Sazuna/UAT_keywords huggingface dataset:
Validation of the Alfvén Wave Solar Atmosphere Model (AWSoM) with Observations from the Low Corona to 1 au. We perform a validation study of the latest version of the Alfvén Wave Solar atmosphere Model (AWSoM) within the Space Weather Modeling Framework. To do so, we compare the simulation results of the model with a comprehensive suite of observations for Carrington rotations representative of the solar minimum conditions extending from the solar corona to the heliosphere up to the Earth. In the low corona (r &lt; 1.25 {\text{}}{R}☉ ), we compare with EUV images from both Solar-Terrestrial Relations Observatory-A/EUVI and Solar Dynamics Observatory/Atmospheric Imaging Assembly and to three-dimensional (3D) tomographic reconstructions of the electron temperature and density based on these same data. We also compare the model to tomographic reconstructions of the electron density from Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph observations (2.55 &lt; r &lt; 6.0{\text{}}{R}☉ ). In the heliosphere, we compare model predictions of solar wind speed with velocity reconstructions from InterPlanetary Scintillation observations. For comparison with observations near the Earth, we use OMNI data. Our results show that the improved AWSoM model performs well in quantitative agreement with the observations between the inner corona and 1 au. The model now reproduces the fast solar wind speed in the polar regions. Near the Earth, our model shows good agreement with observations of solar wind velocity, proton temperature, and density. AWSoM offers an extensive application to study the solar corona and larger heliosphere in concert with current and future solar missions as well as being well suited for space weather predictions.

Keywords: Interplanetary medium, Magnetohydrodynamics, Solar coronal waves, Solar corona, Magnetohydrodynamical simulations
Stellar Chromospheric Activity and Age Relation from Open Clusters in the LAMOST Survey. We identify member stars of more than 90 open clusters in the LAMOST survey. With the method of Fang et al., the chromospheric activity (CA) indices, {log}{R}CaK}{\prime } for 1091 member stars in 82 open clusters and {log}{R}{{H}α }{\prime } for 1118 member stars in 83 open clusters, are calculated. The relations between the average {log}{R}CaK}{\prime }, {log}{R}{{H}α }{\prime } in each open cluster and its age are investigated in different T eff and [Fe/H] ranges. We find that CA starts to decrease slowly from log t = 6.70 to log t = 8.50, and then decreases rapidly until log t = 9.53. The trend becomes clearer for cooler stars. The quadratic functions between log R‧ and log t with 4000 K &lt; T eff &lt; 5500 K are constructed, which can be used to roughly estimate ages of field stars with accuracy about 40% for {log}{R}CaK}{\prime } and 60% for {log}{R}{{H}α }{\prime }.

Keywords: Open star clusters, Stellar ages, Stellar activity
Predicting Lyα Emission from Galaxies via Empirical Markers of Production and Escape in the KBSS. Lyα emission is widely used to detect and confirm high-redshift galaxies and characterize the evolution of the intergalactic medium (IGM). However, many galaxies do not display Lyα emission in typical spectroscopic observations, and intrinsic Lyα emitters represent a potentially biased set of high-redshift galaxies. In this work, we analyze a set of 703 galaxies at 2 ≲ z ≲ 3 with both Lyα spectroscopy and measurements of other rest-frame ultraviolet and optical properties in order to develop an empirical model for Lyα emission from galaxies and understand how the probability of Lyα emission depends on other observables. We consider several empirical proxies for the efficiency of Lyα photon production, as well as the subsequent escape of these photons through their local interstellar medium. We find that the equivalent width of metal-line absorption and the O3 ratio of rest-frame optical nebular lines are advantageous empirical proxies for Lyα escape and production, respectively. We develop a new quantity, {X}LIS}{{O}3}, that combines these two properties into a single predictor of net Lyα emission, which we find describes ∼90% of the observed variance in Lyα equivalent width when accounting for our observational uncertainties. We also construct conditional probability distributions demonstrating that galaxy selection based on measurements of galaxy properties yield samples of galaxies with widely varying probabilities of net Lyα emission. The application of the empirical models and probability distributions described here may be used to infer the selection biases of current galaxy surveys and evaluate the significance of high-redshift Lyα (non)detections in studies of reionization and the IGM. Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation.

