adsabs/SciX_UAT_keywords huggingface dataset:
Tomography of a Solar Plage with the Tenerife Inversion Code

We apply the Tenerife Inversion Code (TIC) to the plage spectropolarimetric observations obtained by the Chromospheric LAyer SpectroPolarimeter (CLASP2). These unprecedented data consist of full Stokes profiles in the spectral region around the Mg II h and k lines for a single slit position, with around two thirds of the 196″ slit crossing a plage region and the rest crossing an enhanced network. A previous analysis of these data had allowed us to infer the longitudinal component of the magnetic field by applying the weak-field approximation (WFA) to the circular polarization profiles, and to assign the inferred magnetic fields to different layers of the solar atmosphere based on the results of previous theoretical radiative transfer investigations. In this work, we apply the recently developed TIC to the same data. We obtain a stratified model atmosphere that fits the intensity and circular polarization profiles at each position along the spectrograph slit and we compare our results for the longitudinal component of the magnetic field with the previously obtained WFA results, highlighting the generally good agreement in spite of the fact that the WFA is known to produce an underestimation when applied to the outer lobes of the Mg II h and k circular polarization profiles. Finally, we use the inverted model atmospheres to give a rough estimation of the energy that could be carried by Alfvén waves propagating in the chromosphere in the plage and network regions, showing that it is sufficient to compensate for the estimated energy losses in the chromosphere of solar active regions.

Keywords: solar magnetic fields; plages; spectropolarimetry; solar chromosphere
Is the Hot, Dense Sub-Neptune TOI-824 b an Exposed Neptune Mantle? Spitzer Detection of the Hot Dayside and Reanalysis of the Interior Composition

The Kepler and TESS missions revealed a remarkable abundance of sub-Neptune exoplanets. Despite this abundance, our understanding of the nature and compositional diversity of sub-Neptunes remains limited, to a large part because atmospheric studies via transmission spectroscopy almost exclusively have aimed for low-density sub-Neptunes, and even those were often affected by high-altitude clouds. The recent TESS discovery of the hot, dense TOI-824 b (2.93 R ⊕ and 18.47 M ⊕) opens a new window into sub-Neptune science by enabling the study of a dense sub-Neptune via secondary eclipses. Here, we present the detection of TOI-824 b's hot dayside via Spitzer secondary-eclipse observations in the 3.6 and 4.5 μm channels, combined with a reanalysis of its interior composition. The measured eclipse depths (142 ${}_{-52}^{+57}$ and ${245}_{-77}^{+75}$ ppm) and brightness temperatures (1463 ${}_{-196}^{+183}$ and ${1484}_{-202}^{+180}$ K) indicate a poor heat redistribution (f < 0.49) and a low Bond albedo (A B < 0.26). We conclude that TOI-824 b could be an "exposed Neptune mantle": a planet with a Neptune-like water-rich interior that never accreted a hydrogen envelope or that subsequently lost it. The hot dayside temperature is then naturally explained by a high-metallicity envelope reemitting the bulk of the incoming radiation from the dayside. TOI-824 b's density is also consistent with a massive rocky core that accreted up to 1% of hydrogen, but the observed eclipse depths favor our high-metallicity general circulation model (GCM) simulation to a solar-metallicity GCM simulation with a likelihood ratio of 7:1. The new insights into TOI-824 b's nature suggest that the sub-Neptune population may be more diverse than previously thought, with some of the dense hot sub-Neptunes potentially not hosting a hydrogen-rich envelope as generally assumed for sub-Neptunes.

Keywords: exoplanets; mini neptunes; exoplanet atmospheres; hot neptunes
Metallicity Dependence of the H/H2 and C+/C/CO Distributions in a Resolved Self-regulating Interstellar Medium

