adsabs/SciX_UAT_keywords huggingface dataset:
Pulsation-driven Mass Loss from Massive Stars behind Stellar Mergers in Metal-poor Dense Clusters

The recent discovery of high-redshift (z > 6) supermassive black holes (SMBH) favors the formation of massive seed BHs in protogalaxies. One possible scenario is the formation of massive stars $\simeq {10}^{3}\mbox{--}{10}^{4}\,{M}_{\odot }$ via runaway stellar collisions in a dense cluster, leaving behind massive BHs without significant mass loss. We study the pulsational instability of massive stars with the zero-age main-sequence (ZAMS) mass ${M}_{\mathrm{ZAMS}}/{M}_{\odot }=300\mbox{--}3000$ and metallicity $Z/{Z}_{\odot }=0\mbox{--}{10}^{-1}$ , and discuss whether or not pulsation-driven mass loss prevents massive BH formation. In the MS phase, the pulsational instability excited by the ɛ-mechanism grows in $\sim {10}^{3}\,\mathrm{yr}$ . As the stellar mass and metallicity increase, the mass-loss rate increases to $\lesssim {10}^{-3}\ {M}_{\odot }\,{\mathrm{yr}}^{-1}$ . In the red supergiant (RSG) phase, the instability is excited by the κ-mechanism operating in the hydrogen ionization zone and grows more rapidly in $\sim 10\,\mathrm{yr}$ . The RSG mass-loss rate is almost independent of metallicity and distributes in the range of $\sim {10}^{-3}\mbox{--}{10}^{-2}\ {M}_{\odot }\,{\mathrm{yr}}^{-1}$ . Conducting stellar structure calculations including feedback due to pulsation-driven winds, we find that the stellar models of ${M}_{\mathrm{ZAMS}}/{M}_{\odot }=300\mbox{--}3000$ can leave behind remnant BHs more massive than $\sim 200\mbox{--}1200\ {M}_{\odot }$ . We conclude that massive merger products can seed monster SMBHs observed at z > 6.

Keywords: stellar evolution; population iii stars; population ii stars
Detection of the 511 keV Galactic Positron Annihilation Line with COSI

The signature of positron annihilation, namely the 511 keV γ-ray line, was first detected coming from the direction of the Galactic center in the 1970s, but the source of Galactic positrons still remains a puzzle. The measured flux of the annihilation corresponds to an intense steady source of positron production, with an annihilation rate on the order of ∼1043 ${\text{}}{e}^{+}\,{{\rm{s}}}^{-1}$ . The 511 keV emission is the strongest persistent Galactic γ-ray line signal, and it shows a concentration toward the Galactic center region. An additional low-surface brightness component is aligned with the Galactic disk; however, the morphology of the latter is not well constrained. The Compton Spectrometer and Imager (COSI) is a balloon-borne soft γ-ray (0.2-5 MeV) telescope designed to perform wide-field imaging and high-resolution spectroscopy. One of its major goals is to further our understanding of Galactic positrons. COSI had a 46-day balloon flight in 2016 May-July from Wanaka, New Zealand, and here we report on the detection and spectral and spatial analyses of the 511 keV emission from those observations. To isolate the Galactic positron annihilation emission from instrumental background, we have developed a technique to separate celestial signals using the COMPTEL Data Space. With this method, we find a 7.2σ detection of the 511 keV line. We find that the spatial distribution is not consistent with a single point source, and it appears to be broader than what has previously been reported.

Keywords: high altitude balloons; gamma-ray lines; gamma-ray telescopes; spectroscopy; galactic center; astronomy data modeling
From Starspots to Stellar Coronal Mass Ejections—Revisiting Empirical Stellar Relations

Upcoming missions, including the James Webb Space Telescope, will soon characterize the atmospheres of terrestrial-type exoplanets in habitable zones around cool K- and M-type stars by searching for atmospheric biosignatures. Recent observations suggest that the ionizing radiation and particle environment from active cool planet hosts may be detrimental to exoplanetary habitability. Since no direct information on the radiation field is available, empirical relations between signatures of stellar activity, including the sizes and magnetic fields of starspots, are often used. Here, we revisit the empirical relation between the starspot size and the effective stellar temperature and evaluate its impact on estimates of stellar flare energies, coronal mass ejections, and fluxes of the associated stellar energetic particle events.

