Sazuna/UAT_keywords huggingface dataset:
Linear Stability in the Inner Heliosphere: Helios Re-evaluated. Wave-particle instabilities driven by departures from local thermodynamic equilibrium have been conjectured to play a role in governing solar wind dynamics. We calculate the statistical variation of linear stability over a large subset of Helios I and II observations of the fast solar wind using a numerical evaluation of the Nyquist stability criterion, accounting for multiple sources of free energy associated with protons and helium including temperature anisotropies and relative drifts. We find that 88% of the surveyed intervals are linearly unstable. The median growth rate of the unstable modes is within an order of magnitude of the turbulent transfer rate, fast enough to potentially impact the turbulent scale-to-scale energy transfer. This rate does not significantly change with radial distance, though the nature of the unstable modes, and which ion components are responsible for driving the instabilities, does vary. The effect of ion-ion collisions on stability is found to be significant; collisionally young wind is much more unstable than collisionally old wind, with very different kinds of instabilities present in the two kinds of wind.

Keywords: Space plasmas, Heliosphere, Plasma physics, Interplanetary turbulence, Fast solar wind, Solar wind, Plasma astrophysics
Automated Mining of the ALMA Archive in the COSMOS Field (A<SUP>3</SUP>COSMOS). II. Cold Molecular Gas Evolution out to Redshift 6. We present new measurements of the cosmic cold molecular gas evolution out to redshift 6 based on systematic mining of the Atacama Large Millimeter/submillimeter Array (ALMA) public archive in the COSMOS deep field (A3COSMOS). Our A3COSMOS data set contains ∼700 galaxies (0.3 ≲ z ≲ 6) with high-confidence ALMA detections in the (sub)millimeter continuum and multiwavelength spectral energy distributions. Multiple gas mass calibration methods are compared, and biases in band conversions (from observed ALMA wavelength to rest-frame Rayleigh-Jeans tail continuum) have been tested. Combining our A3COSMOS sample with ∼1000 CO-observed galaxies at 0 ≲ z ≲ 4 (75% at z &lt; 0.1), we parameterize galaxies’ molecular gas depletion time ({τ }depl}) and molecular gas to stellar mass ratio ({μ }molgas}) each as a function of the stellar mass ({M}\star ), offset from the star-forming main sequence ({{∆ }}{MS}) and cosmic age (or redshift). Our proposed functional form provides a statistically better fit to current data (than functional forms in the literature) and implies a “downsizing” effect (i.e., more-massive galaxies evolve earlier than less-massive ones) and “mass quenching” (gas consumption slows down with cosmic time for massive galaxies but speeds up for low-mass ones). Adopting galaxy stellar mass functions and applying our {μ }molgas} function for gas mass calculation, we for the first time infer the cosmic cold molecular gas density evolution out to redshift 6 and find agreement with CO blind surveys as well as semianalytic modeling. These together provide a coherent picture of cold molecular gas, star formation rate, and stellar mass evolution in galaxies across cosmic time.

Keywords: Submillimeter astronomy, High-redshift galaxies, Galaxy evolution, Interstellar medium
Comparison of the UV and Optical Fe II Emission in Type 1 AGNs. We present the kinematical properties of the UV and optical Fe II emission gas based on the velocity shift and line width measurements of a sample of 223 Type 1 active galactic nuclei (AGNs) at 0.4 &lt; z &lt; 0.8. We find a strong correlation between the line widths of the UV and optical Fe II emission lines, indicating that both Fe II emission features arise from similar distances in the broad-line region (BLR). However, in detail we find differing trends, depending on the width of Fe II. While the velocity shifts and dispersions of the UV Fe II (Fe II uv) and optical Fe II (Fe II opt) emission lines are comparable to each other for AGNs with relatively narrow Fe II opt line widths (i.e., FWHM &lt; 3200 km s-1 Group A), Fe II opt is broader than Fe II uv for AGNs with relatively broad Fe II opt (i.e., FWHM &gt; 3200 km s-1 Group B). Fe II emission lines are on average narrower than Hβ and Mg II for Group A, indicating the Fe II emission region is further out in the BLR, while for Group B AGNs Fe II opt is comparable to Hβ and broader than Mg II. While Fe II emission lines are on average redshifted (40 ± 141 km s-1 and 182 ± 95 respectively for Fe II uv and Fe II opt), indicating inflow, the sample as a whole shows a large range of velocity shifts, suggesting the complex nature of the gas kinematics.

