Sazuna/UAT_keywords huggingface dataset:
Possible Production of Solar Spicules by Microfilament Eruptions. We examine Big Bear Solar Observatory (BBSO) Goode Solar Telescope (GST) high spatial resolution (0"06), high-cadence (3.45 s), Hα-0.8 Å images of central-disk solar spicules, using data of Samanta et al. We compare with coronal-jet chromospheric-component observations of Sterling et al. Morphologically, bursts of spicules, referred to as "enhanced spicular activities" by Samanta et al., appear as scaled-down versions of the jet's chromospheric component. Both the jet and the enhanced spicular activities appear as chromospheric-material strands, undergoing twisting-type motions of ∼20-50 km s-1 in the jet and ∼20-30 km s-1 in the enhanced spicular activities. Presumably, the jet resulted from a minifilament-carrying magnetic eruption. For two enhanced spicular activities that we examine in detail, we find tentative candidates for corresponding erupting microfilaments, but not the expected corresponding base brightenings. Nonetheless, the enhanced-spicular-activities' interacting mixed-polarity base fields, frequent-apparent-twisting motions, and morphological similarities to the coronal jet's chromospheric-temperature component, suggest that erupting microfilaments might drive the enhanced spicular activities but be hard to detect, perhaps due to Hα opacity. Degrading the BBSO/GST-image resolution with a 1"0-FWHM smoothing function yields enhanced spicular activities resembling the "classical spicules" described by, e.g., Beckers. Thus, a microfilament eruption might be the fundamental driver of many spicules, just as a minifilament eruption is the fundamental driver of many coronal jets. Similarly, a 0"5-FWHM smoothing renders some enhanced spicular activities to resemble previously reported "twinned" spicules, while the full-resolution features might account for spicules sometimes appearing as 2D-sheet-like structures.

Keywords: Solar magnetic fields, Solar chromosphere, Solar filament eruptions, Solar magnetic reconnection
Dynamic Kink Instability and Transverse Motions of Solar Spicules. Hydrodynamic jets are unstable to the kink instability (m = 1 mode in cylindrical geometry) owing to the centripetal force, which increases the transverse displacement of the jet. When the jet moves along a magnetic field, the Lorentz force tries to decrease the displacement and stabilize the instability of sub-Alfvénic flows. The threshold of the instability depends on the Alfvén Mach number (the ratio of Alfvén and jet speeds). We suggest that the dynamic kink instability may be important to explain observed transverse motions of type II spicules in the solar atmosphere. We show that the instability may begin for spicules that rise up at the peripheries of vertically expanding magnetic flux tubes because of the decrease of the Alfvén speed in both the vertical and the radial directions. Therefore, inclined spicules may be more unstable and have higher transverse speeds. Periods and growth times of unstable modes in the conditions of type II spicules have values of 30 s and 25-100 s, respectively, which are comparable to the lifetime of the structures. This may indicate an interconnection between high-speed flow and the rapid disappearance of type II spicules in chromospheric spectral lines.

Keywords: Solar spicules, Solar chromosphere, Solar mottles
Efficiency of Electromagnetic Emission by Electrostatic Turbulence in Solar Wind and Coronal Plasmas with Density Inhomogeneities. We present a new method to semianalytically calculate the radiation efficiency of electromagnetic waves emitted at specific frequencies by electrostatic wave turbulence in solar wind and coronal plasmas with random density fluctuations. This method is applied to the case of electromagnetic emission radiated at the fundamental plasma frequency ωp by beam-driven Langmuir wave turbulence during Type III solar bursts. It is supposed that the main radiation mechanism is the linear conversion of electrostatic to electromagnetic waves on the background plasma density fluctuations, at constant frequency. The radiation efficiency (emissivity) of such a process is larger than that obtained in the framework of models where the low frequency density fluctuations and the corresponding ion sound waves are not external but produced by the electrostatic wave turbulence itself through nonlinear wave-wave interactions. Results show that the radiation efficiency of Langmuir wave turbulence into electromagnetic emissions at ωp is nearly constant asymptotically, with the electromagnetic energy density growing linearly with time, and is proportional to the average level of density fluctuations. Comparisons with another analytical method developed by the authors and with space observations are satisfactory.

