Sazuna/UAT_keywords huggingface dataset:
X-Ray Morphology Due to Charge-exchange Emissions Used to Study the Global Structure around Mars. Soft X-ray emissions induced by solar wind ions that collide with neutral material in the solar system have been detected around planets, and were proposed as a remote probe for solar wind interaction with the Martian exosphere. A multi-fluid three-dimensional magnetohydrodynamic model is adopted to derive the global distributions of solar wind particles. Spherically symmetric exospheric H, H2, He, O, and CO2 density profiles and a sophisticated hybrid model that includes charge-exchange and proton-neutral excitation processes are used to study the low triplet line ratio $G=\tfrac{i+f}{r}$ (0.77 ± 0.58) of O VII and the total X-ray luminosity around Mars. We further calculate the emission factor α-value with different neutrals over wide ion-abundance and velocity ranges. Our results are in good agreement with those of previous reports. The evolution of the charge stage of solar wind ions shows that sequential recombination due to charge-exchange can be negligible in the interaction region. This only appears below an altitude of 400 km. The anonymous low disk G-ratio can be easily explained by the collisional quenching effect at neutral densities higher than 1011 cm-3. However, the quenching contribution is small in Mars' exosphere and only appears below 400 km. Charge-exchange with H2 and N2 is still the most likely reason for this low G-ratio. X-ray emissivity maps in collisions with different neutrals differ from each other. A clear bow shock arising from the collision with all the neutrals is in accordance with previous reports. The resulting total X-ray luminosity of 6.55 MW shows better agreement with the XMM-Newton observation of 12.8 ± 1.4 MW than that of previous predictions.

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

Keywords: Globular star clusters, Stellar abundances
Simulation of Solar Wind Turbulence near Corotating Interaction Regions: Superposed Epoch Analysis of Simulations and Observations. The effect of the turbulence that is associated with solar wind corotating interaction regions (CIRs) on transport of galactic cosmic rays remains an outstanding problem in space science. Observations show that the intensities of the plasma and magnetic fluctuations are enhanced within a CIR. The velocity shear layer between the slow and fast wind embedded in a CIR is thought to be responsible for this enhancement in turbulent energy. We perform physics-based magnetohydrodynamic simulations of the plasma background and turbulent fluctuations in the solar wind dominated by CIRs for radial distances between 0.3 and 5 au. A simple but effective approach is used to incorporate the inner boundary conditions for the solar wind and magnetic field for the periods 2007-2008 and 2017-2018. Legendre coefficients at the source surface obtained from the Wilcox Solar Observatory library are utilized for dynamic reconstructions of the current sheet and the fast and slow streams at the inner boundary. The dynamic inner boundary enables our simulations to generate CIRs that are reasonably comparable with observations near Earth. While the magnetic field structure is reasonably well reproduced, the enhancements in the turbulent energy at the stream interfaces are smaller than observed. A superposed epoch analysis is performed over several CIRs from the simulation and compared to the superposed epoch analysis of the observed CIRs. The results for the turbulent energy and correlation length are used to estimate the diffusion tensor of galactic cosmic rays. The derived diffusion coefficients could be used for more realistic modeling of cosmic rays in a dynamically evolving inner heliosphere.

Keywords: Interplanetary turbulence, Solar wind, Corotating streams
Evidence for Population-dependent Vertical Motions and the Long-lived Nonsteady Lopsided Milky Way Warp. We present a Galactic disk vertical velocity analysis using OB type stars (OB stars), red clump (RC) stars, and main-sequence turnoff (MSTO) stars with different average age populations crossmatched with LAMOST DR5 and Gaia DR3. We show that the vertical velocities of the three populations clearly vary with the Galactocentric distance (R) and the younger stellar population has a stronger increasing trend in general. The bending and breathing modes indicated by the vertical motions are dependent on the populations and vary with spatial locations. These vertical motions may be due to the Galactic warp, or minor mergers, or nonequilibrium of the disk. Assuming the warp is the dominant component, we find that the amplitude of the warp (γ, Z  ω ) of OB stars (younger population) is larger than that of RC stars (medium population) and the latter is also larger than that for MSTO stars (older population), which is in agreement with other independent analyses of stellar density distribution, and supports that the warp is a long-lived, nonsteady structure and is time evolving. This conclusion is robust whether the line of nodes ϕ  w  is fixed or is a free parameter (with ϕ  w  being around 3°-8.°5 as the best fit). Furthermore, we find that the warp is lopsided with asymmetries along the azimuthal angle (ϕ).

