adsabs/SciX_UAT_keywords huggingface dataset:
Merger Rate Density of Population III Binary Black Holes Below, Above, and in the Pair-instability Mass Gap

We present the merger rate density of Population III binary black holes (BHs) by means of a widely used binary population synthesis code BSE with extensions to very massive and extreme metal-poor stars. We consider not only low-mass BHs (lBHs: 5-50M⊙) but also high-mass BHs (hBHs: 130-200M⊙), where lBHs and hBHs are below and above the pair-instability mass gap (50-130M⊙), respectively. Population III BH-BHs can be categorized into three subpopulations: BH-BHs without hBHs (hBH0s: mtot ≲ 100M⊙), with one hBH (hBH1s: mtot ∼ 130-260M⊙), and with two hBHs (hBH2s: mtot ∼ 270-400M⊙), where mtot is the total mass of a BH-BH. Their merger rate densities at the current universe are ∼0.1 yr-1 Gpc-3 for hBH0s, and ∼0.01 yr-1 Gpc-3 for the sum of hBH1s and hBH2s, provided that the mass density of Population III stars is ∼1013M⊙ Gpc-3. These rates are modestly insensitive to initial conditions and single star models. The hBH1 and hBH2 mergers can dominate BH-BHs with hBHs discovered in the near future. They have low effective spins ≲0.2 in the current universe. The number ratio of hBH2s to hBH1s is high, ≳0.1. We also find that BHs in the mass gap (up to ∼85M⊙) merge. These merger rates can be reduced to nearly zero if Population III binaries are always wide (≳100R⊙), and if Population III stars always enter into chemically homogeneous evolution. The presence of close Population III binaries (∼10R⊙) is crucial for avoiding the worst scenario.

Keywords: astrophysical black holes; stellar mass black holes; massive stars; close binary stars; common envelope binary stars; population iii stars; gravitational waves
Haze Optical Depth in Exoplanet Atmospheres Varies with Rotation Rate: Implications for Observations

Transmission spectroscopy supports the presence of uncharacterized, light-scattering and -absorbing hazes in the atmospheres of many exoplanets. The complexity of factors influencing the formation, 3D transport, radiative impact, and removal of hazes makes it challenging to match theoretical models to the existing data. Our study simplifies these factors to focus on the interaction between planetary general circulation and haze distribution at the planetary limb. We use an intermediate-complexity general circulation model, ExoPlaSim, to simulate idealized organic haze particles as radiatively active tracers in the atmospheres of tidally locked terrestrial planets for 32 rotation rates. We find three distinct 3D spatial haze distributions, corresponding to three circulation regimes, each with a different haze profile at the limb. All regimes display significant terminator asymmetry. In our parameter space, super-Earth-sized planets with rotation periods greater than 13 days have the lowest haze optical depths at the terminator, supporting the choice of slower rotators as observing targets.

Keywords: exoplanet atmospheres; exoplanet atmospheric dynamics; exoplanets; extrasolar rocky planets
Measuring the Mass–Radius Relation of White Dwarfs Using Wide Binaries

Measuring the mass–radius relation of individual white dwarfs is an empirically challenging task that has been performed for only a few dozen stars. We measure the white dwarf mass–radius relation using the gravitational redshifts and radii of 135 white dwarfs in wide binaries with main-sequence companions. We obtain the radial velocities of these systems using the main-sequence companion, and subtract these Doppler redshifts from the white dwarfs' apparent motions, isolating their gravitational redshifts. We use Gaia data to calculate the surface temperatures and radii of these white dwarfs, thereby deriving an empirical gravitational redshift–radius relation. This work demonstrates the utility of low-resolution Galactic surveys to measure the white dwarf equation of state. Our results are consistent with theoretical models, and represent the largest sample of individual white dwarf gravitational redshift measurements to date.

