Sazuna/UAT_keywords huggingface dataset:
Chemical Evolution in the Milky Way: Rotation-based Ages for APOGEE-Kepler Cool Dwarf Stars. We use models of stellar angular momentum evolution to determine ages for ∼500 stars in the APOGEE-Kepler Cool Dwarfs sample. We focus on lower-main-sequence stars, where other age-dating tools become ineffective. Our age distributions are compared to those derived from asteroseismic and giant samples and solar analogs. We are able to recover gyrochronological ages for old, lower-main-sequence stars, a remarkable improvement over prior work in hotter stars. Under our model assumptions, our ages have a median relative uncertainty of 14%, comparable to the age precision inferred for more massive stars using traditional methods. We investigate trends of Galactic α-enhancement with age, finding evidence of a detection threshold between the age of the oldest α-poor stars and that of the bulk α-rich population. We argue that gyrochronology is an effective tool reaching ages of 10-12 Gyr in K and early M dwarfs. Finally, we present the first effort to quantify the impact of detailed abundance patterns on rotational evolution. We estimate a ∼15% bias in age for cool, α-enhanced (+0.4 dex) stars when standard solar-abundance-pattern rotational models are used for age inference, rather than models that appropriately account for α-enrichment.

Keywords: Stellar rotation, Stellar ages, Galaxy chemical evolution, Stellar evolution
Unveiling Sizes of Compact AGN Hosts with ALMA. We present rest-frame far-infrared (FIR) and optical size measurements of active galactic nucleus (AGN) hosts and star-forming galaxies (SFGs) in the COSMOS field, enabled by high-resolution Atacama Large Millimeter/submillimeter Array (ALMA)/1 mm (0.″1-0.″4) and Hubble Space Telescope (HST)/F814W imaging (∼0.″1). Our sample includes 27 galaxies at z &lt; 2.5, classified as infrared-selected AGN (three sources), X-ray selected AGN (four sources), and non-AGN SFGs (20 sources), for which high-resolution Band 6/7 ALMA images are available at 1 mm from our own observing program as well as archival observations. The sizes and star formation rate surface densities measured from both ALMA/1 mm and HST/F814W images show that obscured AGN host galaxies are more compact than non-AGN SFGs at similar redshift and stellar mass. This result suggests that the obscured accretion phase may be related to galaxies experiencing a compaction of their gaseous component, which could be associated with enhanced central star formation before a subsequent quenching driving the formation of compact passive galaxies. Moreover, most of the detected and stacked rest-frame FIR sizes of AGNs in our sample are similar or more compact than their rest-frame optical sizes, which is consistent with recent results of ALMA-detected sources. This might be explained by the fact that the dusty starbursts take place in the compact regions, and suggests that the star formation mechanisms in the compact regions of AGN hosts are similar to those observed in SFGs observed with ALMA.

Keywords: AGN host galaxies, Galaxy formation, Galaxy structure, Active galactic nuclei, Star formation, Galaxy evolution
The Masses of Isolated Neutron Stars Inferred from the Gravitational Redshift Measurements. For some neutron stars (NSs) in the binary systems, the masses have been accurately measured. While for the isolated neutron stars (INSs), no mass measurement has been reported yet. The situation will change soon thanks to the successful performance of the Neutron Star Interior Composition Explorer (NICER), with which the radius and mass of the isolated PSR J0030+0451 can be simultaneously measured. For most INSs, no mass measurements are possible for NICER because of observational limitations. Benefiting from recent significant progress made on constraining the equation of state of NSs, in this work we propose a way to estimate the masses of the INSs with the measured gravitational redshifts. We apply our method to RX J1856.5-3754, RX J0720.4-3125, and RBS 1223, three members of “The Magnificent Seven” (M7), and estimate their masses to be {1.24}-0.29+0.29 {M}⊙ , {1.23}-0.05+0.10 {M}⊙ , and {1.08}-0.11+0.20 {M}⊙ , respectively. These masses are consistent with that of binary NS systems, suggesting no evidence for experiencing significant accretion of these isolated objects.

