Sazuna/UAT_keywords huggingface dataset:
Carbon Stars from Gaia Data Release 3 and the Space Density of Dwarf Carbon Stars. Carbon stars (with atmospheric C/O &gt; 1) range widely in temperature and luminosity, from low-mass dwarfs to asymptotic giant branch (AGB) stars. The main-sequence dwarf carbon (dC) stars have inherited carbon-rich material from an AGB companion, which has since transitioned to a white dwarf. The dC stars are far more common than C giants, but no reliable estimates of the dC space density have been published to date. We present results from an all-sky survey for carbon stars using the low-resolution XP spectra from Gaia Data Release 3. We developed and measured a set of spectral indices contrasting C2 and CN molecular band strengths in carbon stars against common absorption features found in normal (C/O &lt; 1) stars, such as Ca I, TiO, and Balmer lines. We combined these indices with the XP spectral coefficients as inputs to supervised machine learning algorithms trained on a vetted sample of known C stars from LAMOST. We describe the selection of the carbon candidate sample and provide a catalog of 43,574 candidates dominated by cool C giants in the Magellanic Clouds and at low Galactic latitude in the Milky Way. We report the confirmation of candidate C stars using intermediate-resolution (R ∼ 1800) optical spectroscopy from the Fred Lawrence Whipple Observatory and provide estimates of the sample purity and completeness. From a carefully vetted sample of over 600 dCs, we measure their local space density to be   (about one dC in every local disk volume of radius 50 pc), with a relatively large disk scale height of  pc.

Keywords: Binary stars, Late-type stars, Close binary stars, Carbon stars, Chemically peculiar stars
The Expanding 3 kpc Arms Are Neither Expanding nor Spiral Arms but X1 Orbits Driven by the Galactic Bar. Near the center of our Milky Way is a bar-like structure and the so-called Expanding 3 kpc arms. We currently have limited knowledge of this important region, since we are about 8.2 kpc from the center and cannot directly observe it at optical wavelengths, owing to strong extinction from interstellar dust. Here we present extremely precise very long baseline interferometry measurements of H2O maser sources from the BeSSeL Survey, where extinction is not a problem, which accurately determine the three-dimensional locations and motions of three massive young stars. Combined with previous measurements, these stars delineate a trail of orbits outlining the Milky Way's Galactic bar. We present the first measurements capturing the dynamics of quasi-elliptical (X1) orbits around the Galactic bar. Our findings provide evidence substantiating the existence of such orbits populated by massive young stars. Our measurements of the position and velocity of a number of massive young stars, previously identified with the Expanding 3 kpc arms, show that they are more likely located in the X1 orbits about the Galactic bar. Also, some stars previously assigned to the Norma spiral arm appear to be in these orbits, which suggests that this spiral arm does not extend past the end of the bar.

Keywords: Trigonometric parallax, Galactic center, Star forming regions, Galaxy structure, Radio astrometry, Very long baseline interferometry, Young stellar objects, Astrophysical masers, Galactic bar
Superclustering with the Atacama Cosmology Telescope and Dark Energy Survey. II. Anisotropic Large-scale Coherence in Hot Gas, Galaxies, and Dark Matter. Statistics that capture the directional dependence of the baryon distribution in the cosmic web enable unique tests of cosmology and astrophysical feedback. We use constrained oriented stacking of thermal Sunyaev–Zel'dovich (tSZ) maps to measure the anisotropic distribution of hot gas 2.5–40 Mpc away from galaxy clusters embedded in massive filaments and superclusters. The cluster selection and orientation (at a scale of ∼15 Mpc) use Dark Energy Survey (DES) Year 3 data, while expanded tSZ maps from the Atacama Cosmology Telescope Data Release 6 enable a ∼3× more significant measurement of the extended gas compared to the technique's proof-of-concept. Decomposing stacks into cosine multipoles of order m, we detect a dipole (m = 1) and quadrupole (m = 2) at 8σ–10σ, as well as evidence for m = 4 signal at up to 6σ, indicating sensitivity to late-time non-Gaussianity. We compare to Cardinal simulations with spherical gas models pasted onto dark matter halos. The fiducial tSZ data can discriminate between two models that deplete pressure differently in low-mass halos (mimicking astrophysical feedback), preferring higher average pressure in extended structures. However, uncertainty in the amount of cosmic infrared background contamination reduces the constraining power. Additionally, we apply the technique to DES galaxy density and weak lensing to study for the first time their oriented relationships with tSZ. In the tSZ-to-lensing relation, averaged on 7.5 Mpc (transverse) scales, we observe dependence on redshift but not shape or radial distance. Thus, on large scales, the superclustering of gas pressure, galaxies, and total matter is coherent in shape and extent.

