adsabs/SciX_UAT_keywords huggingface dataset:
Low-mass Stellar and Substellar Content of the Young Cluster Berkeley 59

We present a multiwavelength analysis of the young star cluster Berkeley 59, based on Gaia data and deep IR observations with the 3.58 m Telescopio Nazionale Galileo and Spitzer space telescope. The mean proper motion of the cluster is found to be μ α cosδ ∼ ‑0.63 mas yr‑1 and μ δ ∼ ‑1.83 mas yr‑1, and the kinematic distance of the cluster, ∼1 kpc, is in agreement with previous photometric studies. The present data are the deepest available near-IR observations for the cluster so far and reach below 0.03 M ⊙. The mass function of the cluster region is calculated using the statistically cleaned color–magnitude diagram and is similar to the Salpeter value for the member stars above 0.4 M ⊙. In contrast, the slope becomes shallower (Γ ∼ 0.01 ± 0.18) in the mass range 0.04–0.4 M ⊙, comparable to other nearby clusters. The spatial distribution of young brown dwarfs (BDs) and stellar candidates shows a nonhomogeneous distribution. This suggests that the radiation feedback from massive stars may be a prominent factor contributing to the BD population in the cluster Berkeley 59. We also estimated the star-to-BD ratio for the cluster, which is found to be ∼3.6. The Kolmogorov–Smirnov test shows that the stellar and BD populations significantly differ, and stellar candidates are nearer the cluster center compared to the BDs, suggesting mass segregation in the cluster toward the substellar mass regime.

Keywords: star forming regions; young star clusters; low mass stars; h ii regions
The Tidal Disruption Event AT2021ehb: Evidence of Relativistic Disk Reflection, and Rapid Evolution of the Disk-Corona System

We present X-ray, UV, optical, and radio observations of the nearby (≈78 Mpc) tidal disruption event AT2021ehb/ZTF21aanxhjv during its first 430 days of evolution. AT2021ehb occurs in the nucleus of a galaxy hosting a≈107 M ⊙ black hole (M BH inferred from host galaxy scaling relations). High-cadence Swift and Neutron Star Interior Composition Explorer (NICER) monitoring reveals a delayed X-ray brightening. The spectrum first undergoes a gradual soft → hard transition and then suddenly turns soft again within 3 days at δ t≈272 days during which the X-ray flux drops by a factor of 10. In the joint NICER+NuSTAR observation (δ t = 264 days, harder state), we observe a prominent nonthermal component up to 30 keV and an extremely broad emission line in the iron K band. The bolometric luminosity of AT2021ehb reaches a maximum of ${6.0}_{-3.8}^{+10.4} \% {L}_{\mathrm{Edd}}$ when the X-ray spectrum is the hardest. During the dramatic X-ray evolution, no radio emission is detected, the UV/optical luminosity stays relatively constant, and the optical spectra are featureless. We propose the following interpretations: (i) the soft → hard transition may be caused by the gradual formation of a magnetically dominated corona; (ii) hard X-ray photons escape from the system along solid angles with low scattering optical depth (~a few) whereas the UV/optical emission is likely generated by reprocessing materials with much larger column density-the system is highly aspherical; and (iii) the abrupt X-ray flux drop may be triggered by the thermal-viscous instability in the inner accretion flow, leading to a much thinner disk.

Keywords: tidal disruption; x-ray transient sources; supermassive black holes; time domain astronomy; high energy astrophysics; accretion
It's Dust: Solving the Mysteries of the Intrinsic Scatter and Host-galaxy Dependence of Standardized Type Ia Supernova Brightnesses

The use of Type Ia supernovae (SNe Ia) as cosmological tools has motivated significant effort to understand what drives the intrinsic scatter of SN Ia distance modulus residuals after standardization, characterize the distribution of SN Ia colors, and explain why properties of the host galaxies of the SNe correlate with SN Ia distance modulus residuals. We use a compiled sample of ∼1450 spectroscopically confirmed photometric light curves of SNe Ia and propose a solution to these three problems simultaneously that also explains an empirical 11σ detection of the dependence of Hubble residual scatter on SN Ia color. We introduce a physical model of color where intrinsic SN Ia colors with a relatively weak correlation with luminosity are combined with extrinsic dust-like colors (E(B - V)) with a wide range of extinction parameter values (RV). This model captures the observed trends of Hubble residual scatter and indicates that the dominant component of SN Ia intrinsic scatter is variation in RV. We also find that the recovered E(B - V) and RV distributions differ based on global host-galaxy stellar mass, and this explains the observed correlation (γ) between mass and Hubble residuals seen in past analyses, as well as an observed 4.5σ dependence of γ on SN Ia color. This finding removes any need to ascribe different intrinsic luminosities to different progenitor systems. Finally, we measure biases in the equation of state of dark energy (w) up to ∣Δw∣ = 0.04 by replacing previous models of SN color with our dust-based model; this bias is larger than any systematic uncertainty in previous SN Ia cosmological analyses.

