Sazuna/UAT_keywords huggingface dataset:
Diffusion Coefficients in the Envelopes of White Dwarfs. The diffusion of elements is a key process in understanding the unusual surface composition of white dwarfs and their spectral evolution. The diffusion coefficients of Paquette et al. have been widely used to model diffusion in white dwarfs. We perform new calculations of the coefficients of interdiffusion and ionic thermal diffusion with (1) a more advanced model that uses a recent modification of the calculation of the collision integrals that is more suitable for the partially ionized, partially degenerate, and moderately coupled plasma and (2) classical molecular dynamics. The coefficients are evaluated for silicon and calcium in white dwarf envelopes of hydrogen and helium. A comparison of our results with Paquette et al. shows that the latter systematically underestimates the coefficient of interdiffusion yet provides reliable estimates for the relatively weakly coupled plasmas found in nearly all types of stars, as well as in white dwarfs with hydrogen envelopes. In white dwarfs with cool helium envelopes ( ${T}_{\mathrm{eff}}$ &lt; 15,000 K), the difference grows to more than a factor of two. We also explored the effect of the ionization model used to determine the charges of the ions and found that it can be a substantial source of discrepancy between different calculations. Finally, we consider the relative diffusion timescales of Si and Ca in the context of the pollution of white dwarf photospheres by accreted planetesimals and find factor of ≳3 differences between calculations based on Paquette et al. and our model.

Keywords: Stellar abundances, White dwarf stars, Stellar diffusion
Cosmicflows-4: The Calibration of Optical and Infrared Tully-Fisher Relations. This study is a part of the Cosmicflows-4 project with the aim of measuring the distances of more than ∼10,000 spiral galaxies in the local universe up to ∼15,000 $\mathrm{km}\,{{\rm{s}}}^{-1}$ . New H I line width information has come primarily from the Arecibo Legacy Fast ALFA Survey. Photometry of our sample galaxies has been carried out in optical (SDSS u, g, r, I, and z) and infrared (WISE W1 and W2) bands. Inclinations have been determined using an online graphical interface accessible to a collaboration of citizen scientists. Galaxy distances are measured based on the correlation between the rotation rate of spirals and their absolute luminosity, known as the Tully-Fisher relation (TFR). In this study, we present the calibration of the TFR using a subsample of ∼600 spirals located in 20 galaxy clusters. Correlations among such observables as color, surface brightness, and relative H I content are explored in an attempt to reduce the scatter about the TFR with the goal of obtaining more accurate distances. A preliminary determination of the Hubble constant from the distances and velocities of the calibrator clusters is H0 = 76.0 ± 1.1(stat.) ± 2.3(sys.) km s-1 Mpc-1.

Keywords: Inclination, Galaxy distances, Spiral galaxies, Large-scale structure of the universe, Distance measure, Galaxy structure, H I line emission, Galaxy photometry
Early Optical Observations of GRB 150910A: Bright Jet Optical Afterglow and X-Ray Dipole Radiation from a Magnetar Central Engine. Gamma-ray burst (GRB) 150910A was detected by Swift/Burst Alert Telescope (BAT), and then rapidly observed by Swift/XRT, Swift/Ultraviolet-Optical Telescope, and ground-based telescopes. We report Lick Observatory spectroscopic and photometric observations of GRB 150910A, and we investigate the physical origins of both the optical and X-ray afterglows, incorporating data obtained with BAT and XRT. The light curves show that the jet-emission episode lasts ∼360 s with a sharp pulse from BAT to XRT (Episode I). In Episode II, the optical emission has a smooth onset bump followed by a normal decay (αR,2 ≈ -1.36), as predicted in the standard external shock model, while the X-ray emission exhibits a plateau (αX,1 ≈ -0.36) followed by a steep decay (αX,2 ≈ -2.12). The light curves show obvious chromatic behavior with an excess in the X-ray flux. Our results suggest that GRB 150910A is an unusual GRB driven by a newly born magnetar with its extremely energetic magnetic dipole (MD) wind in Episode II, which overwhelmingly dominates the observed early X-ray plateau. The radiative efficiency of the jet prompt emission is ηγ ≈ 11%. The MD wind emission was detected in both the BAT and XRT bands, making it the brightest among the current sample of MD winds seen by XRT. We infer the initial spin period (P0) and the surface polar cap magnetic field strength (Bp) of the magnetar as 1.02 × 1015 G ≤ Bp ≤ 1.80 × 1015 G and 1 ms ≤ P0V ≤ 1.77 ms, and the radiative efficiency of the wind is ηw ≥ 32%.

