Sazuna/UAT_keywords huggingface dataset:
In the Trenches of the Solar-Stellar Connection. III. The HST/COS Ecliptic-poles Stellar Survey (EclipSS). The Ecliptic-poles Stellar Survey (EclipSS) collected far-ultraviolet (FUV: 1160-1420 Å) spectra of 49 nearby (d ≲ 100 pc) F3-K3 main-sequence stars, located at high ecliptic latitudes (north and south), using the Cosmic Origins Spectrograph of the Hubble Space Telescope. The ecliptic poles receive higher exposures from scanning missions like the Transiting Exoplanet Survey Satellite (high-precision optical photometry) and Extended Roentgen Survey with an Imaging Telescope Array (X-ray monitoring), which can deliver crucial contextual information, not otherwise easily secured. The objective was to support theoretical studies of stellar hot outer atmospheres—chromospheres (∼104 K) and coronae (≳1 MK)—which, among other things, can adversely impact exoplanets via host-star "space weather." Flux-flux diagrams (e.g., C II 1335 Å versus O I 1306 Å) were constructed for the EclipSS stars, solar Cycle 23/24 irradiances, and long-term FUV records of α Cen A (G2 V) and B (K1 V). The EclipSS cohort displays similar minimum ("basal") fluxes to the Sun and solar twin α Cen A, in chromospheric O I 1306 Å. In hotter C II 1335 Å, a downward slump of the basal fluxes—noted in previous, less controlled surveys—can now be explained as an effect of subsolar abundances. The consistent basal minima in chromospheric and higher temperature species at solar metallicity favor the idea that stellar analogs of the solar supergranulation network provide a baseline of high-energy emissions. The magnetic network is replenished by a "local dynamo" independently of the stellar spin. It can operate even when the starspot-spawning internal dynamo has ceased cycling, as during the Sun's 17th century Maunder Minimum.

Keywords: Ultraviolet sources, Solar ultraviolet emission, Maunder minimum, Sunspot cycle, Stellar chromospheres, Stellar activity, Spectroscopy, Solar activity, Solar chromosphere
A New Method for Simulating Photoprocesses in Astrochemical Models. We propose a new model for treating solid-phase photoprocesses in interstellar ice analogs. In this approach, photoionization and photoexcitation are included in more detail, and the production of electronically excited (suprathermal) species is explicitly considered. In addition, we have included nonthermal, nondiffusive chemistry to account for the low-temperature characteristic of cold cores. As an initial test of our method, we have simulated two previous experimental studies involving the UV irradiation of pure solid O2. In contrast to previous solid-state astrochemical model calculations, which have used gas-phase photoabsorption cross-sections, we have employed solid-state cross-sections in our calculations. This method allows the model to be tested using well-constrained experiments rather than poorly constrained gas-phase abundances in interstellar medium regions. Our results indicate that inclusion of nonthermal reactions and suprathermal species allows for reproduction of low-temperature solid-phase photoprocessing that simulates interstellar ices within cold (∼10 K) dense cores such as TMC-1.

Keywords: Interstellar molecules, Ice destruction, Photoionization, Molecular clouds, Astrochemistry, Interstellar dust processes
Green Bank Telescope Observations of <SUP>3</SUP>He<SUP>+</SUP>: Planetary Nebulae. We use the Green Bank Telescope to search for 3He+ emission from a sample of four Galactic planetary nebulae: NGC 3242, NGC 6543, NGC 6826, and NGC 7009. During the era of primordial nucleosynthesis, the light elements 2H, 3He, 4He, and 7Li were produced in significant amounts, and these abundances have since been modified primarily by stars. Observations of 3He+ in H II regions located throughout the Milky Way disk reveal very little variation in the 3He/H abundance ratio—the "3He Plateau"—indicating that the net effect of 3He production in stars is negligible. This is in contrast to much higher 3He/H abundance ratios reported for some planetary nebulae. This discrepancy is known as the "3He Problem." We use radio recombination lines observed simultaneously with the 3He+ transition to make a robust assessment of the spectral sensitivity that these observations achieve. We detect spectral lines at ∼1-2 mK intensities, but at these levels, instrumental effects compromise our ability to measure accurate spectral line parameters. We do not confirm reports of previous detections of 3He+ in NGC 3242 nor do we detect 3He+ emission from any of our sources. This result calls into question all reported detections of 3He+ emission from any planetary nebula. The 3He/H abundance upper limit we derive here for NGC 3242 is inconsistent with standard stellar production of 3He and thus requires that some type of extra-mixing process operates in low-mass stars.

