adsabs/SciX_UAT_keywords huggingface dataset:
Tracers of Dense Gas in the Outer Galaxy

We have mapped $\mathrm{HCN}$ and HCO+ (J = 1 → 0) line emission toward a sample of seven star-forming regions (with $12+\mathrm{log}[{\rm{O}}/{\rm{H}}]$ ranging from 8.34 to 8.69) in the outer Milky Way (Galactocentric distance >9.5 kpc), using the 14 m radio telescope of the Taeduk Radio Astronomy Observatory. We compare these two molecular lines with other conventional tracers of dense gas, millimeter-wave continuum emission from dust and extinction thresholds (A V ≥ 8 mag), inferred from the 13CO line data. $\mathrm{HCN}$ and HCO+ correlate better with the millimeter emission than with the extinction criterion. A significant amount of luminosity comes from regions below the extinction criterion and outside the millimeter clump for all the clouds. The average fraction of $\mathrm{HCN}$ luminosity from within the regions with A V ≥ 8 mag is 0.343 ± 0.225; for the regions of millimeter emission, it is 0.478 ± 0.149. Based on a comparison with column density maps from Herschel, $\mathrm{HCN}$ and HCO+ trace dense gas in high column density regions better than does 13CO. HCO+ is less concentrated than $\mathrm{HCN}$ for outer Galaxy targets, in contrast with the inner Galaxy sample, suggesting that metallicity may affect the interpretation of tracers of dense gas. The conversion factor between the dense gas mass (M dense) and line luminosities of $\mathrm{HCN}$ and HCO+, when integrated over the whole cloud, is comparable to factors used in extragalactic studies.

Keywords: star forming regions; molecular clouds
Spectroscopic Mapping of Io's Surface with HST/STIS: SO2 Frost, Sulfur Allotropes, and Large-scale Compositional Patterns

Io's intense volcanic activity results in one of the most colorful surfaces in the solar system. Ultraviolet and visible-wavelength observations of Io are critical to uncovering the chemistry behind its volcanic hues. Here, we present global, spatially resolved ultraviolet-visible spectra of Io from the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, which bridge the gap between previous highly resolved imagery and disk-integrated spectroscopy, to provide an unprecedented combination of spatial and spectral detail. We use this comprehensive data set to investigate spectral endmembers, map observed spectral features associated with SO2 frost and other sulfur species, and explore possible compositions in the context of Io surface processes. In agreement with past observations, our results are consistent with extensive equatorial SO2 frost deposits that are stable over multidecade timescales, widespread sulfur-rich plains surrounding the SO2 deposits, and the enrichment of Pele's pyroclastic ring and the high-latitude regions in metastable short-chain sulfur allotropes.

Keywords: galilean satellites; io; planetary surfaces; surface composition
Comparison of Two Analytic Energy Balance Models Shows Stable Partial Ice Cover Possible for Any Obliquity

In this study, we compare two analytic energy balance models with an explicit dependence on obliquity to study the likelihood of different stable ice configurations. We compare the results of models with different methods of heat transport and different insolation distributions. We show that stable partial ice cover is possible for any obliquity, provided the insolation distribution is sufficiently accurate. Additionally, we quantify the severity of the transition to the snowball state as different model parameters are varied. In accordance with an earlier study, transitions to the snowball state are more severe for higher values of the albedo contrast and energy transport across latitudes in both models; however, we find that the snowball transition is not equally likely across both models. This work is general enough to apply to any rapidly rotating planet and could be used to study the likelihood of snowball transitions on planets within the habitable region of other stars.

Keywords: exoplanets; solar radiation; theoretical models
Revealing the Drag Instability in One-fluid Nonideal Magnetohydrodynamic Simulations of a 1D Isothermal C-shock