Keywords: starspots; solar energetic particles; stellar coronal mass ejections
The Next Generation Virgo Cluster Survey (NGVS). XXX. Ultra-diffuse Galaxies and Their Globular Cluster Systems

We present a study of ultra-diffuse galaxies (UDGs) in the Virgo Cluster based on deep imaging from the Next Generation Virgo Cluster Survey. Applying a new definition for the UDG class based on galaxy scaling relations, we define samples of 44 and 26 UDGs using expansive and restrictive selection criteria, respectively. Our UDG sample includes objects that are significantly fainter than previously known UDGs: i.e., more than half are fainter than $\langle \mu {\rangle }_{e}\sim 27.5$ mag arcsec-2. The UDGs in Virgo's core region show some evidence for being structurally distinct from "normal" dwarf galaxies, but this separation disappears when considering the full sample of galaxies throughout the cluster. UDGs are more centrally concentrated in their spatial distribution than other Virgo galaxies of similar luminosity, while their morphologies demonstrate that at least some UDGs owe their diffuse nature to physical processes—such as tidal interactions or low-mass mergers—that are at play within the cluster environment. The globular cluster (GC) systems of Virgo UDGs have a wide range in specific frequency (SN), with a higher mean SN than "normal" Virgo dwarfs, but a lower mean SN than Coma UDGs at fixed luminosity. Their GCs are predominantly blue, with a small contribution from red clusters in the more massive UDGs. The combined GC luminosity function is consistent with those observed in dwarf galaxies, showing no evidence of being anomalously luminous. The diversity in their morphologies and their GC properties suggests no single process has given rise to all objects within the UDG class. Based on the available evidence, we conclude that UDGs are simply those systems that occupy the extended tails of the galaxy size and surface brightness distributions.

Keywords: dwarf galaxies; early-type galaxies; low surface brightness galaxies; globular star clusters; nucleated dwarf galaxies
OO Dra: An Algol-type Binary Formed through an Extremely Helium-poor Mass Accretion Revealed by Asteroseismology

Based on 2 minutes of Transiting Exoplanet Survey Satellite data, we analyzed intrinsic oscillations of the primary component and identified seven confident independent δ Scuti frequencies (f1, f2, f3, f4, f7, f11, and f12). Both single-star evolutionary models and mass-accreting models are computed to reproduce the δ Scuti frequencies and the fitting results match well with each other. The stellar parameters of the primary star yielded by asteroseismology are M = ${1.92}_{-0.02}^{+0.10}$ M⊙, Z = ${0.011}_{-0.001}^{+0.006}$ , R = ${2.068}_{-0.007}^{+0.050}$ R⊙, $\mathrm{log}g$ = ${4.090}_{-0.002}^{+0.010}$ , Teff = ${8346}_{-320}^{+244}$ K, and L = ${18.65}_{-2.82}^{+3.31}$ L⊙, which match well with the dynamic ones using the binary model. Furthermore, our asteroseismic results show that OO Dra is another Algol system that has just undergone the rapid mass-transfer stage. The fitting results of single-star evolutionary models indicate that the pulsator is a helium-poor star with an age of ${8.22}_{-1.33}^{+0.12}$ Myr, and the further mass-accreting models show that the primary star looks like an almost unevolved star formed by an extremely helium-poor mass accretion in the Case A evolutionary scenario.

Keywords: eclipsing binary stars; delta scuti variable stars; asteroseismology
Effects of Dust Evolution on the Vertical Shear Instability in the Outer Regions of Protoplanetary Disks

Vertical shear instability (VSI) is a hydrodynamical instability that requires rapid gas cooling and has been suggested to operate in outer regions of protoplanetary disks. VSI drives turbulence with strong vertical motions, which could regulate dust growth and settling. However, dust growth and settling can regulate the VSI because dust depletion makes gas cooling inefficient in outer disk regions that are optically thin to their own thermal emission. In this study, we quantify these potentially stabilizing effects of dust evolution on the VSI based on linear analysis. We construct a model for calculating the cooling timescale, taking into account dust growth beyond micron sizes and size-dependent settling. Combining the model with linear stability analysis, we map the region where the VSI operates, which we call the VSI zone, and estimate the maximum growth rate at each radial position. We find that dust growth, as well as settling, makes the VSI zone more confined around the midplane. This causes a decrease in the growth rate because the vertical shear of the rotation velocity, which is the source of the instability, is weaker at lower altitudes. In our default disk model with 0.01 solar masses, dust growth from 10 μm to 1 mm causes a decrease in the growth rate by a factor of more than 10. The suppression of VSI-driven turbulence by dust evolution may promote further dust evolution in the outer regions and also explain the high degree of dust settling observed in the disk around HL Tau.

