Sazuna/UAT_keywords huggingface dataset:
The Van Hoof Effect over the Blazhko Cycle. We provide the first detection of the Van Hoof effect over a complete Blazhko cycle in the variations of H β, neutral, and ionized metallic lines, measurable on 2782 high-resolution line profiles obtained during the course of a 41 day continuous and unprecedented survey of RR ab star, RR Lyr. We detect phase-lag variations in the velocity-velocity diagrams during the Blazhko period. The Van Hoof effect is maximum at the Blazhko modulation maximum and minimum at the Blazhko modulation minimum. Both turbulent velocities and equivalent widths are correlated with the Van Hoof and Blazhko effects. We investigate the differential motion between the upper and lower photosphere and between the photosphere and high atmosphere in the RR Lyr star. The differential radial velocity and differential acceleration curves show bulges and dents, respectively, during the inward moving atmosphere, but at the pulsation amplitude maximum, the differential acceleration curve is double peaked with a high differential radial-velocity gradient. Correlations between differential radial velocity, separating distance, and differential acceleration are monotonous during the Blazhko cycle, but the double-peak structure, left peak and right peak, is strongly Blazhko antiphased and phased, respectively. We explain the physical mechanisms driving the modulation of these quantities by the ShPM1, ShPM, ShPM2, and ShPM3 receding shocks, and the ShH+He outwarding main shock. The 3D interplay between the Van Hoof, Blazhko, and hypersonic-hydrodynamical effects provides a powerful tool for stellar pulsation and evolution challenges.

Keywords: High resolution spectroscopy, Stellar convection envelopes, Hydrodynamics, Stellar pulsations, Pulsating variable stars, Shocks, Astronomy data analysis, Blazhko effect, RR Lyrae variable stars, Ground-based astronomy, Radial velocity, Stellar evolution
Theoretical Light-curve Models of the Symbiotic Nova CN Cha-Optical Flat Peak for 3 Yr. CN Cha is a slow symbiotic nova characterized by a 3 yr long optical flat peak followed by a rapid decline. We present theoretical light curves for CN Cha, based on hydrostatic approximation, and estimate the white-dwarf (WD) mass to be ~0.6 M ⊙ for a low metal abundance of Z = 0.004. These kinds of flat-peak novae are border objects between classical novae having a sharp optical peak and extremely slow novae, the evolutions of which are too slow to be recognized as nova outbursts on a human timescale. Theoretically, there are two types of nova envelope solutions-static and optically thick wind-in low-mass WDs (≲0.7 M ⊙). Such a nova outburst begins first in a hydrostatic manner, and later it could change to an optically thick wind evolution, due to perturbation by the companion star in the nova envelope. Multiple peaks are a reflection of the relaxation process of the transition. CN Cha supports our explanation of the difference between long-lasting flat-peak novae like CN Cha and multiple-peak novae like V723 Cas, because the companion star is located far outside, and does not perturb, the nova envelope in CN Cha.

Keywords: Cataclysmic variable stars, Stellar winds, Novae
Demographics of Hierarchical Black Hole Mergers in Dense Star Clusters. With about one hundred mergers of binary black holes (BBHs) detected via gravitational waves by the LIGO-Virgo-KAGRA (LVK) Collaboration, our understanding of the darkest objects in the universe has taken unparalleled steps forward. While most of the events are expected to consist of black holes (BHs) directly formed from the collapse of massive stars, some may contain the remnants of previous BBH mergers. In the most massive globular clusters and in nuclear star clusters, successive mergers can produce second- (2G) or higher-generation BHs, and even form intermediate-mass BHs (IMBHs). Overall, we predict that up to ~10%, ~1%, or ~0.1% of the BBH mergers have one component being a 2G, 3G, or 4G BH, respectively. Assuming that ~500 BBH mergers will be detected in O4 by LVK, this means that ~50, ~5, or ~0.5 events, respectively, will involve a 2G, 3G, or 4G BH, if most sources are produced dynamically in dense star clusters. With their distinctive signatures of higher masses and spins, such hierarchical mergers offer an unprecedented opportunity to learn about the BH populations in the densest stellar systems and to shed light on the elusive IMBHs that may form therein.