Keywords: Lyman-alpha galaxies, High-redshift galaxies, Galaxies
The Nearby, Young, χ <SUP>1</SUP> Fornacis Cluster: Membership, Age, and an Extraordinary Ensemble of Dusty Debris Disks. Only four star clusters are known within ∼100 pc of Earth. Of these, the χ 1 For cluster has barely been studied. We use the Gaia DR2 catalog and other published data to establish the cluster membership, structure, and age. The age of and distance to the cluster are ∼40 Myr and 104 pc, respectively. A remarkable, unprecedented aspect of the cluster is the large percentage of M-type stars with warm excess infrared emission due to orbiting dust grains—these stars lie in an annulus that straddles the tidal radius of the cluster. The χ 1 For cluster appears to be closely related to two extensive, previously known, groups of comoving, coeval stars (the Tucana-Horologium and Columba Associations) that are spread over much of the southern sky. While Tuc-Hor and χ 1 For are comoving and coeval, the difference in the frequency of their warm dusty debris disks at M-type stars could hardly be more dramatic.

Keywords: Debris disks, Star clusters
The Nature of Ionized Gas in the Milky Way Galactic Fountain. We address the spatial scale, ionization structure, mass, and metal content of gas at the Milky Way disk-halo interface detected as absorption in the foreground of seven closely spaced, high-latitude halo blue horizontal branch stars with heights z = 3-14 kpc. We detect transitions that trace multiple ionization states (e.g., Ca II, Fe II, Si IV, C IV) with column densities that remain constant with height from the disk, indicating that the gas most likely lies within z &lt; 3.4 kpc. The intermediate ionization state gas traced by C IV and Si IV is strongly correlated over the full range of transverse separations probed by our sight lines, indicating large, coherent structures greater than 1 kpc in size. The low ionization state material traced by Ca II and Fe II does not exhibit a correlation with either N H I  or transverse separation, implying cloudlets or clumpiness on scales less than 10 pc. We find that the observed ratio log(N Si IV /N C IV ), with a median value of -0.69 ± 0.04, is sensitive to the total carbon content of the ionized gas under the assumption of either photoionization or collisional ionization. The only self-consistent solution for photoionized gas requires that Si be depleted onto dust by 0.35 dex relative to the solar Si/C ratio, similar to the level of Si depletion in DLAs and in the Milky Way interstellar medium. The allowed range of values for the areal mass infall rate of warm, ionized gas at the disk-halo interface is 0.0003 &lt; dM gas/dtdA [M ⊙ kpc-2 yr-1] &lt;0.006. Our data support a physical scenario in which the Milky Way is fed by complex, multiphase processes at its disk-halo interface that involve kiloparsec-scale ionized envelopes or streams containing parsec-scale, cool clumps.

Keywords: High resolution spectroscopy, Photoionization, Ultraviolet astronomy, Warm ionized medium, Galaxy evolution, Halo stars, Circumgalactic medium, Intergalactic dust clouds
A Trio of Massive Black Holes Caught in the Act of Merging. We report the discovery of SDSS J0849+1114 as the first known triple Type 2 Seyfert nucleus. It represents three active black holes that are identified from new spatially resolved optical slit spectroscopy using the Dual Imaging Spectrograph on the 3.5 m telescope at the Apache Point Observatory. We also present new complementary observations including the Hubble Space Telescope Wide Field Camera 3 U- and Y-band imaging, Chandra Advanced CCD Imaging Spectrometer S-array X-ray 0.5-8 keV imaging spectroscopy, and NSF Karl G. Jansky Very Large Array radio 9.0 GHz imaging in its most extended A configuration. These comprehensive multiwavelength observations, when combined together, strongly suggest that all three nuclei are active galactic nuclei. While they are now still at kiloparsec-scale separations, where the host-galaxy gravitational potential dominates, the black holes may evolve into a bound triple system in ≲2 Gyr. These triple merger systems may explain the overly massive stellar cores that have been observed in some elliptical galaxies such as M87, which are expected to be unique gravitational wave sources. Similar systems may be more common in the early universe, when galaxy mergers are thought to have been more frequent. Based in part on observations made with the NASA/ESA Hubble Space Telescope. The observations were obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program number GO 13112.