Keywords: Space plasmas, Solar flares, Heliosphere, Plasma physics, Solar wind, Plasma astrophysics, Radio bursts, Solar physics, Solar radio emission, Solar corona, Radio sources
Water Production Rates and Activity of Interstellar Comet 2I/Borisov. We observed the interstellar comet 2I/Borisov using the Neil Gehrels Swift Observatory's Ultraviolet/Optical Telescope. We obtained images of the OH gas and dust surrounding the nucleus at six epochs spaced before and after perihelion (-2.56 to 2.54 au). Water production rates increased steadily before perihelion from (7.0 ± 1.5) × 1026 molecules s-1 on 2019 November 1, to (10.7 ± 1.2) × 1026 molecules s-1 on December 1. This rate of increase in water production rate is quicker than that of most dynamically new comets and at the slower end of the wide range of Jupiter-family comets. After perihelion, the water production rate decreased to (4.9 ± 0.9) × 1026 molecules s-1 on December 21, which is much more rapidly than that of all previously observed comets. Our sublimation model constrains the minimum radius of the nucleus to 0.37 km, and indicates an active fraction of at least 55% of the surface. A(0)fρ calculations show a variation between 57.5 and 105.6 cm with a slight trend peaking before the perihelion, lower than previous and concurrent published values. The observations confirm that 2I/Borisov is carbon-chain depleted and enriched in NH2 relative to water.

Keywords: Small Solar System bodies, Comet nuclei, Exoplanet astronomy, Comets, Comet volatiles
On the Cooling Flow Problem in the Gaseous Halo of the Milky Way. Theoretical and observational arguments suggest that there is a large amount of hot (∼106 K) diffuse gas residing in the Milky Way (MW) halo, but its total mass and spatial distribution are still unclear. In this work, we present a general model for the gas density distribution in the Galactic halo, and investigate the gas evolution under radiative cooling with a series of 2D hydrodynamic simulations. We find that the mass inflow rate in the developed cooling flow increases with gas metallicity and the total gas mass in the halo. For a fixed halo gas mass, the spatial gas distribution affects the onset time of the cooling catastrophe, which starts earlier when the gas distribution is more centrally peaked, but does not substantially affect the final mass inflow rate. The gravity from the Galactic bulge and disk affects gas properties in the inner regions, but has little effect on the final inflow rate either. We confirm our results by investigating cooling flows in several density models adopted from the literature, including the Navarro-Frenk-White (NFW) model, the cored-NFW model, the Maller &amp; Bullock model, and the β model. Typical mass inflow rates in our simulations range from ∼5 M⊙ yr-1 to ∼60 M⊙ yr-1, and are much higher than the observed star formation rate in our Galaxy, suggesting that stellar and active galactic nucleus feedback processes may play important roles in the evolution of the MW and MW-type galaxies.

Keywords: Hydrodynamical simulations, Cooling flows, Galaxy physics, Plasma astrophysics, Galaxy evolution, Circumgalactic medium, Milky Way Galaxy, Galaxy processes
Wind-reprocessed Transients. We consider the situation where the luminosity from a transient event is reprocessed by an optically thick wind. Potential applications are the tidal disruption of stars by black holes (BHs), engine-powered supernovae, and unique fast transients found by current and future wide-field surveys. We derive relations between the injected and observed luminosity for steady and time-dependent winds, and discuss how the temperature is set for scattering-dominated radiative transport. We apply this framework to specific examples of tidal disruption events and the formation of a BH by a massive star, as well as discuss other applications such as deriving observables from detailed hydrodynamic simulations. We conclude by exploring what is inferred about the mass-loss rate and underlying engine powering AT 2018cow if it is explained as a wind-reprocessed transient, demonstrating that its optical emission is consistent with reprocessing of the observed soft X-rays.

