Sazuna/UAT_keywords huggingface dataset:
Additional Evidence for a Pulsar Wind Nebula in the Heart of SN 1987A from Multiepoch X-Ray Data and MHD Modeling. Since the day of its explosion, supernova (SN) 1987A has been closely monitored to study its evolution and to detect its central compact relic. In fact, the formation of a neutron star is strongly supported by the detection of neutrinos from the SN. However, besides the detection in the Atacama Large Millimeter/submillimeter Array (ALMA) data of a feature that is compatible with the emission arising from a protopulsar wind nebula (PWN), the only hint of the existence of such an elusive compact object is provided by the detection of hard emission in NuSTAR data up to ~20 keV. We report on the simultaneous analysis of multiepoch observations of SN 1987A performed with Chandra, XMM-Newton, and NuSTAR. We also compare the observations with a state-of-the-art three-dimensional magnetohydrodynamic simulation of SN 1987A. A heavily absorbed power law, consistent with the emission from a PWN embedded in the heart of SN 1987A, is needed to properly describe the high-energy part of the observed spectra. The spectral parameters of the best-fit power law are in agreement with the previous estimate, and exclude diffusive shock acceleration as a possible mechanism responsible for the observed nonthermal emission. The information extracted from our analysis is used to infer the physical characteristics of the pulsar and the broadband emission from its nebula, in agreement with the ALMA data. Analysis of the synthetic spectra also shows that, in the near future, the main contribution to the Fe K emission line will originate in the outermost shocked ejecta of SN 1987A.

Keywords: Neutron stars, X-ray astronomy, X-ray point sources, Plasma astrophysics, Pulsars, Supernova remnants, Compact objects, X-ray sources, Interstellar synchrotron emission, Shocks, X-ray observatories, Magnetohydrodynamical simulations
S-type Stars Discovered in Medium-resolution Spectra of LAMOST DR9. In this paper, we report on 606 S-type stars identified from Data Release 9 of the LAMOST medium-resolution spectroscopic (MRS) survey; 539 of them are reported for the first time. The discovery of these stars is a three-step process, i.e., selecting with ZrO-band indices greater than 0.25, excluding non-S-type stars with the iterative Support Vector Machine method, and finally retaining stars with absolute bolometric magnitude larger than -7.1. The 606 stars are consistent with the distribution of known S-type stars in the color-magnitude diagram. We estimated the C/Os using the [C/Fe] and [O/Fe] provided by APOGEE and the MARCS model for S-type stars, respectively, and the results of the two methods show that the C/Os of all stars are larger than 0.5. Both the locations on the color-magnitude diagram and C/Os further verify the nature of our S-type sample. Investigating the effect of TiO and atmospheric parameters on ZrO with the sample, we found that log g has a more significant impact on ZrO than T eff and [Fe/H], and both TiO and log g may negatively correlate with ZrO. According to the criterion of Tian et al., a total of 238 binary candidates were found by the zero-point-calibrated radial velocities from the officially released catalog of LAMOST MRS and the catalog of Zhang et al. A catalog of these 606 S-type stars is available from the following link: doi.org/10.12149/101097.

Keywords: S stars
Contrasting the Mechanisms of Reconnection-driven Electron Acceleration with In Situ Observations from MMS in the Terrestrial Magnetotail. The question of how magnetic reconnection accelerates particles is a long-standing problem in space physics and astrophysics. Earth's magnetosphere is an ideal laboratory for investigating this issue via in situ satellite observations. This article presents a statistical study of the electron acceleration produced by different mechanisms in the near-Earth magnetotail using the unique measurement capabilities of the Magnetospheric Multiscale mission. We find that the average acceleration rates and occurrence rates of large acceleration tend to be higher in outflows with greater speeds. Betatron and first-order Fermi accelerations are intensified near the neutral sheet, while the acceleration from E ∣∣ is not only intensified in the neutral sheet but also significant far away from it, likely in the separatrix region. In contrast to previous studies suggesting that the acceleration and energy conversion predominantly occur in the outflow region, we find that the acceleration rate near the X line is comparable to that in the outflow.