C-type shocks are believed to be ubiquitous in turbulent molecular clouds thanks to ambipolar diffusion. We investigate whether the drag instability in 1D isothermal C-shocks, inferred from the local linear theory of Gu & Chen, can appear in nonideal magnetohydrodynamic simulations. Two C-shock models (with narrow and broad steady-state shock widths) are considered to represent the typical environment of star-forming clouds. The ionization-recombination equilibrium is adopted for the one-fluid approach. In the 1D simulation, the inflow gas is continuously perturbed by a sinusoidal density fluctuation with a constant frequency. The perturbations clearly grow after entering the C-shock region until they start being damped at the transition to the post-shock region. We show that the profiles of a predominant Fourier mode extracted locally from the simulated growing perturbation match those of the growing mode derived from the linear analysis. Moreover, the local growth rate and wave frequency derived from the predominant mode generally agree with those from the linear theory. Therefore, we confirm the presence of the drag instability in simulated 1D isothermal C-shocks. We also explore the nonlinear behavior of the instability by imposing larger-amplitude perturbations to the simulation. We find that the drag instability is subject to wave steepening, leading to saturated perturbation growth. Issues concerning local analysis, nonlinear effects, one-fluid approach, and astrophysical applications are discussed.

Keywords: plasma astrophysics; shocks; molecular clouds; interstellar medium; star forming regions; magnetohydrodynamical simulations
TESS Reveals HD 118203 b to be a Transiting Planet

The exoplanet HD 118203 b, orbiting a bright (V = 8.05) host star, was discovered using the radial velocity method by da Silva et al., but was not previously known to transit. Transiting Exoplanet Survey Satellite (TESS) photometry has revealed that this planet transits its host star. Nine planetary transits were observed by TESS, allowing us to measure the radius of the planet to be ${1.136}_{-0.028}^{+0.029}{R}_{J}$ , and to calculate the planet mass to be ${2.166}_{-0.079}^{+0.074}{M}_{J}$ . The host star is slightly evolved with an effective temperature of ${T}_{\mathrm{eff}}={5683}_{-85}^{+84}$ K and a surface gravity of $\mathrm{log}\,g={3.889}_{0.018}^{0.017}$ . With an orbital period of ${6.134985}_{-0.000030}^{+0.000029}$ days and an eccentricity of 0.314 ± 0.017, the planet occupies a transitional regime between circularized hot Jupiters and more dynamically active planets at longer orbital periods. The host star is among the 10 brightest known to have transiting giant planets, providing opportunities for both planetary atmospheric and asteroseismic studies.

Keywords: exoplanet astronomy; exoplanet systems; transit photometry
ARES. II. Characterizing the Hot Jupiters WASP-127 b, WASP-79 b, and WASP-62b with the Hubble Space Telescope

This paper presents the atmospheric characterization of three large, gaseous planets: WASP-127 b, WASP-79 b, and WASP-62 b. We analyzed spectroscopic data obtained with the G141 grism (1.088-1.68 μm) of the Wide Field Camera 3 on board the Hubble Space Telescope using the Iraclis pipeline and the TauREx3 retrieval code, both of which are publicly available. For WASP-127 b, which is the least dense planet discovered so far and is located in the short-period Neptune desert, our retrieval results found strong water absorption corresponding to an abundance of log(H2O) = -2.71 ${}_{-1.05}^{+0.78}$ and absorption compatible with an iron hydride abundance of log(FeH) = $-{5.25}_{-1.10}^{+0.88}$ , with an extended cloudy atmosphere. We also detected water vapor in the atmospheres of WASP-79 b and WASP-62 b, with best-fit models indicating the presence of iron hydride, too. We used the Atmospheric Detectability Index as well as Bayesian log evidence to quantify the strength of the detection and compared our results to the hot Jupiter population study by Tsiaras et al. While all the planets studied here are suitable targets for characterization with upcoming facilities such as the James Webb Space Telescope and Ariel, WASP-127 b is of particular interest due to its low density, and a thorough atmospheric study would develop our understanding of planet formation and migration. * ARES: Ariel Retrieval of Exoplanets School.

Keywords: exoplanet astronomy; exoplanet atmospheres; astronomy data analysis; hubble space telescope
Apples and Oranges: Comparing Black Holes in X-Ray Binaries and Gravitational-wave Sources