Keywords: AGN host galaxies, Active galaxies, Emission line galaxies, Quasars
Resolving the Metallicity Distribution of the Stellar Halo with the H3 Survey. The Galactic stellar halo is predicted to have formed at least partially from the tidal disruption of accreted dwarf galaxies. This assembly history should be detectable in the orbital and chemical properties of stars. The H3 Survey is obtaining spectra for 200,000 stars and, when combined with Gaia data, is providing detailed orbital and chemical properties of Galactic halo stars. Unlike previous surveys of the halo, the H3 target selection is based solely on magnitude and Gaia parallax; the survey therefore provides a nearly unbiased view of the entire stellar halo at high latitudes. In this paper we present the distribution of stellar metallicities as a function of Galactocentric distance and orbital properties for a sample of 4232 kinematically selected halo giants to 100 kpc. The stellar halo is relatively metal-rich, &lt; [{Fe}/{{H}}]&gt; =-1.2, and there is no discernible metallicity gradient over the range 6 &lt; R gal &lt; 100 kpc. However, the halo metallicity distribution is highly structured, including distinct metal-rich and metal-poor components at R gal &lt; 10 kpc and R gal &gt; 30 kpc, respectively. The Sagittarius stream dominates the metallicity distribution at 20-40 kpc for stars on prograde orbits. The Gaia-Enceladus merger remnant dominates the metallicity distribution for radial orbits to ≈30 kpc. Metal-poor stars with [Fe/H] &lt; -2 are a small population of the halo at all distances and orbital categories. We associate the “in situ” stellar halo with stars displaying thick disk chemistry on halo-like orbits; such stars are confined to | z| &lt; 10 {kpc}. The majority of the stellar halo is resolved into discrete features in chemical-orbital space, suggesting that the bulk of the stellar halo formed from the accretion and tidal disruption of dwarf galaxies. The relatively high metallicity of the halo derived in this work is a consequence of the unbiased selection function of halo stars and, in combination with the recent upward revision of the total stellar halo mass, implies a Galactic halo metallicity that is typical for its mass.

Keywords: Milky Way stellar halo, Stellar abundances, Galaxy abundances, Chemical abundances
Local Metallicity Distribution Function Derived from Galactic Large-scale Radial Iron Pattern Modeling. We develop an approach for fitting the results of modeling a wriggling radial large-scale iron pattern along the Galactic disk, derived over young (high-mass) Cepheids, with the metallicity distribution obtained using low-mass long-living dwarf stars in the close solar vicinity. For this purpose, during the step at which the theoretical abundance distribution over low-mass stars in the solar vicinity is computed, we propose the redefinition of the initial mass function so that the resulting theoretical stellar distribution over masses would be close to the distribution in the observed sample. By means of the above algorithm and subsequent corrections of the theoretical metallicity distribution function (MDF), as described in the literature, we have achieved fairly good agreement between the theoretical and observed MDFs for low-mass stars in the local solar vicinity.

Keywords: Milky Way disk, Galaxy abundances, Solar neighborhood
Transfer of Twists from a Mini-filament to Large-scale Loops by Magnetic Reconnection. With high spatial and temporal resolution, Hα data from the New Vacuum Solar Telescope, X-ray images from the X-ray telescope on board Hinode and simultaneous observations from the Solar Dynamics Observatory, we present multiwavelength observations of the interaction between a mini-filament (MF) and its overlying large-scale active-region loops (ARLs) that occurred in AR 12497 on 2016 February 13. The MF was activated by the convergence and cancellation of the magnetic flux under it. Brightenings first appeared at the junction of the MF and its overlying large-scale ARLs. A blowout jet with some plasma blobs was observed to move along the newly formed large-scale ARLs, and caused the oscillations of these loops. The blowout jet exhibited a counterclockwise rotation due to the untwisting motion of the MF, suggesting that the twist is transferred from the MF to the ARLs. The transferred twist was measured to be about 0.34-0.52 turn. During the interaction progress, a group of hot loops formed in the high-temperature wavelength (94 Å). These hot loops connected the west footpoints of the original ARLs and the east footpoints of the MF. The differential emission measure analysis demonstrated that these hot loops contained a high-temperature component (∼8 MK). Meanwhile the footpoints of the ARLs were finally shifted to the west footpoint of the MF. These observations suggest that magnetic reconnection takes place between the MF and its overlying large-scale ARLs and results in a confined untwisting blowout jet.