Keywords: Neutron stars, Neutron star cores, Gravitational waves, Single x-ray stars
Upward Overshooting in Turbulent Compressible Convection. I. Effects of the Relative Stability Parameter, the Prandtl Number, and the Péclet Number. In this paper, we investigate the upward overshooting by three-dimensional numerical simulations. We find that the above convectively stable zone can be partitioned into three layers: the thermal adjustment layer (mixing both entropy and material), the turbulent dissipation layer (mixing material but not entropy), and the thermal dissipation layer (mixing neither entropy nor material). The turbulent dissipation layer is separated from the thermal adjustment layer and the thermal dissipation layer by the first and second zero-points of the vertical velocity correlation. The simulation results are in good agreement with the prediction of the one-dimensional turbulent Reynolds stress model. First, the layer structure is similar. Second, the upper boundary of the thermal adjustment layer is close to the peak of the magnitude of the temperature perturbation. Third, the Péclet number at the upper boundary of the turbulent dissipation layer is close to 1. In addition, we have studied the scalings of the overshooting distance on the relative stability parameter S, the Prandtl number Pr, and the Péclet number Pe. The scaling on S is not unique. The trend is that the overshooting distance decreases with S. Fitting on Pr shows that the overshooting distance increases with Pr. Fitting on Pe shows that the overshooting distance decreases with Pe. Finally, we calculate the ratio of the thickness of the turbulent dissipation layer to that of the thermal adjustment layer. The ratio remains almost constant, with an approximate value of 2.4.

Keywords: Stellar interiors, Stellar convective zones, Stellar structures, Hydrodynamical simulations, Stellar cores
Modeling of the Variable Circumstellar Absorption Features of WD 1145+017. We present an eccentric precessing gas disk model designed to study the variable circumstellar absorption features detected for WD 1145+017, a metal polluted white dwarf with an actively disintegrating asteroid around it. This model, inspired by one recently proposed by Cauley et al., calculates explicitly the gas opacity for any predetermined physical conditions in the disk, predicting the strength and shape of all absorption features, from the UV to the optical, at any given phase of the precession cycle. The successes and failures of this simple model provide valuable insight on the physical characteristics of the gas surrounding the star, notably its composition, temperature, and density. This eccentric disk model also highlights the need for supplementary components, most likely circular rings, in order to explain the presence of zero velocity absorption as well as highly ionized Si IV lines. We find that a precession period of 4.6 ± 0.3 yr can successfully reproduce the shape of the velocity profile observed at most epochs from 2015 April to 2018 January, although minor discrepancies at certain times indicate that the assumed geometric configuration may not be optimal yet. Finally, we show that our model can quantitatively explain the change in morphology of the circumstellar features during transiting events.

Keywords: Circumstellar matter, Debris disks, Chemical abundances, Circumstellar gas
A Possible Enrichment of Heavy and Ultraheavy Ions in Solar Energetic Particle Events Due to a Combined Effect of Stochastic Acceleration and Coulomb Losses. Solar particle events that are rich in 3He typically also exhibit large overabundances of heavy and ultraheavy ions that increase with the mass of the ions. To explain these observations we apply our charge-consistent acceleration model, which takes into account the acceleration efficiency as a function of the charge to mass ratio of the ion, as well as the charge-dependent Coulomb energy losses, to consider the acceleration of ions within a wide range of their nuclear charge. Because the considerations of particle acceleration were restricted so far by tabulated values of ionization and recombination coefficients that were available only for a limited set of ions, we make use of our method developed earlier and calculate the rates of ions resembling the three representative mass groups of ultraheavy ions. We demonstrate that smaller Coulomb losses together with higher acceleration efficiency result in the enhancements of heavy and ultraheavy ions, in accordance with recent observations. We also conclude that the existing measurements of ultraheavy ions in impulsive solar energetic particle events provide evidence in favor of a magnetic turbulence in the acceleration region with spectral index S ≥ 2.