Keywords: Intermediate-mass black holes, Gravitational wave detectors, Black holes, Stellar mass black holes, Gravitational wave sources, Gravitational wave astronomy, Gravitational waves, Astrophysical black holes
Hilbert-Huang Transform Analysis of Quasiperiodic Oscillations in MAXI J1820+070. We present a time-frequency analysis, based on the Hilbert-Huang transform, of the evolution of the low-frequency quasiperiodic oscillations observed in the black hole X-ray binary MAXI J1820+070. Through the empirical mode decomposition method, we decompose the light curve of the quasiperiodic oscillation (QPO) component and measure its intrinsic phase lag between photons from different energy bands. We find that the QPO phase lag is negative (low-energy photons lag behind high-energy photons); meanwhile, the absolute value of the lag increases with energy. By applying the Hilbert transform to the light curve of the QPO, we further extract the instantaneous frequency and amplitude of the QPO. Comparing these results with those from the Fourier analysis, we find that the broadening of the QPO peak is mainly caused by frequency modulation. Through further analysis, we find that these modulations could share a common physical origin with the broadband noise, and can be well explained by the internal shock model of the jet.

Keywords: Accretion, Black hole physics, X-ray binary stars
An Ultradeep Multiband Very Large Array Survey of the Faint Radio Sky (COSMOS-XS): New Constraints on the Optically Dark Population. Attempts to trace star formation with rest-frame UV/optical observations at redshifts z &gt; 2 are affected by the presence of potentially substantial, yet uncertain, dust attenuation. Recent studies have demonstrated the existence of a population of galaxies that are virtually invisible in the observed optical/near-infrared (NIR) due to dust obscuration, but which could contribute substantially to the star formation history at 2 &lt; z &lt; 6. Here, we make use of ultradeep 3 GHz Karl G. Jansky Very Large Array observations from the COSMOS-XS survey to investigate the contribution 20of radio-selected "optically dark" galaxies (undetected to a depth of K  S  ~ 25.9 mag) to the cosmic star formation rate density (SFRD). We identify 19 such "optically dark" sources and utilize recent deblended far-infrared photometry to determine photometric redshifts based on IR and radio information for 11 of them. Through stacking, we infer that the remaining eight sources reside predominantly at high redshift (z &gt; 4). Therefore, we conservatively assume these sources lie between z = 2 and z = 5. We derive the radio luminosity function (LF) for the sample with and without "optically dark" sources by fixing the faint and bright end shape of the radio LF to the local values and allowing for luminosity evolution. By integrating both LFs, we estimate the contribution of the "optically dark" galaxies to the radio SFRD to be $\sim {15}_{-7}^{+7} \% $ at z ~ 5. This is consistent with constraints from NIR-dark and UV-dark sources, while being in disagreement with some estimates using H-dropouts. This result implies that "optically dark" sources play a nonnegligible role at high redshift.

Keywords: Radio continuum emission, Star formation, Galaxy evolution
An Isotope-labeling Study of CO<SUB>2</SUB> Formation Pathways in Molecular Clouds: Ultraviolet Photolysis of CO-H<SUB>2</SUB>O Ice. With the use of reflection-absorption infrared spectroscopy, we investigated the binary ice of CO and H2O at 10 K under ultraviolet irradiation as an analog of the interstellar ice mantle. We employed H2 18O instead of H2 16O to distinguish the formation pathways of CO2, and prepared mixed-ice samples under CO- and H2O-rich conditions as well as bilayered ice, where CO was condensed on H2O ice. After the ultraviolet irradiation onto any sample, we detected infrared absorption bands of C16O2 and C18O16O, which were generated through the CO-CO and CO-H2O reactions, respectively. The additional detection of C18O2 clearly indicated that the photodissociation and regeneration of CO2 also took place in ice. We analyzed the irradiation-time dependence of the C16O2 and C18O16O column densities in CO-rich ice to determine the effective cross sections of the CO2 formation through the CO-CO ( ${\sigma }_{{{\rm{C}}}^{16}{{\rm{O}}}_{2}}$ ) and CO-H2O ( ${\sigma }_{{{\rm{C}}}^{18}{{\rm{O}}}^{16}{\rm{O}}}$ ) reactions simultaneously: ${\sigma }_{{{\rm{C}}}^{16}{{\rm{O}}}_{2}}$ = 3 × 10-21 cm2 and ${\sigma }_{{{\rm{C}}}^{18}{{\rm{O}}}^{16}{\rm{O}}}$ = 5 × 10-18 cm2. Despite the rather small value of ${\sigma }_{{{\rm{C}}}^{16}{{\rm{O}}}_{2}}$ compared to ${\sigma }_{{{\rm{C}}}^{18}{{\rm{O}}}^{16}{\rm{O}}}$ , the former reaction was found to be nonnegligible in terms of the CO2 yield, even at the H2O-rich condition.

