adsabs/SciX_UAT_keywords huggingface dataset:
One Year in the Life of Young Suns: Data-constrained Corona-wind Model of κ1 Ceti

The young magnetically active solar-like stars are efficient generators of ionizing radiation in the form of X-ray and extreme-UV (EUV) flux, stellar wind, and eruptive events. These outputs are the critical factors affecting atmospheric escape and chemistry of (exo)planets around active stars. While X-ray fluxes and surface magnetic fields can be derived from observations, the EUV emission, and wind mass fluxes, coronal mass ejections and associated stellar energetic particle events cannot be directly observed. Here, we present the results of a three-dimensional magnetohydrodynamic (MHD) model with inputs constrained by spectropolarimetric data, Hubble Space Telescope/STIS far-UV and X-ray data, and stellar magnetic maps reconstructed at two epochs separated by 11 months. The simulations show that over the course of the year the global stellar corona had undergone a drastic transition from a simple dipole-like to a tilted dipole with multipole field components and thus provided favorable conditions for corotating interaction regions (CIRs) that drive strong shocks. The dynamic pressures exerted by CIRs are 1300 times larger than those observed from the Sun and can contribute to the atmospheric erosion of early Venus, Earth, Mars, and young Earth-like exoplanets. Our data-constrained MHD model provides the framework to model coronal environments of G-M planet-hosting dwarfs. The model outputs can serve as a realistic input for exoplanetary atmospheric models to evaluate the impact of stellar coronal emission, stellar winds, and CIRs on their atmospheric escape and chemistry that can be tested in the upcoming James Webb Space Telescope and ground-based observations.

Keywords: g dwarf stars; stellar coronae; stellar winds; planet hosting stars; exoplanets; magnetohydrodynamics
The ELM Survey South. II. Two Dozen New Low-mass White Dwarf Binaries

We present the results from our ongoing spectroscopic survey targeting low-mass white dwarf binaries, focusing on the southern sky. We used a Gaia DR2- and eDR3-based selection and identified 28 new binaries, including 19 new extremely low-mass (ELM) white dwarfs, one short period, likely eclipsing, DABZ, and two potential LISA binaries. We present the orbital and atmospheric parameters for each new binary based on our spectroscopic follow up. Four of our new binaries show periodic photometric variability in TESS 2 minutes cadence data, including one new eclipsing double-lined spectroscopic binary. Three others show periodic photometric variability in ZTF, including one new eclipsing binary. We provide estimates for the inclinations and scaled component radii for these ZTF variables, based on light-curve modeling of our high-speed photometric follow-up observations. Our observations have increased the sample of ELM Survey binaries identified in the southern sky to 41, an increase of 64%. Future time domain surveys, such as BlackGEM and the Vera C. Rubin Observatory Legacy Survey of Space and Time, will efficiently identify photometric variables in the southern sky and significantly increase the population of southern sky low-mass white dwarf binaries, leading to a more complete all-sky population of these systems.

Keywords: compact binary stars; eclipsing binary stars; white dwarf stars; spectroscopy
State-selective Charge Exchange in 19.5-100 keV amu-1 O6+ Collision with He and H2

The cross sections of state-selective charge exchange (CX) between highly charged ions and neutrals are important for modeling extreme ultraviolet and soft X-ray emissions in many astrophysical objects with hot plasma impacting cold media. By using cold-target recoil-ion momentum spectroscopy, we measure O6+ CX collisions with He and H2 in the collision energy range of 19.5 to 100 keV amu-1. The relative cross sections of state-selective single CX are reported for electron capture into O5+(1s 2 nl) n = 2, 3, 4, 5, ≥6 and n = 3, 4, 5, ≥6 for He and H2, respectively. With the collision energy increasing to 100 keV amu-1, the main capture channel shifts to higher n for both target species as compared to available theoretical results. We also report state-selective cross sections for double CX with He, where doubly excited states of ${{\rm{O}}}^{4+}(1{s}^{2}{nln}^{\prime} l^{\prime} )$ with ${nln}^{\prime} l^{\prime} $ being 2s 2 (1S), 2s2p (1P), 2p 2 (1D), and 2p 2 (1S) [symmetric configurations] and 2s3l, 2p3l-2s4l, and 2s5l-2p5l [asymmetric configurations] are distinguished. It is found that the contributions of doubly excited states with asymmetric configurations are dominant and symmetric configurations increasingly come into play with the increase of collision energy. The present results provide experimental benchmarks available for theoretical calculations.