The component black holes (BHs) observed in gravitational-wave (GW) binary black hole (BBH) events tend to be more massive and slower spinning than those observed in black hole X-ray binaries (BH-XRBs). Without modeling their evolutionary histories, we investigate whether these apparent tensions in the BH populations can be explained by GW observational selection effects alone. We find that this is indeed the case for the discrepancy between BH masses in BBHs and the observed high-mass X-ray binaries (HMXBs), when we account for statistical uncertainty from the small sample size of just three HMXBs. On the other hand, the BHs in observed low-mass X-ray binaries (LMXBs) are significantly lighter than the astrophysical BBH population, but this may just be due to a correlation between component masses in a binary system. Given their light stellar companions, we expect light BHs in LMXBs. The observed spins in HMXBs and LMXBs, however, are in tension with the inferred BBH spin distribution at the >99.9% level. We discuss possible scenarios behind the significantly larger spins in observed BH-XRBs. One possibility is that a small subpopulation (conservatively <30%) of BBHs have rapidly spinning primary components, indicating that they may have followed a similar evolutionary pathway to the observed HMXBs. In LMXBs, it has been suggested that BHs can spin up by accretion. If LMXB natal spins follow the BBH spin distribution, we find LMXBs must gain an average dimensionless spin of ${0.47}_{-0.11}^{+0.10}$ , but if their natal spins follow the observed HMXB spins, the average spin-up must be <0.03.

Keywords: astrostatistics; stellar mass black holes; x-ray binary stars; gravitational wave astronomy
Prospects for Detecting Gravitational Waves from Eccentric Subsolar Mass Compact Binaries

Due to their small mass, subsolar mass black hole binaries would have to be primordial in origin instead of the result of stellar evolution. Soon after formation in the early universe, primordial black holes can form binaries after decoupling from the cosmic expansion. Alternatively, primordial black holes as dark matter could also form binaries in the late universe due to dynamical encounters and gravitational-wave braking. A significant feature for this channel is the possibility that some sources retain nonzero eccentricity in the LIGO/Virgo band. Assuming all dark matter is primordial black holes with a delta function mass distribution, 1M⊙-1M⊙ binaries formed in this late-universe channel can be detected by Advanced LIGO and Virgo with their design sensitivities at a rate of ${ \mathcal O }(1)$ yr-1, where 12%(3%) of events have eccentricity at a gravitational-wave frequency of 10 Hz, e10 Hz ≥ 0.01(0.1), and nondetection can constrain the binary formation rate within this model. Third generation detectors would be expected to detect subsolar mass eccentric binaries as light as 0.01M⊙ within this channel, if they accounted for the majority of the dark matter. Furthermore, we use simulated gravitational-wave data to study the ability to search for eccentric gravitational-wave signals using a quasi-circular waveform template bank with Advanced LIGO design sensitivity. For a match-filtering targeted search, assuming binaries with a delta function mass of 0.1(1)M⊙ and the eccentricity distribution derived from this late-universe formation channel, 41%(6%) of the signals would be missed compared to the ideal detection rate due to the mismatch in the gravitational-wave signal from eccentricity.

Keywords: gravitational waves; primordial black holes; eccentricity
Self-discharge by Streaming Cosmic Rays

A new nonthermal phenomenon caused by streaming cosmic rays (CRs) in the universe is proposed. The streaming CRs drive the return current of thermal electrons to compensate for the CR current. Then, electric fields are induced by the resistivity of the return current. It is shown that the resistive electric fields can accelerate secondary electrons generated by the streaming CRs. This is the self-discharge by streaming CRs. In this work, the self-discharge condition and the condition for runaway acceleration of secondary electrons are presented. The self-discharge creates high-energy secondary electrons, resulting in enhancements of ionization and nonthermal emission including the Kα emission line of neutral iron. After the self-discharge, the return current of thermal electrons is replaced by the electric current of secondary electrons. Since some generation and amplification of magnetic fields are driven by the return current of thermal electrons, the self-discharge can significantly influence them.

Keywords: cosmic rays; secondary cosmic rays; plasma astrophysics; cosmic magnetic fields theory; astrophysical magnetism; ionization; molecular clouds
Modeling of Condensations in Coronal Loops Produced by Impulsive Heating with Variable Frequencies and Locations

We present the results of models of impulsively heated coronal loops using the 1D hydrodynamic Adaptively Refined Godunov Solver code. The impulsive heating events (which we refer to as nanoflares) are modeled by discrete pulses of energy along the loop. We explore the occurrence of cold condensations due to the effective equivalent of thermal nonequilibrium in loops with steady heating, and examine its dependence on nanoflare timing and intensity and also nanoflare location along the loop, including randomized distributions of nanoflares. We find that randomizing the distribution of nanoflares, both in time/intensity and location, diminishes the likelihood of condensation occurring as compared to distributions with regularly occurring nanoflares with the same average properties. The usual criteria that condensation is favored for heating near loop footpoints and with high cadences are more strict for randomized (as opposed to regular) nanoflare distributions, and for randomized distributions the condensations stay in the loop for a shorter amount of time. That said, condensation can sometimes occur in cases where the average values of parameters (frequency or location) are beyond the critical limits above which condensation does not occur for corresponding steady, non-randomized values of those parameters. These properties of condensation occurring due to randomized heating can be used in the future to investigate the diagnostics of coronal heating mechanisms.