Keywords: Interstellar dust, Laboratory astrophysics, Carbon dioxide, Molecular clouds, Astrochemistry
Testing the Blazar Sequence with Spectra of Recently Discovered Dim Blazars from the Fermi Unassociated Catalog. Recent works have developed samples of blazars from among the Fermi Large Area Telescope unassociated sources via machine-learning comparisons with known blazar samples. Continued analysis of these new blazars tests the predictions of the blazar sequence and enables more flux-complete samples of blazars as a population. Using Fermi, Swift, Wide-field Infrared Survey Explorer, and archival radio data, we construct broadband spectral energy distributions for 106 recently identified blazars. Drawn from the unassociated 4FGL source sample, this new sample has a lower median flux than the overall sample of gamma-ray blazars. By measuring the synchrotron peak frequency, we compare our sample of new blazars with known blazars from the 4LAC catalog. We find that the bulk of the new blazars are similar to high-synchrotron-peaked BL Lac objects, with a higher median synchrotron peak; the sample has a median $\mathrm{log}({\nu }_{\mathrm{syn}}/\mathrm{Hz})=15.5$ via BLaST peak estimation, compared to $\mathrm{log}({\nu }_{\mathrm{syn}}/\mathrm{Hz})=14.2$ for the 4LAC BL Lacs. Finally, we conduct synchrotron self-Compton leptonic modeling, comparing fitted physical and phenomenological properties to brighter blazars. We find that the new blazars have smaller characteristic Lorentz factors γ boost and fitted magnetic fields B, in agreement with blazar sequence predictions. The new blazars have slightly higher Compton dominance ratios than expected, which may point to alternative emission models for these dim blazars. Our results extend the predictions of the blazar sequence to a sample of dimmer blazars, confirming the broad predictions of that theory.

Keywords: Blazars, Catalogs
Chandra, HST/STIS, NICER, Swift, and TESS Detail the Flare Evolution of the Repeating Nuclear Transient ASASSN -14ko. ASASSN-14ko is a nuclear transient at the center of the AGN ESO 253-G003 that undergoes periodic flares. Optical flares were first observed in 2014 by the All-Sky Automated Survey for Supernovae (ASAS-SN) and their peak times are well-modeled with a period of ${115.2}_{-1.2}^{+1.3}$ days and period derivative of -0.0026 ± 0.0006. Here we present ASAS-SN, Chandra, HST/STIS, NICER, Swift, and TESS data for the flares that occurred on 2020 December, 2021 April, 2021 July, and 2021 November. These four flares represent flares 18-21 of the total number of flares observed by ASAS-SN so far since 2014. The HST/STIS UV spectra evolve from blueshifted broad absorption features to redshifted broad emission features over ~10 days. The Swift UV/optical light curves peaked as predicted by the timing model, but the peak UV luminosities that varied between flares and the UV flux in Flare 20 were roughly half the brightness of the other peaks. The X-ray luminosities consistently decreased and the spectra became harder during the UV/optical rise, but apparently without changes in absorption. Finally, two high-cadence TESS light curves from Flare 18 and Flare 12 showed that the slopes during the rising and declining phases changed over time, which indicates some stochasticity in the flare's driving mechanism. Although ASASSN-14ko remains observationally consistent with a repeating partial tidal disruption event, these rich multi-wavelength data are in need of a detailed theoretical model.