Keywords: Magnetars, Gamma-ray bursts, Non-thermal radiation sources
Bivariate Number Distribution of Solar Soft X-Ray Flares. Conventionally, researchers investigated the number distribution of solar flares by univariate analysis using all available data. For the first time, we investigate the bivariate number distribution of peak flux (f) and duration (T) of soft X-ray flares observed by the Geostationary Operational Environmental Satellite during the past 10 years. First, the univariate number distribution of f is found to obey a power law either for each class of flares or for the B or ≥C flares in a certain range of T. But the power-law index of B-class flares is much smaller than those of other higher-class ones. For the ≥C flares, the longer the duration, the smaller the power-law index. The univariate number distribution of T deviates from the power law at shorter durations and is better fitted by a skewed Gaussian function in logarithmic coordinates for almost any given range of f, reflecting the random phenomena in solar flares. Then, based on the univariate analysis, a linear Gaussian function is proposed to describe the bivariate logarithmic number distribution of f and T, from which the local power-law index with respect to either f or T can also be analyzed. The real number distribution of B flares should be in between the observed one and the power-law distribution of stronger flares (≥C). We suggest that nanoflare activity may not be the dominant source of coronal heating.

Keywords: Solar cycle, Solar active regions, Solar corona, Solar x-ray flares, Solar activity
Source-count Distribution of Gamma-Ray Blazars. With 10 years of operation and an exceptional data set, the Fermi-Large Area Telescope allows us to unveil the detailed composition of the extragalactic γ-ray sky above 100 MeV. In this paper, we derive the intrinsic source-count distribution (logN-logS) of extragalactic sources (I.e., blazars) at $| b| \gt 20^\circ $ via the efficiency correction method. With this approach, we are able to measure the distribution down to a photon flux of $\sim {10}^{-10}\,\mathrm{ph}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$ and to an energy flux of ∼10-12 $\,\mathrm{erg}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$ . In both cases, the logN-logS becomes flatter at low fluxes. Moreover, we show that this logN-logS is representative of the blazar population (assuming the majority of unassociated sources are blazars) and allows us to constrain its evolution quite effectively. Among recently proposed evolutionary models, we find that the Pure Density Evolution model best describes the evolutionary properties of the blazar population and that their integrated emission accounts for $\sim {50}_{-5}^{+10} \% $ of the total extragalactic γ-ray background.

Keywords: Cosmological evolution, Gamma-ray sources, Blazars, Active galaxies, Active galactic nuclei
A Parametric Model for the Shapes of Black Hole Shadows in Non-Kerr Spacetimes. The Event Horizon Telescope (EHT) is taking the first images of black holes resolved at horizon scales to measure their shadows and probe accretion physics. A promising avenue for testing the hypothesis that astrophysical black holes are described by the Kerr solution to Einstein's equations is to compare the size and shape of the shadow a black hole casts on the surrounding emission to the predictions of the Kerr metric. We develop here an efficient parametric framework to perform this test. We carry out ray-tracing simulations for several parameterized non-Kerr metrics to create a large data set of non-Kerr shadows that probe the allowed parameter space for the free parameters of each metric. We then perform principal components analysis (PCA) on this set of shadows and show that only a small number of components are needed to accurately reconstruct all shadows within the set. We further show that the amplitude of the PCA components are smoothly related to the free parameters in the metrics and, therefore, that these PCA components can be fit to EHT observations in order to place constraints on the free parameters of these metrics that will help quantify any potential deviations from the Kerr solution.

