Sazuna/UAT_keywords huggingface dataset:
Evolution of Entropy and Mediation of the Solar Wind by Turbulence. We study the evolution of solar wind entropy based on a conservative formulation of solar wind and turbulence transport model equations, and compare the model results to Voyager 2 measurements. For a polytropic index of γ = 5/3 (&gt;1), entropy increases with distance due to the dissipation of turbulence, being about 12.84% higher at 75 au than at 1 au. However, if the polytropic index satisfies γ &lt; 1, entropy decreases. We show that not only the creation of pickup ions, but also stream-shear leads to a decrease of the solar wind speed. We show that the sum of the solar wind flow energy (kinetic plus enthalpy) and turbulent (magnetic) energy is constant, indicating that kinetic solar wind energy is transferred into turbulent energy via stream-shear and pickup ion isotropization, which then in turn heats the solar wind via the dissipation of turbulence. We compare the theoretical solutions of the solar wind entropy, the solar wind density, the thermal gas pressure, the solar wind proton temperature, and the fluctuating magnetic energy with those measured by Voyager 2. The results show that the theoretical results are in good agreement with the observed results.

Keywords: Interplanetary turbulence, The Sun, Solar wind
Dependencies of Kappa Parameter on the Core Energy of Kappa Distributions and Plasma Parameter in the Case of the Magnetosphere of the Earth. Formation of kappa distribution functions and their relaxation to Maxwellian distributions are the main feature of astrophysical and space collisionless plasmas. In this work, we use the magnetosphere of the Earth as a giant plasma laboratory to study the properties of ion kappa distribution functions. Four years of measurements, performed by the multi-satellite Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission during quiet geomagnetic conditions, at geocentric distances from three Earth radii (RE) to the magnetopause at daytime (of the order of 10RE), and up to 20RE at night time are used for the analyses. We find a dependence of the k parameter on the core energy E0 of a single kappa distribution inside the magnetospheric ring current and in the plasma sheet, for different values of the plasma parameter (the ratio between the plasma and magnetic pressures). We show that k increases with E0 for all values of plasma parameter, which supports earlier results obtained for the magnetospheres of the Earth, Jupiter, and Saturn, but using lower statistics. However, contrary to previous results, our studies show that the relation between k and E0 is nonlinear, and most probably is a power law with a nearly constant index. The results obtained are relevant to solve the problem of thermalization of kappa distributions.

Keywords: Space plasmas, Planetary magnetospheres
Three-dimensional Projection Effects on Chemistry in a Planck Galactic Cold Clump. Offsets of molecular line emission peaks from continuum peaks are very common but frequently difficult to explain with a single spherical cloud chemical model. We propose that the spatial projection effects of an irregular three-dimensional (3D) cloud structure can be a solution. This work shows that the idea can be successfully applied to the Planck cold clump G224.4-0.6 by approximating it with four individual spherically symmetric cloud cores whose chemical patterns overlap with each other to produce observable line maps. With the empirical physical structures inferred from the observation data of this clump and a gas-grain chemical model, the four cores can satisfactorily reproduce its 850 μm continuum map and the diverse peak offsets of CCS, HC3N, and N2H+ simultaneously at chemical ages of about 8 × 105 ∼ 3 × 106 yr. The 3D projection effects on chemistry has the potential to explain such asymmetrical distributions of chemicals in many other molecular clouds.

Keywords: Interstellar abundances, Chemical abundances, Dense interstellar clouds, Astrochemistry
The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XX. Ages of Single and Multiple Stellar Populations in Seven Bulge Globular Clusters. In the present work we analyzed seven globular clusters (GCs) selected from their location in the Galactic bulge and with metallicity values in the range -1.30 ≲ [Fe/H] ≲ -0.50. The aim of this work is first to derive cluster ages assuming single stellar populations and second to identify the stars from first (1G) and second generations (2G) from the main sequence, subgiant, and red giant branches, and to derive their age differences. Based on a combination of UV and optical filters used in this project, we apply the Gaussian mixture models to distinguish the multiple stellar populations. Applying statistical isochrone fitting, we derive self-consistent ages, distances, metallicities, and reddening values for the sample clusters. An average age of 12.3 ± 0.4 Gyr was obtained both using DSED and BaSTI (accounting atomic diffusion effects) isochrones, without a clear distinction between the moderately metal-poor and the more metal-rich bulge clusters, except for NGC 6717 and the inner halo NGC 6362 with ∼13.5 Gyr. We derived a weighted mean age difference between the multiple populations hosted by each GC of 41 ± 170 Myr adopting canonical He abundances; whereas for higher He in 2G stars, this difference reduces to 17 ± 170 Myr, but with individual uncertainties of 500 Myr.