Keywords: protoplanetary disks; planetesimals
A Multiwavelength Study of GRS 1716-249 in Outburst: Constraints on Its System Parameters

We present a detailed study of the evolution of the Galactic black hole transient GRS 1716-249 during its 2016-2017 outburst at optical (Las Cumbres Observatory), mid-infrared (Very Large Telescope), near-infrared (Rapid Eye Mount telescope), and ultraviolet (the Neil Gehrels Swift Observatory Ultraviolet/Optical Telescope) wavelengths, along with archival radio and X-ray data. We show that the optical/near-infrared and UV emission of the source mainly originates from a multi-temperature accretion disk, while the mid-infrared and radio emission are dominated by synchrotron emission from a compact jet. The optical/UV flux density is correlated with the X-ray emission when the source is in the hard state, consistent with an X-ray irradiated accretion disk with an additional contribution from the viscous disk during the outburst fade. We find evidence for a weak, but highly variable jet component at mid-infrared wavelengths. We also report the long-term optical light curve of the source and find that the quiescent ${i}^{{\prime} }$ -band magnitude is 21.39 ± 0.15 mag. Furthermore, we discuss how previous estimates of the system parameters of the source are based on various incorrect assumptions, and so are likely to be inaccurate. By comparing our GRS 1716-249 data set to those of other outbursting black hole X-ray binaries, we find that while GRS 1716-249 shows similar X-ray behavior, it is noticeably optically fainter, if the literature distance of 2.4 kpc is adopted. Using several lines of reasoning, we argue that the source distance is further than previously assumed in the literature, likely within 4-17 kpc, with a most likely range of ~4-8 kpc.

Keywords: astrophysical black holes; accretion; jets; x-ray binary stars; low-mass x-ray binary stars; black hole physics
The Faint End of the Quasar Luminosity Function at z ∼ 5 from the Subaru Hyper Suprime-Cam Survey

We present the quasar luminosity function at z ∼ 5 derived from the optical wide-field survey data obtained as a part of the Subaru strategic program (SSP) with the Hyper Suprime-Cam (HSC). From a ∼81.8 deg2 area in the Wide layer of the HSC-SSP survey, we selected 224 candidates of low-luminosity quasars at z ∼ 5 by adopting the Lyman-break method down to i = 24.1 mag. Based on our candidates and spectroscopically confirmed quasars from the Sloan Digital Sky Survey (SDSS), we derived the quasar luminosity function at z ∼ 5, covering a wide luminosity range of -28.76 < M1450 < -22.32 mag. We found that the quasar luminosity function is fitted by a double power-law model with a break magnitude of ${M}_{1450}^{* }=-{25.05}_{-0.24}^{+0.10}$ mag. The inferred number density of low-luminosity quasars is lower, and the derived faint-end slope, $-{1.22}_{-0.10}^{+0.03}$ , is flatter than those of previous studies at z ∼ 5. A compilation of the quasar luminosity function at 4 ≤ z ≤ 6 from the HSC-SSP suggests that there is little redshift evolution in the break magnitude and in the faint-end slope within this redshift range, although previous studies suggest that the faint-end slope becomes steeper at higher redshifts. The number density of low-luminosity quasars decreases more rapidly from z ∼ 5 to z ∼ 6 than from z ∼ 4 to z ∼ 5.

Keywords: quasars; supermassive black holes; luminosity function; active galaxies
Ultra-deep Keck/MOSFIRE Spectroscopic Observations of z 2 Galaxies: Direct Oxygen Abundances and Nebular Excitation Properties

Using deep near-infrared Keck/MOSFIRE observations, we analyze the rest-optical spectra of eight star-forming galaxies in the COSMOS and GOODS-N fields. We reach integration times of ~10 hr in the deepest bands, pushing the limits on current ground-based observational capabilities. The targets fall into two redshift bins, of five galaxies at z ~ 1.7 and three galaxies at z ~ 2.5, and were selected as likely to yield significant auroral-line detections. Even with long integration times, detection of the auroral lines remains challenging. We stack the spectra together into subsets based on redshift, improving the signal-to-noise ratio on the [O III]λ4364 auroral emission line and, in turn, enabling a direct measurement of the oxygen abundance for each stack. We compare these measurements to commonly employed strong-line ratios alongside measurements from the literature. We find that the stacks fall within the distribution of z > 1 literature measurements, but a larger sample size is needed to robustly constrain the relationships between strong-line ratios and oxygen abundance at high redshift. We additionally report detections of [O I]λ6302 for nine individual galaxies and composite spectra of 21 targets in the MOSFIRE pointings. We plot their line ratios on the [O III]λ5008/Hβ versus [O I]λ6302/Hα diagnostic diagram, comparing our targets to local galaxies and H II regions. We find that the [O I]/Hα ratios in our sample of galaxies are consistent with being produced in gas ionized by α-enhanced massive stars, as has been previously inferred for rapidly forming galaxies at early cosmic times.