Keywords: Solar atmosphere, Solar coronal transients, Solar magnetic flux emergence, Solar magnetic reconnection, Solar coronal loops, Solar active regions, Solar filaments, Solar observatories, Solar magnetic fields, Solar corona, Solar activity, Solar chromosphere
Understanding the Plasma and Magnetic Field Evolution of a Filament Using Observations and Nonlinear Force-free Field Modeling. We present observations and magnetic field models of an intermediate filament present on the Sun in 2012 August, associated with a polarity inversion line that extends from AR 11541 in the east into the quiet Sun at its western end. A combination of Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly, SDO/Helioseismic and Magnetic Imager (HMI), and Global Oscillation Network Group Hα data allow us to analyze the structure and evolution of the filament from 2012 August 4 23:00 UT to 2012 August 6 08:00 UT when the filament was in equilibrium. By applying the flux rope insertion method, nonlinear force-free field models of the filament are constructed using SDO/HMI line-of-sight magnetograms as the boundary condition at the two times given above. Guided by observed filament barbs, both modeled flux ropes are split into three sections each with a different value of axial flux to represent the nonuniform photospheric field distribution. The flux in the eastern section of the rope increases by 4 × 1020 Mx between the two models, which is in good agreement with the amount of flux canceled along the internal PIL of AR 11541, calculated to be 3.2 × 1020 Mx. This suggests that flux cancellation builds flux into the filament’s magnetic structure. Additionally, the number of field line dips increases between the two models in the locations where flux cancellation, the formation of new filament threads, and growth of the filament is observed. This suggests that flux cancellation associated with magnetic reconnection forms concave-up magnetic field that lifts plasma into the filament. During this time, the free magnetic energy in the models increases by 0.2 × 1031 ergs.

Keywords: Solar prominences, Solar filaments, Solar magnetic fields, Solar coronal mass ejections, Solar activity, Solar evolution
An Efficient Spectral Selection of M Giants Using XGBoost. In optical bands, the spectra of M giants often overlap with those of M dwarfs due to their similarities, especially for low or moderate resolution spectra. Traditionally, several feature indices, such as Na I, CaH, TiO5, and K I, are used to distinguish between M giants and M dwarfs. However, these features are selected by experience based on a small amount of standard spectra. Hence, it is not clear if these features are the most effective ones to detect M giants. In this paper, we use a machine-learning method, eXtreme Gradient Boosting (XGBoost), to discern M giants from M dwarfs for spectroscopic surveys. The important feature bands for distinguishing between M giants and M dwarfs are accurately identified by the XGBoost method through evaluating and quantifying the importance of each feature in spectra, including Na I, B1, and Ca II, which are consistent with previous studies. Moreover, we find that a blend feature around 6564 Å (named B2) is sensitive to luminosity and that the feature combinations of both B1 versus CaH and B2 versus CaH, based on the average spectral flux, are important in distinguishing M giants from M dwarfs. Furthermore, our XGBoost prediction model achieves 99.79% overall accuracy and 96.87% recognition precision for M giants, outperforming the other three popular machine-learning algorithms (i.e., SVM, random forests, and ELM). Using such a prediction model, we detected 28,714 M-giant spectra from LAMOST DR5 and thus provided a larger amount of M giants for related scientific research.