Keywords: Space plasmas, Planetary magnetospheres, Plasma physics
Li-rich Giants in LAMOST Survey. III. The Statistical Analysis of Li-rich Giants. The puzzle of the Li-rich giant is still unsolved, contradicting the prediction of the standard stellar models. Although the exact evolutionary stages play a key role in the knowledge of Li-rich giants, a limited number of Li-rich giants have been observed with high-quality asteroseismic parameters to clearly distinguish the stellar evolutionary stages. Based on the LAMOST Data Release 7 (DR7), we applied a data-driven neural network method to derive the parameters for giant stars, which contain the largest number of Li-rich giants. The red giant stars are classified into three stages of Red Giant Branch (RGB), Primary Red Clump (PRC), and Secondary Red Clump (SRC) relying on the estimated asteroseismic parameters. In the statistical analysis of the properties (i.e., stellar mass, carbon, nitrogen, Li-rich distribution, and frequency) of Li-rich giants, we found that (1) most of the Li-rich RGB stars are suggested to be the descendants of Li-rich pre-RGB stars and/or the result of engulfment of planet or substellar companions; (2) the massive Li-rich SRC stars could be the natural consequence of Li depletion from the high-mass Li-rich RGB stars; and (3) internal mixing processes near the helium flash can account for the phenomenon of Li richness on PRC that dominated the Li-rich giants. Based on the comparison of [C/N] distributions between Li-rich and normal PRC stars, the Li-enriched processes probably depend on the stellar mass.

Keywords: Giant stars, Chemically peculiar giant stars, Classification, Stellar abundances, Stellar evolution
Kinetic Simulations of Instabilities and Particle Acceleration in Cylindrical Magnetized Relativistic Jets. Relativistic magnetized jets, such as those from AGN, GRBs, and XRBs, are susceptible to current- and pressure-driven MHD instabilities that can lead to particle acceleration and nonthermal radiation. Here, we investigate the development of these instabilities through 3D kinetic simulations of cylindrically symmetric equilibria involving toroidal magnetic fields with electron-positron pair plasma. Generalizing recent treatments by Alves et al. and Davelaar et al., we consider a range of initial structures in which the force due to toroidal magnetic field is balanced by a combination of forces due to axial magnetic field and gas pressure. We argue that the particle energy limit identified by Alves et al. is due to the finite duration of the fast magnetic dissipation phase. We find a rather minor role of electric fields parallel to the local magnetic fields in particle acceleration. In all investigated cases, a kink mode arises in the central core region with a growth timescale consistent with the predictions of linearized MHD models. In the case of a gas-pressure-balanced (Z-pinch) profile, we identify a weak local pinch mode well outside the jet core. We argue that pressure-driven modes are important for relativistic jets, in regions where sufficient gas pressure is produced by other dissipation mechanisms.

Keywords: Jets, High energy astrophysics
High-energy Emission Component, Population, and Contribution to the Extragalactic Gamma-Ray Background of Gamma-Ray-emitting Radio Galaxies. In this study, we systematically studied the X-ray to GeV gamma-ray spectra of 61 Fermi Large Area Telescope detected radio galaxies. We found an anticorrelation between peak frequency and peak luminosity in the high-energy spectral component of radio galaxies, similar to blazars. With this sample, we also constructed a gamma-ray luminosity function (GLF) of gamma-ray-loud radio galaxies. We found that blazar-like GLF shapes can reproduce their redshift and luminosity distribution, but the log N-log S relation prefers models with more low-z radio galaxies. Utilizing our latest GLF, the contribution of radio galaxies to the extragalactic gamma-ray background is found to be 1%-10%. We further investigated the nature of gamma-ray-loud radio galaxies. Compared to radio or X-ray flux-limited radio galaxy samples, the gamma-ray-selected sample tends to lack high radio power galaxies like FR II radio galaxies. We also found that only ~10% of radio galaxies are GeV gamma-ray loud. Radio galaxies may contribute to the cosmic MeV gamma-ray background comparable to blazars if gamma-ray-quiet radio galaxies have X-ray to gamma-ray spectra like Cen A, with a small gamma-ray-to-X-ray flux ratio.