Keywords: white dwarf stars; da stars; gaia
Beyond Spectroscopy. I. Metallicities, Distances, and Age Estimates for Over 20 Million Stars from SMSS DR2 and Gaia EDR3

Accurate determinations of stellar parameters and distances for large complete samples of stars are keys for conducting detailed studies of the formation and evolution of our Galaxy. Here we present stellar atmospheric parameters (effective temperature, luminosity classifications, and metallicity) estimates for some 24 million stars determined from the stellar colors of SMSS DR2 and Gaia EDR3, based on training data sets with available spectroscopic measurements from previous high/medium/low-resolution spectroscopic surveys. The number of stars with photometric-metallicity estimates is 4-5 times larger than that collected by the current largest spectroscopic survey to date-LAMOST-over the course of the past decade. External checks indicate that the precision of the photometric-metallicity estimates are quite high, comparable to or slightly better than that derived from spectroscopy, with typical values around 0.05-0.15 dex for both dwarf and giant stars with [Fe/H] > -2.01.0, 0.10-0.20 dex for giant stars with -2.0 < [Fe/H] ≤ -1.0, and 0.20-0.25 dex for giant stars with [Fe/H] ≤ -2.0, and include estimates for stars as metal-poor as [Fe/H] ~ -3.5, substantially lower than previous photometric techniques. Photometric-metallicity estimates are obtained for an unprecedented number of metal-poor stars, including a total of over three million metal-poor (MP; [Fe/H] ≤ -1.0) stars, over half a million very metal-poor (VMP; [Fe/H] ≤ -2.0) stars, and over 25,000 extremely metal-poor (EMP; [Fe/H] ≤ -3.0) stars. Moreover, distances are determined for over 20 million stars in our sample. For the over 18 million sample stars with accurate Gaia parallaxes, stellar ages are estimated by comparing with theoretical isochrones. Astrometric information is provided for the stars in our catalog, along with radial velocities for ~10% of our sample stars, taken from completed/ongoing large-scale spectroscopic surveys.

Keywords: metallicity; stellar distance; stellar ages; sky surveys
Hydrodynamics of Small Transient Brightenings in the Solar Corona

Small scale transients occur in the solar corona at much higher frequencies than flares and play a significant role in coronal dynamics. Here we study three well-identified transients discovered by Hi-C and also detected by the EUV channels of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. We use 0D enthalpy-based hydrodynamical simulations and produce synthetic light curves to compare with AIA observations. We have modeled these transients as loops of ~1.0 Mm length depositing energies ~1023 erg in ~50 s. The simulated synthetic light curves show reasonable agreement with the observed light curves. During the initial phase, conduction flux from the corona dominates over the radiation, like impulsive flaring events. Our results further show that the time-integrated net enthalpy flux is positive, hence into the corona. The fact that we can model the observed light curves of these transients reasonably well by using the same physics as those for nanoflares, microflares, and large flares, suggests that these transients may have a common origin.

Keywords: solar corona; solar coronal heating; solar coronal loops; solar coronal transients; solar transition region; hydrodynamical simulations; solar flares
A Machine-learning Approach to Integral Field Unit Spectroscopy Observations. I. H ii Region Kinematics

SITELLE is a novel integral field unit spectroscopy instrument that has an impressive spatial (11 by 11 arcmin), spectral coverage, and spectral resolution (R ∼ 1-20,000). SIGNALS is anticipated to obtain deep observations (down to 3.6 × 10-17erg s-1 cm-2) of 40 galaxies, each needing complex and substantial time to extract spectral information. We present a method that uses Convolution Neural Networks (CNN) for estimating emission-line parameters in optical spectra obtained with SITELLE as part of the SIGNALS large program. Our algorithm is trained and tested on synthetic data representing typical emission spectra for H ii regions based on Mexican Million Models database (3MdB) BOND simulations. The network's activation map demonstrates its ability to extract the dynamical (broadening and velocity) parameters from a set of five emission lines (e.g., Hα, N [ii] doublet, and S [ii] doublet) in the SN3 (651-685 nm) filter of SITELLE. Once trained, the algorithm was tested on real SITELLE observations in the SIGNALS program of one of the southwest fields of M33. The CNN recovers the dynamical parameters with an accuracy better than 5 $\mathrm{km}\,{{\rm{s}}}^{-1}$ in regions with a signal-to-noise ratio greater than 15 over the Hα line. More importantly, our CNN method reduces calculation time by over an order of magnitude on the spectral cube with native spatial resolution when compared with standard fitting procedures. These results clearly illustrate the power of machine-learning algorithms for the use in future IFU-based missions. Subsequent work will explore the applicability of the methodology to other spectral parameters such as the flux of key emission lines.