Keywords: Cosmology, Weak gravitational lensing, Galaxy clusters, Large-scale structure of the universe, Superclusters, Sunyaev-Zeldovich effect, Cosmic web, Intergalactic filaments
The Hot Accretion Flow Evolution in the Black Hole X-Ray Binary MAXI J1348-630. MAXI J1348-630, as a low-mass black hole binary system in the Galaxy, showed an X-ray outburst in 2019. We analyzed the Insight Hard X-ray Modulation Telescope spectral data in the low hard state and intermediate state during the outburst from MJD 58510 to 58519 at the energy band from 2 to 100 keV. During the entire process, a thin disk extending to the innermost stable circular orbit (ISCO) from a large truncated disk (truncated radius &gt;5 ISCO) suggested the corona geometry evolution. There exist time lags between the radio and hard X-ray flux peaks: the 30–100 keV flux is about 5 days ahead of the radio flux, the 11–30 keV flux is about 4 days ahead, and the reflection fraction is about 2 days ahead, with the accretion disk approaching the ISCO about 1 day before radio peak. This disk–corona–jet coupling and evolution suggest the corona contains two phases of cold dense material and hot gas, with the high-temperature region of the corona cooling fast. The strong radio emission accompanying a thin accretion disk with a relatively high accretion rate favors a magnetic tower jet mechanism.

Keywords: Stellar accretion disks, Black hole physics, X-ray binary stars, Relativistic jets
Hypervelocity Stars Trace a Supermassive Black Hole in the Large Magellanic Cloud. Hypervelocity stars (HVSs) are produced by the Hills mechanism when a stellar binary is disrupted by a supermassive black hole (SMBH). The HVS Survey detected 21 unbound B-type main-sequence stars in the Milky Way's outer halo that are consistent with ejection via the Hills mechanism. We revisit the trajectories of these stars in light of proper motions from Gaia DR3 and modern constraints on the Milky Way–Large Magellanic Cloud (LMC) orbit. We find that half of the unbound HVSs discovered by the HVS Survey trace back not to the Galactic Center but to the LMC. Motivated by this finding, we construct a forward model for HVSs ejected from an SMBH in the LMC and observed through the selection function of the HVS Survey. The predicted spatial and kinematic distributions of the simulated HVSs are remarkably similar to the observed distributions. In particular, we reproduce the conspicuous angular clustering of HVSs around the constellation Leo. This clustering occurs because HVSs from the LMC are boosted by ∼300 km s‑1 by the orbital motion of the LMC, and stars launched parallel to this motion are preferentially selected as HVS candidates. We find that the birth rate and clustering of LMC HVSs cannot be explained by supernova runaways or dynamical ejection scenarios not involving an SMBH. From the ejection velocities and relative number of Magellanic versus Galactic HVSs, we constrain the mass of the LMC SMBH to be   (≃6 × 105 M⊙).

Keywords: Astrophysical black holes
Do Red Galaxies Form More Stars than Blue Galaxies?. A new model is proposed in which typical galaxies form most of their stellar mass in a phase with an intrinsically red stellar population. In the standard picture, galaxies with intrinsically red stellar populations are believed to have old stellar populations, so that only galaxies with blue stellar populations have significant star formation, and subsequent changes to the stellar population come predominantly from aging and merging populations that have already formed. However, several observational puzzles have developed that are difficult to reconcile with this standard scenario. The most massive blue star-forming galaxies, presumed to be at the end of their stellar mass growth, are ∼1 dex less massive, have a ∼1 dex lower M*/MBH ratio, and have a bottom-lighter IMF than local quiescent galaxies. Here, a new solution is proposed: at low temperature and high metallicity, galaxies can continue to form stars efficiently without being able to form O and B stars. These red star-forming galaxies would have many of the same properties of the population currently described as post-starburst galaxies, allowing a new interpretation of their origin. Finally, additional falsifiable observational predictions of this model are also discussed.