Keywords: Stellar nucleosynthesis, Planetary nebulae, Galaxy chemical evolution
The Wolf-Rayet + Black Hole Binary NGC 300 X-1: What is the Mass of the Black Hole?. We present new X-ray and UV observations of the Wolf-Rayet + black hole (BH) binary system NGC 300 X-1 with the Chandra X-ray Observatory and the Hubble Space Telescope Cosmic Origins Spectrograph. When combined with archival X-ray observations, our X-ray and UV observations sample the entire binary orbit, providing clues to the system geometry and interaction between the BH accretion disk and the donor star wind. We measure a binary orbital period of 32.7921 ± 0.0003 hr, in agreement with previous studies, and perform phase-resolved spectroscopy using the X-ray data. The X-ray light curve reveals a deep eclipse, consistent with inclination angles of i = 60°-75°, and a pre-eclipse excess consistent with an accretion stream impacting the disk edge. We further measure radial velocity variations for several prominent far-UV spectral lines, most notably H II λ1640 and C IV λ1550. We find that the He II emission lines systematically lag the expected Wolf-Rayet star orbital motion by a phase difference of ∆φ ∼ 0.3, while C IV λ1550 matches the phase of the anticipated radial velocity curve of the Wolf-Rayet donor. We assume the C IV λ1550 emission line follows a sinusoidal radial velocity curve (semi-amplitude = 250 km s-1) and infer a BH mass of 17 ± 4 M☉. Our observations are consistent with the presence of a wind-Roche lobe overflow accretion disk, where an accretion stream forms from gravitationally focused wind material and impacts the edge of the BH accretion disk.

Keywords: X-ray binary stars, High mass x-ray binary stars, Stellar mass black holes, Wolf-Rayet stars, Astrophysical black holes
What Produces Dust Polarization in the HH 212 Protostellar Disk at 878 μm: Dust Self-scattering or Dichroic Extinction?. We report the results of new dust polarization of a nearly edge-on disk in the HH 212 protostellar system, obtained with the Atacama Large Millimeter/submillimeter Array at ∼0.035″ (14 au) resolution in a continuum at λ ∼ 878 μm. Dust polarization is detected within ∼44 au of the central source, where a rotationally supported disk has formed. The polarized emission forms V-shaped structures opening to the east, and probably to the west, arising from the disk surfaces and arm structures further away in the east and west, which could be due to potential spiral arms excited in the outer disk. The orientations of the polarization are mainly parallel to the minor axis of the disk, with some in the western part tilting slightly away from the minor axis to form a concave shape with respect to the center. This tilting of the orientations of the polarization is expected from dust self-scattering, e.g., by 50-75 μm grains in a young disk. The intensity and degree of the polarization both peak near the central source with a small dip at the central source and decrease toward the edges. These decreases in the intensity and degree of polarization are expected from dichroic extinction by grains aligned by poloidal fields, but may also be consistent with dust self-scattering if the grain size decreases toward the edges. It is possible that both mechanisms are needed to produce the observed dust polarization, suggesting the presence of both grain growth and poloidal fields in the disk.