Keywords: Milky Way disk
A Study of Particle Transport in Young Pulsar Wind Nebulae. The broadband emission of numerous pulsar wind nebula (PWNe) in our Galaxy can be well described by synchrotron radiation and inverse Compton scattering from relativistic particles, specifically electrons and positrons. However, the particle transport mechanism is still under debate. We use here a time-dependent model to investigate the particle transport process of the young PWN, while the particle cooling processes are also analyzed. Following applications of the model to six young PWNe, our results show that (1) the particle cooling process is dominated by adiabatic loss in the low-energy band but by synchrotron loss in the high-energy band; (2) the advection dominates the particle transport process in the low-energy band, whereas the advection and diffusion codominate in the high-energy band, indicating that both advection and diffusion play an important role in particle transport; and (3) the diffusion coefficient is (2-360) × 1024 cm2 s-1 at the electron energy of 1 TeV, i.e., about 3 orders of magnitude smaller than the value considered to be the average in the Galaxy. We conclude that a slow-diffusion mechanism may explain the multiband observation of the sample of six young PWNe considered in this study.

Keywords: Supernova remnants, Pulsar wind nebulae, Pulsars
Models of Rotating Infall for the B335 Protostar. Models of the protostellar source, B335, are developed using axisymmetric three-dimensional models to resolve conflicts found in one-dimensional models. The models are constrained by a large number of observations, including ALMA, Herschel, and Spitzer data. Observations of the protostellar source B335 with ALMA show redshifted absorption against a central continuum source indicative of infall in the HCO+ and HCN J = 4 → 3 transitions. The data are combined with a new estimate of the distance to provide strong constraints to three-dimensional radiative transfer models including a rotating, infalling envelope, outflow cavities, and a very small disk. The models favor ages since the initiation of collapse between 3 × 104 and 4 × 104 yr for both the continuum and the lines, resolving a conflict found in one-dimensional models. The models underpredict the continuum emission seen by ALMA, suggesting an additional component such as a pseudo-disk. The best-fitting model is used to convert variations in the 4.5 μm flux in recent years into a model for a variation of a factor of 5-7 in luminosity over the last 8 yr.

Keywords: Star formation, Interstellar clouds
Standing Sausage Perturbations in Solar Coronal Slabs with Continuous Transverse Density Profiles: Cutoff Wavenumbers, Evanescent Eigenmodes, and Oscillatory Continuum. The lack of observed sausage perturbations in solar active region loops is customarily attributed to the relevance of cutoff axial wavenumbers and the consequent absence of trapped modes (called "evanescent eigenmodes" here). However, some recent eigenvalue problem studies suggest that cutoff wavenumbers may disappear for those equilibria where the external density varies sufficiently slowly, thereby casting doubt on the rarity of candidate sausage perturbations. We examine the responses of straight, transversely structured coronal slabs to small-amplitude sausage-type perturbations that excite axial fundamentals, by solving the pertinent initial value problem with eigensolutions for a closed domain. The density variation in the slab exterior is dictated by some steepness parameter μ, and cutoff wavenumbers are theoretically expected to be present (absent) when μ ≥ 2 (μ &lt; 2). However, our numerical results show no qualitative difference in the system evolution when μ varies, despite the differences in the modal behavior. Only oscillatory eigenmodes are permitted when μ ≥ 2. Our discrete eigenspectrum becomes increasingly closely spaced when the domain broadens, and an oscillatory continuum results for a truly open system. Oscillatory eigenmodes remain allowed and dominate the system evolution when μ &lt; 2. We show that the irrelevance of cutoff wavenumbers does not mean that all fast waves are evanescent. Rather, it means that an increasing number of evanescent eigenmodes emerge when the domain size increases. We conclude that sausage perturbations remain difficult to detect, even for the waveguide formulated here.