Keywords: atomic spectroscopy; atomic physics; collision physics; atomic data benchmarking; charge exchange recombination
New Illumination and Temperature Constraints of Mercury's Volatile Polar Deposits

Images from the Mercury Dual Imaging System (MDIS) aboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging mission reveal low-reflectance polar deposits that are interpreted to be lag deposits of organic-rich, volatile material. Interpretation of these highest-resolution images of Mercury's polar deposits has been limited by the available topography models, so local high-resolution (125 m pixel-1) digital elevation models (DEMs) were made using a combination of data from the Mercury Laser Altimeter (MLA) and from shape-from-shading techniques using MDIS images. Local DEMs were made for eight of Mercury's north polar craters; these DEMs were then used to create high-resolution simulated image, illumination, and thermal models. The simulated images reveal that the pixel brightness variations imaged within Mercury's low-reflectance deposits are consistent with scattered light reflecting off of topography and do not need to be explained by volatile compositional differences as previously suggested. The illumination and thermal models show that these low-reflectance polar deposits extend beyond the permanently shadowed region, more than 1.0 km in some locations, and correspond to a maximum surface temperature of greater than 250 K but less than 350 K. The low-reflectance boundaries of all eight polar deposits studied here show a close correspondence with the surface stability boundary of coronene (C24H12). While coronene should only be viewed as a proxy for the myriad volatile compounds that may exist in Mercury's polar deposits, coronene's surface stability boundary supports the idea that Mercury's low-reflectance polar deposits are composed of macromolecular organic compounds, consistent with the hypotheses of exogenous transport and in situ production.

Keywords: mercury (planet); planetary polar regions; polycyclic aromatic hydrocarbons
Selective Dynamical Imaging of Interferometric Data

Recent developments in very long baseline interferometry (VLBI) have made it possible for the Event Horizon Telescope (EHT) to resolve the innermost accretion flows of the largest supermassive black holes on the sky. The sparse nature of the EHT's (u, v)-coverage presents a challenge when attempting to resolve highly time-variable sources. We demonstrate that the changing (u, v)-coverage of the EHT can contain regions of time over the course of a single observation that facilitate dynamical imaging. These optimal time regions typically have projected baseline distributions that are approximately angularly isotropic and radially homogeneous. We derive a metric of coverage quality based on baseline isotropy and density that is capable of ranking array configurations by their ability to produce accurate dynamical reconstructions. We compare this metric to existing metrics in the literature and investigate their utility by performing dynamical reconstructions on synthetic data from simulated EHT observations of sources with simple orbital variability. We then use these results to make recommendations for imaging the 2017 EHT Sgr A* data set.

Keywords: astrophysical black holes; very long baseline interferometry; aperture synthesis; interferometry
Resolving the Radio Emission from the Quasar P172+18 at z = 6.82

We present high angular resolution imaging of the quasar PSO J172.3556+18.7734 at z = 6.82 with the Very Long Baseline Array (VLBA). This source currently holds the record of being the highest redshift radio-loud quasar. These observations reveal a dominant radio source with a flux density of 398.4 ± 61.4 μJy at 1.53 GHz, a deconvolved size of 9.9 × 3.5 mas (52.5 × 18.6 pc), and an intrinsic brightness temperature of (4.7 ± 0.7) × 107 K. A weak unresolved radio extension from the main source is also detected at the ∼3.1σ level. The total flux density recovered with the VLBA at 1.53 GHz is consistent with that measured with the Very Large Array (VLA) at a similar frequency. The quasar is not detected at 4.67 GHz with the VLBA, suggesting a steep spectral index with a limit of ${\alpha }_{4.67}^{1.53}\lt -$ <!-- --> 1.55. The quasar is also not detected with the VLBA at 7.67 GHz. The overall characteristics of the quasar suggest that it is a very young radio source similar to lower redshift gigahertz peaked spectrum radio sources, with an estimated kinematic age of ∼103 yr. The VLA observations of this quasar revealed a second radio source in the field 23"1 away. This radio source, which does not have an optical or IR counterpart, is not detected with the VLBA at any of the observed frequencies. Its nondetection at the lowest observed VLBA frequency suggests that it is resolved out, implying a size larger than ∼0"17. It is thus likely situated at lower redshift than the quasar.