Keywords: Solar energetic particles, Solar flares, Solar particle emission
Discovery of Two Pulsating Extremely Low-mass Pre-white Dwarf Candidates in the TESS Eclipsing Binaries. We report the discovery of two new pulsating extremely low-mass pre-white dwarf (pre-ELMV) candidates in the Transiting Exoplanet Survey Satellite (TESS) eclipsing binaries, TIC 149160359 and TIC 416264037. Their light curves show a typical feature of EL CVn-type binaries. The light-curve modeling indicates that they are both detached systems with very low-mass ratios (q ≃ 0.1). Based on the photometric solutions, the masses and radii of the two main-sequence primary components are estimated, and those of the secondaries are deduced. The results show that the less-massive components of the two binaries are both probably thermally bloated, pre-ELMVs. Apart from the eclipsing light changes, short-period light variations are clearly shown in their residual light curves. We have made the Fourier analysis of their light-curve residuals with the Period04 program. TIC 149160359 was found to pulsate in 21 independent frequencies, 17 of which are between 21 and 35 day-1 and the others are between 63 and 77 day-1. The Fourier amplitude spectrum of TIC 416264037 also shows two frequency concentration ranges. Out of nine independent frequencies, seven reside within the low-frequency range of 12.5-19.9 day-1. Two pulsating signals, f 4 = 122.2698 day-1 and f 10 = 112.3603 day-1, were detected in the high-frequency region. These low-frequency signals that are detected on TIC 149160359 and TIC 416264037 are probably due to the intrinsic pulsations of their δ Sct-type primary components. However, the high-frequency signals are likely to come from the pulsations of the pre-ELM WD components. This brings the number of pre-ELMV candidates to 12.

Keywords: Eclipsing binary stars, White dwarf stars, Delta Scuti variable stars
Spectral Structures of Type II Solar Radio Bursts and Solar Energetic Particles. We investigated the relationship between the spectral structures of type II solar radio bursts in the hectometric and kilometric wavelength ranges and solar energetic particles (SEPs). To examine the statistical relationship between type II bursts and SEPs, we selected 26 coronal mass ejection (CME) events with similar characteristics (e.g., initial speed, angular width, and location) observed by the Large Angle and Spectrometric Coronagraph, regardless of the characteristics of the corresponding type II bursts and the SEP flux. Then, we compared associated type II bursts observed by the Radio and Plasma Wave Experiment on board the Wind spacecraft and the SEP flux observed by the Geostationary Operational Environmental Satellite orbiting around the Earth. We found that the bandwidth of the hectometric type II bursts and the peak flux of the SEPs has a positive correlation (with a correlation coefficient of 0.64). This result supports the idea that the nonthermal electrons of type II bursts and the nonthermal ions of SEPs are generated by the same shock and suggests that more SEPs may be generated for a wider or stronger CME shock with a longer duration. Our result also suggests that considering the spectral structures of type II bursts can improve the forecasting accuracy for the peak flux of gradual SEPs.

Keywords: Solar coronal radio emission, Interplanetary shocks, Solar flares, Heliosphere, Solar energetic particles, The Sun, Radio astrometry, Interplanetary particle acceleration, Solar radio emission, Solar coronal mass ejections, Interplanetary physics
Observation of Acceleration of H I Clouds within the Fermi Bubbles. The ∼200 H I clouds observed to be entrained in the Fermi bubble wind show a trend of increasing maximum | {V}LSR}| with Galactic latitude. We analyze previous observations and present new data from the Green Bank Telescope that rule out systematic effects as the source of this phenomenon. Instead, it is likely evidence for acceleration of the clouds. The data suggest that clouds in the lower 2 kpc of the Fermi bubbles, within the bubble boundaries established from X-ray studies, have an outflow velocity that rises from ≈150 to 200 {km} {{{s}}}-1 close to the Galactic center and reaches ≈330 {km} {{{s}}}-1 at a distance of 2.5-3.5 kpc. These parameters are also consistent with the kinematics of ultraviolet absorption lines from highly ionized species observed against two targets behind the Fermi bubbles at b = -6.°6 and b = +11.°2. The implied neutral cloud lifetime is 4-10 Myr.