Keywords: Black hole physics, Supernovae, Radiative transfer
The FLASHES Survey. I. Integral Field Spectroscopy of the CGM around 48 z ≃ 2.3-3.1 QSOs. We present the pilot study of the Fluorescent Lyman-Alpha Structures in High-z Environments Survey; the largest integral field spectroscopy survey to date of the circumgalactic medium at z = 2.3-3.1. We observed 48 quasar fields with the Palomar Cosmic Web Imager to an average (2σ) limiting surface brightness of 6 × 10-18 erg s-1 cm-2 arcsec-2 (in a 1″ aperture and ∼20 Å bandwidth). Extended H I Lyα emission is discovered around 37/48 of the observed quasars, ranging in projected radius from 14 to 55 proper kiloparsecs (pkpc), with one nebula exceeding 100 pkpc in effective diameter. The dimming-adjusted circularly averaged surface brightness profile peaks at 1 × 10-15 erg s-1 cm-2 arcsec-2 at R⊥ ∼ 20 pkpc and integrated luminosities range from 0.4 to 9.4 × 1043 erg s-1. The emission appears to have an eccentric morphology and an average covering factor of ∼30%-40% at small radii. On average, the nebular spectra are redshifted with respect to both the systemic redshift and Lyα peak of the quasar spectrum. The integrated spectra of the nebulae mostly have single- or double-peaked profiles with global dispersions ranging from 143 to 708 km s-1, though the individual Gaussian components of lines with complex shapes mostly have dispersions ≤400 km s-1, and the flux-weighted velocity centroids of the lines vary by thousands of km s-1 with respect to the QSO redshifts. Finally, the root-mean-square velocities of the nebulae are found to be consistent with those expected from gravitational motions in dark matter halos of mass ${\mathrm{Log}}_{10}({M}_{{\rm{h}}}[{M}_{\odot }])\simeq {12.2}_{-1.2}^{+0.7}$ Log 10 ( M h [ M ⊙ ] ) ≃ 12.2 - 1.2 + 0.7 . We compare these results to existing surveys at higher and lower redshift.

Keywords: Quasars, Galaxy environments, Circumgalactic medium, Galaxy evolution, Intergalactic medium, Galaxies
Spectral Classification of B Stars: The Empirical Sequence Using SDSS-IV/APOGEE Near-IR Data. We present a semi-empirical spectral classification scheme for normal B-type stars using near-infrared (NIR) spectra (1.5-1.7 μm) from the Sloan Digital Sky Survey Apache Point Observatory Galaxy Evolution Experiment (APOGEE2)-N data release 14 (DR14) database. The main motivation for working with B-type stars is their importance in the evolution of young stellar clusters; however, we also take advantage of having a numerous sample (316 stars) of B-type star candidates in APOGEE2-N, for which we also have optical (3600-9100 Å) counterparts from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey. By first obtaining an accurate spectral classification of the sources using the LAMOST DR3 spectra and the canonical spectral classification scheme, we found a linear relation between optical spectral types and the equivalent widths of the hydrogen lines of the Brackett series in the APOGEE2-N NIR spectra. This relation extends smoothly from a similar relation for O and early B stars found by Roman-Lopes et al. This way, we obtain a catalog of B-type sources with features in both the optical and NIR and a classification scheme refined down to one spectral subclass.

Keywords: Infrared astronomy, Optical identification, B stars, Spectroscopy
Dynamics of Laterally Propagating Flames in X-Ray Bursts. I. Burning Front Structure. We investigate the structure of laterally propagating flames through the highly stratified burning layer in an X-ray burst. Two-dimensional hydrodynamics simulations of flame propagation are performed through a rotating plane-parallel atmosphere, exploring the structure of the flame. We discuss the approximations needed to capture the length and timescales at play in an X-ray burst and describe the flame acceleration observed. Our studies complement other multidimensional studies of burning in X-ray bursts.

Keywords: Neutron stars, Hydrodynamical simulations, Open source software, Hydrodynamics, Nucleosynthesis, Computational methods, Nuclear astrophysics, X-ray bursts
Identification of a Group III CEMP-no Star in the Dwarf Spheroidal Galaxy Canes Venatici I. CEMP-no stars, a subclass of carbon-enhanced metal-poor (CEMP) stars, are one of the most significant stellar populations in galactic archeology, because they dominate the low end of the metallicity distribution function, providing information on the early star formation and chemical-evolution history of the Milky Way and its satellite galaxies. Here we present an analysis of low-resolution (R ∼ 1800) optical spectroscopy for a CEMP giant, SDSS J132755.56+333521.7, observed with the Large Binocular Telescope (LBT), one of the brightest (g ∼ 20.5) members of the classical dwarf spheroidal galaxy, Canes Venatici I (CVn I). Many CEMP stars discovered to date have very cool effective temperatures (Teff &lt; 4500 K), resulting in strong veiling by molecular carbon bands over their optical spectra at low/medium spectral resolution. We introduce a technique to mitigate the carbon-veiling problem to obtain reliable stellar parameters, and validate this method with LBT low-resolution optical spectra of the ultra-metal-poor ([Fe/H] = -4.0) CEMP-no dwarf, G 77-61, and seven additional very cool CEMP stars, which have published high-resolution spectroscopic parameters. We apply this technique to the LBT spectrum of SDSS J132755.56+333521.7. We find that this star is well described with parameters Teff = 4530 K, log g = 0.7, [Fe/H] = -3.38, and absolute carbon abundance A(C) = 7.23, indicating that it is likely the first Group III CEMP-no star identified in CVn I. The Group III identification of this star suggests that it is a member of the extremely metal-poor population in CVn I, which may have been accreted into its halo.

