Sazuna/UAT_keywords huggingface dataset:
Planets Around Solar Twins/Analogs (PASTA). I. High-precision Stellar Chemical Abundances for 17 Planet-hosting Stars and the Condensation Temperature Trend. The Sun is depleted in refractory elements compared to nearby solar twins, which may be linked to the formation of giant or terrestrial planets. Here we present high-resolution, high signal-to-noise spectroscopic data for 17 solar-like stars hosting planets, obtained with Magellan II/MIKE, to investigate whether this depletion is related to planet formation. We derive stellar parameters, including stellar atmosphere, age, radius, mass, and chemical abundances for 22 elements from carbon to europium through line-by-line differential analysis. Our uncertainties range from 0.01 dex for Fe and Si to 0.08 dex for Sr, Y, and Eu. By comparing the solar abundances to those of the 17 stars, we investigate the differential abundance ([X/Fe]solar─[X/Fe]star) versus condensation temperature (Tc) trend. In particular, we apply Galactic chemical evolution corrections to five solar twins within the full sample. Our results conform to previous studies that the Sun is relatively depleted in refractory compared to volatile elements. For both five solar twins and the rest of the solar-like stars, we find that all stars hosting known gas giant planets exhibit negative Tc trend slopes, suggesting that the Sun is relatively depleted in refractory elements compared to similar giant planet-hosting stars. Additionally, we find no correlation between Tc trend slopes and the total mass of detected terrestrial planets in each system, suggesting that terrestrial planet formation may not be the cause of refractory element depletion in the Sun. *This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: Stellar abundances, Exoplanet formation, Solar analogs, Planet hosting stars
Chemically Self-consistent Modeling of the Globular Cluster NGC 2808 and its Effects on the Inferred Helium Abundance of Multiple Stellar Populations. The helium abundances in the multiple populations that are now known to comprise all closely studied Milky Way globular clusters (GCs) are often inferred by fitting isochrones generated from stellar evolutionary models to GC photometry. It is therefore important to build stellar models that are chemically self-consistent in terms of their structure, atmosphere, and opacity. In this work we present the first chemically self-consistent stellar models of the Milky Way GC NGC 2808 using MARCS model atmospheres, OPLIB high-temperature radiative opacities, and AESOPUS low-temperature radiative opacities. These stellar models were fit to the NGC 2808 photometry using Fidanka, a new software tool that was developed to optimally fit cluster photometry to isochrones and for population synthesis. Fidanka can determine, in a relatively unbiased way, the ideal number of distinct populations that exist within a data set and then fit isochrones to each population. We achieve this outcome through a combination of Bayesian Gaussian mixture modeling and a novel number density estimation algorithm. Using Fidanka and F275W – F814W photometry from the Hubble UV Globular Cluster Survey, we find that the helium abundance of the second generation of stars in NGC 2808 is higher than the first generation by 15% ± 3%. This is in agreement with previous studies of NGC 2808. This work, along with previous work by A. Dotter et al. focused on NGC 6752, demonstrates that chemically self-consistent models of GCs do not significantly alter inferred helium abundances and are therefore unlikely to be worth the significant additional time investment.

Keywords: Globular star clusters, Stellar evolutionary models
Spin Evolution and Mass Distribution of Galactic Binary Neutron Stars. Binary neutron stars (BNSs) detected in the Milky Way have total masses distributing narrowly around ∼2.6–2.7M⊙, while the BNS merger GW190425 detected via a gravitational wave has a significantly larger mass (∼3.4M⊙). This difference is not well understood, yet. In this paper, we investigate the BNS spin evolution via an improved binary star evolution model and its effects on the BNS observability, with the implementation of various relevant astrophysical processes. We find that the first-born neutron star component in low-mass BNSs can be spun up to millisecond pulsars by the accretion of Roche-lobe overflow from its companion and its radio lifetime can be comparable to the Hubble time. However, most high-mass BNSs have substantially shorter radio lifetimes than low-mass BNSs, and thus a smaller probability of being detected via radio emission. Adopting the star formation and metal enrichment history of the Milky Way given by observations, we obtain the survived Galactic BNSs with pulsar components from our population synthesis model and find that their distributions on the diagrams of the spin period versus the spin period time derivative ( ) and the orbital period versus the eccentricity (Porb–e) can well match those of the observed Galactic BNSs. The total mass distribution of the observed Galactic BNSs can also be matched by the model. A significant fraction (∼19%–22%) of merging BNSs at redshift z ∼ 0 have masses ≳3M⊙, which seems compatible with the GW observations. Future radio observations may detect many more Galactic BNSs, which will put strong constraints on the spin evolution of BNSs during their formation processes.