Keywords: early universe; radio loud quasars; quasars; radio continuum emission; extragalactic radio sources; radio interferometry; very long baseline interferometry; high-redshift galaxies
An HST Survey of Protostellar Outflow Cavities: Does Feedback Clear Envelopes?

We study protostellar envelope and outflow evolution using Hubble Space Telescope NICMOS or WFC3 images of 304 protostars in the Orion molecular clouds. These near-IR images resolve structures in the envelopes delineated by the scattered light of the central protostars with 80 au resolution, and they complement the 1.2 μm to 870 μm spectral energy distributions (SEDs) obtained with the Herschel Orion Protostar Survey program. Based on their 1.60 μm morphologies, we classify the protostars into five categories: nondetections, point sources without nebulosity, bipolar cavity sources, unipolar cavity sources, and irregulars. We find point sources without associated nebulosity are the most numerous, and show through monochromatic Monte Carlo radiative transfer modeling that this morphology occurs when protostars are observed at low inclinations or have low envelope densities. We also find that the morphology is correlated with the SED-determined evolutionary class, with Class 0 protostars more likely to be nondetections, Class I protostars to show cavities, and flat-spectrum protostars to be point sources. Using an edge detection algorithm to trace the projected edges of the cavities, we fit power laws to the resulting cavity shapes, thereby measuring the cavity half-opening angles and power-law exponents. We find no evidence for the growth of outflow cavities as protostars evolve through the Class I protostar phase, in contradiction with previous studies of smaller samples. We conclude that the decline of mass infall with time cannot be explained by the progressive clearing of envelopes by growing outflow cavities. Furthermore, the low star formation efficiency inferred for molecular cores cannot be explained by envelope clearing alone.

Keywords: protostars; stellar feedback; molecular clouds; near infrared astronomy; stellar jets; early stellar evolution
CLEAR: Paschen-β Star Formation Rates and Dust Attenuation of Low-redshift Galaxies

We use Paschen-β (Paβ; 1282 nm) observations from the Hubble Space Telescope G141 grism to study the star formation and dust-attenuation properties of a sample of 29 low-redshift (z < 0.287) galaxies in the CANDELS Lyα Emission at Reionization survey. We first compare the nebular attenuation from Paβ/Hα with the stellar attenuation inferred from the spectral energy distribution, finding that the galaxies in our sample are consistent with an average ratio of the continuum attenuation to the nebular gas of 0.44, but with a large amount of excess scatter beyond the observational uncertainties. Much of this scatter is linked to a large variation between the nebular dust attenuation as measured by (space-based) Paβ to (ground-based) Hα to that from (ground-based) Hα/Hβ. This implies there are important differences between attenuation measured from grism-based/wide-aperture Paβ fluxes and the ground-based/slit-measured Balmer decrement. We next compare star formation rates (SFRs) from Paβ to those from dust-corrected UV. We perform a survival analysis to infer a census of Paβ emission implied by both detections and nondetections. We find evidence that galaxies with lower stellar mass have more scatter in their ratio of Paβ to attenuation-corrected UV SFRs. When considering our Paβ detection limits, this observation supports the idea that lower-mass galaxies experience "burstier" star formation histories. Together, these results show that Paβ is a valuable tracer of a galaxy's SFR, probing different timescales of star formation and potentially revealing star formation that is otherwise missed by UV and optical tracers.

Keywords: star formation; starburst galaxies; interstellar dust extinction
Theoretical Spectroscopic Study of Isopropyl Alcohol (CH3-CHOH-CH3)