Keywords: Stellar classification, Astrostatistics techniques, M giant stars, M stars
Tracing the Formation of Molecular Clouds in a Low-metallicity Galaxy: An H I Narrow Self-absorption Survey of the Large Magellanic Cloud. Cold atomic hydrogen clouds are the precursors of molecular clouds. Due to self-absorption, the opacity of cold atomic hydrogen may be high, and this gas may constitute an important mass component of the interstellar medium. Atomic hydrogen gas can be cooled to temperatures much lower than found in the cold neutral medium through collisions with molecular hydrogen. In this paper, we search for H I narrow self-absorption (HINSA) features in the Large Magellanic Cloud (LMC) as an indicator of such cold H I clouds, and use the results to quantify atomic masses and atomic-to-molecular gas ratio. Our search for HINSA features was conducted toward molecular clouds in the LMC using the ATCA+Parkes H I survey and the MAGMA CO survey. HINSA features are prevalent in the surveyed sightlines. This is the first detection of HINSA in an external galaxy. The HINSA-H I/{{{H}}}2 ratio in the LMC varies from 0.5 × 10-3 to 3.4 × 10-3 (68% interval), with a mean value of (1.31 ± 0.03) × 10-3, after correcting for the effect of foreground H I gas. This is similar to the Milky Way value and indicates that similar fractions of cold gas exist in the LMC and the Milky Way, despite their differing metallicities, dust content and radiation fields. The low ratio also confirms that, as with the Milky Way, the formation timescale of molecular clouds is short. The ratio shows no radial gradient, unlike the case for stellar metallicity. No correlation is found between our results and those from previous H I absorption studies of the LMC.

Keywords: Radio astronomy, Interstellar atomic gas, Abundance ratios, Dwarf galaxies, Molecular clouds, Large Magellanic Cloud, Interstellar absorption, Interstellar medium, Metallicity, Milky Way Galaxy
Chemical Properties of Two Dense Cores in a Planck Galactic Cold Clump G168.72-15.48. To deepen our understanding of the chemical properties of the Planck Galactic Cold Clump (PGCC) G168.72-15.48, we performed observations of nine molecular species, namely, c-C3H, H2CO, HC5N, HC7N, SO, CCH, N2H+, CH3OH, and CH3CCH, toward two dense cores in PGCC G168.72-15.48 using the Tianma Radio Telescope and Purple Mountain Observatory Telescope. We detected c-C3H, H2CO, HC5N, N2H+, CCH, and CH3OH in both G168-H1 and G168-H2 cores, whereas HC7N and CH3CCH were detected only in G168-H1 and SO was detected only in G168-H2. Mapping observations reveal that the CCH, N2H+, CH3OH, and CH3CCH emissions are well coupled with the dust emission in G168-H1. Additionally, N2H+ exhibits an exceptionally weak emission in the denser and more evolved G168-H2 core, which may be attributed to the N2H+ depletion. We suggest that the N2H+ depletion in G168-H2 is dominated by N2 depletion, rather than the destruction by CO. The local thermodynamic equilibrium calculations indicate that the carbon-chain molecules of CCH, HC5N, HC7N, and CH3CCH are more abundant in the younger G168-H1 core. We found that starless core G168-H1 may have the properties of cold dark clouds based on its abundances of carbon-chain molecules. While, the prestellar core G168-H2 exhibits lower carbon-chain molecular abundances than the general cold dark clouds. With our gas-grain astrochemical model calculations, we attribute the observed chemical differences between G168-H1 and G168-H2 to their different gas densities and different evolutionary stages.

Keywords: Interstellar molecules, Star formation
Exploring the Grain Properties in the Disk of HL Tau with an Evolutionary Model. We model the ALMA and Very Large Array (VLA) millimeter radial profiles of the disk around HL Tau to constrain the properties of the dust grains. We adopt the disk evolutionary models of Lynden-Bell &amp; Pringle and calculate their temperature and density structure and emission. These disks are heated by the internal viscosity and irradiated by the central star and a warm envelope. We consider a dust size distribution n(a) da ∝ a -3.5 da, and vary the maximum grain size in the atmosphere and the midplane, a max = 100 μm, 1 mm, and 1 cm. We also include dust settling and vary the dust-to-gas mass ratio from 1 to 9 times the ISM value. We find that the models that can fit the observed level of emission along the profiles at all wavelengths have an atmosphere with a maximum grain size a max = 100 μm, and a midplane with a max = 1 cm. The disk substructure, with a deficit of emission in the gaps, can be due to dust properties in these regions that are different from those in the rings. We test an opacity effect (different a max) and a dust mass deficit (smaller dust-to-gas mass ratio) in the gaps. We find that the emission profiles are better reproduced by models with a dust deficit in the gaps, although a combined effect is also possible. These models have a global dust-to-gas mass ratio twice the ISM value, needed to reach the level of emission of the 7.8 mm VLA profile.