Keywords: Accretion, Neutron stars, X-ray binary stars, Compact binary stars, Gravitational wave sources, Stellar evolution
The Impact of Particle Drifts on the Flux of High-energy Solar Protons and He Ions Arriving at Earth from Compact Solar Sources. We present a numerical model to investigate the role of the ion mass-charge ratio (m/q) in determining the flux of MeV–GeV solar energetic particles (SEPs), released impulsively from a compact source near the Sun at 1 au. The equations of motion are numerically integrated for 0.1–1 GeV n‑1 H+, 3He2+, and 4He2+ test ions as they move in the Parker spiral interplanetary magnetic field (IMF) carried by the solar wind. Pitch-angle scattering is included by using an ad hoc scattering operator, resulting in a parallel mean free path corresponding to "weak" scattering (λ = 1 au). Our modeled field also includes a flat heliospheric current sheet (HCS) at the ecliptic plane. We consider both A– and A+ IMF polarities and determine the time-flux profile at 1 au, at multiple observation locations, for each ion species and energy. We find that the proximity of the observer to the HCS, magnetic connectivity, and the drifts that depend on kinetic energy, m/q, and IMF polarity strongly impact the resulting flux–time profile. We find significant differences between the onset time, decay time, peak flux, and initial flux of the three ion species at 1 au. This contrast in the decay phase of the three species is evident in the four edges of the magnetically well-connected areas at 1 au. For magnetically poorly connected observers to the source, the onset of the proton flux with respect to that of 3He2+, and 4He2+ can be delayed for several hours depending on the observer's relative heliographic latitude and the SEPs' energy.

Keywords: Solar energetic particles
Insights into Galaxy Evolution from Interpretable Sparse Feature Networks. Galaxy appearances reveal the physics of how they formed and evolved. Machine learning (ML) models can now exploit galaxies' information-rich morphologies to predict physical properties directly from image cutouts. Learning the relationship between pixel-level features and galaxy properties is essential for building a physical understanding of galaxy evolution, but we are still unable to explicate the details of how deep neural networks represent image features. To address this lack of interpretability, we present a novel neural network architecture called a Sparse Feature Network (SFNet). SFNets produce interpretable features that can be linearly combined in order to estimate galaxy properties like optical emission line ratios or gas-phase metallicity. We find that SFNets do not sacrifice accuracy in order to gain interpretability, and that they perform comparably well to cutting-edge models on astronomical ML tasks. Our novel approach is valuable for finding physical patterns in large data sets and helping astronomers interpret ML results.

Keywords: Astronomy image processing, Convolutional neural networks, Galaxies
A Study of Cosmological Models Based on the Long Gamma-Ray Burst Duration Histogram. The duration of more than one thousand gamma-ray bursts (GRBs) was measured by using the Swift satellite. Besides the redshift distribution of GRBs, the burst duration is another significant property of GRBs that can be analyzed. In this paper, we first find the detection rate of Swift/Burst Alert Telescope for a cosmological model with the ωCDM model. Then, by performing a Monte Carlo simulation, we find the "long" GRB duration histogram to compare the cosmological model with the ωCDM model and the ΛCDM model. The χ2 minimization method is employed to determine the optimal value of α in the dark energy equation of state, P = cω(z)ρ, with ω(z) = ‑1 + α z. We show that for the ωCDM model, all values of α within α = [0, 0.16] range are considered acceptable within two standard deviations.