Keywords: Stellar populations, Initial mass function, Star formation, Galaxy evolution
Measurement of the Forward Shock Velocities of the Supernova Remnant N132D Based on the Thermal X-Ray Emission. Measuring shock velocities is crucial for understanding the energy transfer processes at the shock fronts of supernova remnants (SNRs), including acceleration of cosmic rays. Here we present shock velocity measurements on the SNR N132D, based on the thermal properties of the shock-heated interstellar medium. We apply a self-consistent model developed in our previous work to X-ray data from deep Chandra observations with an effective exposure of ∼900 ks. In our model, both temperature and ionization relaxation processes in postshock plasmas are simultaneously calculated, so that we can trace back to the initial condition of the shock-heated plasma to constrain the shock velocity. We reveal that the shock velocity ranges from 800 to 1500 km s‑1 with moderate azimuthal dependence. Although our measurement is consistent with the velocity determined by independent proper motion measurements in the south rim regions, a large discrepancy between the two measurements (up to a factor of 4) is found in the north rim regions. This implies that a substantial amount of the kinetic energy has been transferred to the nonthermal component through highly efficient particle acceleration. Our results are qualitatively consistent with the gamma-ray observations of this SNR.

Keywords: Gamma-ray sources, Plasma astrophysics, Large Magellanic Cloud, Supernova remnants, Interstellar medium, Shocks, Cosmic rays
The Missing Link of Sulfur Chemistry in TMC-1: The Detection of c-C<SUB>3</SUB>H<SUB>2</SUB>S from the GOTHAM Survey. We present the spectroscopic characterization of cyclopropenethione in the laboratory and detect it in space using the Green Bank Telescope Observations of TMC-1: Hunting Aromatic Molecules survey. The detection of this molecule—the missing link in understanding the C3H2S isomeric family in TMC-1—completes the detection of all three low-energy isomers of C3H2S, as both CH2CCS and HCCCHS have been previously detected in this source. The total column density of this molecule (NT of   cm‑2 at an excitation temperature of   K) is smaller than both CH2CCS and HCCCHS and follows nicely the relative dipole principle (RDP), a kinetic rule of thumb for predicting isomer abundances that suggests that, all other chemistry among a family of isomers being the same, the member with the smallest dipole (μ) should be the most abundant. The RDP now holds for the astronomical abundance ratios of both the S-bearing and O-bearing counterparts observed in TMC-1; however, CH2CCO continues to elude detection in any astronomical source.

Keywords: Chemical abundances, Astrochemistry
The Halo Occupation Distribution Modeling of X-Ray-selected Active Galactic Nuclei at 0.6 &lt; z &lt; 2.6 in the COSMOS Field. We conduct precise measurements of active galactic nucleus (AGN) clustering at z ∼ 1 and z ∼ 2 by measuring the two-point cross-correlation function (CCF) between galaxies and X-ray-selected AGNs, and the two-point autocorrelation function (ACF) of galaxies in the COSMOS field, to interpret the CCF results. The galaxy sample was selected from the COSMOS2015 catalog, while the AGN sample was chosen from the Chandra-COSMOS Legacy Survey catalog. For the AGN samples at z ∼ 1 and z ∼ 2, we calculated AGN bias values of b = 1.16 (1.16; 1.31) and b = 2.95 (2.30; 3.55), respectively. These values correspond to typical host dark matter halo (DMH) masses of log(Mtyp/M⊙) = 11.82 (11.82; 12.12) and log(Mtyp/M⊙) = 12.80 (12.38; 13.06), respectively. Subsequently, we performed halo occupation distribution (HOD) modeling of X-ray-selected AGNs using the CCF and ACF of galaxies. We found a significant satellite AGN population at z ∼ 1 all over the DMH mass (MDMH) range occupied by AGNs, while z ∼ 2 AGNs in our sample are associated with higher-mass DMHs and smaller satellite fractions. The HOD analysis suggests a marginal tendency of increasing satellite slope with redshift, but larger samples are needed to confirm this with sufficient statistical significance. We find that the best-fit values of the satellite slope in both redshift bins are greater than 0, suggesting a tendency of increasing satellite AGN number with MDMH.