Keywords: Globular star clusters, Galactic bulge
Rotational Desorption of Ice Mantles from Suprathermally Rotating Grains around Young Stellar Objects. Ice mantles on dust grains play a central role in astrochemistry. Water and complex organic molecules (COMs) are thought to first form on the ice mantles and subsequently are released into the gas phase due to star-formation activity. However, the critical question is whether ice mantles can survive stellar radiation when grains are being heated from {T}_{d}∼ 10 K to ≳100 K. In this paper, we first study the effect of suprathermal grain rotation driven by the intense radiation of young stellar objects on the ice mantles. We find that the entire ice mantles can be disrupted into small fragments by centrifugal stress before the water ice and COMs desorb via thermal sublimation. We then study the consequence of resulting ice fragments and find that tiny fragments of radius a ≲ 10 Å exhibit a transient release of COMs due to thermal spikes, whereas larger fragments can facilitate thermal sublimation at much higher rates than from the original icy grain, or the same rate but with temperatures of ∼20-40 K lower. We find that rotational desorption is efficient for hot cores/corinos from the inner to outer regions where the temperature drops to T_{gas}∼ 40 K and n_{H} ∼ 104 cm-1. We discuss the implications of this mechanism for desorption of COMs and water ice in various environments, including outflow cavity walls, photodissociation regions, and protoplanetary disks. Finally, we show that very large aggregate grains can be disrupted into individual icy grains via a rotational disruption mechanism, followed by rotational desorption of ice mantles.

Keywords: Interstellar dust, Interstellar molecules, Dense interstellar clouds, Astrochemistry, Star formation, Protostars
Dynamical Relics of the Ancient Galactic Halo. We search for dynamical substructures in the LAMOST DR3 very metal-poor (VMP) star catalog. After cross-matching with Gaia DR2, there are ∼3300 VMP stars with available high-quality astrometric information that have halo-like kinematics. We apply a method based on the self-organizing map StarGO to find groups clustered in the 4D space of orbital energy and angular momentum. We identify 57 dynamically tagged groups (DTGs), which we label DTG-1 to DTG-57. Most of them belong to existing massive substructures in the nearby halo, such as the Gaia Sausage or Sequoia. The stream identified by Helmi et al. is recovered, but the two disjointed portions of the substructure appear to have distinct dynamical properties. The very retrograde substructure Rg5 found previously by Myeong et al. is also retrieved. We report six new DTGs with highly retrograde orbits, two with very prograde orbits, and 12 with polar orbits. By mapping other data sets (APOGEE halo stars, and catalogs of r-process-enhanced and carbon-enhanced metal-poor [CEMP] stars) onto the trained neuron map, we can associate stars with detailed chemical abundances with the DTGs and look for associations with chemically peculiar stars. The highly eccentric Gaia Sausage groups contain representatives of both debris from the satellite itself (which is α-poor) and the Splashed Disk, sent up into eccentric halo orbits from the encounter (and which is α-rich). The new prograde substructures also appear to be associated with the Splashed Disk. The DTGs belonging to the Gaia Sausage host two relatively metal-rich r-II stars and six CEMP stars in different subclasses, consistent with the idea that the Gaia Sausage progenitor is a massive dwarf galaxy. Rg5 is dynamically associated with two highly r-process-enhanced stars with [Fe/H] ∼ -3. This finding indicates that its progenitor might be an ultrafaint dwarf galaxy that has experienced r-process enrichment from neutron star mergers.