Keywords: solar physics; solar corona; solar coronal heating; solar coronal loops
IRIS2+: A Comprehensive Database of Stratified Thermodynamic Models in the Low Solar Atmosphere

We present the most comprehensive collection of stratified-in-optical-depth thermodynamic models of the lower solar atmosphere. This database, named IRIS2+, consists of 40,320 synthetic representative profiles (RPs) and their corresponding representative model atmospheres (RMAs). The latter result from inverting the observed RPs, which are the result of clustering multiline spectral profiles observed by the Interface Region Imaging Spectrograph in 126 active regions (ARs). Each AR was clustered in 320 RPs considering five solar features: umbra, pore or pore-like, penumbra, plage, and quiet Sun. The multiline spectral profiles contain 12 lines with encoded physical information from the top of the chromosphere to the midphotosphere. These 12 spectral lines, six chromospheric and six photospheric, were simultaneously inverted with the Stockholm Inversion Code. Therefore, the stratified-in-optical-depth low solar atmosphere models obtained in this study are better constrained than those obtained from the nonsimultaneous inversion of individual lines. Each tuple in the database contains an inverted RP, its corresponding RMA, the solar feature label where the observed RP was clustered, its heliocentric angle, and its date and time of observation. The database may be used as an inversion code for any of the lines present in the RPs, and the RMAs may be used for synthesizing spectral lines in the chromosphere and photosphere or as mean constraints for numerical models of the solar atmosphere.

Keywords: the sun; solar photosphere; solar chromosphere; radiative transfer
ALMA Reveals a Large Overdensity and Strong Clustering of Galaxies in Quasar Environments at z 4

We present an Atacama Large Millimeter/submillimeter Array (ALMA) survey of CO(4-3) line emitting galaxies in 17 quasar fields at z ~ 4 aimed at performing the first systematic search of dusty galaxies in high-z quasar environments. Our blind search of galaxies around the quasars results in five CO emitters with S/N ≥ 5.6 within a projected radius of R ≲ 1.5 h -1 cMpc and a velocity range of δv = ±1000 km s-1 around the quasar. In blank fields, we expect to detect only 0.28 CO emitters within the same volume, implying a total overdensity of ${17.6}_{-7.6}^{+11.9}$ in our fields, and indicating that quasars trace massive structures in the early universe. We quantify this overdensity by measuring the small-scale clustering of CO emitters around quasars, resulting in a cross-correlation length of ${r}_{0,\mathrm{QG}}={8.37}_{-2.04}^{+2.42}\,{h}^{-1}\,$ cMpc, assuming a fixed slope γ = 1.8. This contradicts the reported mild overdensities (x1.4) of Lyα emitters (LAEs) in the same fields at scales of R ≲ 7 h -1 cMpc, which are well described by a cross-correlation length ${3.0}_{-1.4}^{+1.5}$ times lower than that measured for CO emitters. We discuss some possibilities to explain this discrepancy, including low star formation efficiency, and excess of dust in galaxies around quasars. Finally, we constrain, for the first time, the clustering of CO emitters at z ~ 4, finding an autocorrelation length of r 0,CO = 3.14 ±1.71 h -1 cMpc (with γ = 1.8). Our work, together with the previous study of LAEs around quasars, traces simultaneously the clustering properties of both optical and dusty galaxy populations in quasars fields, stressing the importance of multiwavelength studies, and highlighting important questions about galaxy properties in high-z dense environments.