Keywords: galaxies; galaxy evolution; emission line galaxies; interstellar medium; high-redshift galaxies
Generation of Short-scale Electrostatic Fields in the Solar Atmosphere and the Role of Helium Ions

Theoretical models are presented to show that expansion of plasma in the radial direction from a denser solar surface to a rarefied upper atmosphere with short-scale inhomogeneous field-aligned flows and currents in the form of thin threads itself is an important source of electrostatic instabilities. Multifluid theory shows that the shear flow-driven purely growing electric fields appear in the transition region. On the other hand, plasma kinetic theory predicts that the short-scale current sheets (or filaments) produce current-driven electrostatic ion acoustic (CDEIA) waves in the hydrogen plasma of the transition region that damp out in the system through wave-particle interactions and increase the temperature. Similar processes take place in the solar corona and act positively for increasing the temperature further and maintaining it. The shear flow-driven instabilities and CDEIA waves have short perpendicular wavelengths of the order of 1 m and low frequencies of the order of 1 or several Hz when the ions' shear flow scale length is considered to be of the order of 1 km. It is pointed out that the purely growing fluid instabilities turn into oscillatory instabilities and the growth rates of kinetic CDEIA wave instabilities are reduced when the dynamics of 10% helium ions is taken into account along with 90% hydrogen ions. Therefore, the role of helium ions should not be ignored in the study of wave dynamics in solar plasma.

Keywords: solar coronal waves
Physically Motivated Fit to Mass Surface Density Profiles Observed in Galaxies

Polytropes have gained renewed interest because they account for several seemingly disconnected observational properties of galaxies. Here we study whether polytropes are also able to explain the stellar mass distribution within galaxies. We develop a code to fit surface density profiles using polytropes projected in the plane of the sky (propols). Sérsic profiles are known to be good proxies for the global shapes of galaxies and we find that, ignoring central cores, propols, and Sérsic profiles are indistinguishable within observational errors (within 5% over five orders of magnitude in surface density). The range of physically meaningful polytropes yields Sérsic indexes between 0.4 and 6. The code has been systematically applied to ~750 galaxies with carefully measured mass density profiles and including all morphological types and stellar masses ( $7\lt {\rm{log}}[{M}_{\star }/{{\rm{M}}}_{\odot }]\lt 12$ ). The propol fits are systematically better than Sérsic profiles when ${\rm{log}}({M}_{\star }/{{\rm{M}}}_{\odot })\lesssim 9$ and systematically worse when ${\rm{log}}({M}_{\star }/{{\rm{M}}}_{\odot })\gtrsim 10$ . Although with large scatter, the observed polytropic indexes increase with increasing mass and tend to cluster around m = 5. For the most massive galaxies, propols are very good at reproducing their central parts, but they do not handle well cores and outskirts overall. Polytropes are self-gravitating systems in thermal meta-equilibrium as defined by the Tsallis entropy. Thus, the above results are compatible with the principle of maximum Tsallis entropy dictating the internal structure in dwarf galaxies and in the central region of massive galaxies.

Keywords: gravitational equilibrium; galaxy dark matter halos; galaxy structure; galaxy stellar halos; milky way formation; galaxy properties; galaxy physics
Radius-dependent Spin Transition of Dark Matter Halos

A numerical detection of the radius-dependent spin transition of dark matter halos is reported. Analyzing the data from the IllustrisTNG simulations, we measure the halo spin vectors at several inner radii within the virial boundaries and investigate their orientations in the principal frames of the tidal and velocity shear fields, called the Tweb and Vweb, respectively. The halo spin vectors in the high-mass section exhibit a transition from the Tweb intermediate to major principal axes as they are measured at more inner radii, which holds for both the dark matter and baryonic components. The radius threshold at which the transition occurs depends on the smoothing scale, R f , becoming larger as R f decreases. For the case of the Vweb, the occurrence of the radius-dependent spin transition is witnessed only when R f ≥ 1 h -1 Mpc. Repeating the same analysis but with the vorticity vectors, we reveal a critical difference from the spins. The vorticity vectors are always perpendicular to the Tweb (Vweb) major principal axes, regardless of R f , which indicates that the halo inner spins are not strongly affected by the generation of vorticity. It is also shown that the halo spins, as well as the Tweb (Vweb) principal axes, have more directional coherence over a wide range of radial distances in the regions where the vorticity vectors have higher magnitudes. The physical interpretations and implications of our results are discussed.