Keywords: h ii regions; emission nebulae; convolutional neural networks; neural networks; supernova remnants; interstellar medium
An Energy Balance Model for Rapidly and Synchronously Rotating Terrestrial Planets

This paper describes the habitable energy balance model for exoplanet observations (HEXTOR), which is a model for calculating latitudinal temperature profiles on Earth and other rapidly rotating planets. HEXTOR includes a lookup table method for calculating the outgoing infrared radiative flux and the planetary albedo, which provides improvements over other approaches to parameterizing radiative transfer in an energy balance model (EBM). Validation cases are presented for present-day Earth and other Earth-sized planets with aquaplanet and land planet conditions from 0° to 45° obliquity. A tidally locked coordinate system is also implemented in the EBM, which enables calculation of the horizontal temperature profile for planets in synchronous rotation around low-mass stars. This coordinate-transformed model is applied to cases for TRAPPIST-1e as defined by the TRAPPIST Habitable Atmosphere Intercomparison protocol, which demonstrates better agreement with general circulation models than with the latitudinal EBM. Advances in applying EBMs to exoplanets can be made by using general circulation models as a benchmark for tuning as well as by conducting intercomparisons between EBMs with different physical parameterizations.

Keywords: planetary climates; exoplanet atmospheres; astrobiology; computational methods; hierarchical models
Evolution and Final Fate of Solar Metallicity Stars in the Mass Range 7–15 M ⊙. I. The Transition from Asymptotic Giant Branch to Super-AGB Stars, Electron Capture, and Core-collapse Supernova Progenitors

According to a standard initial mass function, stars in the range 7–12 M ⊙ constitute ∼50% (by number) of the stars more massive than ∼7 M ⊙, but in spite of this, their evolutionary properties, and in particular their final fate, are still scarcely studied. In this paper, we present a detailed study of the evolutionary properties of solar metallicity nonrotating stars in the range 7–15 M ⊙, from the pre-main-sequence phase up to the presupernova stage or an advanced stage of the thermally pulsing phase, depending on the initial mass. We find that (1) the 7.00 M ⊙ star develops a degenerate CO core and evolves as a classical asymptotic giant branch (AGB) star in the sense that it does not ignite the C-burning reactions, (2) stars with initial mass M ≥ 9.22 M ⊙ end their lives as core-collapse supernovae, (3) stars in the range 7.50 ≤ M/M ⊙ ≤ 9.20 develop a degenerate ONeMg core and evolve through the thermally pulsing super-AGB phase, (4) stars in the mass range 7.50 ≤ M/M ⊙ ≤ 8.00 end their lives as hybrid CO/ONeMg or ONeMg WDs, and (5) stars with initial mass in the range 8.50 ≤ M/M ⊙ ≤ 9.20 may potentially explode as electron-capture supernovae.

Keywords: stellar evolutionary models; late stellar evolution; stellar evolution; supernovae; core-collapse supernovae; asymptotic giant branch stars; massive stars
ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Evidence for a Molecular Jet Launched at an Unprecedented Early Phase of Protostellar Evolution

Protostellar outflows and jets play a vital role in star formation as they carry away excess angular momentum from the inner disk surface, allowing the material to be transferred toward the central protostar. Theoretically, low-velocity and poorly collimated outflows appear from the beginning of the collapse at the first hydrostatic core (FHSC) stage. With growing protostellar core mass, high-density jets are launched, entraining an outflow from the infalling envelope. Until now, molecular jets have been observed at high velocity (≳100 km s-1) in early Class 0 protostars. We, for the first time, detect a dense molecular jet in SiO emission with low velocity (~4.2 km s-1, deprojected ~24 km s-1) from source G208.89-20.04Walma (hereafter G208Walma) using ALMA Band 6 observations. This object has some characteristics of FHSCs, such as a small outflow/jet velocity, extended 1.3 mm continuum emission, and N 2D+ line emission. Additional characteristics, however, are typical of early protostars: collimated outflow and SiO jet. The full extent of the outflow corresponds to a dynamical timescale of ~ ${930}_{-100}^{+200}$ yr. The spectral energy distribution also suggests a very young source having an upper limit of T bol ~ 31 K and L bol ~ 0.8 L ⊙. We conclude that G208Walma is likely in the transition phase from FHSC to protostar, and the molecular jet has been launched within a few hundred years of initial collapse. Therefore, G208Walma may be the earliest object discovered in the protostellar phase with a molecular jet.