Keywords: Galaxy jets
Improving Cosmological Constraints from Galaxy Cluster Number Counts with CMB-cluster-lensing Data: Results from the SPT-SZ Survey and Forecasts for the Future. We show the improvement to cosmological constraints from galaxy cluster surveys with the addition of cosmic microwave background (CMB)-cluster lensing data. We explore the cosmological implications of adding mass information from the 3.1σ detection of gravitational lensing of the CMB by galaxy clusters to the Sunyaev-Zel'dovich (SZ) selected galaxy cluster sample from the 2500 deg2 SPT-SZ survey and targeted optical and X-ray follow-up data. In the ΛCDM model, the combination of the cluster sample with the Planck power spectrum measurements prefers ${\sigma }_{8}{\left({{\rm{\Omega }}}_{m}/0.3\right)}^{0.5}=0.831\pm 0.020$ . Adding the cluster data reduces the uncertainty on this quantity by a factor of 1.4, which is unchanged whether the 3.1σ CMB-cluster lensing measurement is included or not. We then forecast the impact of CMB-cluster lensing measurements with future cluster catalogs. Adding CMB-cluster lensing measurements to the SZ cluster catalog of the ongoing SPT-3G survey is expected to improve the expected constraint on the dark energy equation of state w by a factor of 1.3 to σ(w) = 0.19. We find the largest improvements from CMB-cluster lensing measurements to be for σ 8, where adding CMB-cluster lensing data to the cluster number counts reduces the expected uncertainty on σ 8 by respective factors of 2.4 and 3.6 for SPT-3G and CMB-S4.

Keywords: Cosmology, Sigma8
Cosmic-Ray-driven Multiphase Gas Formed via Thermal Instability. Cosmic rays (CRs) are an important energy source in the circumgalactic medium that impact the multiphase gas structure and dynamics. We perform two-dimensional CR-magnetohydrodynamic simulations to investigate the role of CRs in accelerating multiphase gas formed via thermal instability. We compare outflows driven by CRs to those driven by a hot wind with equivalent momentum. We find that CR-driven outflow produces lower density contrast between cold and hot gas due to nonthermal pressure support, and yields a more filamentary cloud morphology. While entrainment in a hot wind can lead to cold gas increasing due to efficient cooling, CRs tend to suppress cold gas growth. The mechanism of this suppression depends on magnetic field strength, with CRs either reducing cooling or shredding the clouds by differential acceleration. Despite the suppression of cold gas growth, CRs are able to launch the cold clouds to observed velocities without rapid destruction. The dynamical interaction between CRs and multiphase gas is also sensitive to the magnetic field strength. In relatively strong fields, the CRs are more important for direct momentum input to cold gas. In relatively weak fields, the CRs impact gas primarily by heating, which modifies gas pressure.

Keywords: Galactic winds, Circumgalactic medium, Interstellar medium, Cosmic rays
The Hyper-inflation Stage in the Coronal Mass Ejection Formation: A Missing Link That Connects Flares, Coronal Mass Ejections, and Shocks in the Low Corona. We analyze the formation and three-dimensional (3D) evolution of two coronal mass ejections (CMEs) and their associated waves in the low corona via a detailed multi-viewpoint analysis of extreme-ultraviolet observations. We analyze the kinematics in the radial and lateral directions and identify three stages in the early evolution of the CME: (1) a hyper-inflation stage, when the CME laterally expands at speeds of ~1000 km s-1, followed by (2) a shorter and slower expansion stage of a few minutes and ending with (3) a self-similar phase that carries the CME into the middle corona. The first two stages coincide with the impulsive phase of the accompanying flare, the formation and separation of an EUV wave from the CME, and the start of the metric type II radio burst. Our 3D analysis suggests that the hyper-inflation phase may be a crucial stage in the CME formation with wide-ranging implications for solar eruption research. It likely represents the formation stage of the magnetic structure that is eventually ejected into the corona, as the white-light CME. It appears to be driven by the injection of poloidal flux into the ejecting magnetic structure, which leads to the lateral (primarily) growth of the magnetic flux rope. The rapid growth results in the creation of EUV waves and eventually shocks at the CME flanks that are detected as metric type II radio bursts. In other words, the hyper-inflation stage in the early CME evolution may be the "missing" link between CMEs, flares, and coronal shocks.