Keywords: AGN host galaxies, Black hole physics, Radio cores, High energy astrophysics, Surveys, Active galaxies, Galaxy triplets, X-ray active galactic nuclei, Galaxy mergers, Astrophysical black holes
Chemical Abundances along the 1G Sequence of the Chromosome Maps: The Globular Cluster NGC 3201. The Hubble Space Telescope (HST) UV Legacy Survey of Galactic Globular Clusters (GCs) has investigated multiple stellar populations by means of the “chromosome map” (ChM) diagnostic tool that maximizes the separation between stars with different chemical compositions. One of the most challenging features revealed by ChM analysis is the apparent inhomogeneity among stars belonging to the first population, a phenomenon largely attributed to He variations. However, this explanation is not supported by uniformity in the p-capture elements of these stars. The HST survey has revealed that the GC NGC 3201 shows exceptionally wide coverage in the {{{∆ }}}{{F}275{{W}},{{F}}814{{W}}} parameter of the ChM. We present a chemical abundance analysis of 24 elements in 18 giants belonging to the first population of this GC and having a wide range in {{{∆ }}}{{F}275{{W}},{{F}}814{{W}}}. As far as the p-capture elements are concerned, the chemical abundances are typical of first-generation (1G) stars, as expected from the location of our targets in the ChM. Based on radial velocities and chemical abundance arguments, we find that the three stars with the lowest {{{∆ }}}{{F}275{{W}},{{F}}814{{W}}} values are binary candidates. This suggests that at least those stars could be explained with binarity. These results are consistent with evidence inferred from multiband photometry that evolved blue stragglers (BSs) populate the bluest part of the 1G sequence in the ChM. The remaining 15 spectroscopic targets show a small range in the overall metallicity by ∼0.10 dex, with stars at higher {{{∆ }}}{{F}275{{W}},{{F}}814{{W}}} values having higher absolute abundances. We suggest that a small variation in metals and binarity governs the color spread of the 1G in the ChM and that evolved BSs contribute to the bluest tail of the 1G sequence. Based on observations collected at the European Southern Observatory under ESO program 0101.D-0113(A) and the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

Keywords: Globular star clusters, Hertzsprung Russell diagram, Stellar populations, Chemical abundances, Population II stars
The Distribution of Ultra-diffuse and Ultra-compact Galaxies in the Frontier Fields. Large low-surface-brightness galaxies have recently been found to be abundant in nearby galaxy clusters. In this paper, we investigate these ultra-diffuse galaxies (UDGs) in the six Hubble Frontier Fields galaxy clusters: A2744, MACS J0416.1-2403, MACS J0717.5+3745, MACS J1149.5+2223, AS1063, and A370. These are the most massive (1-3 × 1015 M ⊙) and distant (0.308 &lt; z &lt; 0.545) systems in which this class of galaxy has yet been discovered. We estimate that the clusters host of the order of ∼200-1400 UDGs inside the virial radius (R 200), consistent with the UDG abundance-halo-mass relation found in the local universe, and suggest that UDGs may be formed in clusters. Within each cluster, however, we find that UDGs are not evenly distributed. Instead their projected spatial distributions are lopsided, and they are deficient in the regions of highest mass density as traced by gravitational lensing. While the deficiency of UDGs in central regions is not surprising, the lopsidedness is puzzling. The UDGs, and their lopsided spatial distributions, may be associated with known substructures late in their infall into the clusters, meaning that we find evidence both for formation of UDGs in clusters and for UDGs falling into clusters. We also investigate the ultra-compact dwarfs (UCDs) residing in the clusters, and find that the spatial distributions of UDGs and UCDs appear anticorrelated. Around 15% of UDGs exhibit either compact nuclei or nearby point sources. Taken together, these observations provide additional evidence for a picture in which at least some UDGs are destroyed in dense cluster environments and leave behind a residue of UCDs.