Keywords: Active galactic nuclei, X-ray active galactic nuclei
How Does a Protostar Form by Magnetized Gravitational Collapse?. Star formation through dynamical magnetized collapse remains an area of active astrophysical research. We carry out a comprehensive exploration on the magnetized gravitational collapse of a nonrotating self-gravitating initially spherically symmetric prestellar cloud core using two-dimensional nonideal magnetohydrodynamic simulations incorporating ambipolar diffusion and ohmic dissipation. Our study encompasses a broader range of equations of state (EOSs) in the form of P(ρ) ∝ ρΓ, with the aim of constraining the choice of EOSs for allowing star formation. Our results reveal that the collapse with a Γ no stiffer than 4/3, complemented by magnetized virial theorem, allows the dynamical contraction of the prestellar core to happen continuously where a central point mass forms and steadily builds up its mass from the infalling envelope, with a mass accretion rate of the order of  . The choice of an isothermal EOS most naturally facilitates the collapse as a magnetic analog of the inside-out collapse. In addition to that, our study exhibits that the nonisothermal magnetized collapse models with a Γ no stiffer than 4/3 qualitatively demonstrate similar infall features to those of an isothermal EOS. Furthermore, the collapse models with a Γ stiffer than 4/3 fail to ensure sufficient cooling to allow the direct mass growth of the central point mass, thus delaying the infall. Our work can offer deeper insights in understanding the significance of EOSs on the magnetized gravitational collapse, enabling star formation.

Keywords: Magnetohydrodynamics, Star forming regions, Molecular clouds, Pre-main sequence stars, Star formation, Gravitational collapse, Protostars, Magnetic fields
How the CME on 2023 April 21 Triggered the First Severe Geomagnetic Storm of Solar Cycle 25. The first severe (G4) geomagnetic storm of Solar Cycle 25 occurred on 2023 April 23–24, following the arrival of a coronal mass ejection (CME) on April 23. The characteristics of this CME, measured from coronagraphs (speed and mass), did not indicate that it would trigger such an intense geomagnetic storm. In this work, our aim is to understand why this CME led to such a geoeffective outcome. Our analysis spans from the source active region to the corona and inner heliosphere through 1 au using multiwavelength, multi-viewpoint remote sensing observations and in situ data. We find that rotation and possibly deflection of the CME resulted in an axial magnetic field nearly parallel to the ecliptic plane during the Earth encounter, which might explain the storm's severity. Additionally, we find that imaging away from the Sun–Earth line is crucial in hindcasting the CME time of arrival at Earth. The position (0.39 au) and detailed images from the SoloHI telescope on board the Solar Orbiter mission, in combination with SOHO and STEREO images, helped decisively with the three-dimensional reconstruction of the CME.

Keywords: Ejecta, Space weather, Solar physics, Solar coronal mass ejections, Magnetic storms
The Origin of the Nano-Hertz Stochastic Gravitational-wave Background: The Contribution from z ≳ 1 Supermassive Black Hole Binaries. The nano-Hertz gravitational wave background (GWB) is a key probe of supermassive black hole (SMBH) formation and evolution if the background arises predominantly from SMBH binaries (SMBHBs). The GWB amplitude, which is typically quantified as the characteristic strain, Ayr at a frequency 1 yr‑1, encodes significant astrophysical information about the SMBHB population, including the SMBHB mass and redshift distributions. Recent results from a number of pulsar timing arrays have identified a common-spectrum noise process, correlated between pulsars, that is consistent with a loud GWB signal with Ayr ∼ 2 × 10‑15, which is higher than most predictions Ayr ≲ 10‑15. These predictions usually assume theoretically motivated but highly uncertain prescriptions for SMBH seeding and evolution. Recent observations, largely by the James Webb Space Telescope, have uncovered a population of obscured, overmassive, accreting black holes in the early Universe that may suggest that the black hole mass density and net accretion were larger at high redshifts than previously thought. In this work, we use two simple, flexible models of SMBH evolution to explore the possible range of GWB amplitudes, given observational constraints. In particular, we explore enhanced contributions to the GWB from high redshift (z ≳ 1) SMBHBs. We find that the GWB amplitude may be higher than fiducial predictions by as much as ∼1 dex if much of the SMBH mass density was established by z ∼ 1. Beyond pulsar timing constraints, further observations of the high redshift SMBH population from the James Webb Space Telescope and the Laser Interferometer Space Antenna will be key for constraining the GWB contribution of mid-high-z SMBHBs.