Keywords: Accretion, Polarimetry, Young stellar objects, Star formation, Magnetic fields
Self-gravitating Equilibria of Non-minimally Coupled Dark Matter Halos. We investigate self-gravitating equilibria of halos constituted by dark matter (DM) non-minimally coupled to gravity. In particular, we consider a theoretically motivated non-minimal coupling that may arise when the averaging/coherence length L associated with the fluid description of the DM collective behavior is comparable to the local curvature scale. In the Newtonian limit, such a non-minimal coupling amounts to a modification of the Poisson equation by a term L2∇2ρ proportional to the Laplacian of the DM density ρ itself. We further adopt a general power-law equation of state p ∝ ρΓrα relating the DM dynamical pressure p to density ρ and radius r, as expected for phase-space density stratification during the gravitational assembly of halos in a cosmological context. We confirm previous findings that, in the absence of non-minimal coupling, the resulting density ρ(r) features a steep central cusp and an overall shape mirroring the outcomes of N-body simulations in the standard ΛCDM cosmology, as described by the classic Navarro-Frenk-White or Einasto profiles. Most importantly, we find that the non-minimal coupling causes the density distribution to develop an inner core and a shape that closely follows the Burkert profile out to several core scale radii. In fact, we highlight that the resulting mass distributions can fit, with an accuracy comparable to Burkert's one, the coadded rotation curves of dwarf, DM-dominated galaxies. Finally, we show that non-minimally coupled DM halos are consistent with the observed scaling relation between the core radius r0 and core density ρ0, in terms of a universal core surface density ρ0 × r0 among different galaxies.

Keywords: Cosmology, Non-standard theories of gravity, Dark matter
The Subterahertz Solar Cycle: Polar and Equatorial Radii Derived from SST and ALMA. At subterahertz frequencies—i.e., millimeter and submillimeter wavelengths—there is a gap in measurements of the solar radius, as well as other parameters of the solar atmosphere. As the observational wavelength changes, the radius varies because the altitude of the dominant electromagnetic radiation is produced at different heights in the solar atmosphere. Moreover, radius variations throughout long time series are indicative of changes in the solar atmosphere that may be related to the solar cycle. Therefore, the solar radius is an important parameter for the calibration of solar atmospheric models enabling a better understanding of the atmospheric structure. In this work, we use data from the Solar Submillimeter-wave Telescope (SST) and the Atacama Large Millimeter/submillimeter Array (ALMA) at frequencies of 100, 212, 230, and 405 GHz to measure the equatorial and polar radii of the Sun. The radii measured with extensive data from the SST agree with the radius-versus-frequency trend present in the literature. The radii derived from ALMA maps at 230 GHz also agree with the radius-versus-frequency trend, whereas the 100 GHz radii are slightly above the values reported by other authors. In addition, we analyze the equatorial and polar radius behavior over the years by determining the correlation coefficient between solar activity and subterahertz radius time series at 212 and 405 GHz (SST). The variations of the SST-derived radii over 13 yr are correlated to the solar activity when considering equatorial regions of the solar atmosphere and anticorrelated when considering polar regions. The ALMA-derived radius time series for 100 and 230 GHz show very similar behaviors with those of SST.

Keywords: Solar atmosphere, Solar radio emission, Center to limb observations, Time series analysis
TeV Cosmic-Ray Nucleus Acceleration in Shell-type Supernova Remnants with Hard γ-Ray Spectra. The emission mechanism for hard γ-ray spectra from supernova remnants (SNRs) is still a matter of debate. Recent multiwavelength observations of the TeV source HESS J1912+101 show that it is associated with an SNR with an age of ∼100 kyr, making it unlikely produce the TeV γ-ray emission via leptonic processes. We analyzed Fermi observations of it and found an extended source with a hard spectrum. HESS J1912+101 may represent a peculiar stage of SNR evolution that dominates the acceleration of TeV cosmic rays. By fitting the multiwavelength spectra of 13 SNRs with hard GeV γ-ray spectra with simple emission models with a density ratio of GeV electrons to protons of ∼10-2, we obtain reasonable mean densities and magnetic fields with a total energy of ∼1050 erg for relativistic ions in each SNR. Among these sources, only two of them, namely SN 1006 and RCW 86, favor a leptonic origin for the γ-ray emission. The magnetic field energy is found to be comparable to that of accelerated relativistic ions and their ratio has a tendency to increase with the age of SNRs. These results suggest that TeV cosmic rays mainly originate from SNRs with hard γ-ray spectra.