Keywords: Solar coronal seismology, Magnetohydrodynamics, Solar coronal waves
The Chemical Enrichment of the Milky Way Disk Evaluated Using Conditional Abundances. Chemical abundances of Milky Way disk stars are empirical tracers of its enrichment history. However, they capture joint-information that is valuable to disentangle. In this work, we quantify how individual abundances evolve across the present-day Galactic radius, at fixed supernovae contribution ([Fe/H], [Mg/Fe]). We use 18,135 Apache Point Observatory Galactic Evolution Experiment Data Release 17 red clump stars and 7943 GALactic Archaeology with HERMES Data Release 3 main-sequence stars to compare the abundance distributions conditioned on ([Fe/H], [Mg/Fe]) across 3-13 kpc and 6.5-9.5 kpc, respectively. We examine 15 elements: C, N, Al, K (light), O, Si, S, Ca, (α), Mn, Ni, Cr, Cu, (iron-peak) Ce, Ba (s-process) and Eu (r-process). We find that the conditional neutron-capture and light elements most significantly trace variations in the disk's enrichment history, with absolute conditional radial gradients ≤0.03 dex kpc-1. The other elements studied have absolute conditional gradients ≲0.01 dex kpc-1. We uncover structured conditional abundance variations with [Fe/H] for the low-α, but not the high-α , sequence. The average scatter between the mean conditional abundances at different radii is σ intrinsic ≈ 0.02 dex (Ce, Eu, Ba σ intrinsic &gt; 0.05 dex). These results serve as a measure of the magnitude via which different elements trace Galactic radial enrichment history once fiducial supernovae correlations are accounted for. Furthermore, we uncover subtle systematic variations in moments of the conditional abundance distributions and bimodal differences in [Al/Fe]. These suggest a nonuniform enrichment of each chemical cell, and will presumably constrain chemical evolution models of the Galaxy.

Keywords: Stellar abundances, Astrostatistics techniques, Chemical abundances, Milky Way disk, Milky Way Galaxy
Searches for Extremely Metal-poor Galaxies Using Arecibo Legacy Fast ALFA-Selected Dwarf Galaxies. We present a study of nearby dwarf galaxies selected from the Arecibo Legacy Fast ALFA (ALFALFA) blind H I survey. A primary goal of the project was to utilize a nonstandard selection method with the hope of detecting previously unrecognized extremely metal-poor (XMP) galaxies. The study was motivated by the recent discovery of two XMP galaxies, Leo P and Leoncino, which were both originally found via the ALFALFA survey. We have obtained narrowband Hα images for 42 dwarf systems, many of which are located in the Local Void in front of the Pisces-Perseus Supercluster. Spectra for 11 of the best candidates resulted in the determination of metal abundances for 10 of the systems. None were found to be extremely metal-poor, although one system (AGC 123350) was found to have an oxygen abundance of log(O/H)+12 = 7.46, or ~6% solar. One of the galaxies in our sample exhibits a high oxygen abundance for its luminosity, suggesting the possibility that it may have a tidal origin. * Based in part on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

