friction, random and ordered angular momentum and the response of dark matter halos to condensation of baryons. We find that halos containing only DM are characterized by Einasto's profiles, and that the profile flattens with increasing content of baryons, and increasing values of random angular momentum. The analytical results obtained in the first part of the paper were applied to well studied clusters whose inner profiles have slopes flatter than NFW predictions (A611, A383) or are characterized by profiles in agreement with the NFW model (MACS J1423.8+2404, RXJ1133). By using independently-measured baryonic fraction, a typical spin parameter value $\lambda \simeq 0.03$, and adjusting the random angular momentum, we re-obtain the mass and density profiles of the quoted clusters. Finally, we show that the baryonic mass inside $\simeq 10$ kpc, $M_{b,in}$ is correlated with the total mass of the clusters, %finding a correlation among the two quantities, as $M_{b,in} \propto M_{500}^{0.4}$.
Using a sample of 28 HII regions from the literature with measured temperature inhomogeneity parameter, t^2, we present a statistical correction to the chemical abundances determined with the direct method. We used the t^2 values to correct the oxygen gaseous abundances and consider the oxygen depletion into dust to calculate the total abundances for these objects. This correction is used to obtain a new calibration of Pagel's strong-line method to determine oxygen abundances in HII regions. Our new calibration simultaneously considers the temperature structure, the ionization structure, and the fraction of oxygen depleted into dust grains. Previous calibrations in the literature have included one or two of these factors; this is the first time all three are taken into account. This recalibration conciliates the systematic differences among the temperatures found from different methods. We find that the total correction due to thermal inhomogeneities and dust depletion amounts to an increase in the O/H ratio of HII regions by factors of 1.7 to 2.2 (or 0.22 to 0.35 dex). This result has important implications in various areas of astrophysics such as the study of the higher end of the initial mass function, the star formation rate, and the mass-metallicity relation of galaxies, among others.
Chameleon scalar fields are dark energy candidates which suppress fifth forces in high density regions of the universe by becoming massive. We consider chameleon models as effective field theories and estimate quantum corrections to their potentials. Requiring that quantum corrections be small, so as to allow reliable predictions of fifth forces, leads to an upper bound $m < 0.0073 (\rho / 10 {\rm g\, cm}^{-3})^{1/3}$eV for gravitational strength coupling whereas fifth force experiments place a lower bound of $m>0.0042$\,eV. An improvement of less than a factor of two in the range of fifth force experiments could test all classical chameleon field theories whose quantum corrections are well-controlled and couple to matter with nearly gravitational strength regardless of the specific form of the chameleon potential.
We review observational evidence for a matter-antimatter asymmetry in the early universe, which leads to the remnant matter density we observe today. We also discuss observational bounds on the presence of antimatter in the present day universe, including the possibility of a large lepton asymmetry in the cosmic neutrino background. We briefly review the theoretical framework within which baryogenesis, the dynamical generation of a matter-antimatter asymmetry, can occur. As an example, we discuss a testable minimal model that simultaneously explains the baryon asymmetry of the universe, neutrino oscillations and dark matter.
Soft limits of inflationary correlation functions are both observationally relevant and theoretically robust. Various theorems can be proven about them that are insensitive to detailed model-building assumptions. In this paper, we re-derive several of these theorems in a universal way. Our method makes manifest why soft limits are such an interesting probe of the spectrum of additional light fields during inflation. We illustrate these abstract results with a detailed case study of the soft limits of quasi-single-field inflation.
Scalar-tensor theories are among the simplest extensions of general relativity. In theories with light scalars, deviations from Einstein's theory of gravity are determined by the scalar mass m_s and by a Brans-Dicke-like coupling parameter \omega_{BD}. We show that gravitational-wave observations of nonspinning neutron star-black hole binary inspirals can be used to set upper bounds on the combination m_s/\sqrt{\omega_{BD}}. We estimate via a Fisher matrix analysis that individual observations with signal-to-noise ratio \rho would yield (m_s/\sqrt{\omega_{\rm BD}})(\rho/10)\lesssim 10^{-15}, 10^{-16} and 10^{-19} eV for Advanced LIGO, ET and eLISA, respectively. A statistical combination of multiple observations may further improve this bound.
The cross section for radiative capture of neutron on carbon-14 is calculated using the model-independent formalism of halo effective field theory. The dominant contribution from E1 transition is considered, and the cross section is expressed in terms of elastic scattering parameters of the effective range expansion. Contributions from both resonant and non-resonant interaction are calculated. Significant interference between these leads to a capture contribution that deviates from simple Breit-Wigner resonance form.
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