Keywords: Black hole physics, Spacetime metric, Black holes, Principal component analysis, General relativity, Geodesics, Astronomical simulations
Fluid Theory of Coherent Magnetic Vortices in High-β Space Plasmas. In situ observations in Earth's and Saturn's magnetosheaths and in the solar wind reveal the presence of Alfvén vortices as intermittent structures in the range of scales from fluid lengths down to a few ion lengths. The density and the magnetic field associated with them appear to be compressible for higher plasma betas. Until now, only incompressible Alfvén vortices have been known. Motivated by space plasma observations, we develop a new model of magnetic vortices in high-beta plasmas with anisotropic temperature, possessing compressible density and magnetic field, whose typical size ranges from fluid to ion scales. At magnetofluid scales, we find novel nonpropagating field-aligned cylindrical monopoles and inclined propagating dipoles. Their transverse magnetic and velocity fluctuations are aligned, but not identical, and they exhibit density and compressible magnetic field fluctuations δn and $\delta {B}_{\parallel }$ localized inside the vortex core. In the presence of thermal anisotropy and acoustic effects, they may be correlated or anticorrelated, $\delta n/\delta {B}_{\parallel }=\mathrm{constant}\,\gtrless \,0;$ fluctuations whose velocity along the magnetic field is below the ion thermal speed are always correlated. At ion or kinetic scales (with the smallest radii $\sim c/{\omega }_{\mathrm{pi}},{\rho }_{\mathrm{Li}}$ ) and in the absence of acoustic perturbations, only dipolar Alfvén vortices survive with properties similar to those at fluid scales, except that δn/n0 reaches the level of $\delta {B}_{\parallel }/{B}_{0}$ . We also find pressure-balanced kinetic slow magnetosonic dipoles, possessing finite ${E}_{\parallel }$ and purely compressional magnetic field perturbation, whose existence is facilitated by a strong ion temperature anisotropy.

Keywords: Planetary magnetospheres, Magnetohydrodynamics, Solar wind, Plasma physics
Expansion of Hot Plasma with Kappa Distribution into Cold Plasma. The X-ray emission of coronal flare sources can be explained by considering the kappa electron distribution. Motivated by this fact, we study the problem of how hot plasma with the kappa distribution of electrons is confined in these sources. For comparison, we analyze the same problem, but with the Maxwellian distribution. We use a 3D particle-in-cell code, which is large in one direction and thus effectively only one-dimensional, but describe all electromagnetic effects. In the case with the Maxwellian distribution, and in agreement with the previous studies, we show a formation of the double layer at the hot-cold transition region that suppresses the flux of hot electrons from hot plasma into the cold one. In the case with the kappa distribution, contrary to the Maxwellian case, we found that there are several fronts with the double layers in the hot-cold transition region. It is caused by a more extended tail in the kappa case than in the Maxwellian one. The electrons from the extended tail freely escape from the hot plasma into a cold one. They form a beam that generates the return current and also Langmuir turbulence, where Langmuir waves accumulated at some locations. At these locations, owing to the ponderomotive force, Langmuir waves generate density depressions, where the double layers with the thermal fronts that suppress the hot electron flux, are formed. We also show how protons accelerate in these processes. Finally, we compare the Kappa and Maxwellian cases and discuss how these processes could be observed.

Keywords: Space plasmas, Solar flares, Plasma astrophysics, Solar x-ray emission, Computational methods, Radio bursts, Solar radio emission
A Search for Optical AGN Variability in 35,000 Low-mass Galaxies with the Palomar Transient Factory. We present an analysis of the long-term optical variability for ∼50,000 nearby (z &lt; 0.055) galaxies from the NASA-Sloan Atlas, 35,000 of which are low-mass (M* &lt; 1010 M⊙). We use difference imaging of Palomar Transient Factory (PTF) R-band observations to construct light curves with typical baselines of several years. We then search for subtle variations in the nuclear light output. We determine whether detected variability is AGN-like by assessing the fit quality to a damped random walk model. We identify 417 variability-selected AGNs, including 237 with stellar masses between 107 and 1010 M⊙. 75% of low-mass galaxies with AGN-like variability have narrow emission lines dominated by star formation. After controlling for nucleus magnitude, the fraction of variable AGNs is constant down to M* = 109 M⊙, suggesting no drastic decline in the BH occupation fraction down to this stellar mass regime. Combining our NASA-Sloan Atlas sample with samples of nearby galaxies with broad Hα emission, we find no dependence of variability properties with black hole mass. Our PTF work demonstrates the promise of long-term optical variability searches in low-mass galaxies for finding AGNs missed by other selection techniques.