Keywords: type ia supernovae; cosmology; interstellar dust; circumstellar dust; dark energy; accelerating universe; supernovae
Value-added Catalog of M-giant Stars in LAMOST DR9

In this work, we update the catalog of M-giant stars from the low-resolution spectra of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release 9. There are 58,076 M giants identified from the classification pipeline with seven temperature subtypes from M0 to M6. The 2471 misclassified non-M-giant stars are white dwarf binaries, early types, and M dwarfs. And the contamination rate is 4.2% in the M-giants sample. A total of 372 carbon stars were identified by CaH spectral indices, and were further confirmed by the LAMOST spectra. We update the correlation between the (W1 - W2)0 color and [M/H] from APOGEE DR17. We calculate the radial velocities of all M giants by applying cross-correlation to the spectra between 8000 and 8950 Å with synthetic spectra from ATLAS9. Taking star distances less than 4 kpc from Gaia EDR3 as the standard, we refitted the photometric distance relation of M giants. And based on our M-giant stars, we select a group of Sagittarius stream members, whose sky and 3D velocity distributions are well consistent with K-giant Saggitarius stream members found in Yang et al. With our M giants, we find that the disk is asymmetric out to R = 25 kpc, which is 5 kpc further out than detected using K giants.

Keywords: m giant stars; milky way disk; catalogs
Revisiting Black Hole Hyperaccretion in the Center of Gamma-Ray Bursts for the Lower Mass Gap

The ultrarelativistic jets triggered by neutrino annihilation processes or Blandford-Znajek (BZ) mechanisms in stellar-mass black hole (BH) hyperaccretion systems are generally considered to power gamma-ray bursts (GRBs). Due to the high accretion rate, the central BHs might grow rapidly on a short timescale, providing a new way to understand the lower mass gap problem. In this paper, we use the BH hyperaccretion model to investigate BH mass growth based on observational GRB data. The results show that (i) if the initial BH mass is set as 3 M ⊙, the neutrino annihilation processes are capable of fueling the BHs to escape the lower mass gap for more than half of long-duration GRBs (LGRBs), while the BZ mechanism is inefficient in triggering BH growth for LGRBs; (ii) the mean BH mass growth in the case of LGRBs without observable supernova (SN) association is much larger than that in the case of LGRBs associated with SNe for both mechanisms, which implies that more massive progenitors or lower SN explosion energies prevail throughout the former cases; (iii) for the short-duration GRBs, the mean BH mass growth is satisfied with the mass supply limitation in the scenario of compact object mergers, but the hyperaccretion processes are unable to rescue BHs from the gap in binary neutron star (NS) mergers or the initial BH mass being 3 M ⊙ after NS-BH mergers.

Keywords: accretion; astrophysical black holes; neutrino astronomy; gamma-ray bursts; magnetic fields
Multiple Populations in Low-mass Globular Clusters: Eridanus

Multiple populations (MPs), characterized by variations in light elemental abundances, have been found in stellar clusters in the Milky Way, Magellanic Clouds, as well as several other dwarf galaxies. Based on a large number of observations, mass has been suggested to be a key parameter affecting the presence and appearance of MPs in stellar clusters. To further investigate the existence of MPs in low-mass clusters and explore the mass threshold for the formation of MPs, we carried out a project studying the composition of the stellar population in several low-mass Galactic globular clusters. Here we present our study on the cluster Eridanus. With blue-UV low-resolution spectra obtained with the OSIRIS/Multi-object spectrograph on the Gran Telescopio Canarias, we computed the spectral indices of CH and CN for a sample of giant stars and derived their carbon and nitrogen abundances using model spectra. A significant dispersion in the initial surface abundance of nitrogen was found in the sample, indicating the existence of MPs in Eridanus. Inspecting the age-initial mass distribution of in situ clusters with MPs, we find a slight trend that initial mass increases with increasing age, and the lowest initial masses of $\mathrm{log}{M}_{\mathrm{initial}}$ ~ 4.98 and 5.26 are found at the young and old end, respectively, which might provide a rough reference for the mass threshold for clusters to form MPs. However, more observations of clusters with low initial masses are still necessary before any firm conclusion can be drawn.