Keywords: Cosmological models, Gamma-ray bursts, Dark energy
Exploring the Key Features of Repeating Fast Radio Bursts with Machine Learning. Fast radio bursts (FRBs) are enigmatic high-energy events with unknown origins, which are observationally divided into two categories, i.e., repeaters and nonrepeaters. However, there are potentially a number of nonrepeaters that may be misclassified, as repeating bursts are missed due to the limited sensitivity and observation periods, thus misleading the investigation of their physical properties. In this work, we propose a repeater identification method based on the t-distributed Stochastic Neighbor Embedding algorithm and apply the classification to the first Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) catalog. We find that the spectral morphology parameters, specifically spectral running (r), represent the key features for identifying repeaters from the nonrepeaters. Also, the results suggest that repeaters are more biased toward narrowband emission, whereas nonrepeaters are inclined toward broadband emission. We provide a list of 163 repeater candidates, five of which are confirmed with an updated repeater catalog from CHIME/FRB. Our findings improve our understanding of the various properties underlying repeaters and nonrepeaters, as well as guidelines for future FRB detection and categorization.

Keywords: Radio bursts, Classification systems, Radio transient sources
Flux-rope-mediated Turbulent Magnetic Reconnection. We present a new model of magnetic reconnection in the presence of turbulence. The new model differs from the Lazarian–Vishniac turbulent reconnection theory by emphasizing the role of locally coherent magnetic structures, whose existence is shown to be permitted by the properties of magnetic field line separation in turbulent plasma. Local coherence allows storage of magnetic helicity inside the reconnection layer in the form of locally coherent twisted flux ropes. We then introduce the "Alfvén horizon" to explain why the global reconnection rate can be governed by locally coherent magnetic field structure instead of by field line wandering, formally extending to 3D the principle that reconnection can be made fast by fragmentation of the global current layer. Coherence is shown to dominate over field line dispersion if the anisotropy of the turbulence at the perpendicular scale matching the thickness of a marginally stable current layer exceeds the aspect ratio of the current layer. Finally, we conjecture that turbulence generated within the reconnection layer may produce a critically balanced state that maintains the system in the flux-rope-mediated regime. The new model successfully accounts for the major features of 3D numerical simulations of self-generated turbulent reconnection, including reconnection rates of 0.01 in resistive MHD and 0.1 with collisionless physics.

Keywords: Space plasmas, Magnetohydrodynamics, Solar flares, Solar magnetic reconnection, Astrophysical fluid dynamics, Solar coronal heating, Solar wind, Solar corona, Solar magnetic fields, Magnetic fields
Revisiting the Fundamental Planes of Black Hole Activity for Strong Jet Sources. Whether the X-ray emissions of strong jet sources originate from disk+coronas or jets is still controversial. In this work, we constructed a strong jet sample containing 50 flat-spectrum radio quasars, 51 low-synchrotron-peaked BL Lac objects, and 18 intermediate-synchrotron-peaked BL Lac objects to explore the origin of X-ray emissions. Generally, blazars are the typical radio-loud active galactic nucleus with a powerful jet toward the observer, causing their broadband emissions to be boosted. By considering the Doppler boosting effect, we obtain the intrinsic radio–X-ray correlation and the fundamental plane (FP) of black hole activity for the strong jet sources: the intrinsic radio–X-ray correlation is  , which favor the jet-dominated mode; the intrinsic FP is    , which can be interpreted by the hybrid mode of jet+standard disk. Our results suggest that the X-ray emissions of strong jet sources are dominated by the jets, but there may also be a small contribution from the disk. In addition, the radio–X-ray correlation and FP of strong jet sources do not have a significant dependence on the Eddington-ratio.