Keywords: Gamma-ray sources, Galactic cosmic rays, Supernova remnants, Non-thermal radiation sources, Gamma-ray astronomy
Ring Formation in Protoplanetary Disks Driven by an Eccentric Instability. We find that, under certain conditions, protoplanetary disks may spontaneously generate multiple, concentric gas rings without an embedded planet through an eccentric cooling instability. Using both linear theory and nonlinear hydrodynamics simulations, we show that a variety of background states may trap a slowly precessing, one-armed spiral mode that becomes unstable when a gravitationally stable disk rapidly cools. The angular momentum required to excite this spiral comes at the expense of nonuniform mass transport that generically results in multiple rings. For example, one long-term hydrodynamics simulation exhibits four long-lived, axisymmetric gas rings. We verify the instability evolution and ring-formation mechanism from first principles with our linear theory, which shows remarkable agreement with the simulation results. Dust trapped in these rings may produce observable features consistent with observed disks. Additionally, direct detection of the eccentric gas motions may be possible when the instability saturates, and any residual eccentricity left over in the rings at later times may also provide direct observational evidence of this mechanism.

Keywords: Hydrodynamical simulations, Hydrodynamics, Analytical mathematics, Protoplanetary disks, Stellar accretion disks
Sustaining Star Formation in the Galactic Star Cluster M 36?. We present comprehensive characterization of the Galactic open cluster M 36. Some 200 member candidates, with an estimated contamination rate of ∼8%, have been identified on the basis of proper motion and parallax measured by the Gaia DR2. The cluster has a proper motion grouping around ( ${\mu }_{\alpha }\cos \delta =-0.15\pm 0.01$ &lt;!-- --&gt; mas yr-1, and μδ = - 3.35 ± 0.02 mas yr-1), distinctly separated from the field population. Most member candidates have parallax values 0.7-0.9 mas, with a median value of 0.82 ± 0.07 mas (distance ∼1.20 ± 0.13 kpc). The angular diameter of $27^{\prime} \pm 0\buildrel{\,\prime}\over{.} 4$ &lt;!-- --&gt; determined from the radial density profile then corresponds to a linear extent of 9.42 ± 0.14 pc. With an estimated age of ∼15 Myr, M 36 is free of nebulosity. To the southwest of the cluster, we discover a highly obscured (AV up to ∼23 mag), compact (∼ $1\buildrel{\,\prime}\over{.} 9\times 1\buildrel{\,\prime}\over{.} 2$ &lt;!-- --&gt; ) dense cloud, within which three young stellar objects in their infancy (ages ≲0.2 Myr) are identified. The molecular gas, 3.6 pc in extent, contains a total mass of (2-3) × 102 M⊙, and has a uniform velocity continuity across the cloud, with a velocity range of -20 to -22 km s-1, consistent with the radial velocities of known star members. In addition, the cloud has a derived kinematic distance marginally in agreement with that of the star cluster. If physical association between M 36 and the young stellar population can be unambiguously established, this manifests a convincing example of prolonged star formation activity spanning up to tens of Myr in molecular clouds.

Keywords: Stellar kinematics, Stellar dynamics, Molecular clouds, Extinction, Pre-main sequence stars, Open star clusters
On-disk Solar Coronal Condensations Facilitated by Magnetic Reconnection between Open and Closed Magnetic Structures. Coronal condensation and rain are a crucial part of the mass cycle between the corona and chromosphere. In some cases, condensation and subsequent rain originate in the magnetic dips formed during magnetic reconnection. This provides a new and alternative formation mechanism for coronal rain. Until now, only off-limb, rather than on-disk, condensation events during reconnection have been reported. In this paper, employing extreme-ultraviolet (EUV) images of the Solar Terrestrial Relations Observatory (STEREO) and Solar Dynamics Observatory (SDO), we investigate the condensations facilitated by reconnection from 2011 July 14-15, when STEREO was in quadrature with respect to the Sun-Earth line. Above the limb, in STEREO/EUV Imager (EUVI) 171 Å images, higher-lying open structures move downward, reconnect with the lower-lying closed loops, and form dips. Two sets of newly reconnected structures then form. In the dips, bright condensations occur in the EUVI 304 Å images repeatedly, which then flow downward to the surface. In the on-disk observations by SDO/Atmospheric Imaging Assembly (AIA) in the 171 Å channel, these magnetic structures are difficult to identify. Dark condensations appear in the AIA 304 Å images, and then move to the surface as on-disk coronal rain. The cooling and condensation of coronal plasma is revealed by the EUV light curves. If only the on-disk observations were be available, the relation between the condensations and reconnection, shown clearly by the off-limb observations, could not be identified. Thus, we suggest that some on-disk condensation events seen in transition region and chromospheric lines may be facilitated by reconnection.