Keywords: globular star clusters; stellar abundances
The Missing Link between Black Holes in High-mass X-Ray Binaries and Gravitational-wave Sources: Observational Selection Effects

There are few observed high-mass X-ray binaries (HMXBs) that harbor massive black holes (BHs), and none are likely to result in a binary black hole (BBH) that merges within a Hubble time; however, we know that massive merging BBHs exist from gravitational-wave (GW) observations. We investigate the role that X-ray and GW observational selection effects play in determining the properties of their respective detected binary populations. We find that, as a result of selection effects, detectable HMXBs and detectable BBHs form at different redshifts and metallicities, with detectable HMXBs forming at much lower redshifts and higher metallicities than detectable BBHs. We also find disparities in the mass distributions of these populations, with detectable merging BBH progenitors pulling to higher component masses relative to the full detectable HMXB population. Fewer than 3% of detectable HMXBs host BHs >35M ⊙ in our simulated populations. Furthermore, we find the probability that a detectable HMXB will merge as a BBH system within a Hubble time is ≃0.6%. Thus, it is unsurprising that no currently observed HMXB is predicted to form a merging BBH with high probability.

Keywords: gravitational wave sources; high mass x-ray binary stars; stellar mass black holes
Investigating the Effect of Solar Ambient and Data Characteristics on Ca II K Observations and Line Profile Measurements

We analyzed state-of-the-art observations of the solar atmosphere to investigate the dependence of the Ca II K brightness of several solar features on spectral bandwidth and spatial resolution of the data. In particular, we study data obtained at the Swedish Solar Telescope with the Crisp Imaging Spectropolarimeter and Chromospheric Imaging Spectrometer instruments. The analyzed data, which are characterized by a spectral bandwidth of 0.12 Å and a spatial resolution of 0.″078, were acquired close to the disk center by targeting a quiet-Sun area and an active region. We convolved the original observations with Gaussian kernels to degrade their spectral bandwidth and spatial resolution to the instrumental characteristics of the most prominent series of Ca II K observations available to date. We then studied the effect of data degradation on the observed regions and on parameters derived from Ca II K line measurements that are largely employed as diagnostics of the solar and stellar chromospheres. We find that the effect of degrading the spectral resolution of Ca II K observations and line profiles depends on both the employed bandwidth and observed solar region. Besides, we found that the spatial degradation impacts the data characterized by a broad bandwidth to a larger extent compared to those acquired with a narrow band. However, the appearance of the observed solar regions is only slightly affected by the spatial resolution of data with bandwidths up to 1 Å and in the range [3,10] Å. Finally, we derived relationships that can be used to intercalibrate results from observations taken with different instruments in diverse regions of the solar atmosphere.

Keywords: solar chromosphere; plages; solar photosphere; sunspots; solar activity
Mutual Inclination of Ultra-short-period Planets with Time-varying Stellar J 2 Moments

Systems with ultra-short-period (USP) planets tend to possess larger mutual inclinations compared to those with planets located farther from their host stars. This could be explained due to precession caused by stellar oblateness at early times when the host star was rapidly spinning. However, stellar oblateness reduces over time due to the decrease in the stellar rotation rate, and this may further shape the planetary mutual inclinations. In this work, we investigate in detail how the final mutual inclination varies under the effect of a decreasing J 2. We find that different initial parameters (e.g., the magnitude of J 2 and planetary inclinations) will contribute to different final mutual inclinations, providing a constraint on the formation mechanisms of USP planets. In general, if the inner planets start in the same plane as the stellar equator (or coplanar while misaligned with the stellar spin axis), the mutual inclination decreases (or increases then decreases) over time due to the decay of the J 2 moment. This is because the inner orbit typically possesses less orbital angular momentum than the outer ones. However, if the outer planet is initially aligned with the stellar spin while the inner one is misaligned, the mutual inclination nearly stays the same. Overall, our results suggest that either USP planets formed early and acquired significant inclinations (e.g., ≳30° with its companion or ≳10° with its host star spin axis for Kepler-653 c) or they formed late (≳Gyr) when their host stars rotated slower.