Keywords: Accretion, Black hole physics, X-ray astronomy, BL Lacertae objects, Radio jets, Blazars, Galaxy accretion disks, Flat-spectrum radio quasars, Active galactic nuclei
Constraints on Cosmic-Ray Acceleration in Bright Gamma-Ray Bursts with Observations of Fermi. Gamma-ray bursts (GRBs) are widely suggested as potential sources of ultrahigh-energy cosmic rays. The kinetic energy of the jets dissipates, leading to the production of an enormous amount of gamma-ray photons and possibly also the acceleration of protons. The accelerated protons will interact with the radiation of the GRB via the photomeson and Bethe–Heitler processes, which can initiate electromagnetic cascades. This process can give rise to broadband radiation up to the GeV–TeV gamma-ray regime. The expected gamma-ray flux from cascades depends on the properties of the GRB jet, such as the dissipation radius Rdiss, the bulk Lorentz factor Γ, and the baryon loading factor ηp. Therefore, observations of Fermi-LAT can impose constraints on these important parameters. In this study, we select 12 GRBs of high keV–MeV fluence and constrain the baryon loading factor, under different combinations of the bulk Lorentz factor and the dissipation radius based on Fermi-LAT's measurements. Our findings indicate a strong constraint of ηp &lt; 10 for most selected GRBs over a large parameter space except for large dissipation radii (≳1015 cm) and high bulk Lorentz factors (≳600). The constraint is comparable to, and in some GRBs even stronger than, that from high-energy neutrinos for stacked GRBs. Our results suggest that for a typical bulk Lorentz factor of several hundred, the dissipation radii of GRBs need to be large to avoid overshooting the GeV gamma-ray flux during the prompt emission phase of GRBs, which can be used to constrain GRBs.

Keywords: Neutrino astronomy, Cosmic ray sources, Gamma-ray bursts, High energy astrophysics
Modeling the Impact of Moderate External UV Irradiation on Disk Chemistry. The chemistry within a protoplanetary disk is greatly affected by external radiation from the local stellar environment. Previous work has focused on extreme radiation fields, representative of the center of something like the Orion Nebula Cluster. However, even in such environments, many disks exist at the edges of a cluster where the lower stellar density leads to radiation fields weaker by orders of magnitude compared to the center. We present new chemical models of a T Tauri disk in the presence of a moderately increased interstellar radiation field (ISRF). Such an environment has a background UV strength 10–100 times higher than the galactic average ISRF. Moderate radiation fields are among the most prevalent disk-harboring environments and have interesting implications for the chemistry of the outer disk radii. We find that the external UV radiation creates an outer ionization front that impacts the cold disk chemistry to varying degrees, depending on outer disk structure. Certain molecules like C+, N2H+, C, and CS are more strongly impacted by the ISRF in their abundance, column density, and observable emission. Other abundant species like HCO+ and CO are less affected by the external UV flux in the outer disk under such moderate UV conditions. Further, we demonstrate that the chemistry occurring in the inner tens of au is relatively unchanged, which suggests that even in moderately externally irradiated disks the inner disk chemistry may be more similar to isolated disks like those in, e.g., the Taurus and Lupus star-forming regions.

Keywords: Chemical reaction network models, Protoplanetary disks, Astrochemistry
Effects of Subhalos on Interpreting Highly Magnified Sources Near Lensing Caustics. Large magnification factors near gravitational lensing caustics of galaxy-cluster lenses allow the study of individual stars or compact stellar associations at cosmological distances. We study how the presence of sub-galactic subhalos, an inevitable consequence of cold dark matter, can alter the property of caustics and hence change the interpretation of highly magnified sources that lie atop them. First, we consider a galaxy-cluster halo populated with subhalos sampled from a realistic subhalo mass function calibrated to N-body simulations. Then, we compare a semianalytical approximation and an adaptive ray-shooting method that we employ to quantify the property of the caustics. As a case study, we investigate Earendel, a z = 6.2 candidate of magnified single- or multiple-star system with a lone lensed image atop the critical curve in the Sunrise Arc. We find that the source size constraint (≲0.3 pc) previously derived from macrolens models should be relaxed by a factor of a few to 10 when subhalos are accounted for, therefore allowing the possibility of a compact star cluster. The subhalos could introduce an astrometric perturbation that is ≲0 5, which does not contradict observation. These conclusions are largely robust to changes in the subhalo population. Subhalos therefore should be seriously accounted for when interpreting the astrophysical nature of similar highly magnified sources uncovered in recent high-z observations.