Keywords: Solar activity, Solar coronal waves, Solar coronal mass ejections
Formation of the Asymmetric Accretion Disk from Stellar Wind Accretion in an S-type Symbiotic Star. The accretion process in a typical S-type symbiotic star, targeting AG Draconis, is investigated through 3D hydrodynamical simulations using the FLASH code. Regardless of the wind velocity of the giant star, an accretion disk surrounding the white dwarf is always formed. In models where the wind is faster than the orbital velocity of the white dwarf, the disk size and accretion rate are consistent with the predictions under Bondi-Hoyle-Lyttleton (BHL) conditions. In slower-wind models, unlike the BHL predictions, the disk size does not grow, and the accretion rate increases to a considerably higher level, up to &gt;20% of the mass-loss rate of the giant star. The accretion disk in our fiducial model is characterized by a flared disk with a radius of 0.16 au and a scale height of 0.03 au. The disk mass of ~5 × 10-8 M ⊙ is asymmetrically distributed, with the density peak toward the giant star being about 50% higher than the density minimum in the disk. Two inflowing spiral features are clearly identified, and their relevance to the azimuthal asymmetry of the disk is pointed out. The flow in the accretion disk is found to be sub-Keplerian, at about 90% of the Keplerian speed, which indicates a caveat of overestimating the O VI emission region from the spectroscopy of Raman-scattered O VI features at 6825 and 7082 Å.

Keywords: Stellar accretion disks, Hydrodynamical simulations, Symbiotic binary stars
On the Stability of Low-mass Planets with Supercritical Hydrospheres. Short-period, low-mass water-rich planets are subject to strong irradiation from their host star, resulting in hydrospheres in a supercritical state. In this context, we explore the role of irradiation on small terrestrial planets that are moderately wet in the low-mass regime (0.2-1 M ⊕). We investigate their bulk properties for water content in the 0.01-5% range by making use of an internal structure model that is coupled to an atmosphere model. This coupling allows us to take into account both the compression of the interior due to the weight of the hydrosphere and the possibility of atmospheric instability in the low-mass regime. We show that, even for low masses and low water content, these planets display inflated atmospheres. For extremely low planetary masses and high irradiation temperatures, we find that steam atmospheres become gravitationally unstable when the ratio η of their scale height to planetary radius exceeds a critical value of ~0.1. This result is supported by observational data, as all currently detected exoplanets exhibit values of η smaller than 0.013. Depending on their water content, our results show that highly irradiated, low-mass planets up to 0.9 M ⊕ with significative hydrospheres are not in a stable form and should lose their volatile envelope.

Keywords: Exoplanet astronomy, Exoplanet atmospheric composition , Planetary structure, Exoplanet structure
Unusually High HCO<SUP>+</SUP>/CO Ratios in and outside Supernova Remnant W49B. Galactic supernova remnants (SNRs) and their environments provide the nearest laboratories to study SN feedback. We performed molecular observations toward SNR W49B, the most luminous Galactic SNR in the X-ray band, aiming to explore signs of multiple feedback channels of SNRs on nearby molecular clouds (MCs). We found very broad HCO+ lines with widths of dv ~ 48-75 km s-1 in the SNR southwest, providing strong evidence that W49B is perturbing MCs at a systemic velocity of V  LSR  = 61-65 km s-1, and placing the W49B at a distance of 7.9 ± 0.6 kpc. We observed unusually high-intensity ratios of HCO+ J=1-0/CO J=1-0 not only at shocked regions (1.1 ± 0.4 and 0.70 ± 0.16) but also in quiescent clouds over 1 pc away from the SNR's eastern boundary (≥0.2). By comparing with the magnetohydrodynamics shock models, we interpret that the high ratio in the broad-line regions can result from a cosmic-ray (CR) induced chemistry in shocked MCs, where the CR ionization rate is enhanced to around 10-102 times of the Galactic level. The high HCO+/CO ratio outside the SNR is probably caused by the radiation precursor, while the luminous X-ray emission of W49B can explain a few properties in this region. The above results provide observational evidence that SNRs can strongly influence the molecular chemistry in and outside the shock boundary via their shocks, CRs, and radiation. We propose that the HCO+/CO ratio is a potentially useful tool to probe an SNR's multichannel influence on MCs.

