adsabs/SciX_UAT_keywords huggingface dataset:
Investigating the Impact of Metallicity on Star Formation in the Outer Galaxy. I. VLT/KMOS Survey of Young Stellar Objects in Canis Major

The effects of metallicity on the evolution of protoplanetary disks may be studied in the outer Galaxy where the metallicity is lower than in the solar neighborhood. We present the VLT/KMOS integral field spectroscopy in the near-infrared of ~120 candidate young stellar objects (YSOs) in the CMa-ℓ224 star-forming region located at a Galactocentric distance of 9.1 kpc. We characterize the YSO accretion luminosities and accretion rates using the hydrogen Brγ emission and find a median accretion luminosity of $\mathrm{log}({L}_{\mathrm{acc}})=-{0.82}_{-0.82}^{+0.80}{L}_{\odot }$ . Based on the measured accretion luminosities, we investigate the hypothesis of star formation history in the CMa-ℓ224. Their median values suggest that Cluster C, where most of YSO candidates have been identified, might be the most evolved part of the region. The accretion luminosities are similar to those observed toward low-mass YSOs in the Perseus and Orion molecular clouds, and they do not reveal the impact of lower metallicity. Similar studies in other outer Galaxy clouds covering a wide range of metallicities are critical to gain a complete picture of star formation in the Galaxy.

Keywords: star forming regions
Lithium Abundances in Giants as a Function of Stellar Mass: Evidence for He Flash as the Source of Li Enhancement in Low-mass Giants

In this work, we studied the distribution of lithium abundances in giants as a function of stellar mass. We used a sample of 1240 giants common among Kepler photometric and LAMOST medium-resolution (R ≈ 7500) spectroscopic survey fields. The asteroseismic ΔP-Δν diagram is used to define core He-burning red clump giants and red giant branch stars with an inert He core. Li abundances have been derived using spectral synthesis for all sample stars. Directly measured values of asteroseismic parameters ΔP (or ΔΠ1) and Δν are either taken from the literature or measured in this study. Of the 777 identified red clump giants, we found 668 low-mass (≤2 M ⊙) primary red clump giants and 109 high-mass (>2 M ⊙) secondary red clump giants. Observed Li abundances in secondary red clump giants agree with the theoretical model predictions. The lack of Li-rich giants among secondary red clump giants and the presence of Li-rich, including super Li-rich, giants among primary red clump stars reinforces the idea that helium flash holds the key for Li enrichment among low-mass giants. The results will further constrain theoretical models searching for a physical mechanism for Li enhancement among low-mass red clump giants. Results also serve as observational evidence that only giants with mass less than ≈2 M ⊙ develop a degenerate He core and undergo He flash.

Keywords: stellar abundances; red giant clump; helium burning; asteroseismology
UV-bright Star-forming Clumps and Their Host Galaxies in UVCANDELS at 0.5 ≤ z ≤ 1

Giant star-forming clumps are a prominent feature of star-forming galaxies (SFGs) and contain important clues on galaxy formation and evolution. However, the basic demographics of clumps and their host galaxies remain uncertain. Using the Hubble Space Telescope/Wide Field Camera 3 F275W images from the Ultraviolet Imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, we detect and analyze giant star-forming clumps in galaxies at 0.5 ≤ z ≤ 1, connecting two epochs when clumps are common (at cosmic high noon, z ~ 2) and rare (in the local Universe). We construct a clump sample whose rest-frame 1600 Å luminosity is 3 times higher than the most luminous local H II regions (M UV ≤ -16 AB). In our sample, 35% ± 3% of low-mass galaxies (log[M ∗/M ⊙] < 10) are clumpy (i.e., containing at least one off-center clump). This fraction changes to 22% ± 3% and 22% ± 4% for intermediate (10 ≤ log[M ∗/M ⊙] ≤ 10.5) and high-mass (log[M ∗/M ⊙] > 10.5) galaxies, in agreement with previous studies. When compared to similar-mass nonclumpy SFGs, low- and intermediate-mass clumpy SFGs tend to have higher star formation rates (SFRs) and bluer rest-frame U - V colors, while high-mass clumpy SFGs tend to be larger than nonclumpy SFGs. However, clumpy and nonclumpy SFGs have similar Sérsic index, indicating a similar underlying density profile. Furthermore, we investigate how the UV luminosity of star-forming regions correlates with the physical properties of host galaxies. On average, more luminous star-forming regions reside in more luminous, smaller, and/or higher specific SFR galaxies and are found closer to their hosts' galactic centers.