Keywords: T Tauri stars, Young stellar objects, Radiative transfer equation, Protoplanetary disks, Stellar accretion disks
Observations and 3D Magnetohydrodynamic Modeling of a Confined Helical Jet Launched by a Filament Eruption. We present a detailed analysis of a confined filament eruption and jet associated with a C1.5 class solar flare. Multi-wavelength observations from the Global Oscillations Network Group and Solar Dynamics Observatory reveal the filament forming over several days following the emergence and then partial cancellation of a minority polarity spot within a decaying bipolar active region. The emergence is also associated with the formation of a 3D null point separatrix that surrounds the minority polarity. The filament eruption occurs concurrently with brightenings adjacent to and below the filament, suggestive of breakout and flare reconnection, respectively. The erupting filament material becomes partially transferred into a strong outflow jet (∼60 km s-1) along coronal loops, becoming guided back toward the surface. Utilizing high-resolution Hα observations from the Swedish Solar Telescope/CRisp Imaging SpectroPolarimeter, we construct velocity maps of the outflows, demonstrating their highly structured but broadly helical nature. We contrast the observations with a 3D magnetohydrodynamic simulation of a breakout jet in a closed-field background and find close qualitative agreement. We conclude that the suggested model provides an intuitive mechanism for transferring twist/helicity in confined filament eruptions, thus validating the applicability of the breakout model not only to jets and coronal mass ejections but also to confined eruptions and flares.

Keywords: Solar chromosphere, Solar flares, Solar filament eruptions, Magnetohydrodynamical simulations
The Interstellar Ribbon: A Unifying Explanation. The Interstellar Boundary Explorer (IBEX) mission discovered the presence of a global structure in energetic neutral atom emissions from the outer heliosphere not predicted by any model—the IBEX “ribbon.” In the search for possible explanations, observations have pointed to a likely source from neutral atoms produced through charge exchange with the outflowing solar wind, the secondary solar wind, which then undergoes charge exchange again beyond the heliopause within the very local interstellar medium. Here we study the plasma structure beyond the heliopause created from a range of secondary neutral atom sources: (1) solar wind atoms, (2) pickup atoms inside the termination shock, and (3) suprathermal atoms from the inner heliosheath, between the termination shock and heliopause. All of these particle sources populate the plasma environment beyond the heliopause. At the high end of the observational energy range of IBEX (3.1-6.0 keV FWHM), the significantly broadened and positionally shifted energetic neutral atom signature of the ribbon suggests plasma structure associated primarily with secondary suprathermal atoms from the inner heliosheath. The population created from this suprathermal population extends well above 6 keV (the top of the IBEX energy range) and provides a source for an extremely broad (&gt;60° in angular) width shifted southward (&gt;10°) in latitude from the direction centered on the local interstellar magnetic field. Thus, the extension of plasma structure to energies above IBEX provides a unified explanation of the ribbon created primarily from secondary solar wind atoms to a broadened and shifted structure (the broad ribbon or belt) created primarily from secondary suprathermal atoms in the heliosheath.

Keywords: Interstellar medium, Heliosphere
Aggregate Growth and Internal Structures of Chondrite Parent Bodies Forming from Dense Clumps. The major components of chondrites are chondrules and matrix. Measurements of volatile abundance in Semarkona chondrules suggest that chondrules formed in a dense clump that had a higher solid density than the gas density in the solar nebula. We investigate collisions between chondrules and matrix in the surface region of dense clumps using fluffy aggregate growth models. Our simulations show that the collisional growth of aggregates composed of chondrules and matrix takes place in the clumps well before they experience gravitational collapse. The internal structure of chondrite parent bodies (CPBs) can be thereby determined by aggregate growth. We find that the aggregate growth generates two scales within CPBs. The first scale is involved with the small-scale distribution of chondrules and determined by the early growth stage, where chondrules accrete aggregates composed of matrix grains. This accretion can reproduce the thickness of the matrix layer around chondrules found in chondrites. The other scale is related to the large-scale distribution of chondrules. Its properties (e.g., the abundance of chondrules and the overall size) depend on the gas motion within the clump, which is parameterized in this work. Our work thus suggests that the internal structure of CPBs may provide important clues about their formation conditions and mechanisms.

Keywords: Meteorites, Asteroids, Planet formation