Keywords: Carbon stars, Dwarf galaxies, Chemical abundances, Spectroscopy, Population II stars, Metallicity, Chemically peculiar stars
Tidally Distorted, Iron-enhanced Exoplanets Closely Orbiting Their Stars. The transiting planet candidate KOI 1843.03 ( $0.6\,{R}_{\oplus }$ radius, 4.245 hr orbital period, $0.46\,{M}_{\odot }$ host star) has the shortest orbital period of any known planet. Here we show, using the first three-dimensional interior structure simulations of ultra-short-period tidally distorted rocky exoplanets, that KOI 1843.03 may be shaped like an American football, elongated along the planet-star axis with an aspect ratio of up to 1.79. Furthermore, for KOI 1843.03 to have avoided tidal disruption (wherein the planet is pulled apart by the tidal gravity of its host star) on such a close-in orbit, KOI 1843.03 must be as iron-rich as Mercury (about 66% by mass iron compared to Mercury's 70% by mass iron). Of the ultra-short-period (Porb ≲ 1 day) planets with physically meaningful constraints on their densities characterized to date, just under half (four out of nine) are iron-enhanced. As more are discovered, we will better understand the diversity of rocky planet compositions and the variety of processes that lead to planetary iron enhancement.

Keywords: Computational methods, Planetary interior, Exoplanets
Core-collapse Supernova Explosions Driven by the Hadron-quark Phase Transition as a Rare r-process Site. Supernova explosions of massive stars are one of the primary sites for the production of the elements in the universe. Up to now, stars with zero-age main-sequence masses in the range of 35-50 M⊙ had mostly represented the failed supernova explosion branch. In contrast, it has been demonstrated recently that the appearance of exotic phases of hot and dense matter, associated with a sufficiently strong phase transition from nuclear matter to the quark-gluon plasma at high baryon density, can trigger supernova explosions of such massive supergiant stars. Here, we present the first results obtained from an extensive nucleosynthesis analysis for material being ejected from the surface of the newly born proto-neutron stars of such supernova explosions. These ejecta contain an early neutron-rich component and a late-time high-entropy neutrino-driven wind. The nucleosynthesis robustly overcomes the production of nuclei associated with the second r-process peak, at nuclear mass number A ≃ 130, and proceeds beyond the formation of the third peak (A ≃ 195) to the actinides. These yields may account for metal-poor star observations concerning r-process elements such as strontium and europium in the Galaxy at low metallicity, while the actinide yields suggests that this source may be a candidate contributing to the abundances of radioactive 244Pu measured in deep-sea sediments on Earth.

Keywords: Nuclear astrophysics, Supernovae, Nucleosynthesis
Constraining the Milky Way Mass Profile with Phase-space Distribution of Satellite Galaxies. We estimate the Milky Way (MW) halo properties using satellite kinematic data including the latest measurements from Gaia DR2. With a simulation-based 6D phase-space distribution function (DF) of satellite kinematics, we can infer halo properties efficiently and without bias, and handle the selection function and measurement errors rigorously in the Bayesian framework. Applying our DF from the EAGLE simulation to 28 satellites, we obtain an MW halo mass of $M={1.23}_{-0.18}^{+0.21}\times {10}^{12}{M}_{\odot }$ and a concentration of $c={9.4}_{-2.1}^{+2.8}$ with the prior based on the M-c relation. The inferred mass profile is consistent with previous measurements but with better precision and reliability due to the improved methodology and data. Potential improvement is illustrated by combining satellite data and stellar rotation curves. Using our EAGLE DF and best-fit MW potential, we provide much more precise estimates of the kinematics for those satellites with uncertain measurements. Compared to the EAGLE DF, which matches the observed satellite kinematics very well, the DF from the semi-analytical model based on the dark-matter-only simulation Millennium II (SAM-MII) over-represents satellites with small radii and velocities. We attribute this difference to less disruption of satellites with small pericenter distances in the SAM-MII simulation. By varying the disruption rate of such satellites in this simulation, we estimate a ∼5% scatter in the inferred MW halo mass among hydrodynamics-based simulations.