Keywords: Galactic winds, Galactic center, Interstellar atomic gas
Efficient Production of S<SUB>8</SUB> in Interstellar Ices: The Effects of Cosmic-Ray-driven Radiation Chemistry and Nondiffusive Bulk Reactions. In this work, we reexamine sulfur chemistry occurring on and in the ice mantles of interstellar dust grains, and report the effects of two new modifications to standard astrochemical models: namely, (a) the incorporation of cosmic-ray-driven radiation chemistry and (b) the assumption of fast, nondiffusive reactions for key radicals in the bulk. Results from our models of dense molecular clouds show that these changes can have a profound influence on the abundances of sulfur-bearing species in ice mantles, including a reduction in the abundance of solid-phase H2S and HS, and a significant increase in the abundances of OCS, SO2, as well as pure allotropes of sulfur, especially S8. These pure-sulfur species—though nearly impossible to observe directly—have long been speculated to be potential sulfur reservoirs and our results represent possibly the most accurate estimates yet of their abundances in the dense interstellar medium. Moreover, the results of these updated models are found to be in good agreement with available observational data. Finally, we examine the implications of our findings with regard to the as-yet-unknown sulfur reservoir thought to exist in dense interstellar environments.

Keywords: Interstellar molecules, Astrochemistry, Dense interstellar clouds, Interstellar dust processes, Cosmic rays
Quasi-periodic Pulsations of Gamma-Ray Emissions from a Solar Flare on 2017 September 6. We investigate quasi-periodic pulsations (QPPs) of high-energy nonthermal emissions from an X9.3 flare (SOL2017-Sep-06T11:53), the most powerful flare since the beginning of solar cycle 24. The QPPs are identified as a series of regular and repeating peaks in the light curves in the γ- and hard X-ray (HXR) channels recorded by the Konus-Wind, as well as the radio and microwave fluxes measured by the CALLISTO radio spectrograph during the impulsive phase. The periods are determined from the global wavelet and Fourier power spectra as 24-30 s in the HXR and microwave channels, which are associated with nonthermal electrons, and ∼20 s in the γ-ray band related to nonthermal ions. Both nonthermal electrons and ions may be accelerated by repetitive magnetic reconnection during the impulsive phase. However, we could not rule out other mechanisms, such as magnetohydrodynamic oscillation in a sausage mode. The QPP detected in this study is useful for understanding the particle acceleration and dynamic process in solar flares and also bridging the gap between stellar and solar flares because the energy realm of the X9.3 solar flare is almost comparable to a typical stellar flare.

Keywords: Solar flares, Solar gamma-ray emission, Solar x-ray emission, Solar radio emission, Solar oscillations
Discovery of a Rare Late-type, Low-mass Wolf-Rayet Star in the LMC. We report the serendipitous discovery of an object, UVQS J060819.93-715737.4, with a spectrum dominated by extremely intense, narrow C II emission lines. The spectrum is similar to those of the very rare, late-type [WC11] low-mass Wolf-Rayet stars. Despite the recognition of these stars as a distinct class decades ago, there remains barely a handful of Galactic members, all of which are also planetary-nebula central stars. Although no obvious surrounding nebulosity is present in J0608, [O II], [N II], and [S II] emission suggest the presence of an inconspicuous, low-excitation nebula. There is low-amplitude incoherent photometric variability on timescales of days to years, as well as numerous prominent P Cygni profiles, implying mass loss. There are indications of a binary companion. The star is located on the outskirts of the LMC, and the observed radial velocity (∼+250 km s-1) and proper motion strongly suggest membership. If indeed an LMC member, this is the first extragalactic late [WC] star, and the first with an accurately determined luminosity, as the Galactic examples are too distant for precise parallax determinations. A high-quality, broad-coverage spectrum of the prototype of the late [WC] class, CPD -56° 8032, is also presented. We discuss different excitation mechanisms capable of producing the great strength of the C II emission. Numerous autoionizing levels of C II are definitely populated by processes other than dielectronic recombination. Despite the spectacular emission spectra, observational selection makes objects such as these difficult to discover. Members of the [WC11] class may in fact be considerably more common than the handful of previously known late [WC] stars.