Accurate spectroscopic parameters of isopropyl alcohol, a volatile organic compound present on Earth and in extraterrestrial atmospheres, are provided. The work pursues the study of the far-infrared region, describing the distribution of the low-lying vibrational energy levels that can be populated at very low temperatures, having effects on the detectability and identification. The potential energy surface shows 27 almost equivalent minima producing 27 subcomponents of the levels due to tunneling effects. Computations have been performed using highly correlated ab initio calculations, accurate enough to distinguish between the rotational parameters of the two quasi-identical conformers gauche and trans. A variational procedure in three dimensions depending on three interacting internal rotations, the internal rotation of the two methyl groups and the internal rotation of the hydroxyl group, is employed to compute the energies. The 27 subcomponents of the ground vibrational state can be grouped into three series of nine energy levels located around 0.000, 1.693, and 81.927 cm‑1 whose energy difference is due to the OH torsion effect. The nine subcomponents integrated in each series derive from the torsion of the two methyl groups. The computations reproduce accurately the available experimental data. New predicted properties can help the spectroscopic analysis of the rotational-vibrational spectra in the gas phase and further detections of vibrationally excited isopropyl alcohol.

Keywords: interstellar medium
New Determinations of the Surface Abundances of HD 1280

New abundances for several chemical elements are measured for HD 1280 using updated atomic data and spectrum synthesis. The abundances of calcium and scandium are solar whereas strontium is mildly overabundant. The abundances of helium, magnesium, titanium, chromium, manganese, iron and barium are in good agreement with a former abundance analysis. This reinforces the status of HD 1280 as a normal rapidly rotating A star with essentially normal abundances of elements lighter than iron and mild overabundances of heavier elements which may actually have been present in the environment where the star was born.

Keywords: a stars; am stars
Cross-correlation Techniques to Mitigate the Interloper Contamination for Line Intensity Mapping Experiments

Line intensity mapping (LIM) serves as a potent probe in astrophysics, relying on the statistical analysis of integrated spectral line emissions originating from distant star-forming galaxies. While LIM observations hold the promise of achieving a broad spectrum of scientific objectives, a significant hurdle for future experiments lies in distinguishing the targeted spectral line emitted at a specific redshift from undesired line emissions originating at different redshifts. The presence of these interloping lines poses a challenge to the accuracy of cosmological analyses. In this study, we introduce a novel approach to quantify line–line cross-correlations (LIM-LLX), enabling us to investigate the target signal amid instrumental noise and interloping emissions. For example, at a redshift of z ∼ 3.7, we observed that the measured auto-power spectrum of C II 158 exhibited substantial bias, from interloping line emission. However, cross-correlating C II 158 with CO(6–5) lines using an FYST-like experiment yielded a promising result, with a signal-to-noise ratio of ∼10. This measurement is notably unbiased. Additionally, we explore the extensive capabilities of cross-correlation by leveraging various CO transitions to probe the tomographic Universe at lower redshifts through LIM-LLX. We further demonstrate that incorporating low-frequency channels, such as 90 and 150 GHz, into FYST's EoR-Spec-like experiment can maximize the potential for cross-correlation studies, effectively reducing the bias introduced by instrumental noise and interlopers.

Keywords: line intensities; observational cosmology
Atmosphere Escape Inferred from Modeling the Hα Transmission Spectrum of WASP-121b

The escaping atmospheres of hydrogen driven by stellar X-ray and extreme ultraviolet (XUV) have been detected around some exoplanets by the excess absorption of Lyα in the far-ultraviolet band. In the optical band the excess absorption of Hα is also found by ground-based instruments. However, it is not certain if the escape of the atmosphere driven by XUV can result in such absorption. Here we present the XUV-driven hydrodynamic simulation coupled with the calculation of detailed level population and the process of radiative transfer for WASP-121b. Our fiducial model predicts a mass-loss rate of ∼1.28 × 1012 g s-1 for WASP-121b. Due to the high temperature and Lyα intensity predicted by the fiducial model, many hydrogen atoms are populated into the first excited state. As a consequence, the transmission spectrum of Hα simulated by our model is broadly consistent with the observation. Compared with the absorption of Hα at different observation times, the stellar XUV emission varies in the range of 0.5-1.5 times fiducial value, which may reflect the variation of the stellar activity. Finally, we find that the supersonic regions of the planetary wind contribute a prominent portion to the absorption of Hα by comparing the equivalent width of Hα, which hints that a transonic outflow of the upper atmosphere driven by XUV irradiation of the host star can be detected by a ground-based telescope and that Hα can be a good indicator of escaping atmosphere.