Keywords: cosmology; large-scale structure of the universe
TESS Hunt for Young and Maturing Exoplanets (THYME). VII. Membership, Rotation, and Lithium in the Young Cluster Group-X and a New Young Exoplanet

The public, all-sky surveys Gaia and TESS provide the ability to identify new young associations and determine their ages. These associations enable study of planetary evolution by providing new opportunities to discover young exoplanets. A young association was recently identified by Tang et al. and Fürnkranz et al. using astrometry from Gaia (called "Group-X" by the former). In this work, we investigate the age and membership of this association, and we validate the exoplanet TOI 2048 b, which was identified to transit a young, late G dwarf in Group-X using photometry from TESS. We first identified new candidate members of Group-X using Gaia EDR3 data. To infer the age of the association, we measured rotation periods for candidate members using TESS data. The clear color-period sequence indicates that the association is the same age as the 300 ± 50 Myr old NGC 3532. We obtained optical spectra for candidate members that show lithium absorption consistent with this young age. Further, we serendipitously identify a new, small association nearby Group-X, which we call MELANGE-2. Lastly, we statistically validate TOI 2048 b, which is a 2.1 ± 0.2 R ⊕ radius planet on a 13.8-day orbit around its 300 Myr old host star.

Keywords: young star clusters; stellar rotation; exoplanets
Discovery of a Candidate Hypervelocity Star Originating from the Sagittarius Dwarf Spheroidal Galaxy

In this Letter, we report the discovery of an intriguing hypervelocity star (HVS; J1443+1453) candidate that is probably from the Sagittarius Dwarf Spheroidal galaxy (Sgr dSph). The star is an old and very metal-poor low-mass main-sequence turn-off star (age ∼14.0 Gyr and [Fe/H] = -2.23 dex) and has a total velocity of ${559.01}_{-87.40}^{+135.07}$ km s-1 in the Galactic rest frame and a heliocentric distance of ${2.90}_{-0.48}^{+0.72}$ kpc. The velocity of J1443+1453 is larger than the escape speed at its position, suggesting that it is a promising HVS candidate. By reconstructing its trajectory in the Galactic potential, we find that the orbit of J1443+1453 intersects closely with that of Sgr dSph ${37.8}_{-6.0}^{+4.6}$ Myr ago, when the latter has its latest pericentric passage through the Milky Way. The encounter occurs at a distance ${2.42}_{-0.77}^{+1.80}$ kpc from the center of Sgr dSph, a distance that is smaller than the size of the Sgr dSph. The chemical properties of this star are also consistent with those of an Sgr dSph-associated globular cluster, or of the Sgr stream member stars. Our finding suggests that J1443+1453 is an HVS that is either tidally stripped from the Sgr dSph or ejected from the Sgr dSph by the gravitational slingshot effect, requiring a (central) massive/intermediate-mass black hole or a (central) massive primordial black hole in the Sgr dSph.

Keywords: hypervelocity stars; galaxy kinematics; sagittarius dwarf spheroidal galaxy; galaxy stellar halos; chemical abundances
The Spatial Distribution of Type Ia Supernovae within Host Galaxies

We study how type Ia supernovae (SNe Ia) are spatially distributed within their host galaxies, using data taken from the Sloan Digital Sky Survey (SDSS). This paper specifically tests the hypothesis that the SNe Ia rate traces the r-band light of the morphological component to which supernovae belong. A sample of supernovae is taken from the SDSS SN Survey, and host galaxies are identified. Each host galaxy is decomposed into a bulge and disk, and the distribution of supernovae is compared to the distribution of disk and bulge light. Our methodology is relatively unaffected by seeing. We find that, in galaxies dominated by disk light, SNe Ia trace light closely. The situation is less clear for bulges and ellipticals, because of resolution effects, but the available evidence is also consistent with the hypothesis that bulge/elliptical SNe Ia follow light.

Keywords: type ia supernovae; galaxies; galaxy structure; transient sources