Keywords: AGN host galaxies, Sky surveys, Variable radiation sources, Dwarf galaxies, Active galactic nuclei
The CARMA-NRO Orion Survey: Protostellar Outflows, Energetics, and Filamentary Alignment. We identify 45 protostellar outflows in CO maps of the Orion A giant molecular cloud from the Combined Array for Research in Millimeter-wave Astronomy-Nobeyama Radio Observatory Orion survey. Our sample includes 11 newly detected outflows. We measure the mass and energetics of the outflows, including material at low velocities, by correcting for cloud contributions. The total momentum and kinetic energy injection rates of outflows are comparable to the turbulent dissipation rate of the cloud. We also compare the outflow position angles to the orientation of C18O filaments. We find that the full sample of outflows is consistent with being randomly oriented with respect to the filaments. A subsample of the most reliable measurements shows a moderately perpendicular outflow-filament alignment that may reflect accretion of mass across filaments and onto the protostellar cores.

Keywords: Stellar feedback, Interstellar filaments, Giant molecular clouds, Star formation, Interstellar medium, Protostars
Temporal Evolution of the Rotation of the Interplanetary Magnetic Field B<SUB>X</SUB>, B<SUB>y</SUB>, and B<SUB>z</SUB> Components. The daily interplanetary magnetic field (IMF) BX, By, and Bz components from 1967 January 1 to 2018 December 31 listed in the OMNI database are used to investigate their periodicity and study temporal variation of their rotation cycle lengths through continuous wavelet transform, autocorrelation, and cross-correlation analyses. The dominant rotation period in each of the daily BX, By, and Bz components is 27.4 days, implying the existence of rotational modulation in the three time series. The dependence of the rotation cycle lengths for both BX and By components on solar cycle phase almost shows the same result. The rotation cycle lengths for both BX and By components increase from the start to the first year of a new Schwabe cycle, then decrease gradually from the first to the fourth year, and finally fluctuate around the 27.4-day period within a small amplitude from the fourth year to the end of the Schwabe solar cycle. For the Bz component, its rotation cycle length does not show such a solar cycle variation. The significant periods in the variation of BX rotation are 2.9, 3.4, 4.3, 4.9, 10.5, and 11.9 yr, and there exist significant periods of 3.4, 9.9, and 14.1 yr in the variation of By rotation. The relationship of solar activity with BX and By components is complex. The possible mechanisms for the temporal variation of the rotation period of the three components are discussed.

Keywords: Interplanetary magnetic fields
Recovering Age-Metallicity Distributions from Integrated Spectra: Validation with MUSE Data of a Nearby Nuclear Star Cluster. Current instruments and spectral analysis programs are now able to decompose the integrated spectrum of a stellar system into distributions of ages and metallicities. The reliability of these methods has rarely been tested on nearby systems with resolved stellar ages and metallicities. Here we derive the age-metallicity distribution of M54, the nucleus of the Sagittarius dwarf spheroidal galaxy, from its integrated Multi-Unit Spectroscopic Explorer (MUSE) spectrum. We find a dominant old (8-14 Gyr), metal-poor (-1.5 dex) component and a young (1 Gyr), metal-rich (+0.25 dex) component—consistent with the complex stellar populations measured from individual stars in the same MUSE data set. There is excellent agreement between the (mass-weighted) average age and metallicity of the resolved and integrated analyses. Differences are only 3% in age and 0.2 dex metallicity. By co-adding individual stars to create M54's integrated spectrum, we show that the recovered age-metallicity distribution is insensitive to the magnitude limit of the stars or the contribution of blue horizontal branch stars—even when including additional blue wavelength coverage from the WiFeS Atlas of Galactic Globular cluster Spectra survey. However, we find that the brightest stars can induce the spurious recovery of an old (&gt;8 Gyr), metal-rich (+0.25 dex) stellar population, which is otherwise not expected from our understanding of chemical enrichment in M54. The overall derived stellar mass-to-light ratio of M54 is M/LV = 1.46 with a scatter of 0.22 across the field of view, which we attribute to the stochastic contribution of a young, metal-rich component. These findings provide strong evidence that complex stellar population distributions can be reliably recovered from integrated spectra of extragalactic systems.