Keywords: galaxy evolution; galaxy formation; starburst galaxies; star forming regions; galaxy structure; galaxy properties
Variations in Line Profiles of Atomic Transitions in RR Lyrae Stars

We have investigated the absorption shapes of atomic lines and Hα in RR Lyrae stars. We used the database of high-resolution spectra gathered with the Las Campanas Observatory du Pont Telescope, analyzing a set of about 2700 short exposure spectra of 17 RRab and 5 RRc variables. To increase the signal-to-noise ratio of the spectra for each star, we first coadded spectra in small photometric phase bins, and then coadded metallic line profiles in velocity space. The resulting line absorption shapes vary with photometric phase in a consistent manner for all RRab stars, while exhibiting no obvious phase-related variations for the RRc stars. We interpret these line profile variations in terms of velocity gradients in the photospheric layers that produce absorption line profiles. The Hα profiles are much broader, indicative of shock temperatures of order 100,000 K.

Keywords: rrab variable stars; rrc variable stars; stellar abundances; stellar atmospheres
Amplification and Saturation of Turbulent Magnetic Fields in Collapsing Primordial Gas Clouds

Recent numerical studies suggest that magnetic fields play an important role in primordial star formation in the early Universe. However, the detailed evolution of the magnetic field in the collapse phase still has uncertainties because of the complicated physics associated with turbulence in a collapsing magnetized system. Here, we perform a suite of numerical MHD simulations that follow the collapse of magnetized, turbulent primordial gas clouds to investigate the evolution of the magnetic field associated with the turbulence, assuming a polytropic equation of state with exponent γ eff and with various numerical resolutions. In addition, we generalize the analytic theory of magnetic field growth/saturation so that it can deal with various exponents γ eff and turbulence energy spectra. We find that the numerical results are well reproduced by the theory for various γ eff through the collapse phase during the formation of the first stars. The magnetic field is eventually amplified by a factor of 1012–1015 due to kinematic and nonlinear turbulent dynamo effects and reaches 3%–100% of the equipartition level, depending on γ eff. We also find that the transition between the kinematic and nonlinear stages can be analytically estimated. These results indicate that the strong magnetic field accompanied by supersonic turbulence is a general property and suggest that it can play a crucial role in the formation of the first stars.

Keywords: early universe; magnetohydrodynamical simulations; collapsing clouds; population iii stars; magnetic fields; hydrodynamics
Tidal Disruption Events from Eccentric Orbits and Lessons Learned from the Noteworthy ASASSN-14ko

Stars grazing supermassive black holes (SMBHs) on bound orbits may survive tidal disruption, causing periodic flares. Inspired by the recent discovery of the periodic nuclear transient ASASSN-14ko, a promising candidate for a repeating tidal disruption event (TDE), we study the tidal deformation of stars approaching SMBHs on eccentric orbits. With both analytical and hydrodynamic methods, we show the overall tidal deformation of a star is similar to that in a parabolic orbit provided that the eccentricity is above a critical value. This allows one to make use of existing simulation libraries from parabolic encounters to calculate the mass fallback rate in eccentric TDEs. We find the flare structures of eccentric TDEs show a complicated dependence on both the SMBH mass and the orbital period. For stars orbiting SMBHs with relatively short periods, we predict significantly shorter-lived duration flares than those in parabolic TDEs, which can be used to predict repeating events if the mass of the SMBH can be independently measured. Using an adiabatic mass-loss model, we study the flare evolution over multiple passages, and show the evolved stars can survive many more passages than main-sequence stars. We apply this theoretical framework to the repeating TDE candidate ASASSN-14ko and suggest that its recurrent flares originate from a moderately massive (M ≳ 1 M ⊙), extended (likely ≈10 R ⊙), evolved star on a grazing, bound orbit around the SMBH. Future hydrodynamic simulations of multiple tidal interactions will enable realistic models on the individual flare structure and the evolution over multiple flares.