Keywords: Solar ultraviolet emission, Solar magnetic reconnection, Plasma physics, Solar corona, Solar magnetic fields
A Swift Fix for Nuclear Outbursts. In November 2020, the Swift team announced an update to the UltraViolet and Optical Telescope calibration to correct for the loss of sensitivity over time. This correction affects observations in the three near-ultraviolet (UV) filters, by up to 0.3 mag in some cases. As UV photometry is critical to characterizing tidal disruption events (TDEs) and other peculiar nuclear outbursts, we recomputed published Swift data for TDEs and other singular nuclear outbursts with Swift photometry in 2015 or later as a service to the community. Using archival UV, optical, and infrared photometry, we ran host SED fits for each host galaxy. From these, we computed synthetic host magnitudes and host-galaxy properties. We calculated host-subtracted magnitudes for each transient and computed blackbody fits. In addition to the nuclear outbursts, we include the ambiguous transient ATLAS18qqn (AT2018cow), which has been classified as a potential TDE on an intermediate-mass black hole. Finally, with updated bolometric light curves, we recover the relationship of Hinkle et al., where more-luminous TDEs decay more slowly than less-luminous TDEs, with decreased scatter compared to the original relationship.

Keywords: Black hole physics, Supermassive black holes, Near ultraviolet astronomy, Tidal disruption, Transient sources, Active galactic nuclei
Energetics and 3D Structure of Elementary Events in Solar Coronal Heating. Parker first proposed (1972) that coronal heating was the necessary outcome of an energy flux caused by the tangling of coronal magnetic field lines by photospheric flows. In this paper we discuss how this model has been modified by subsequent numerical simulations outlining in particular the substantial differences between the "nanoflares" introduced by Parker and "elementary events," defined here as small-scale spatially and temporally isolated heating events resulting from the continuous formation and dissipation of field-aligned current sheets within a coronal loop. We present numerical simulations of the compressible 3D MHD equations using the HYPERION code. We use two clustering algorithms to investigate the properties of the simulated elementary events: an IDL implementation of a density-based spatial clustering of applications with noise technique, and our own physical distance clustering algorithm. We identify and track elementary heating events in time, both in temperature and in Joule heating space. For every event we characterize properties such as density, temperature, volume, aspect ratio, length, thickness, duration, and energy. The energies of the events are in the range of 1018-1021 erg, with durations shorter than 100 s. A few events last up to 200 s and release energies up to 1023 erg. While high temperatures are typically located at the flux tube apex, the currents extend all the way to the footpoints. Hence, a single elementary event cannot at present be detected. The observed emission is due to the superposition of many elementary events distributed randomly in space and time within the loop.

Keywords: Solar coronal heating, Magnetohydrodynamical simulations
Polarized Radiation and the Emergence of Biological Homochirality on Earth and Beyond. It has been proposed that spin-polarized cosmic radiation can induce asymmetric changes in helical biopolymers that may account for the emergence of biological homochirality. The parity violation in the weak interaction has direct consequences on the transport of polarization in cosmic ray showers. In this paper, we show that muons retain their polarization down to energies at which they can initiate enantioselective mutagenesis. Therefore, muons are most likely to succeed in establishing the connection between broken symmetries in the standard model of particle physics and that found in living organisms. We calculate the radiation doses deposited by primary and secondary cosmic rays at various prime targets for the searches of life in the solar system: Mars, Venus, Titan, icy moons and planetesimals, and discuss the implications for the enantioselective mutagenesis proposed as to be the driver of homochiralization. Earth is unusual in that spin-polarized muons dominate the cosmic radiation at its surface.

Keywords: Cosmic ray showers, Astrobiology, Cosmic rays