We study the metallicity dependence of the H/H2 and C+/C/CO distributions in a self-regulated interstellar medium (ISM) across a broad range of metallicities (0.1 < Z/Z⊙ < 3). To this end, we conduct high-resolution (particle mass of 1 M⊙) hydrodynamical simulations coupled with a time-dependent H2 chemistry network. The results are then post-processed with an accurate chemistry network to model the associated C+/C/CO abundances, based on the time-dependent non-steady-state ("nonequilibrium") H2 abundances. We find that the time-averaged star formation rate and the ISM structure are insensitive to metallicity. The column densities relevant for molecular shielding appear correlated with the volume densities in gravitationally unstable gas. As metallicity decreases, H2 progressively deviates from steady state ("equilibrium") and shows shallow abundance profiles until they sharply truncate at the photodissociation fronts. In contrast, the CO profile is sharp and controlled by photodissociation as CO quickly reaches steady state. We construct effective 1D cloud models that successfully capture the time-averaged chemical distributions in simulations. At low metallicities, the steady-state model significantly overestimates the abundance of H2 in the diffuse medium. The overestimated H2, however, has little impact on CO. Consequently, the mass fraction of CO-dark H2 gas is significantly lower than what a fully steady-state model predicts. The mass ratios of H2/C+ and H2/C both show a weaker dependence on {Z}^{{\prime} }$ than H2/CO, which potentially indicates that C+ and C could be alternative tracers for H2 at low {Z}^{{\prime} }$ in terms of mass budget. Our chemistry code for post-processing is publicly available.

Keywords: interstellar medium; astrochemistry; hydrodynamical simulations
Signatures of X-Ray-dominated Chemistry in the Spectra of Exoplanetary Atmospheres

High-energy radiation from stars impacts planetary atmospheres, deeply affecting their chemistry and providing departures from chemical equilibrium. While the upper atmospheric layers are dominated by ionizations induced by extreme-ultraviolet radiation, deeper into the atmosphere, molecular abundances are controlled by a characteristic X-ray-dominated chemistry, mainly driven by an energetic secondary electron cascade. In this work, we aim at identifying molecular photochemically induced fingerprints in the transmission spectra of a giant planet atmosphere. We have developed a numerical code capable of synthesizing transmission spectra with arbitrary spectral resolution, exploiting updated infrared photoabsorption cross sections. Chemical mixing ratios are computed using a photochemical model tailored to investigate high-energy ionization processes. We find that in the case of high levels of stellar activity, synthetic spectra in both low and high resolutions show significant, potentially observable out-of-equilibrium signatures arising mainly from CO, CH4, C2H2, and HCN.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; star-planet interactions
The SDSS-Gaia View of the Color-Magnitude Relation for Blue Horizontal-branch Stars

We present an updated sample of blue horizontal-branch (BHB) stars selected from the photometric and spectroscopic data from Sloan Digital Sky Survey and its associated project Sloan Extension for Galactic Understanding and Exploration (SEGUE). With these data, we selected candidates for A-type stars in the color-color space and then a mixture modeling technique was implemented in order to distinguish between BHB and main-sequence/blue-straggler stars based on their surface gravity values ( $\mathrm{log}\,g$ ) estimated by the SEGUE Stellar Parameter Pipeline. Our robust approach allows us to attribute individual probabilities of each star truly being in the BHB stage. Hence, our method is advantageous in comparison to previous SEGUE BHB selections that adopted simple $\mathrm{log}\,g$ cuts. We also revisit the color-magnitude relation for these stars and propose two calibrations, based on updated distances for Galactic globular clusters, to estimate absolute magnitudes with (g - r)0 and (u - r)0 colors.

Keywords: horizontal branch stars; stellar distance
Lepto-hadronic Jet-disk Model for the Multiwavelength SED of M87

The low-luminosity active galactic nuclei M87, archetype of Fanaroff-Riley I radio galaxies, was observed in a historically quiet state in 2017. While one-zone leptonic jet models alone cannot explain the core radio-to-gamma-ray spectrum, we explore a hybrid jet-disk scenario. In this work, we model the overall spectral energy distribution of M87's core with a dominating one-zone lepto-hadronic jet component, coupled with the contribution from the accretion flow. We find close-to-equipartition parameter sets for which the jet component fits the radio-to-optical data as well as the gamma-ray band, while the accretion flow mainly contributes to the X-ray band. The effects of gamma-ray absorption by the extragalactic background light during the propagation toward Earth are probed and are found to be negligible for this model. The neutrino flux produced by such scenarios is also calculated, but remains below the current instruments' sensitivity.