Keywords: supermassive black holes; galaxy nuclei; tidal disruption
Synthesizing Stellar Populations in South Pole Telescope Galaxy Clusters. I. Ages of Quiescent Member Galaxies at 0.3 < z < 1.4

Using stellar population synthesis models to infer star formation histories (SFHs), we analyze photometry and spectroscopy of a large sample of quiescent galaxies that are members of Sunyaev-Zel'dovich (SZ)-selected galaxy clusters across a wide range of redshifts. We calculate stellar masses and mass-weighted ages for 837 quiescent cluster members at 0.3 < z < 1.4 using rest-frame optical spectra and the Python-based Prospector framework, from 61 clusters in the SPT-GMOS Spectroscopic Survey (0.3 < z < 0.9) and three clusters in the SPT Hi-z cluster sample (1.25 < z < 1.4). We analyze spectra of subpopulations divided into bins of redshift, stellar mass, cluster mass, and velocity-radius phase-space location, as well as by creating composite spectra of quiescent member galaxies. We find that quiescent galaxies in our data set sample a diversity of SFHs, with a median formation redshift (corresponding to the lookback time from the redshift of observation to when a galaxy forms 50% of its mass, t 50) of z = 2.8 ± 0.5, which is similar to or marginally higher than that of massive quiescent field and cluster galaxy studies. We also report median age-stellar mass relations for the full sample (age of the universe at t 50 (Gyr) = 2.52 (±0.04)-1.66 (±0.12) log10(M/1011 M ⊙)) and recover downsizing trends across stellar mass; we find that massive galaxies in our cluster sample form on aggregate ~0.75 Gyr earlier than lower-mass galaxies. We also find marginally steeper age-mass relations at high redshifts, and report a bigger difference in formation redshifts across stellar mass for fixed environment, relative to formation redshifts across environment for fixed stellar mass.

Keywords: high-redshift galaxy clusters; quenched galaxies; galaxy spectroscopy; spectral energy distribution; galaxy evolution; galaxy quenching
An 600 pc View of the Strongly Lensed, Massive Main-sequence Galaxy J0901: A Baryon-dominated, Thick Turbulent Rotating Disk with a Clumpy Cold Gas Ring at z = 2.259

We present a high-resolution kinematic study of the massive main-sequence star-forming galaxy (SFG) SDSS J090122.37+181432.3 (J0901) at z = 2.259, using ~0.″36 Atacama Large Millimeter/submillimeter Array CO(3-2) and ~0.″1-0.″5 SINFONI/VLT Hα observations. J0901 is a rare, strongly lensed but otherwise normal massive ( $\mathrm{log}({M}_{\star }/{M}_{\odot })\sim 11$ ) main-sequence SFG, offering a unique opportunity to study a typical massive SFG under the microscope of lensing. Through forward dynamical modeling incorporating lensing deflection, we fit the CO and Hα kinematics in the image plane out to about one disk effective radius (R e ~ 4 kpc) at an ~600 pc delensed physical resolution along the kinematic major axis. Our results show high intrinsic dispersions of the cold molecular and warm ionized gas (σ 0,mol. ~ 40 km s-1 and σ 0,ion. ~ 66 km s-1) that remain constant out to R e; a moderately low dark matter fraction (f DM ~ 0.3-0.4) within R e; and a centrally peaked Toomre Q parameter-agreeing well with the previously established σ 0 versus z, f DM versus Σbaryon, and Q's radial trends using large-sample non-lensed main-sequence SFGs. Our data further reveal a high stellar mass concentration within ~1-2 kpc with little molecular gas, and a clumpy molecular gas ring-like structure at R ~ 2-4 kpc, in line with the inside-out quenching scenario. Our further analysis indicates that J0901 had assembled half of its stellar mass only ~400 Myr before its observed cosmic time, and the cold gas ring and dense central stellar component are consistent with signposts of a recent wet compaction event of a highly turbulent disk found in recent simulations.

Keywords: galaxy kinematics; high-redshift galaxies; strong gravitational lensing; dark matter; molecular gas
Variability of Magnetically Dominated Jets from Accreting Black Holes

Structured jets have recently been invoked to explain the complex emission of gamma-ray bursts (GRBs), such as GW170817. Based on accretion simulations, the jets are expected to have a structure that is more complex than a simple top-hat structure. Also, the structure of the launch regions of blazar jets should influence their large-scale evolution. This was recently revealed by the interactions of jet components in TXS 0506+056, where the jet was observed at a viewing angle close to zero. Observational studies have also shown an anticorrelation between the jet variability, measured, e.g., by its minimum variability timescale, and the Lorentz factor, which spans several orders of magnitude and covers both blazars and GRBs samples. Motivated by those observational properties of black hole sources, we investigate the accretion inflow and outflow properties by means of numerical gamma-ray MHD simulations. We perform axisymmetric calculations of the structure and evolution of a central engine, composed of a magnetized torus around a Kerr black hole that is launching a nonuniform jet. We probe the jet energetics at different points along the line of sight, and we measure the jet-time variability as localized in these specific regions. We quantify our results by computing the minimum variability timescales and power density spectra. We reproduce the MTS-Γ correlation and we attribute it to the black hole's spin as the main driving parameter of the engine. We also find that the power density spectral slope is not strongly affected by the black hole's spin, while it differs for various viewing angles.