Keywords: Strong gravitational lensing, Caustic curve, Cold dark matter
Equatorial Enhancement in the Dustiest OH/IR Stars in the Galactic Bulge. We have detected the 10 μm silicate feature and the 11.3 μm crystalline forsterite feature in absorption in 21 oxygen-rich asymptotic giant branch stars in the Galactic bulge. The depths of the 10 μm feature indicate highly obscured circumstellar environments. The additional crystalline features may suggest either an extended envelope or dust formation in a high-density environment. We have also modeled the spectral energy distributions (SEDs) of the sample using radiative transfer models, and compared the results to wind speeds measured using 1612 MHz circumstellar OH masers, as well as previous estimates of circumstellar properties. The 16 sources with measured pulsation periods appear on sequence D of the mid-IR period─luminosity relation, associated with the long secondary period. We suspect that all of these sources are in fact fundamental-mode pulsators. At least two sources appear on the fundamental-mode sequence when accounting for the dust content. For the remainder, these sources are also likely fundamental-mode pulsators with extended envelopes. Taken as a whole, the high optical depths, crystalline features, discrepancies between observed and modeled wind speeds, pulsation periods longer than other fundamental-mode pulsators, and SED and pulsation properties similar to those with known equatorially enhanced circumstellar envelopes (e.g., OH 26.5+0.6 and OH 30.1─0.7) lead us to believe that these sources are likely to be equatorially enhanced.

Keywords: Galactic bulge, Stellar mass loss, Asymptotic giant branch stars, Stellar winds, Long period variable stars, Circumstellar dust
Starburst Galaxies in Their Last Billion Years: An Hδ Absorption Line Selected Sample. In this paper, we focus on the study of starburst galaxies in their final billion years. Our galaxy selection is based solely on the presence of the Hδ absorption line, which permits the later evolution of starburst galaxies to be traced, coinciding with the emergence of A-type stars in these galaxies. We propose a novel method that utilizes star formation rate and UVJ colors to classify galaxies in the sample, and use the spectral features to mark their stages of evolution. Our in-depth analysis of the Mg II line indicates the substantial increase in the number of F- and G-type stars when a galaxy evolves from star-forming to quiescent phase. Furthermore, we identify active galactic nuclei in this sample to explore their roles in the later stage of the star formation history of galaxies.

Keywords: Starburst galaxies, Star formation, Post-starburst galaxies
Adiabatic Index in Fluid Models of Collisionless Black Hole Accretion. Models of highly sub-Eddington accretion onto black holes commonly use a single-fluid model for the collisionless, near-horizon plasma. These models must specify an equation of state. It is common to use an ideal gas with p = (γ ‑ 1)u and γ = 4/3, 13/9, or 5/3, but these produce significantly different outcomes. We discuss the origins of this discrepancy and the assumptions underlying the single-fluid model. The main result of this investigation is that under conditions relevant to low-luminosity black hole accretion the best choice of single-fluid adiabatic index is close to but slightly less than 5/3. Along the way we provide a simple equilibrium model for the relation between the ion-to-electron dissipation ratio and the ion-to-electron temperature ratio, and explore the implications for electron temperature fluctuations in Event Horizon Telescope sources.

Keywords: Accretion, Supermassive black holes, Magnetohydrodynamics, Plasma physics, Low-luminosity active galactic nuclei
Observations of the X-Ray Millihertz Quasiperiodic Oscillations in Hercules X-1. With a systematic timing investigation of the persistent X-ray binary pulsar Her X-1 based on a large number of Insight-HXMT observations between 2017 and 2019, we confirm the presence of X-ray millihertz quasiperiodic oscillations (mHz QPOs) at ∼0.01 Hz. By applying wavelet analysis in our data analysis procedures, we first identify ∼0.005–0.009 Hz QPOs coexisting with the ∼0.01 Hz QPOs. Wavelet analysis suggests that these QPO features show transient behaviors, that the frequencies of mHz QPOs evolve in short timescales. There exists a positive relation between QPO centroid frequency (from ∼0.005 to 0.009 Hz) and X-ray luminosity, while the 10 mHz QPO frequencies remain nearly constant for different luminosities, which suggests different physical mechanisms for the two types of mHz QPOs. The 10 mHz QPOs in both X-ray and UV bands would have the same origin related to the beat frequency where the Alfvén radius is close to the corotation radius, and the 5 mHz QPOs may originate from magnetic disk precession.

Keywords: Neutron stars, X-ray binary stars