Keywords: relativistic jets; non-thermal radiation sources; gamma-ray sources; cosmic ray sources; astrophysical black holes; low-luminosity active galactic nuclei; high energy astrophysics; active galactic nuclei; particle astrophysics
Transits of Known Planets Orbiting a Naked-eye Star

Some of the most scientifically valuable transiting planets are those that were already known from radial velocity (RV) surveys. This is primarily because their orbits are well characterized and they preferentially orbit bright stars that are the targets of RV surveys. The Transiting Exoplanet Survey Satellite (TESS) provides an opportunity to survey most of the known exoplanet systems in a systematic fashion to detect possible transits of their planets. HD 136352 (Nu2 Lupi) is a naked-eye (V = 5.78) G-type main-sequence star that was discovered to host three planets with orbital periods of 11.6, 27.6, and 108.1 days via RV monitoring with the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph. We present the detection and characterization of transits for the two inner planets of the HD 136352 system, revealing radii of ${1.482}_{-0.056}^{+0.058}$ R⊕ and ${2.608}_{-0.077}^{+0.078}$ R⊕ for planets b and c, respectively. We combine new HARPS observations with RV data from the Keck/High Resolution Echelle Spectrometer and the Anglo-Australian Telescope, along with TESS photometry from Sector 12, to perform a complete analysis of the system parameters. The combined data analysis results in extracted bulk density values of ${\rho }_{b}={7.8}_{-1.1}^{+1.2}$ g cm-3 and ${\rho }_{c}={3.50}_{-0.36}^{+0.41}$ g cm-3 for planets b and c, respectively, thus placing them on either side of the radius valley. The combination of the multitransiting planet system, the bright host star, and the diversity of planetary interiors and atmospheres means this will likely become a cornerstone system for atmospheric and orbital characterization of small worlds.

Keywords: exoplanets; exoplanet atmospheres; exoplanet structure; transit photometry; radial velocity
138175 (2000 EE104) and the Source of Interplanetary Field Enhancements

We present the first optical observations taken to characterize the near-Earth object 138175 (2000 EE104). This body is associated with interplanetary field enhancements (IFEs), thought to be caused by interactions between the solar wind magnetic field and solid material trailing in the orbit of the parent body. Based on optical photometry, the radius (in meters) and mass (in kilograms) of an equal-area sphere are found to be ${r}_{n}=250{(0.1/{p}_{R})}^{1/2}$ and ${M}_{n}={10}^{11}{(0.1/{p}_{R})}^{3/2}$ , respectively, where pR is the red geometric albedo and a density of ρ = 1500 kg m-3 is assumed. The measured colors are intermediate between those of C-type (primitive) and S-type (metamorphosed) asteroids but, with correction for the likely effects of phase reddening, are more consistent with a C-type classification than with S-type. No evidence for co-moving companions larger than ∼40(0.1/pR) m in radius is found, and no dust particle trail is detected, setting a limit to the trail optical depth of τ ≤ 2 × 10-9. Consideration of the size distribution produced by impact pulverization makes it difficult to generate the mass of nanodust (minimum 105-106 kg) required to account for IFEs, unless the size distribution is unusually steep. Furthermore, impact pulverization timescales for source objects of the required size are much longer than the dynamical timescale. While the new optical data do not definitively refute the hypothesis that boulder pulverization is the source of IFEs, neither do they provide any support for it.

Keywords: near-earth objects; asteroids; interplanetary magnetic fields
The Galactic Halo Contribution to the Dispersion Measure of Extragalactic Fast Radio Bursts

A new model of the Milky Way (MW) halo component of the dispersion measure (DM) for extragalactic sources, such as fast radio bursts, is presented in light of recent diffuse X-ray observations. In addition to the spherical component of isothermal gas (kT ∼ 0.3 keV) in hydrostatic equilibrium with the Galactic gravitational potential, our model includes a disk-like nonspherical hot gas component to reproduce the directional dependence of the observed X-ray emission measure (EM). The total gas mass (1.2 × 1011 M⊙) is dominated by the spherical component, and is consistent with the total baryon mass of the MW expected from the dark matter mass and the cosmic baryon-to-dark-matter ratio. Our model predicts a mean halo DM of $43\,\mathrm{pc}\ {\mathrm{cm}}^{-3}$ , with a full range of 30- $245\,\mathrm{pc}\ {\mathrm{cm}}^{-3}$ over the whole sky. The large scatter seen in the X-ray EM data implies a ∼0.2 dex (rms) fluctuation of the MW halo DM. We provide an analytic formula to estimate the MW halo DM of our model along any line of sight, which can be easily used to compute the total MW component of DM toward extragalactic sources, in combination with existing DM models of the warm ionized medium associated with the Galactic disk.