Keywords: R-process, Milky Way stellar halo, Milky Way formation
Detection of Fluorine in Hot Extreme Helium Stars. The main objective of this paper is to explore abundances of fluorine in hot extreme helium stars (EHes). Overabundance of fluorine is a characteristic feature for cool EHes and R Coronae Borealis stars and further enforces their close connection. For hot EHes this relationship with the cooler EHes, based on their fluorine abundance is unexplored. We present in this paper the first abundance estimates of fluorine determined from singly ionized fluorine lines (F II) for 10 hot EHe stars from optical spectra. Fluorine abundances were determined using the F II lines in two windows centered at 3505 Å and 3850 Å. Six of the 10 stars show significant enhancement of fluorine similar to the cool EHes. Two carbon-poor hot EHes show no signature of fluorine and have a significant low upper limit for the F abundance. These fluorine abundances are compared with the other elemental abundances observed in these stars, which provide an idea about the formation and evolution of these stars. The trends of fluorine with C, O, and Ne show that significant helium burning after a CO-He white dwarf merger can account for a majority of the observed abundances. Predictions from simulations of white dwarf mergers are discussed in light of the observed abundances.

Keywords: Helium-rich stars, Stellar abundances, Hydrogen deficient stars, Chemically peculiar stars
The Clustering of X-Ray Luminous Quasars. The clustering of active galactic nuclei (AGNs) sheds light on their typical large (Mpc-scale) environments, which can constrain the growth and evolution of supermassive black holes. Here we measure the clustering of luminous X-ray-selected AGNs in the Stripe 82X and XMM-XXL-north surveys around the peak epoch of black hole growth, in order to investigate the dependence of luminosity on large-scale AGN environment. We compute the auto-correlation function of AGNs in two luminosity bins, 1043 ≤ L_{X} &lt; 1044.5 erg s-1 at z ∼ 0.8 and LX ≥ 1044.5 erg s-1 at z ∼ 1.8, and calculate the AGN bias taking into account the redshift distribution of the sources using three different methods. Our results show that while the less luminous sample has an inferred typical halo mass that is smaller than for the more luminous AGNs, the host halo mass may be less dependent on luminosity than suggested in previous work. Focusing on the luminous sample, we calculate a typical host halo mass of ∼1013 M_{☉} h-1, which is similar to previous measurements of moderate-luminosity X-ray AGNs and significantly larger than the values found for optical quasars of similar luminosities and redshifts. We suggest that the clustering differences between different AGN selection techniques are dominated by selection biases, and not due to a dependence on AGN luminosity. We discuss the limitations of inferring AGN triggering mechanisms from halo masses derived by large-scale bias.

Keywords: X-ray active galactic nuclei, High-luminosity active galactic nuclei, Clustering
Equilibrium Tidal Response of Jupiter: Detectability by the Juno Spacecraft. An observation of Jupiter's tidal response is anticipated for the ongoing Juno spacecraft mission. We combine self-consistent, numerical models of Jupiter's equilibrium tidal response with observed Doppler shifts from the Juno gravity science experiment to test the sensitivity of the spacecraft to tides raised by the Galilean satellites and the Sun. The concentric Maclaurin spheroid (CMS) method finds the equilibrium shape and gravity field of a rotating, liquid planet with the tide raised by a satellite, expanded in Love numbers (knm). We present improvements to the CMS theory that eliminate an unphysical center-of-mass offset and study in detail the convergence behavior of the CMS approach. We demonstrate that the dependence of knm with orbital distance is important when considering the combined tidal response for Jupiter. Conversely, the details of the interior structure have a negligible influence on knm for models that match the zonal harmonics J2, J4, and J6, already measured to high precision by Juno. As the mission continues, improved coverage of Jupiter's gravity field at different phases of Io's orbit is expected to yield an observed value for the degree-two Love number (k22) and potentially select higher-degree knm. We present a test of the sensitivity of the Juno Doppler signal to the calculated knm, which suggests the detectability of k33, k42, and k31, in addition to k22. A mismatch of a robust Juno observation with the remarkably small range in calculated Io equilibrium, k22 = 0.58976 ± 0.0001, would indicate a heretofore uncharacterized dynamic contribution to the tides.