Keywords: quasars; quasar-galaxy pairs; high-redshift galaxies; co line emission; clustering; large-scale structure of the universe; submillimeter astronomy
Detailed Chemical Abundances for a Benchmark Sample of M Dwarfs from the APOGEE Survey

Individual chemical abundances for 14 elements (C, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Ni) are derived for a sample of M dwarfs using high-resolution, near-infrared H-band spectra from the Sloan Digital Sky Survey-IV/Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. The quantitative analysis included synthetic spectra computed with 1D LTE plane-parallel MARCS models using the APOGEE Data Release 17 line list to determine chemical abundances. The sample consists of 11 M dwarfs in binary systems with warmer FGK dwarf primaries and 10 measured interferometric angular diameters. To minimize atomic diffusion effects, [X/Fe] ratios are used to compare M dwarfs in binary systems and literature results for their warmer primary stars, indicating good agreement (<0.08 dex) for all studied elements. The mean abundance difference in primaries minus this work's M dwarfs is -0.05 ± 0.03 dex. It indicates that M dwarfs in binary systems are a reliable way to calibrate empirical relationships. A comparison with abundance, effective temperature, and surface gravity results from the APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) Data Release 16 finds a systematic offset of [M/H], T eff, log g = +0.21 dex, -50 K, and 0.30 dex, respectively, although ASPCAP [X/Fe] ratios are generally consistent with this study. The metallicities of the M dwarfs cover the range of [Fe/H] = -0.9 to +0.4 and are used to investigate Galactic chemical evolution via trends of [X/Fe] as a function of [Fe/H]. The behavior of the various elemental abundances [X/Fe] versus [Fe/H] agrees well with the corresponding trends derived from warmer FGK dwarfs, demonstrating that the APOGEE spectra can be used to examine Galactic chemical evolution using large samples of selected M dwarfs.

Keywords: near infrared astronomy; m dwarf stars; stellar abundances; wide binary stars; exoplanets
Assessment of Callisto Gravity-field Determination Using the Inter-satellite Range-rate Link

China will launch the "Tianwen-IV" mission around 2030, focusing on the orbiting exploration of Jupiter and Callisto, a moon of Jupiter. As part of this ambitious mission, a main satellite will carry another satellite that will be released in the Jupiter system to continue its journey toward Uranus. Considering the current mission planning, we propose an inter-satellite radio-observation mode that differs from the conventional observation mode of tracking from Earth to precisely determine the orbit of the satellites. Given the significance of the Callisto gravity field model in both science objectives and satellite navigation, we have conducted a series of simulation experiments to evaluate the potential of this inter-satellite range-rate data for accurately estimating the Callisto gravity field. The results obtained from the analysis demonstrate that by utilizing 40 days of ground station observations, it is possible to estimate the gravity field model of Callisto up to a degree of 70. Remarkably, when combining these ground station observations with inter-satellite observations, a comparable level of accuracy can be achieved with just 10 days of observations. Furthermore, with reduced inter-satellite observation noise, accuracy improves, enabling estimation up to 80 degrees or higher. Initial inter-satellite distance selection impacts estimation accuracy. These findings serve as a valuable test bed for the future "Tianwen-IV" mission to perform precise orbit determination and gravity field model estimation to reduce reliance on deep space stations.

Keywords: gravitational fields; callisto
A Model for Gradual-phase Heating Driven by MHD Turbulence in Solar Flares

Coronal flare emission is commonly observed to decay on timescales longer than those predicted by impulsively driven, one-dimensional flare loop models. This discrepancy is most apparent during the gradual phase, where emission from these models decays over minutes, in contrast to the hour or more often observed. Magnetic reconnection is invoked as the energy source of a flare, but should deposit energy into a given loop within a matter of seconds. Models which supplement this impulsive energization with a long, persistent ad hoc heating have successfully reproduced long-duration emission, but without providing a clear physical justification. Here we propose a model for extended flare heating by the slow dissipation of turbulent Alfvén waves initiated during the retraction of newly reconnected flux tubes through a current sheet. Using one-dimensional simulations, we track the production and evolution of MHD wave turbulence trapped by reflection from high-density gradients in the transition region. Turbulent energy dissipates through nonlinear interaction between counter-propagating waves, modeled here using a phenomenological one-point closure model. Atmospheric Imaging Assembly EUV light curves synthesized from the simulation were able to reproduce emission decay on the order of tens of minutes. We find this simple model offers a possible mechanism for generating the extended heating demanded by observed coronal flare emissions self-consistently from reconnection-powered flare energy release.

Keywords: solar flares; magnetohydrodynamical simulations; solar extreme ultraviolet emission