Keywords: Galaxy clusters, Nucleated dwarf galaxies, Dwarf galaxies, Ultracompact dwarf galaxies, Galaxies, Low surface brightness galaxies
A 3D Dust Map Based on Gaia, Pan-STARRS 1, and 2MASS. We present a new three-dimensional map of dust reddening, based on Gaia parallaxes and stellar photometry from Pan-STARRS 1 and 2MASS. This map covers the sky north of a decl. of -30°, out to a distance of a few kiloparsecs. This new map contains three major improvements over our previous work. First, the inclusion of Gaia parallaxes dramatically improves distance estimates to nearby stars. Second, we incorporate a spatial prior that correlates the dust density across nearby sightlines. This produces a smoother map, with more isotropic clouds and smaller distance uncertainties, particularly to clouds within the nearest kiloparsec. Third, we infer the dust density with a distance resolution that is four times finer than in our previous work, to accommodate the improvements in signal-to-noise enabled by the other improvements. As part of this work, we infer the distances, reddenings, and types of 799 million stars. (Our 3D dust map can be accessed at doi:10.7910/DVN/2EJ9TX or through the Python package dustmaps, while our catalog of stellar parameters can be accessed at doi:10.7910/DVN/AV9GXO. More information about the map, as well as an interactive viewer, can be found at argonaut.skymaps.info.) We obtain typical reddening uncertainties that are ∼30% smaller than those reported in the Gaia DR2 catalog, reflecting the greater number of photometric passbands that enter into our analysis.

Keywords: Interstellar dust, Galaxy structure, Galaxy stellar content, Interstellar dust extinction, Interstellar reddening
The Dark Matter Distributions in Low-mass Disk Galaxies. II. The Inner Density Profiles. Dark-matter-only simulations predict that dark matter halos have steep, cuspy inner density profiles, while observations of dwarf galaxies find a range of inner slopes that are often much shallower. There is debate whether this discrepancy can be explained by baryonic feedback or if it may require modified dark matter models. In Paper I of this series, we obtained high-resolution integral field Hα observations for 26 dwarf galaxies with M * = 108.1-109.7 {\text{}}{M}⊙ . We derived rotation curves from our observations, which we use here to construct mass models. We model the total mass distribution as the sum of a generalized Navarro-Frenk-White (NFW) dark matter halo and the stellar and gaseous components. Our analysis of the slope of the dark matter density profile focuses on the inner 300-800 pc, chosen based on the resolution of our data and the region resolved by modern hydrodynamical simulations. The inner slope measured using ionized and molecular gas tracers is consistent, and it is additionally robust to the choice of stellar mass-to-light ratio. We find a range of dark matter profiles, including both cored and cuspy slopes, with an average of {ρ }DM}∼ {r}-0.74+/- 0.07, shallower than the NFW profile, but steeper than those typically observed for lower-mass galaxies with M * ∼ 107.5 {\text{}}{M}⊙ . Simulations that reproduce the observed slopes in those lower-mass galaxies also produce slopes that are too shallow for galaxies in our mass range. We therefore conclude that supernova feedback models do not yet provide a fully satisfactory explanation for the observed trend in dark matter slopes.

Keywords: Galaxy structure, Galaxy kinematics, Dark matter, Dwarf galaxies
Expansion of Solar Coronal Hot Electrons in an Inhomogeneous Magnetic Field: 1D PIC Simulation. The expansion of hot electrons in flaring magnetic loops is crucial to understanding the dynamics of solar flares. In this paper we investigate, for the first time, the transport of hot electrons in a magnetic mirror field based on a 1D particle-in-cell simulation model. The hot electrons with small pitch angles transport into the cold plasma, which leads to the generation of Langmuir waves in the cold plasma and ion acoustic waves in the hot plasma. The large pitch angle electrons can be confined by the magnetic mirror, resulting in the different evolution timescale between electron parallel and perpendicular temperatures. This will cause the formation of electron temperature anisotropy, which then generates the whistler waves near the interface between hot electrons and cold electrons. The whistler waves can scatter the large pitch angle electrons to smaller value through the cyclotron resonance, leading to electrons escaping from the hot region. These results indicate that the whistler waves may play an important role in the transport of electrons in flaring magnetic loops. The findings from this study provide some new insights to understand the electron dynamics of solar flares.