Keywords: exoplanets; hot jupiters; exoplanet atmospheres; upper atmosphere; atmospheric composition; stellar spectral lines; stellar activity
The Solar Minimum Eclipse of 2019 July 2. III. Inferring the Coronal T e with a Radiative Differential Emission Measure Inversion

Differential emission measure (DEM) inversion methods use the brightness of a set of emission lines to infer the line-of-sight (LOS) distribution of the electron temperature (T e ) in the corona. DEM inversions have been traditionally performed with collisionally excited lines at wavelengths in the extreme ultraviolet and X-ray. However, such emission is difficult to observe beyond the inner corona (1.5 R ⊙), particularly in coronal holes. Given the importance of the T e distribution in the corona for exploring the viability of different heating processes, we introduce an analog of the DEM specifically for radiatively excited coronal emission lines, such as those observed during total solar eclipses (TSEs) and with coronagraphs. This radiative-DEM (R-DEM) inversion utilizes visible and infrared emission lines that are excited by photospheric radiation out to at least 3 R ⊙. Specifically, we use the Fe X (637 nm), Fe XI (789 nm), and Fe XIV (530 nm) coronal emission lines observed during the 2019 July 2 TSE near solar minimum. We find that, despite a large T e spread in the inner corona, the distribution converges to an almost isothermal yet bimodal distribution beyond 1.4 R ⊙, with T e ranging from 1.1 to 1.4 in coronal holes and from 1.4 to 1.65 MK in quiescent streamers. Application of the R-DEM inversion to the Predictive Science Inc. magnetohydrodynamic simulation for the 2019 eclipse validates the R-DEM method and yields a similar LOS Te distribution to the eclipse data.

Keywords: solar corona; solar eclipses; solar coronal streamers; solar coronal holes; solar optical telescopes
Coronal Heating Law Constrained by Microwave Gyroresonant Emission

The question why the solar corona is much hotter than the visible solar surface still puzzles solar researchers. Most theories of the coronal heating involve a tight coupling between the coronal magnetic field and the associated thermal structure. This coupling is based on two facts: (i) the magnetic field is the main source of the energy in the corona and (ii) the heat transfer preferentially happens along the magnetic field, while is suppressed across it. However, most of the information about the coronal heating is derived from the analysis of extreme ultraviolet or soft X-ray emissions, which are not explicitly sensitive to the magnetic field. This paper employs another electromagnetic channel—the sunspot-associated microwave gyroresonant emission, which is explicitly sensitive to both the magnetic field and thermal plasma. We use nonlinear force-free field reconstructions of the magnetic skeleton dressed with a thermal structure as prescribed by a field-aligned hydrodynamics to constrain the coronal heating model. We demonstrate that the microwave gyroresonant emission is extraordinarily sensitive to details of the coronal heating. We infer heating model parameters consistent with observations.

Keywords: solar coronal heating; solar magnetic fields; solar coronal radio emission
High-resolution Simulations of the Inner Heliosphere in Search of the Kelvin-Helmholtz Waves

The Kelvin-Helmholtz instability (KHI) can be generated at velocity shears in plasmas. While shears are abundant in the solar wind, whether they generate KHI in situ remains an open question, because of the lack of models that can simultaneously resolve the global structure of the expanding solar wind and the local structure of much smaller-scale velocity shears. In this paper, we use the Grid Agnostic MHD for Extended Research Applications model whose high resolving power, in combination with a highly refined spatial grid, allowed us to extend the simulation from global scales roughly into the first decade of the inertial range (~1.5 × 105 km, which we refer to as mesoscale). We employ this computational capability to extract from the simulation the local properties of radial and azimuthal solar wind velocity shears and investigate their KH stability using a linear dispersion relation, which includes both the finite width of the shear and plasma compressibility. We find that radial shears, which dominate the global structure of the inner heliosphere, are stabilized by compressibility. However, depending on the local Alfvén speed, sound speed, shear thickness, and the strength of the stabilizing azimuthal magnetic field, the azimuthal shears generated inside stream interaction regions could be KH-unstable. While our highly resolved simulation allowed us to analyze the local properties of the velocity shears, its resolution was still insufficient to confirm the instability. We argue that even higher resolution simulations are required to reproduce in situ generation of KHI at velocity shears in the solar wind.

Keywords: heliosphere; magnetohydrodynamical simulations; solar wind