Keywords: star formation; low mass stars; stellar jets; stellar winds; protostars; astrochemistry; stellar mass loss; stellar evolution; young stellar objects; early stellar evolution
Polarization Measurements of Selected Young Stars with Circumstellar Dusty Disks

BVRI polarization measurements of 14 selected young stars with circumstellar dust disks are presented. The interstellar polarization in the direction of these stars is not significant. The observed polarization data and its wavelength-dependence indicate that it is intrinsic, due to scattering by circumstellar, asymmetric dusty disks/envelopes.

Keywords: starlight polarization; circumstellar matter; pre-main sequence stars; herbig ae/be stars; protoplanetary disks
On the Distances to the X-Ray Binaries Cygnus X-3 and GRS 1915+105

In this paper we significantly improve estimates of distance to the X-ray binary systems Cyg X-3 and GRS 1915+105. We report a highly accurate trigonometric parallax measurement for Cyg X-3 using the Very Long Baseline Array at 43 GHz, placing the source at a distance of ${9.67}_{-0.48}^{+0.53}$ kpc. We also use Galactic proper motions and line-of-sight radial velocity measurements to determine three-dimensional (3D) kinematic distances to both systems, under the assumption that they have low peculiar velocities. This yields distances of 8.95 ± 0.96 kpc for Cyg X-3 and 9.4 ± 0.6 (statistical) ± 0.8 (systematic) for GRS 1915+105. The good agreement between parallax and 3D kinematic distances validates the assumption of low peculiar velocities, and hence small natal kicks, for both of the systems. For a source with a low peculiar velocity, given its parallax distance, Cyg X-3 should have a V LSR near -64 ± 5 km s-1. Our measurements imply a slightly higher inclination angle, and hence lower black hole mass, for GRS 1915+105 than found from previous work by Reid et al. and strengthen arguments from X-ray polarization that Cyg X-3 would be an ultraluminous X-ray source if viewed face-on.

Keywords: radio astrometry; x-ray binary stars; very long baseline interferometry; stellar distance
Effects of Photoionization and Photoheating on Lyα Forest Properties from Cholla Cosmological Simulations

The density and temperature properties of the intergalactic medium (IGM) reflect the heating and ionization history during cosmological structure formation, and are primarily probed by the Lyα forest of neutral hydrogen absorption features in the observed spectra of background sources. We present the methodology and initial results from the Cholla IGM Photoheating Simulation (CHIPS) suite performed with the graphics process unit-accelerated Cholla code to study the IGM at high, uniform spatial resolution maintained over large volumes. In this first paper, we examine the IGM structure in CHIPS cosmological simulations that include IGM uniform photoheating and photoionization models where hydrogen reionization is completed early or by redshift z ∼ 6. Comparing with observations of the large- and small-scale Lyα transmitted flux power spectra P(k) at redshifts 2 ≲ z ≲ 5.5, the relative agreement of the models depends on scale, with the self-consistent Puchwein et al. IGM photoheating and photoionization model in good agreement with the flux P(k) at k ≳ 0.01 s km-1 at redshifts 2 ≲ z ≲ 3.5. On larger scales, the P(k) measurements increase in amplitude from z ∼ 4.6 to z ∼ 2.2, faster than the models, and lie in between the model predictions at 2.2 ≲ z ≲ 4.6 for k ≈ 0.002-0.01 s km-1. We argue that the models could improve by changing the He II photoheating rate associated with active galactic nuclei to reduce the IGM temperature at z ∼ 3. At higher redshifts, z ≳ 4.5, the observed flux P(k) amplitude increases at a rate intermediate between the models, and we argue that for models where hydrogen reionization is completed late (z ∼ 5.5-6), resolving this disagreement will require inhomogeneous or "patchy" reionization. We then use an additional set of simulations to demonstrate that our results have numerically converged and are not strongly affected by varying cosmological parameters.