Keywords: Tidal distortion, Solar system gas giant planets, Jupiter, Tides, Planetary interior, Jovian satellites
Infrared Properties of Asymptotic Giant Branch Stars in Our Galaxy and the Magellanic Clouds. We investigate the infrared properties of asymptotic giant branch (AGB) stars in our Galaxy and the Magellanic Clouds using various infrared observational data and theoretical models. We use catalogs for the sample of 4996 AGB stars in our Galaxy and about 39,000 AGB stars in the Magellanic Clouds from the available literature. For each object in the sample, we cross-identify the 2MASS, Wide-field Infrared Survey Explorer, and Spitzer counterparts. To compare the physical properties of O- and C-rich AGB stars in our Galaxy and the Magellanic Clouds, we present IR two-color diagrams (2CDs) using various photometric data. We perform radiative transfer model calculations for AGB stars using various possible parameters of central stars and dust shells. Using the dust opacity functions of amorphous silicate and carbon, the theoretical dust shell models can roughly reproduce the observations of AGB stars on various IR 2CDs. Compared with our Galaxy, we find that the Magellanic Clouds are deficient in AGB stars with thick dust shells. Compared with the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC) is more deficient in AGB stars with thick dust shells. This could be because the Magellanic Clouds are more metal-poor than our Galaxy and the LMC is more metal-rich than the SMC. We also present the IR properties of known pulsating variables. Investigating the magnitude distributions at mid-IR (MIR) bands for AGB stars in the Magellanic Clouds, we find that the SMC is more deficient in bright AGB stars at MIR bands compared with the LMC.

Keywords: Infrared astronomy, Asymptotic giant branch stars, Circumstellar dust, Radiative transfer
All at Once: Transient Pulsations, Spin-down, and a Glitch from the Pulsating Ultraluminous X-Ray Source M82 X-2. The first pulsating ultraluminous X-ray source (PULX) to be identified is M82 X-2. After the discovery in 2014, NuSTAR observed the M82 field 15 times throughout 2015 and 2016. In this paper, we report the results of pulsation searches in all of these data sets and find only one new detection. This new detection allows us to refine the orbital period of the source and measure an average spin-down rate between 2014 and 2016 of ∼-6 × 10-11 Hz s-1, which is in contrast to the strong spin-up seen during the 2014 observations, representing the first detection of spin-down in a PULX system. Thanks to the improved orbital solution allowed by this new detection, we are also able to detect pulsations in additional segments of the original 2014 data set. We find a glitch superimposed on the very strong and variable spin-up already reported - the first positive glitch identified in a PULX system. We discuss the new findings in the context of current leading models for PULXs.

Keywords: Accretion, Orbital motion, X-ray astronomy, Neutron stars, Pulsar timing method, Fast Fourier transform, Pulsars, Time domain astronomy, Compact objects
The First Ultracompact Roche Lobe-Filling Hot Subdwarf Binary. We report the discovery of the first short-period binary in which a hot subdwarf star (sdOB) filled its Roche lobe and started mass transfer to its companion. The object was discovered as part of a dedicated high-cadence survey of the Galactic plane named the Zwicky Transient Facility and exhibits a period of P = 39.3401(1) minutes, making it the most compact hot subdwarf binary currently known. Spectroscopic observations are consistent with an intermediate He-sdOB star with an effective temperature of T_{eff} = 42,400 ± 300 K and a surface gravity of log (g) = 5.77 ± 0.05. A high signal-to-noise ratio GTC+HiPERCAM light curve is dominated by the ellipsoidal deformation of the sdOB star and an eclipse of the sdOB by an accretion disk. We infer a low-mass hot subdwarf donor with a mass MsdOB = 0.337 ± 0.015 M_{☉} and a white dwarf accretor with a mass MWD = 0.545 ± 0.020 M_{☉}. Theoretical binary modeling indicates the hot subdwarf formed during a common envelope phase when a 2.5-2.8 M_{☉} star lost its envelope when crossing the Hertzsprung gap. To match its current P_{orb}, T_{eff}, log (g), and masses, we estimate a post-common envelope period of P_{orb} ≈ 150 minutes and find that the sdOB star is currently undergoing hydrogen shell burning. We estimate that the hot subdwarf will become a white dwarf with a thick helium layer of ≈0.1 M_{☉}, merge with its carbon/oxygen white dwarf companion after ≈17 Myr, and presumably explode as a thermonuclear supernova or form an R CrB star.

Keywords: White dwarf stars, B subdwarf stars, Compact binary stars, Stellar evolution
Deciphering the 3D Orion Nebula-I: Expanding Shells in the Huygens Region. Based on imaging and spectroscopic data, we develop a 3D model for the Huygens Region of the Orion Nebula. θ^{1} Ori C, the hottest star in the Trapezium, is surrounded by a wind-blown Central Bubble that opens SW into the Extended Orion Nebula. Outside of this feature lies a layer of ionized gas at about 0.4 pc from θ^{1} Ori C. Both of these features are moving rapidly away from θ^{1} Ori C with an expansion age for the Central Bubble of only 15,000 yr.