Keywords: Active galactic nuclei, Black holes, High energy astrophysics
On the Metallicities and Kinematics of the Circumgalactic Media of Damped Lyα Systems at z   2.5. We use medium- and high-resolution spectroscopy of close pairs of quasars to analyze the circumgalactic medium (CGM) surrounding 32 damped Lyα absorption systems (DLAs). The primary quasar sightline in each pair probes an intervening DLA in the redshift range 1.6 &lt; z abs &lt; 3.5, such that the secondary sightline probes absorption from Lyα and a large suite of metal-line transitions (including O I, C II, C IV, Si II, and Si IV) in the DLA host galaxy's CGM at transverse distances 24 kpc ≤ R ⊥ ≤ 284 kpc. Analysis of Lyα in the CGM sightlines shows an anticorrelation between R ⊥ and H I column density (N HI) with 99.8% confidence, similar to that observed around luminous galaxies. The incidences of C II and Si II with N &gt; 1013 cm-2 within 100 kpc of DLAs are larger by 2σ than those measured in the CGM of Lyman break galaxies (C f (N CII ) &gt; 0.89 and ${{\rm{C}}}_{f}({N}_{\mathrm{Si}{\rm\small{II}}})={0.75}_{-0.17}^{+0.12}$ ). Metallicity constraints derived from ionic ratios for nine CGM systems with negligible ionization corrections and N HI &gt; 1018.5 cm-2 show a significant degree of scatter (with metallicities/limits across the range $-2.06\lesssim \mathrm{log}Z/{Z}_{\odot }\lesssim -0.75$ ), suggesting inhomogeneity in the metal distribution in these environments. Velocity widths of C IV λ1548 and low-ionization metal species in the DLA versus CGM sightlines are strongly (&gt;2σ) correlated, suggesting that they trace the potential well of the host halo over R ⊥ ≲ 300 kpc scales. At the same time, velocity centroids for C IV λ1548 differ in DLA versus CGM sightlines by &gt;100 km s-1 for ~50% of velocity components, but few components have velocities that would exceed the escape velocity assuming dark matter host halos of ≥1012 M ☉. * The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Keywords: Damped Lyman-alpha systems, Quasar absorption line spectroscopy, Circumgalactic medium
Quantifying the Key Factors Affecting the Escape of Planetary Atmospheres. The habitability of Earth-like planets is an increasingly important subject in astrophysics and in planetary sciences. Atmospheric escape plays a vital role in the evolution of the habitability of Earth-like planets. By systematically analyzing the numerical simulation results of the interactions between the planetary atmospheres and the stellar winds, in this work, we evaluate various factors related to the atmospheric nonthermal ion escape rates, including planetary parameters (e.g., mass, density, radius, semimajor axis, etc.) and stellar wind parameters (e.g., density, velocity, and interplanetary magnetic field (IMF) strength). Furthermore, we determine and quantify the key factors affecting the planetary atmospheric nonthermal ion escape rates. Our results show that the correlation coefficients between planetary atmospheric nonthermal ion escape rates and stellar wind density, IMF strength, and the ratio of the planetary radius to the planetary semimajor axis are 0.98 (0.88), 0.95 (0.81), and 0.87 (0.59), respectively, in the scenario of maximum (minimum) dynamic wind pressure. This means that the planetary atmospheric nonthermal ion escape rates increase with the increasing stellar wind density, the increasing IMF strength, and the increasing ratio of the planetary radius to the planetary semimajor axis. Generally, the nonthermal ion escape rates of planetary atmospheres are more sensitive to stellar wind parameters than to others. In addition, we determine the functional relations of the above three significant parameters for evaluating and quantifying the effects of such key physical factors on the nonthermal ion escape rates of the planetary atmospheres. Our findings will be very useful for better understanding the key factors that influence the escapes of planetary atmospheres.

Keywords: Solar system planets, Stellar winds, Astrobiology, Star-planet interactions, Habitable planets, Exoplanet atmospheres
Low-surface-brightness Galaxies are Missing in the Observed Stellar Mass Function. We investigate the impact of the surface-brightness (SB) limit on the galaxy stellar mass functions (GSMFs) using galaxy catalogs generated from the Horizon Run 5 (HR5) simulation. We compare the stellar-to-halo-mass relation, GSMF, and size-stellar mass relation of the HR5 galaxies with observational data and other cosmological simulations. The mean SB of simulated galaxies are computed using their effective radii, luminosities, and colors. To examine the cosmic SB dimming effect, we compute k-corrections from the spectral energy distributions of individual simulated galaxy at each redshift, apply the k-corrections to the galaxies, and conduct mock surveys based on the various SB limits. We find that the GSMFs are significantly affected by the SB limits at the low-mass end. This approach can ease the discrepancy between the GSMFs obtained from simulations and observations at 0.6 ≲ z ≤ 2. We also find that a redshift survey with an SB selection limit of ${\left\langle {\mu }_{r}\right\rangle }^{e}=$ 25 mag arcsec-2 will miss 20% of galaxies with ${M}_{\star }^{g}={10}^{9}\,{M}_{\odot }$ at z = 0.625. The missing fraction of low-surface-brightness galaxies increases to 35%, 55%, and 80% at z = 0.9, 1.1, and 1.9, respectively, at the same SB limit.