Keywords: Dwarf irregular galaxies, Starburst galaxies, Galaxy chemical evolution, Star forming regions, H I line emission, Galaxy abundances, Star formation, Galaxy spectroscopy, Metallicity
The Low-redshift Lyman Continuum Survey: Optically Thin and Thick Mg II Lines as Probes of Lyman Continuum Escape. The Mg II λλ2796, 2803 doublet has been suggested as a useful indirect indicator for the escape of Lyα and Lyman continuum (LyC) photons in local star-forming galaxies. However, studies to date have focused on small samples of galaxies with strong Mg II or strong LyC emission. Here, we present the first study of Mg II to probe a large dynamic range of galaxy properties, using newly obtained high-signal-to-noise, moderate-resolution spectra of Mg II, for a sample of 34 galaxies selected from the Low-redshift Lyman Continuum Survey. We show that the galaxies in our sample have Mg II profiles ranging from strong emission to P-Cygni profiles to pure absorption. We find that there is a significant trend (with a possibility of spurious correlations of ~2%) that galaxies that are detected as strong LyC emitters (LCEs) show larger equivalent widths of Mg II emission, while non-LCEs tend to show evidence of more scattering and absorption features in Mg II. We then find that Mg II strongly correlates with Lyα in both equivalent width and escape fraction, regardless of whether emission or absorption dominates the Mg II profiles. Furthermore, we show that, for galaxies that are categorized as Mg II emitters, one can use the information of Mg II, metallicity, and dust to estimate the escape fraction of LyC within a factor of ~3. These findings confirm that Mg II lines can be used as a tool for selecting galaxies as LCEs and thus serve as an indirect indicator for the escape of Lyα and LyC.

Keywords: Optical astronomy, Reionization, Galaxy evolution, Emission line galaxies
Asteroseismology: Looking for Axions in the Red Supergiant Star Alpha Ori. In this work, for the first time, we use seismic data as well as surface abundances to model the supergiant α-Ori, with the goal of setting an upper bound on the axion-photon coupling constant g  a γ . We find that, in general, stellar models with g  a γ  ∈ [0.002; 2.0] × 10-10 GeV-1 agree with the observational data, but beyond that upper limit, we do not find stellar models that are compatible with the observational constraints and the current literature. From g  a γ  = 3.5 × 10-10 GeV-1 on, the algorithm did not find any fitting models. Even so, all the axionic models considered present distinct internal profiles from the reference case, without axions. Moreover, as the axion energy losses become more significant, the behavior of the stellar models becomes more diversified, even with very similar input parameters. Nonetheless, the consecutive increments of g  a γ  still show systematic tendencies, resulting from the axion energy losses. Moreover, we establish three important conclusions: (1) the increased luminosity and higher neutrino production are measurable effects, possibly associated with axion energy losses; (2) stellar models with axion energy loss show a quite distinct internal structure; and (3) the importance of future asteroseismic missions in observing low-degree nonradial modes in massive stars is emphasized-as internal gravity waves probe the near-core regions, where axion effects are most intense. Thus, more seismic data will allow us to constrain g  a γ  better and to prove or dismiss the existence of axion energy loss inside massive stars.

Keywords: Red supergiant stars, Stellar pulsations, Stellar evolutionary models, Chemical abundances, Asteroseismology, Particle physics, Stellar evolution
Temporal Behaviors of Magnetic Helicity Injections by Self and Mutual Sunspot Rotations. Magnetic helicity is a physical parameter used to quantify the complexity of magnetic fields, providing an indication of the energy state in the coronal magnetic structure. We investigate the temporal evolution of magnetic helicity and its relationship to the occurrence of a variety of flares in the solar active region NOAA 12297, which was well observed using the Solar Dynamics Observatory/Helioseismic and Magnetic Imager in 2015 March. The active region produced many M-class flares and an X-class flare in two distinctive areas, both of which had a similar magnetic evolution, i.e., the opposite polarity of an emerging flux developed beside a preexisting sunspot, but exhibited flares with different magnitudes and frequencies. We derived the spatiotemporal evolution of the magnetic helicity injections and evaluated how spinning and braiding helicity injections evolved with time in the two areas. In one area, we observed a remarkable evolution, in which a negative spinning helicity injection in the preexisting sunspot increased in a positive helicity system, followed by the occurrence of the X-class flare. The negative helicity injection was clearly caused by the flux emergence that developed along the outer edge of the preexisting sunspot. The other area showed positive braiding helicity injections, with spinning helicity injections fluctuating concurrently with flux emergence, changing their signs several times, i.e., variable energy, and helicity input. The observed temporal behaviors of the helicity injections may explain different types of flare occurrences in the regions.