Keywords: Space plasmas, Solar flares
Multivariate Analysis of BATSE Gamma-Ray Burst Properties Using Skewed Distributions. The number of classes of gamma-ray bursts (GRBs), besides the well-established short and long ones, remains a debatable issue. It was already shown, however, that when invoking skewed distributions, the {log}{T}90 and {log}{T}90-{log}{H}32 spaces are adequately modeled with mixtures of only two such components, implying two GRB types. Herein, a comprehensive multivariate analysis of several multidimensional parameter spaces is conducted for the BATSE sample of GRBs, with the usage of skewed distributions. It is found that the number of extracted components varies between the examined parameter sets, and ranges from 2 to 4, with higher-dimensional spaces allowing for more classes. Monte Carlo testing implies that these additional components are likely to be artifacts owing to the finiteness of the data and to be a result of examining a particular realization of the data as a random sample, resulting in spurious identifications.

Keywords: Gamma-ray bursts, Astronomy data analysis, Astrostatistics
Accelerated Expansion of the Universe in the Model with Nonuniform Pressure. We present the particular case of the Stephani solution for shear-free perfect fluid with uniform energy density and nonuniform pressure. Such models appeared as possible alternative to the consideration of the exotic forms of matter like dark energy that would cause the acceleration of universe expansion. These models are characterized by the spatial curvature, depending on time. We analyze the properties of the cosmological model obtained on the basis of exact solution of the Stephani class, and adapt it to the recent observational data. The spatial geometry of the model is investigated. We show that despite possible singularities, the model can describe the current stage of the universe’s evolution.

Keywords: Cosmology, Cosmological models, Expanding universe, Einstein field equations, Accelerating universe
Energy Origination and Triggering Mechanism of a Series of Homologous Confined Flares. Using the Hα data from the New Vacuum Solar Telescope at the Fuxian Solar Observatory together with multiwavelength images and magnetograms obtained by the Solar Dynamics Observatory, we study the detailed process of three homologous confined flares in active region NOAA 11861 on 2013 October 12. All of the three flares occurred at the same location, with similar morphologies and comparable classes. Through analyzing the evolution of magnetic field and flow field, we found an emergence of magnetic flux and a strong shearing motion between two opposite polarities near the following sunspot. The magnetic flux and the average transverse field strength exhibited a decrease before each eruption and reached the lowest point at the onset of each eruption. By calculating the shearing and the emergence energy in the photosphere, we found that the integral of energy injected from the photosphere, for a few hours, could provide enough energy for the flares. The reconnection between different loops was observed in Hα images during the occurrence of each flare. These results suggest that the emerging magnetic flux and the shearing motion in the photosphere can inject the energy to the sheared magnetic loops and the energy was finally released via magnetic reconnection to power the solar flares.

Keywords: Solar active region velocity fields, Solar active region magnetic fields, Solar flares, Sunspots, Solar chromosphere
Spallation-altered Accreted Compositions for X-Ray Bursts: Impact on Ignition Conditions and Burst Ashes. Model predictions of X-ray burst ashes and light curves depend on the composition of the material accreted from the companion star, in particular the abundance of CNO elements. It has previously been pointed out that spallation in the atmosphere of the accreting neutron star can destroy heavy elements efficiently. In this work we study this spallation using a realistic reaction network that follows the complete spallation cascade and takes into account not only destruction, but also production of elements by the spallation of heavier species. We find an increased survival probability of heavier elements compared to previous studies, resulting in significantly higher CNO abundances. We provide resulting compositions as a function of accretion rate, and explore their impact on 1D multi-zone X-ray burst models. We find significant changes in the composition of the burst ashes, which will affect the thermal and compositional structure of accreted neutron star crusts.

Keywords: X-ray bursts, X-ray bursters