Keywords: magnetic fields; kerr black holes; accretion; magnetohydrodynamics; gamma-ray bursts; blazars; relativistic jets
Acceleration and Release of Solar Energetic Particles Associated with a Coronal Shock on 2021 September 28 Observed by Four Spacecraft

The main driver of the acceleration of solar energetic particles (SEPs) is believed to be shocks driven by coronal mass ejections. Extreme-ultraviolet (EUV) waves are thought to be the propagating footprint of the shock on the solar surface. One of the key questions in SEP research is the timing of the SEP release with respect to the time when the EUV wave magnetically connects with an observer. Taking advantage of close-to-the-Sun measurements by Parker Solar Probe (PSP) and Solar Orbiter (SolO), we investigate an SEP event that occurred on 2021 September 28 and was observed at different locations by SolO, PSP, STEREO-A, and near-Earth spacecraft. During this time, SolO, PSP, and STEREO-A shared similar nominal magnetic footpoints relative to the SEP source region but were at different heliocentric distances. We find that the SEP release times estimated at these four locations were delayed compared to the times when the EUV wave intercepted the footpoints of the nominal magnetic fields connecting to each spacecraft by around 30–60 minutes. Combining observations in multiple wavelengths of radio, white light, and EUV with a geometrical shock model, we analyze the associated shock properties and discuss the acceleration and delayed release processes of SEPs in this event as well as the accuracy and limitations of using EUV waves to determine the SEP acceleration and release times.

Keywords: solar coronal mass ejections; solar energetic particles; solar coronal mass ejection shocks
Regolith Inhibits Salt and Ice Crystallization in Mg(ClO4)2 Brine, Implying More Persistent and Potentially Habitable Brines on Mars

On Mars, liquid water may form in regolith when perchlorate salts absorb water vapor and dissolve into brine, or when ice-salt mixtures reach their melting temperature and thaw. Brines created in this way can chemically react with minerals, alter the mechanical properties of regolith, mobilize salts in the soil, and potentially create habitable environments. Although Martian brines would exist in contact with regolith, few studies have investigated how regolith alters the formation and stability of brines at Mars-relevant conditions. To fill this gap, we studied magnesium perchlorate brine in a Martian regolith simulant at salt concentrations up to 5.8 wt.%. We measured the water mass fraction and water activity between 3 and 98% relative humidity at 25 °C using the isopiestic method, and monitored salt and ice crystallization between -150 °C and 20 °C with differential scanning calorimetry. Results show that regolith inhibits salt and ice crystallization, allowing water to form and persist at much colder and drier conditions than pure brine. Remarkably, in several samples, neither salt nor ice crystallized at any conditions. These results suggest that brines could exist in regolith for longer periods of the Martian year than previously thought, and could persist indefinitely under certain conditions. By retaining water, inhibiting salt and ice crystallization, and maintaining habitable water activity, briny regolith may be a more favorable environment for life than pure brine alone. These findings indicate the critical importance of brine-regolith interactions for understanding the properties, evolution, and potential habitability of Mars's surface.

Keywords: regolith; surface processes; mars; planetary surfaces
CO Emission Delineating the Interface between the Milky Way Nuclear Wind Cavity and the Gaseous Disk

Based on the MWISP survey, we study high-z CO emission toward the tangent points, in which the distances of the molecular clouds (MCs) are well determined. In the region of l = 12°-26° and ∣b∣ ≲ 5.°1, a total of 321 MCs with ∣z∣ ≳ 110 pc are identified, of which nearly 30 extreme high-z MCs (EHMCs at ∣z∣ ≳ 260 pc) are concentrated in a narrow region of R GC ~ 2.6-3.1 kpc. The EHMC concentrations, together with other high-z MCs at R GC ≲ 2.3-2.6 kpc, constitute molecular crater-wall structures surrounding the edges of the H I voids that are physically associated with the Fermi bubbles. Intriguingly, some large high-z MCs, which lie in the crater walls above and below the Galactic plane, show cometary structures with the head toward the plane, favoring the scenario that the entrained molecular gas moves with the multiphase flows from the plane to the high-z regions. We suggest that the Milky Way nuclear wind has a significant impact on the Galactic gaseous disk. The powerful nuclear wind at ~3-6 Myr ago is likely responsible for the observational features: (1) the enhanced CO gas lying in the edges of the H I voids, (2) the deficiency of atomic and molecular gas within R GC ≲ 3 kpc, (3) the possible connection between the EHMC concentrations and the 3 kpc arm, and (4) the elongated high-z MCs with the tail pointing away from the Galactic plane.