Keywords: Hydrodynamical simulations
Low-metallicity Galaxies from the Dark Energy Survey. We present a new selection of 358 blue compact dwarf galaxies (BCDs) from 5000 square degrees in the Dark Energy Survey, and the spectroscopic follow-up of a subsample of 68 objects. For the subsample of 34 objects with deep spectra, we measure the metallicity via the direct T  e  method using the auroral [O III]λ 4363 emission line. These BCDs have an average oxygen abundance of 12+log(O/H) = 7.8, with stellar masses between 107 and 108 M ⊙ and specific star-formation rates between ~10-9 and 10-7 yr-1. We compare the position of our BCDs with the mass-metallicity (M-Z) and luminosity-metallicity (L-Z) relation derived from the Local Volume Legacy sample. We find the scatter about the M-Z relation is smaller than the scatter about the L-Z relation. We identify a correlation between the offsets from the M-Z and L-Z relation that we suggest is due to the contribution of metal-poor inflows. Finally, we explore the validity of the mass-metallicity-SFR fundamental plane in the mass range probed by our galaxies. We find that BCDs with stellar masses smaller than 108 M ⊙ do not follow the extrapolation of the fundamental plane. This result suggests that mechanisms other than the balance between inflows and outflows may be at play in regulating the position of low-mass galaxies in the M-Z-SFR space.

Keywords: Galaxy properties, Galaxy chemical evolution, Dwarf galaxies, Compact dwarf galaxies, Scaling relations, Metallicity
A Novel Survey for Young Substellar Objects with the W-band Filter. VI. Spectroscopic Census of Substellar Members and the IMF of the σ Orionis Cluster. Low-mass stars and substellar objects are essential in tracing the initial mass function (IMF). We study the nearby young σ Orionis cluster (d ~ 408 pc, age ~ 1.8 Myr) using deep near-infrared (NIR) photometric data in the J, W, and H bands from WIRCam on the Canada-France-Hawaii Telescope. We use the water absorption feature to select brown dwarfs photometrically and confirm their nature spectroscopically with IRTF-SpeX. Additionally we select candidate low-mass stars for spectroscopy and analyze their membership and those of literature sources using astrometry from Gaia DR3. We obtain NIR spectra for 28 very-low-mass stars and brown dwarfs and estimate their spectral type between M3 and M8.5 (masses ranging between 0.3 and 0.01 M ☉). Apart from these, we also identify five new planetary-mass candidates which require further spectroscopic confirmation of youth. We compile a comprehensive catalog of 170 spectroscopically confirmed members in the central region of the cluster, for a wide mass range of ~19-0.004 M ☉. We estimate the star-to-brown-dwarf ratio to be ~4, within the range reported for other nearby star-forming regions. With the updated catalog of members we trace the IMF down to 4 M Jup and we find that a two-segment power law fits the substellar IMF better than a log-normal distribution.

Keywords: Star forming regions, Brown dwarfs, Initial mass function, Low mass stars
Model-independent Mass Reconstruction of the Hubble Frontier Field Clusters with MARS Based on Self-consistent Strong-lensing Data. We present a new strong-lensing (SL) mass reconstruction of the six Hubble Frontier Fields (HFF) clusters with the MAximum-entropy ReconStruction (MARS) algorithm. MARS is a new free-form inversion method, which suppresses spurious small-scale fluctuations while achieving excellent convergence in positions of multiple images. For each HFF cluster, we obtain a model-independent mass distribution from the compilation of the self-consistent SL data in the literature. With 100-200 multiple images per cluster, we reconstruct solutions with small scatters of multiple images in both source (~0.″02) and image planes (0.″05-0.″1), which are lower than the previous results by a factor of 5-10. An outstanding case is the MACS J0416.1-2403 mass reconstruction, which is based on the largest high-quality SL data set where all 236 multiple images/knots have spectroscopic redshifts. Although our solution is smooth on a large scale, it reveals group/galaxy-scale peaks where the substructures are required by the data. We find that in general, these mass peaks are in excellent spatial agreement with the member galaxies, although MARS never uses the galaxy distributions as priors. Our study corroborates the flexibility and accuracy of the MARS algorithm and demonstrates that MARS is a powerful tool in the JWST era, when a 2-3 times larger number of multiple image candidates become available for SL mass reconstruction, and self-consistency within the data set becomes a critical issue.

Keywords: Galaxy clusters, Dark matter distribution, Strong gravitational lensing