Keywords: H II regions
A Multifrequency ALMA Characterization of Substructures in the GM Aur Protoplanetary Disk. The protoplanetary disk around the T Tauri star GM Aur was one of the first hypothesized to be in the midst of being cleared out by a forming planet. As a result, GM Aur has had an outsized influence on our understanding of disk structure and evolution. We present 1.1 and 2.1 mm ALMA continuum observations of the GM Aur disk at a resolution of ∼50 mas (∼8 au), as well as HCO+ J = 3 - 2 observations at a resolution of ∼100 mas. The dust continuum shows at least three rings atop faint, extended emission. Unresolved emission is detected at the center of the disk cavity at both wavelengths, likely due to a combination of dust and free-free emission. Compared to the 1.1 mm image, the 2.1 mm image shows a more pronounced "shoulder" near R ∼ 40 au, highlighting the utility of longer-wavelength observations for characterizing disk substructures. The spectral index α features strong radial variations, with minima near the emission peaks and maxima near the gaps. While low spectral indices have often been ascribed to grain growth and dust trapping, the optical depth of GM Aur's inner two emission rings renders their dust properties ambiguous. The gaps and outer disk (R &gt; 100 au) are optically thin at both wavelengths. Meanwhile, the HCO+ emission indicates that the gas cavity is more compact than the dust cavity traced by the millimeter continuum, similar to other disks traditionally classified as "transitional."

Keywords: Circumstellar dust, Protoplanetary disks, Planet formation, Long baseline interferometry
Upward Overshooting in Turbulent Compressible Convection. II. Simulations at Large Relative Stability Parameters. In this paper, we present the results of three-dimensional numerical simulation of upward overshooting in turbulent compressible convection at large relative stability parameter S. Similar to the previous simulations at small S, we find that the convectively stable zone can be partitioned into three layers: the thermal adjustment layer, the turbulent dissipation layer, and the thermal dissipation layer. Despite of this similarity, there exist significant differences in several aspects. First, for small S, the thermal structure is altered considerably near the interface between the convectively unstable and stable zones. For extremely large S, the thermal structure is only slightly changed. Second, the overshooting distance decreases at small S, but it can increase when S is large enough. Third, for small S, the fluid motions tend to be less active when S increases. However, the fluid motions can be more active when S is large enough. We find that the structure of counter cells has a significant impact on the penetration depth.

Keywords: Stellar interiors, Stellar convective zones, Stellar structures, Hydrodynamical simulations, Stellar cores
The 3D Distribution of Long-period Mira Variables in the Galactic Disk. Long-period Mira variable stars are considered to have relatively high initial masses and may be potentially useful as tracers of spiral arm structure of the Milky Way. From 2004 to 2017, we monitored long-period Mira candidates selected from the IRAS color-color diagram in the near-infrared K' band. As an initial result of this study, we found 108 Mira variables and determined their periods, mean magnitudes, and amplitudes. Most of them are located between 0° and 90° in Galactic longitude. The peak of their period distribution is at around 500 days, which is longer than the typical value for Mira variables selected in optical surveys. Distances to our Mira variables have also been estimated using the period-luminosity relation (PLR) in 3.4 μm with the help of a three-dimensional map of interstellar extinction. While the Ks-band PLR has a large scatter at longer periods (log P &gt; 2.6), the PLR based on the Wide-field Infrared Survey Explorer 3.4 μm data has a much smaller scatter. We compare the spatial distribution of our sample to the spiral arms in the literature, and discuss the possible association of the long-period Mira variables with the spiral arms although the limited spatial coverage and the limited distance accuracy of the current sample prevent us from drawing a firm conclusion.

Keywords: Distance indicators, Spiral arms, Asymptotic giant branch stars, Mira variable stars, Milky Way Galaxy
Heating of the Solar Wind by Ion Acoustic Waves. Calculations are made of the energy supplied to the solar wind by the rapid decay of density fluctuations, identified as ion acoustic waves. It is shown that this process supplies an appreciable fraction, perhaps nearly all, of the observed heating of the solar wind. This process may be an important step in the conversion of magnetic turbulence to particle energy.

Keywords: Solar coronal heating, Solar wind, Heliosphere