Keywords: computational methods; large-scale structure of the universe; lyman alpha forest; hydrodynamical simulations
Precision of Mass and Radius Determination for Neutron Stars from the ATHENA Mission

In this paper we show that X-ray spectral observations of the ATHENA mission, which is planned to launch in 2031, can constrain the equation of state (EOS) of superdense matter. We use our well-constrained continuum-fitting method to determine the mass and radius of a neutron star. Model spectra of the emission from a neutron star were calculated using the atmosphere code ATM24. In the next step, those models were fitted to simulated spectra of the neutron star calculated for ATHENA's Wide Field Imager (WFI) detector, using satellite calibration files. To simulate the spectra we assumed three different values of effective temperature, surface gravity, and gravitational redshift. These cases relate to three different neutron star masses and radii. This analysis allows us to demonstrate both the precision of our method and the need for a fast detector onboard ATHENA. A large grid of theoretical spectra was calculated with various parameters and a hydrogen-helium-iron composition of solar proportions. These spectra were fitted to the simulated spectrum to estimate the precision of mass and radius determination. In each case, we obtained very precise values with errors in the range 3%-10% for mass and 2%-8% for radius within 1σ confidence. We show here that, with the ATHENA WFI detector, such a determination could be used to constrain the EOS of superdense neutron star matter.

Keywords: neutron stars; compact objects; stellar atmospheres
Ganymede's Surface Properties from Millimeter and Infrared Thermal Emission

We present thermal observations of Ganymede from the Atacama Large Millimeter Array (ALMA) in 2016-2019 at a spatial resolution of 300-900 km (0"1-0"2 angular resolution) and frequencies of 97.5, 233, and 343.5 GHz (wavelengths of 3, 1.3, and 0.87 mm); the observations collectively covered all Ganymede longitudes. We determine the global thermophysical properties using a thermal model that considers subsurface emission and depth- and temperature-dependent thermophysical and dielectric properties, in combination with a retrieval algorithm. The data are sensitive to emission from the upper ∼0.5 m of the surface, and we find a millimeter emissivity of 0.75-0.78 and (sub)surface porosities of 10%-40%, corresponding to effective thermal inertias of 400-800 J m-2 K-1 s-1/2. Combined with past infrared results, as well as modeling presented here of a previously unpublished night-time infrared observation from Galileo's photopolarimeter-radiometer instrument, the multiwavelength constraints are consistent with a compaction profile whereby the porosity drops from ∼85% at the surface to ${10}_{-10}^{+30}{\rm{ \% }}$ at depth over a compaction length scale of tens of centimeters. We present maps of temperature residuals from the best-fit global models, which indicate localized variations in thermal surface properties at some (but not all) dark terrains and at impact craters, which appear 5-8 K colder than the model. Equatorial regions are warmer than predicted by the model, in particular near the centers of the leading and trailing hemispheres, while the midlatitudes (∼30°-60°) are generally colder than predicted; these trends are suggestive of an exogenic origin.

Keywords: galilean satellites; jovian satellites; radio interferometry; planetary surfaces; surface processes
On the Migration Origin of the Hercules Moving Group with GAIA, LAMOST, APOGEE, and GALAH Surveys

Using Gaia DR3 data and the wavelet transformation technique, we study the substructures of the Hercules moving group (HMG): Hercules 1 (H1) and Hercules 2 (H2). Spectroscopic survey data from LAMOST, APOGEE, and GALAH are used to obtain metallicities and ages of stars belonging to the HMG. Our analysis leads to several key findings as follows: (a) the HMG is on average richer in metallicity than the Galactic disk, with H2 being metal richer than H1; (b) the HMG likely has a radial metallicity gradient distinct from that of the disk; (c) the HMG is on average older than the disk, with H2 being older than H1; (d) the HMG likely has a radial age gradient distinct from that of the disk; and (e) the metallicity and age distributions of the HMG depend mainly on the Galactic radius but show no dependence on the azimuthal velocity. Taken all together, we conclude that the HMG is composed primarily of stars undergoing radial migration. We suggest that the HMG is associated with a higher-order dynamical resonance of the bar of the Galaxy.

Keywords: stellar kinematics; metallicity; milky way dynamics