Keywords: Solar flares, Solar magnetic fields
Shock Breakout from Stellar Envelopes: The Relativistic Limit. We calculate the observed luminosity and spectrum following the emergence of a relativistic shock wave from a stellar edge. Shock waves propagating at 0.6 &lt; Γsh β sh, where Γsh is the shock Lorentz factor, and β sh is its associated reduced velocity, heat the stellar envelope to temperatures exceeding ~50 keV, allowing for a vigorous production of electron and positron pairs. Pairs significantly increase the electron-scattering optical depth and regulate the temperature through photon generation, producing distinct observational signatures in the escaping emission. Assuming Wien equilibrium, we find analytic expressions for the temperature and pair density profiles in the envelope immediately after shock passage, and compute the emission during the expansion phase. Our analysis shows that, in pair-loaded regions, photons are produced at a roughly uniform rest-frame energy of ~200 keV, and reinforce previous estimates that the shock breakout signal will be detected as a short burst of energetic γ-ray photons, followed by a longer phase of X-ray emission. We test our model on a sample of low-luminosity gamma-ray bursts using a closure relation between the γ-ray burst duration, the radiation temperature, and the γ-ray isotropic equivalent energy, and find that some of the events are consistent with the relativistic shock breakout model. Finally, we apply our results to explosions in white dwarfs and neutron stars, and find that typical type Ia supernovae emit ~1041 erg in the form of ~1 MeV photons.

Keywords: Supernova dynamics, High energy astrophysics, Special relativity, Relativistic fluid dynamics, Shocks, Supernovae, Gamma-rays
Investigating the Narrow-line Region Dynamics in Nearby Active Galaxies. We present dynamical models of the narrow-line region (NLR) outflows in the nearby Seyfert galaxies Mrk 3, Mrk 78, NGC 1068, and NGC 4151 using observations from the Hubble Space Telescope and Apache Point Observatory. We employ long-slit spectroscopy to map the spatially resolved outflow and rotational velocities of the ionized gas. We also perform surface brightness decompositions of host galaxy images to constrain the enclosed stellar mass distributions as functions of distance from the supermassive black holes (SMBHs). Assuming that the NLR gas is accelerated by active galactic nuclei (AGN) radiation pressure, and subsequently decelerated by the host galaxy and SMBH gravitational potentials, we derive outflow velocity profiles where the gas is launched in situ at multiple distances from the SMBH. We find a strong correlation between the turnover (from acceleration to deceleration) radii from our models, with the turnovers seen in the observed velocities and spatially resolved mass outflow rates for the AGN with bolometric luminosities &gt; 1044 erg s-1. This consistency indicates that radiation pressure is the dominant driving mechanism behind the NLR outflows in these moderate-luminosity AGNs, with a force multiplier ~500 yielding the best agreement between the modeled and observed turnover radii. However, in Meena et al. we found that this trend may not hold at lower luminosities, where our modeled turnover distance for NGC 4051 is much smaller than in the observed kinematics. This result may indicate that either additional force(s) are responsible for accelerating the NLR outflows in low-luminosity AGNs, or higher spatial resolution observations are required to quantify their turnover radii.

Keywords: AGN host galaxies, Supermassive black holes, Emission line galaxies, Galaxy mass distribution, Seyfert galaxies, Active galactic nuclei, Galaxy winds, Galaxy kinematics, Galaxy rotation curves