Keywords: Milky Way dark matter halo, Hydrodynamical simulations, Bayesian statistics, Dwarf galaxies, Milky Way dynamics, Proper motions, N-body simulations, Milky Way mass
The Luminosity Distribution of Short Gamma-Ray Bursts under a Structured Jet Scenario. The joint detection of gravitational wave (GW) and electromagnetic radiation from the binary neutron star merger event GW170817 marks a breakthrough in the field of multi-messenger astronomy. The short gamma-ray burst (sGRB) GRB 170817A, associated with this binary neutron star merger event, has an isotropic-equivalent gamma-ray radiation luminosity of 1.6 × 1047 erg s-1, which is much lower than that of other sGRBs. The measurement of the superluminal movement of the radio afterglow emission confirms the presence of the relativistic jet, and the emission features can be well explained by the structured jet model. In this paper, we calculate the luminosity distribution of sGRBs and its evolution with redshift based on the structured (Gaussian) jet model, and find that the typical luminosity increase with redshift, for nearby sGRBs (such as for luminosity distance less than 200 Mpc) the typical gamma-ray luminosity is just around 1047-1048 erg s-1, which naturally explains the very low radiation luminosity of GRB 170817A. We derived the detection probability of sGRBs by Fermi-GBM and found that the expected detection rate of sGRBs is only about 1 yr-1 within the distance of several hundred Mpc. We explored the effect of the power-law index α of the merger time distribution on the observed characteristics and found that it had little effect on the observed luminosity and viewing-angle distributions. However, it is very interesting that, for different values of α, the distributions of the number of observed sGRBs are quite different, so it is possible to determine the value of α through observed distributions of the number of sGRBs. We used the Bayesian method to make a quantitative analysis and found that the value of α may be identified when the number of observed sGRBs with known redshifts is more than 200. Finally, we compare our results of gamma-ray luminosity distribution with sGRBs with known redshifts, and found that our results are consistent with the observation, which implies that our simulation results can reproduce the observed luminosity distribution well.

Keywords: Gamma-ray astronomy, Gamma-ray bursts, Astronomical methods
Kinematics and Dynamics of Multiphase Outflows in Simulations of the Star-forming Galactic Interstellar Medium. Galactic outflows produced by stellar feedback are known to be multiphase in nature. Observations and simulations indicate that the material within several kiloparsecs of galactic disk midplanes consists of warm clouds embedded within a hot wind. A theoretical understanding of the outflow phenomenon, including both winds and fountain flows, requires study of the interactions among thermal phases. We develop a method to quantify these interactions via measurements of mass, momentum, and energy flux exchanges using temporally and spatially averaged quantities and conservation laws. We apply this method to a star-forming interstellar medium simulation based on the TIGRESS framework, for solar neighborhood conditions. To evaluate the extent of interactions among the phases, we examine the validity of the "ballistic model," which predicts the trajectories of the warm phase (5050 K &lt; T &lt; 2 × 104 K) treated as non-interacting clouds. This model is successful at intermediate vertical velocities ( $50\,\mathrm{km}\,{{\rm{s}}}^{-1}\lesssim | {V}_{z}| \lesssim 100\,\mathrm{km}\,{{\rm{s}}}^{-1}$ ), but at higher velocities, we observe an excess in simulated warm outflow compared to the ballistic model. This discrepancy cannot be fully accounted for by cooling of high-velocity, intermediate-temperature (2 × 104 K &lt; T &lt; 5 × 105 K) gas. We examine the fluxes of mass, momentum, and energy and conclude that the warm phase gains mass via cooling of the intermediate phase and momentum from the hot (T &gt; 5 × 105 K) phase. The large energy flux from the hot outflow, transferred to the warm and intermediate phases, is quickly radiated away. A simple interaction model implies an effective warm cloud size in the fountain flow of a few 100 pc, showing that warm-hot flux exchange mainly involves a few large clouds rather than many small ones.

Keywords: Galaxy fountains, Stellar feedback, Galaxy winds, Interstellar medium, Magnetohydrodynamical simulations