Keywords: exoplanet dynamics; exoplanet evolution; exoplanet formation; planetary system formation
Improving Coronal Hole Detections and Open Flux Estimates

One systematic limitation of solar coronal hole (CH) detection at extreme ultraviolet (EUV) wavelengths is the obscuration of dark regions of the corona by brighter structures along the line of sight. Another problem arises when using CHs to compute the Sun's open magnetic flux, where surface measurements of the radial magnetic field, ${B}_{r}^{\odot }$ , are situated slightly below the effective height of coronal EUV emission. In this paper, we explore these two limitations utilizing a thermodynamic magnetohydrodynamic (MHD) model of the corona for Carrington rotation (CR) 2101, where we generate CH detections from EUV 193 Å images of the corona forward-modeled from the MHD solution, and where the modeled open field is known. We demonstrate a method to combine EUV images into a full Sun map that helps alleviate CH obscuration called the minimum intensity disk merge (MIDM). We also show the variation in measured open flux and CH area that is due to the effective height differences between EUV and ${B}_{r}^{\odot }$ measurements. We then apply the MIDM method to SDO/AIA 193 Å observations from CR 2101, and conduct an analogous analysis. In this case, the MIDM method uses time-varying images, the effects of which are discussed. We show that overall, the MIDM method and an appreciation of the effective height mismatch provide a useful new way to extract a broader view of CHs, especially near the poles. In turn, they enable improved estimates of the open magnetic flux, and help facilitate comparisons between models and observations.

Keywords: solar corona; solar coronal holes; solar surface; astronomy software; astronomy data analysis
Rapid Growth of Galactic Supermassive Black Holes through Accreting Giant Molecular Clouds during Major Mergers of Their Host Galaxies

Understanding the formation of the supermassive black holes (SMBHs) present in the centers of galaxies is a crucial topic in modern astrophysics. Observations have detected SMBHs with masses of 109 M ⊙ in the high-redshift galaxies with z ~ 7. However, how SMBHs grew to such huge masses within the first billion years after the Big Bang remains elusive. One possible explanation is that SMBHs grow quickly through the frequent mergers of galaxies, which provides sustainable gas to maintain rapid growth. This study presents the hydrodynamics simulations of the SMBHs' growth with their host galaxies using the GIZMO code. In contrast to previous simulations, we have developed a giant molecular cloud (GMC) model by separating molecular gas particles from atomic gas particles and then evolving them independently. During major mergers, we show that the more massive molecular gas particles' cloud bears stronger dynamical friction. Consequently, GMCs are substantially accreted onto the galactic centers that grow SMBHs from ~107 to ~109 M ⊙ within 300 Myr, which explains the rapid growth of SMBHs, and this accretion also triggers a violent starburst at the galactic center. Furthermore, we examine the impact of minor mergers on the bulge of a Milky Way-like galaxy and find that the size and mass of the bulge can increase from 0.92 to 1.9 kpc and from 4.7 × 1010 to 7 × 1010 M ⊙.

Keywords: supermassive black holes; galaxy evolution; galactic bulge; starburst galaxies; galaxy mergers; computational astronomy
Effective Inspiral Spin Distribution of Primordial Black Hole Binaries

We investigate the probability distribution of the effective inspiral spin, the mass ratio, and the chirp mass of primordial black hole (PBH) binaries, incorporating the effect of the critical phenomena of gravitational collapse. As a leading order estimation, each binary is assumed to be formed from two PBHs that are randomly chosen according to the probability distribution of single PBHs, and the accretion effects on the mass and spin of each PBH are not considered for simplicity. We find that, although the critical phenomena can lead to large spins on the low-mass tail, the effective inspiral spin of the binary is statistically very small, $\sqrt{{\unicode{x02329}}{{\chi }}_{{\rm{e}}{\rm{f}}{\rm{f}}}^{2}{\unicode{x0232A}}}\sim {10}^{-3}$ . We also see that there is almost no anticorrelation between the effective inspiral spin and the mass ratio, which can be inferred from observations.