Keywords: interstellar medium; molecular clouds; galactic winds; milky way disk; interstellar dynamics; stellar feedback
Short-exposure Image Reconstruction with The Power Spectrum Extended (PSE) Method

We analyze, in the framework of high angular resolution imaging, a novel image reconstruction method denoted as PSE (which stands for power spectrum extended). It works in the Fourier space, combining the information from both the average power spectrum of the images and a phase estimation from an ad-hoc shift-and-add process. PSE allows to perform image reconstruction up to the diffraction limit of the telescope from a series of short-exposure frames, with a refined lucky-imaging selection process. The method is well adapted to partially corrected adaptive-optics images, in particular in case of low Strehl corrections, and/or small diameter telescopes. In this paper we analyze the PSE technique by means of Monte-Carlo simulations and compare it with the ISFAS lucky-imaging method. Comparative performances were investigated using three metrics: Strehl ratio for reconstructed point-like sources, intensity ratio for binary stars, and least-square distance between images for a simulated artificial satellite. We found that PSE provides an improvement of a factor ~2 over ISFAS on the Strehl ratio in the case of faint point sources. It seems also to give better images reconstruction on some kinds of extended objects (planets or binary stars with small magnitude difference). PSE has also the advantage to be very fast and well adapted to real-time image reconstruction.

Keywords: astronomy software; artificial satellites; astronomical methods
On the Chemical and Kinematic Consistency between N-rich Metal-poor Field Stars and Enriched Populations in Globular Clusters

Interesting chemically peculiar field stars may reflect their stellar evolution history and their possible origin in a different environment from where they are found now; this is one of the most important research fields in Galactic archeology. To explore this further, we have used the CN-CH bands around 4000 Å to identify N-rich metal-poor field stars in LAMOST DR3. Here we expand our N-rich, metal-poor field star sample to ∼100 stars in LAMOST DR5, where 53 of them are newly found in this work. We investigate light elements of common stars between our sample and APOGEE DR14. While Mg, Al, and Si abundances generally agree with the hypothesis that N-rich metal-poor field stars come from enriched populations in globular clusters, it is still inconclusive for C, N, and O. After integrating the orbits of our N-rich field stars and a control sample of normal metal-poor field stars, we find that N-rich field stars have different orbital parameter distributions compared to the control sample - specifically, apocentric distances, maximum vertical amplitude (Zmax), orbital energy, and z-direction angular momentum (Lz). The orbital parameters of N-rich field stars indicate that most of them are inner-halo stars. The kinematics of N-rich field stars support their possible GC origin. The spatial and velocity distributions of our bona fide N-rich field star sample are important observational evidence to constrain simulations of the origin of these interesting objects.

Keywords: chemically peculiar stars; chemical abundances; stellar kinematics; globular star clusters; milky way stellar halo; cn stars; quasar absorption line spectroscopy; stellar dynamics; milky way evolution
MeV Gamma-Ray Source Contribution to the Inner Galactic Diffuse Emission

The origin of the inner Galactic emission, measured by COMPTEL with a flux of ~10-2 MeV cm-2 s-1 sr-1 in the 1-30 MeV energy range from the inner Galactic region, has remained unsettled since its discovery. In this paper, we elaborate on a model of individual MeV gamma-ray sources unresolved by COMPTEL. This is conducted for sources crossmatched between the Swift-BAT and Fermi-LAT catalogs by interpolating the energy spectra in the hard X-ray and GeV gamma-ray ranges, as well as unmatched sources between the two catalogs. We find that the source contribution to the COMPTEL emission would be at least ~20%. Combined with the Galactic diffuse emission, which is not well constrained, the COMPTEL emission can be roughly reproduced in some cases.

Keywords: cosmic rays; galactic cosmic rays; gamma-ray sources; gamma-rays; diffuse radiation