Keywords: Galaxy chemical evolution, Stellar populations, Galaxy stellar content, Galaxy nuclei, Galaxy ages, Mass-to-light ratio, Metallicity
Insights into the Formation and Evolution History of the Galactic Disk System. We present a kinematic analysis of a sample of 23,908 G- and K-type dwarfs in the Galactic disk. Based on the α-abundance ratio, [α/Fe], we separated our sample into low-α thin-disk and high-α thick-disk stars. We find a ${V}_{\phi }$ gradient of -28.2 km s-1 dex-1 over [Fe/H] for the thin disk and an almost flat trend of the velocity dispersions of ${V}_{{\rm{R}}}$ , ${V}_{\phi }$ , and ${V}_{{\rm{Z}}}$ components with [Fe/H]. The metal-poor (MP; [Fe/H] &lt;-0.3) thin-disk stars with low- ${V}_{\phi }$ velocities have high eccentricities (e) and small perigalacticon distances ( ${r}_{{\rm{p}}}$ ), while the high- ${V}_{\phi }$ MP thin-disk stars possess low e and large ${r}_{{\rm{p}}}$ . Interestingly, half of the super-metal-rich ([Fe/H]&gt; + 0.1) stars in the thin disk exhibit low-e, solar-like orbits. Accounting for the inhomogeneous metallicity distribution of the thin-disk stars with various kinematics requires radial migration by churning—it apparently strongly influences the current structure of the thin disk; we cannot rule out the importance of blurring for the high-e stars. We derive a rotation velocity gradient of +36.9 km s-1 dex-1 for the thick disk and decreasing trends of velocity dispersions with increasing [Fe/H]. The thick-disk population also has a broad distribution of eccentricity, and the number of high-e stars increases with decreasing [Fe/H]. These kinematic behaviors could be the result of a violent mechanism, such as a gas-rich merger or the presence of giant turbulent clumps, early in the history of its formation. Dynamical heating by minor mergers and radial migration may also play roles in forming the current thick-disk structure.

Keywords: Stellar kinematics, Milky Way disk, Astronomy data analysis
Keeping It Cool: Much Orbit Migration, yet Little Heating, in the Galactic Disk. A star in the Milky Way's disk can now be at a Galactocentric radius quite distant from its birth radius for two reasons: either its orbit has become eccentric through radial heating, which increases its radial action JR ("blurring"), or merely its angular momentum Lz has changed and thereby its guiding radius ("churning"). We know that radial orbit migration is strong in the Galactic low-α disk and set out to quantify the relative importance of these two effects, by devising and applying a parameterized model ( ${{\boldsymbol{p}}}_{{\boldsymbol{m}}}$ ) for the distribution $p({L}_{z},{J}_{R},\tau ,\left[\mathrm{Fe}/{\rm{H}}\right]| {{\boldsymbol{p}}}_{{\boldsymbol{m}}})$ in the stellar disk. This model describes the orbit evolution for stars of age τ and metallicity $\left[\mathrm{Fe}/{\rm{H}}\right]$ , presuming that coeval stars were initially born on (near-)circular orbits, and with a unique $\left[\mathrm{Fe}/{\rm{H}}\right]$ at a given birth angular momentum and age. We fit this model to APOGEE red clump stars, accounting for the complex selection function of the survey. The best-fit model implies changes of angular momentum of $\sqrt{\langle {\rm{\Delta }}{L}_{z}{\rangle }^{2}}\approx 619\,\mathrm{kpc}\,\mathrm{km}\,{{\rm{s}}}^{-1}\ {(\tau /6\mathrm{Gyr})}^{0.5}$ and changes of radial action as $\sqrt{\langle {\rm{\Delta }}{J}_{R}{\rangle }^{2}}\approx 63\,\mathrm{kpc}\,\mathrm{km}\,{{\rm{s}}}^{-1}{(\tau /6\mathrm{Gyr})}^{0.6}$ at 8 kpc. This suggests that the secular orbit evolution of the disk is dominated by diffusion in angular momentum, with radial heating being an order of magnitude lower.

Keywords: Galaxy stellar disks, Galaxy dynamics, Milky Way dynamics, Milky Way disk, Galaxy abundances, Milky Way evolution, Milky Way Galaxy