Keywords: circumgalactic medium; radio transient sources; diffuse x-ray background
Constraining the Progenitor System of the Type Ia Supernova 2021aefx

We present high-cadence optical and ultraviolet light curves of the normal Type Ia supernova (SN) 2021aefx, which shows an early bump during the first two days of observation. This bump may be a signature of interaction between the exploding white dwarf and a nondegenerate binary companion, or it may be intrinsic to the white dwarf explosion mechanism. In the case of the former, the short duration of the bump implies a relatively compact main-sequence companion star, although this conclusion is viewing-angle dependent. Our best-fit companion-shocking and double-detonation models both overpredict the UV luminosity during the bump, and existing nickel-shell models do not match the strength and timescale of the bump. We also present nebular spectra of SN 2021aefx, which do not show the hydrogen or helium emission expected from a nondegenerate companion, as well as a radio nondetection that rules out all symbiotic progenitor systems and most accretion disk winds. Our analysis places strong but conflicting constraints on the progenitor of SN 2021aefx; no current model can explain all of our observations.

Keywords: binary stars; supernovae; type ia supernovae; white dwarf stars
Astro-COLIBRI-The COincidence LIBrary for Real-time Inquiry for Multimessenger Astrophysics

Astro-COLIBRI is a novel tool that evaluates alerts of transient observations in real time, filters them by user-specified criteria, and puts them into their multiwavelength and multimessenger context. Through fast generation of an overview of persistent sources as well as transient events in the relevant phase space, Astro-COLIBRI contributes to an enhanced discovery potential of both serendipitous and follow-up observations of the transient sky. The software's architecture comprises a Representational State Transfer Application Programming Interface, both a static and a real-time database, a cloud-based alert system, as well as a website and apps for iOS and Android as clients for users. The latter provide a graphical representation with a summary of the relevant data to allow for the fast identification of interesting phenomena along with an assessment of observing conditions at a large selection of observatories around the world.

Keywords: high energy astrophysics; transient sources; gamma-ray transient sources; time domain astronomy; gravitational waves; neutrino astronomy
CLusters in the UV as EngineS (CLUES). I. Survey Presentation and FUV Spectral Analysis of the Stellar Light

The CLusters in the Uv as EngineS (CLUES) survey is a Cosmic Origins Spectrograph (COS) campaign aimed at acquiring the 1130-1770 Å rest-frame spectroscopy of very young (<20 Myr) and massive (>104 M ⊙) star clusters in galaxies that are part of the Hubble treasury program Legacy ExtraGalactic UV Survey. In this first paper of a series, we describe the CLUES sample consisting of 20 young star clusters and report their physical properties as derived by both multiwavelength photometry and far-UV (FUV) spectroscopy with Hubble Space Telescope. Thanks to the synergy of the two different data sets, we build a coherent picture of the diverse stellar populations found in each region (with sizes of 40-160 pc). We associate the FUV-brightest stellar population to the central targeted star cluster and the other modeled population to the diffuse stars that are included in the COS aperture. We observe better agreement between photometric and spectroscopic ages for star clusters younger than 5 Myr. For clusters older than 5 Myr, photometry and spectroscopy measurements deviate, with the latter producing older ages, due to the degeneracy of photometric models. FUV spectroscopy enables us to better constrain the stellar metallicities, a parameter that optical colors are insensitive to. Finally, the derived E(B - V) are quite similar, with a tendency for FUV spectroscopy to favor solutions with higher extinctions. The recovered masses are in agreement within a factor of 2 for all of the clusters.