Keywords: Planetary nebulae nuclei, WC stars, Planetary nebulae
The Gaia-ESO Survey: Carbon Abundance in the Galactic Thin and Thick Disks. This paper focuses on carbon, which is one of the most abundant elements in the universe and is of high importance in the field of nucleosynthesis and galactic and stellar evolution. The origin of carbon and the relative importance of massive and low- to intermediate-mass stars in producing it is still a matter of debate. We aim at better understanding the origin of carbon by studying the trends of [C/H], [C/Fe], and [C/Mg] versus [Fe/H] and [Mg/H] for 2133 FGK dwarf stars from the fifth Gaia-ESO Survey internal data release (GES iDR5). The availability of accurate parallaxes and proper motions from Gaia DR2 and radial velocities from GES iDR5 allows us to compute Galactic velocities, orbits, absolute magnitudes, and, for 1751 stars, Bayesian-derived ages. Three different selection methodologies have been adopted to discriminate between thin- and thick-disk stars. In all the cases, the two stellar groups show different [C/H], [C/Fe], and [C/Mg] and span different age intervals, with the thick-disk stars being, on average, older than the thin-disk ones. The behaviors of [C/H], [C/Fe], and [C/Mg] versus [Fe/H], [Mg/H], and age all suggest that C is primarily produced in massive stars. The increase of [C/Mg] for young thin-disk stars indicates a contribution from low-mass stars or the increased C production from massive stars at high metallicities due to the enhanced mass loss. The analysis of the orbital parameters R med and | {Z}\max | supports an “inside-out” and “upside-down” formation scenario for the disks of the Milky Way. Based on observations collected with the FLAMES instrument at VLT/UT2 (Paranal Observatory, ESO, Chile), for the Gaia-ESO Large Public Spectroscopic Survey (188.B-3002, 193.B-0936).

Keywords: Stellar abundances, Galaxy stellar content, Late-type stars, Stellar ages
Structural and Dynamical Analysis of 0.1 pc Cores and Filaments in the 30 Doradus-10 Giant Molecular Cloud. High-resolution (&lt;0.1 pc) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the 30Dor-10 molecular cloud 15 pc north of R136 are presented. The 12CO 2-1 emission morphology contains clumps near the locations of known mid-IR massive protostars, as well as a series of parsec-long filaments oriented almost directly toward R136. There is elevated kinetic energy (line widths at a given size scale) in 30Dor-10 compared to other Large Magellanic Cloud and Galactic star formation regions, consistent with large-scale energy injection to the region. Analysis of the cloud substructures is performed by segmenting emission into disjoint approximately round “cores” using clumpfind, by considering the hierarchical structures defined by isointensity contours using dendrograms, and by segmenting into disjoint long thin “filaments” using Filfinder. Identified filaments have widths ∼0.1 pc. The inferred balance between gravity and kinematic motions depends on the segmentation method: entire objects identified with clumpfind are consistent with freefall collapse or virial equilibrium with moderate external pressure, whereas many dendrogram-identified parts of hierarchical structures have higher mass surface densities ΣLTE than if gravitational and kinetic energies were in balance. Filaments have line masses that vary widely compared to the critical line mass calculated assuming thermal and nonthermal support. Velocity gradients in the region do not show any strong evidence for accretion of mass along filaments. The upper end of the “core” mass distribution is consistent with a power law with the same slope as the stellar initial mass function.

Keywords: Stellar feedback, Star forming regions, Molecular clouds, Large Magellanic Cloud, Star formation, Interstellar medium
Substructure of Visibility Functions from Scattered Radio Emission of Pulsars through Space VLBI. We report on the substructure of visibility functions in the delay domain of PSRs B0329+54, B0823+26, B0834+06, B1933+16, and B0833-45 (Vela) observed with Earth-Earth and RadioAstron space-Earth two-element interferometers at frequencies of 324 and 1668 MHz. All visibility functions display unresolved spikes distributed over a range of delays. They are due to band-limited scintillation noise and related to the scattering time. The envelopes for each but the Vela pulsar are well fit by a single Lorentzian, which we interpret as being indicative of isotropic scattering on the plane of the sky due to a thin scattering screen between the pulsar and us. In contrast, the envelope for the Vela pulsar needs to be mostly fit by at least two Lorentzians, a narrow and a broad one at the same zero delay. We interpret this characteristic as indicative of anisotropic scattering due to a more complex structure of scattering screens in the supernova remnant. The possibility of describing the delay visibility functions by Lorentzians is likely a general property of pulsars and offers a new way of describing the scattering parameters of the intervening interstellar medium. Furthermore, for all of our pulsars, the unresolved spikes in visibility functions of similar projected baselines were well correlated, indicating that the telescopes are located in the same diffraction spot. The correlation vanished for visibilities from largely different baselines, when some radio telescopes are not in the same spot.

Keywords: Interstellar scattering, Very long baseline interferometry, Radio pulsars, Interstellar scintillation