Keywords: black holes; cosmology
Abundance Analysis of New r-process-enhanced Stars from the HESP-GOMPA Survey

We present a study on the detailed chemical abundances of five new relatively bright r-process-enhanced stars that were initially observed as part of the SDSS/MARVELS pre-survey. These stars were selected, on the basis of their metallicities and carbon abundances, among a total of 60 stars, for high-resolution spectroscopic follow-up as part of the HESP-GOMPA survey (Hanle Echelle SPectrograph—Galactic survey Of Metal Poor stArs). Here we discuss the three new r-I and two new r-II stars found in this survey. We have carried out a detailed abundance analysis for each of these stars, at a resolving power of R ∼ 30,000, and we compare our results to the existing literature. We could measure three of the first r-process-peak elements (Sr, Y, and Zr) in all five stars, while Ba, Ce, Nd, Sm, Eu, and Dy could be detected among the second r-process-peak elements. Thorium could also be detected in one of the targets, which is found to be an actinide-boost star. We have carried out a comparative study among the subpopulations of the r-process-enhanced stars and other stars of the Milky Way halo population to constrain the origin of this class of objects. These bright r-process-enhanced stars provide an excellent opportunity to study the nucleosynthesis history of this population in great detail, and shed light on their chemical-enrichment histories.

Keywords: r-process; nucleosynthesis; high resolution spectroscopy; chemical abundances
Deuterium Escape on Photoevaporating Sub-Neptunes

We investigate the evolution of the deuterium-to-hydrogen (D/H) mass ratio driven by EUV photoevaporation of hydrogen-rich atmospheres of close-in sub-Neptunes around solar-type stars. For the first time, the diffusion-limited approach in conjunction with energy-limited photoevaporation is considered in evaluating deuterium escape from evolving exoplanet H/He envelopes. We find that the planets with smaller initial gas envelopes and thus smaller sizes can lead to weaker atmospheric escape, which facilitates hydrogen-deuterium fractionation. Specifically, in our grid of simulations with a low envelope mass fraction of less than 0.005, a low-mass sub-Neptune (4-5 M ⊕) at about 0.25-0.4 au or a high-mass sub-Neptune (10-15 M ⊕) at about 0.1-0.25 au can increase the D/H values by greater than 20% over 7.5 Gyr. Akin to the helium-enhanced envelopes of sub-Neptunes due to photoevaporating escape, the planets along the upper boundary of the radius valley are the best targets to detect high D/H ratios. The ratio can rise by a factor of ≲1.65 within 7.5 Gyr in our grid of evolutionary calculations. The D/H ratio is expected to be higher in thinner envelopes as long as the planets do not become bare rocky cores.

Keywords: exoplanet atmospheric composition; exoplanet atmospheric evolution; exoplanets; mini neptunes
An Extensive Catalog of Early-type Dwarf Galaxies in the Local Universe: Morphology and Environment

We present an extensive catalog of 5405 early-type dwarf (dE) galaxies located in the various environments, i.e., clusters, groups, and fields, of the local universe (z < 0.01). The dEs are selected through visual inspection of the Legacy survey's g-r-z combined tricolor images. The inspected area, covering a total sky area of 7643 deg2, encompasses two local clusters (Virgo and Fornax), 265 groups, and the regions around 586 field galaxies of M K < -21 mag. The catalog aims to be one of the most extensive and publicly accessible collections of data on dEs, despite its complex completeness limits, which may not accurately represent its statistical completeness. The strength of the catalog lies in the morphological characteristics, including nucleated, tidal, and ultradiffuse dEs. The two clusters contribute nearly half (2437 out of 5405) of the dEs, and the 265 groups contribute 2103 dEs. There are 864 dEs in 586 fields, i.e., ~1.47 dEs per field. Using a standard definition commonly used in literature, we identify 100 ultradiffuse galaxies (UDGs), which compose ~2% of the dE population. We find that 40% of our sample dEs harbor a central nucleus, and among the UDG population, a majority (79%) are nonnucleated. About 1.3% of dEs suffer from ongoing tidal disturbance by nearby massive galaxies, and only 0.03% show a sign of recent dwarf-dwarf mergers. The association between dEs and their nearest bright neighbor galaxies suggests that dEs are more likely created where their neighbors are non-star-forming ones.

Keywords: dwarf galaxies; early-type galaxies; low surface brightness galaxies; galaxy nuclei; galaxy groups; galaxy clusters; field galaxies