Keywords: observational astronomy; ultraviolet surveys; young star clusters
Surface Rotation and Photometric Activity for Kepler Targets. II. G and F Main-sequence Stars and Cool Subgiant Stars

Dark magnetic spots crossing the stellar disk lead to quasiperiodic brightness variations, which allow us to constrain stellar surface rotation and photometric activity. The current work is the second of this series, where we analyze the Kepler long-cadence data of 132,921 main-sequence F and G stars and late subgiant stars. Rotation-period candidates are obtained by combining wavelet analysis with autocorrelation function. Reliable rotation periods are then selected via a machine-learning (ML) algorithm, automatic selection, and complementary visual inspection. The ML training data set comprises 26,521 main-sequence K and M stars from Paper I. To supplement the training, we analyze in the same way as Paper I, i.e., automatic selection and visual inspection, 34,100 additional stars. We finally provide rotation periods Prot and associated photometric activity proxy Sph for 39,592 targets. Hotter stars are generally faster rotators than cooler stars. For main-sequence G stars, Sph spans a wider range of values with increasing effective temperature, while F stars tend to have smaller Sph values in comparison with cooler stars. Overall for G stars, fast rotators are photometrically more active than slow rotators, with Sph saturating at short periods. The combined outcome of the two papers accounts for average Prot and Sph values for 55,232 main-sequence and subgiant FGKM stars (out of 159,442 targets), with 24,182 new Prot detections in comparison with McQuillan et al. The upper edge of the Prot distribution is located at longer Prot than found previously.

Keywords: stellar rotation; stellar activity; starspots; low mass stars; catalogs; photometry; astronomy data analysis
Early Results from GLASS-JWST. XXII. Rest-frame UV-Optical Spectral Properties of Lyα Emitting Galaxies at 3 < z < 6

Lyα emission is possibly the best indirect diagnostic of Lyman continuum (LyC) escape since the conditions that favor the escape of Lyα photons are often the same that allow for the escape of LyC photons. In this work, we present the rest-frame UV-optical spectral characteristics of 11 Lyα emitting galaxies at 3 < z < 6-the redshift range that optimizes between intergalactic medium attenuation effects and temporal proximity to the epoch of reionization. From a combined analysis of JWST/NIRSpec and MUSE data, we present the Lyα escape fraction and study its correlation with other physical properties of galaxies that might facilitate Lyα escape. We find that our galaxies have low masses (80% of the sample with ${\mathrm{log}}_{10}\ {M}_{\star }\lt 9.5\ {M}_{\odot }$ ), compact sizes (median R e ~ 0.7 kpc), low dust content, moderate [O III]/[O II] flux ratios (mean ~ 6.8 ± 1.2), and moderate Lyα escape fractions (mean ${f}_{\mathrm{esc}}^{\mathrm{Ly}\alpha }\ \sim $ 0.11). Our sample shows characteristics that are broadly consistent with low-redshift galaxies with Lyα emission, which are termed as "analogs" of the high-redshift population. We predict the LyC escape fraction in our sample to be low (0.03-0.07), although larger samples in the postreionization epoch are needed to confirm these trends.

Keywords: galaxies; high-redshift galaxies; lyman-alpha galaxies
Environmental Impacts on the Rest-frame UV Size and Morphology of Star-forming Galaxies at z 2

We report the measurement of rest-frame UV size and morphology of Hα-emission-selected star-forming galaxies (HAEs) in four protoclusters at z ~ 2 (PKS 1138-262, USS 1558-003, PHz G237.0+42.5, and CC 2.2) using archival Hubble Space Telescope Advanced Camera Survey (HST/ACS) F814W data. We compare the measurement of 122 HAEs in protoclusters detected by HST/ACS to a coeval comparison field sample of 436 HAEs. We find the size distributions of protocluster and field HAEs are similar with a typical half-light radius of ~2.5 kpc. At fixed stellar mass, there is no significant difference between HAEs in the protocluster and in the field, which is also supported by stacking analyses. This result suggests that the environment does not significantly affect the size of galaxies during the star-forming phase at this epoch. Based on the Sérsic index and nonparametric morphologies, HAE morphologies in both environments at z ~ 2 in rest-frame UV are consistent with disk-like star-forming galaxies, although we also find 29% ± 4% HAEs showing disturbed morphologies. The fraction of disturbed galaxies is higher in the protocluster environment, with 39% ± 8% protocluster HAEs showing disturbed morphologies, compared to 26% ± 4% in the comparison field. The apparent disturbed morphologies are correlated with higher star formation activity and may be caused by either in situ giant clumps or mergers.

Keywords: protoclusters; high-redshift galaxies