Keywords: Gravitational wave astronomy, Supermassive black holes, Galaxy mergers, Quasars
Revisiting X-Ray Afterglows of Jetted Tidal Disruption Events with the External Reverse Shock. We investigate the external reverse shock (RS) region of relativistic jets as the origin of X-ray afterglows of jetted tidal disruption events (TDEs) that exhibit luminous jets accompanied by fast-declining nonthermal X-ray emissions. We model the dynamics of jet propagating within an external density medium, accounting for continuous energy injection driven by accretion activities. We compute the time-dependent synchrotron and inverse Compton emissions from the RS region. Our analysis demonstrates that the RS scenario can potentially explain the X-ray light curves and spectra of four jetted TDEs, namely, AT 2022cmc, Swift J1644, Swift J2058, and Swift J1112. Notably, the rapid steepening of the late-stage X-ray light curves can be attributed jointly to the jet break and cessation of the central engine as the accretion rate drops below the Eddington limit. Using parameters obtained from X-ray data fitting, we also discuss the prospects for γ-ray and neutrino detection.

Keywords: Tidal disruption, Relativistic jets, Transient sources, Radiative processes
Cosmic Filament Spin. I. A Comparative Study in Observation. In the cosmic web, filaments play a crucial role in connecting walls to clusters and also act as an important stage for galaxy formation and evolution. Recent observational studies claim that filaments have spin. In this study, we examined the potential impact of diversity in filament identification algorithms and galaxy survey data sets on the quantification of filament spin. The results of this study demonstrate qualitative agreement with previous research, suggesting that a reliable filament spin signal is detectable when the viewing angle of the filament spine is larger than 80° under a rough estimation. The detected filament spin signal is intricately linked to the viewing angle, dynamic temperature, etc. The quantitative difference of filament spin signal among samples is slightly dependent on the filament identification algorithms, while the value is relatively greater dependent on the redshift space distortion effect in the galaxy sample.

Keywords: Galaxy environments, Cosmic web, Astrostatistics, Large-scale structure of the universe
Investigating the Temperature Sensitivity of UV Line Ratios in the 280 nm Region of Solar-like Stars. Stellar UV spectra are fundamental diagnostics of physical and magnetic properties of stars. For instance, lines like Mg II at 280 nm serve as valuable indicators of stellar activity, providing insights into the activity levels of Sun-like stars and their potential influence on the atmospheres of orbiting planets. On the other hand, the effective temperature (Teff) is a fundamental stellar parameter, critical for determining stellar properties such as mass, age, composition, and evolutionary status. In this study, we investigate the temperature sensitivity of three lines in the mid-UV range (i.e., Mg II 280.00 nm, Mg I 285.20 nm, and Si I 286.15 nm). Using spectra from the International Ultraviolet Explorer, we analyze the behavior of the ratios of their corresponding indices (core/continuum) for a sample of calibrating solar-like stars and find that the ratio R = Mg II/Mg I best traces Teff through a log–log relation. The Teff estimated using this relation on a test sample of solar-like stars agree with the Teff from the literature at the 95% confidence level. The observed results are interpreted making use of response functions as diagnostics. This study extends the well-established use of line depth ratio–temperature relationships, traditionally applied in the visible and near-infrared ranges, to the mid-UV spectrum. With the growing interest in stellar UV spectroscopy, results presented in this paper are potentially relevant for future missions such as HWO, MANTIS, and UVEX.

Keywords: Ultraviolet astronomy, Stellar chromospheres, Stellar effective temperatures, Stellar physics
Emergence of Two Inertial Subranges in Solar Wind Turbulence: Dependence on Heliospheric Distance and Solar Activity. The solar wind is highly turbulent, and intermittency effects are observed for fluctuations within the inertial range. By analyzing magnetic field spectra and fourth-order moments, we perform a comparative study of turbulence and intermittency in different types of solar wind, measured during periods of solar minima and a maximum. Using eight fast-solar-wind intervals measured during solar minima between 0.3 and 3.16 au, we find a clear signature of two inertial subranges with f‑3/2 and f‑5/3 power laws in the magnetic power spectra. The intermittency, measured through the scaling law of the kurtosis of the magnetic field fluctuations, further confirms the existence of two different power laws separated by a clear break. A systematic study of the evolution of the said subranges as a function of heliospheric distance shows the correlation of the break scale with both the turbulence outer scale and the typical ion scales. During solar maximum, on the contrary, the two subranges are not omnipresent, thus showing more variability in the power spectra and intermittency scaling properties.

Keywords: Space plasmas, Magnetohydrodynamics, Heliosphere, Interplanetary turbulence, Solar wind, Interplanetary magnetic fields, Alfven waves, Spectral index