Keywords: Molecular clouds, Supernova remnants, X-ray sources, Shocks, Cosmic rays
ADDGALS: Simulated Sky Catalogs for Wide Field Galaxy Surveys. We present a method for creating simulated galaxy catalogs with realistic galaxy luminosities, broadband colors, and projected clustering over large cosmic volumes. The technique, denoted ADDGALS (Adding Density Dependent GAlaxies to Lightcone Simulations), uses an empirical approach to place galaxies within lightcone outputs of cosmological simulations. It can be applied to significantly lower-resolution simulations than those required for commonly used methods such as halo occupation distributions, subhalo abundance matching, and semi-analytic models, while still accurately reproducing projected galaxy clustering statistics down to scales of r ~ 100 h -1kpc . We show that ADDGALS catalogs reproduce several statistical properties of the galaxy distribution as measured by the Sloan Digital Sky Survey (SDSS) main galaxy sample, including galaxy number densities, observed magnitude and color distributions, as well as luminosity- and color-dependent clustering. We also compare to cluster-galaxy cross correlations, where we find significant discrepancies with measurements from SDSS that are likely linked to artificial subhalo disruption in the simulations. Applications of this model to simulations of deep wide-area photometric surveys, including modeling weak-lensing statistics, photometric redshifts, and galaxy cluster finding, are presented in DeRose et al., and an application to a full cosmology analysis of Dark Energy Survey (DES) Year 3 like data is presented in DeRose et al. We plan to publicly release a 10,313 square degree catalog constructed using ADDGALS with magnitudes appropriate for several existing and planned surveys, including SDSS, DES, VISTA, Wide-field Infrared Survey Explorer, and Rubin Observatory's Legacy Survey of Space and Time.

Keywords: Galaxy dark matter halos, Large-scale structure of the universe, Dark matter, Quantum cosmology, Galaxy evolution, N-body simulations
Four-hundred Very Metal-poor Stars Studied with LAMOST and Subaru. I. Survey Design, Follow-up Program, and Binary Frequency. The chemical abundances of very metal-poor stars provide important constraints on the nucleosynthesis of the first generation of stars and early chemical evolution of the Galaxy. We have obtained high-resolution spectra with the Subaru Telescope for candidates of very metal-poor stars selected with a large survey of Galactic stars carried out with LAMOST. In this series of papers, we report on the elemental abundances of about 400 very metal-poor stars and discuss the kinematics of the sample obtained by combining the radial velocities measured in this study and recent astrometry obtained with Gaia. This paper provides an overview of our survey and follow-up program, and reports radial velocities for the whole sample. We identify seven double-lined spectroscopic binaries from our high-resolution spectra, for which radial velocities of the components are reported. We discuss the frequency of such relatively short-period binaries at very low metallicity.

Keywords: Population II stars, Stellar abundances, Chemical abundances
Four-hundred Very Metal-poor Stars Studied with LAMOST and Subaru. II. Elemental Abundances. We present homogeneous abundance analysis of over 20 elements for 385 very metal-poor (VMP) stars based on the LAMOST survey and follow-up observations with the Subaru Telescope. It is the largest high-resolution VMP sample (including 363 new objects) studied by a single program, and the first attempt to accurately determine evolutionary stages for such a large sample based on Gaia parallaxes. The sample covers a wide metallicity range from [Fe/H] ≲ -1.7 down to [Fe/H] ~ -4.3, including over 110 objects with [Fe/H] ≤ -3.0. The expanded coverage in evolutionary status makes it possible to define the abundance trends respectively for giants and turnoff stars. The newly obtained abundance data confirm most abundance trends found by previous studies, but also provide useful updates and new samples of outliers. The Li plateau is seen in main-sequence turnoff stars with -2.5 &lt; [Fe/H] &lt; -1.7 in our sample, whereas the average Li abundance is clearly lower at lower metallicity. Mg, Si, and Ca are overabundant with respect to Fe, showing decreasing trend with increasing metallicity. Comparisons with chemical evolution models indicate that the overabundance of Ti, Sc, and Co are not well reproduced by current theoretical predictions. Correlations are seen between Sc and α-elements, while Zn shows a detectable correlation only with Ti but not with other α-elements. The fraction of carbon-enhanced stars ([C/Fe] &gt; 0.7) is in the range of 20%-30% for turnoff stars depending on the treatment of objects for which C abundance is not determined, which is much higher than that in giants (~8%). Twelve Mg-poor stars ([Mg/Fe] &lt; 0.0) have been identified in a wide metallicity range from [Fe/H] ~ -3.8 through -1.7. Twelve Eu-rich stars ([Eu/Fe] &gt; 1.0) have been discovered in -3.4 &lt; [Fe/H] &lt; -2.0, enlarging the sample of r-process-enhanced stars with relatively high metallicity.

Keywords: Population II stars, Chemical abundances, Galaxy chemical evolution