adsabs/SciX_UAT_keywords huggingface dataset:
High-resolution X-Ray Spectroscopy of Interstellar Iron toward Cygnus X-1 and GX 339-4

We present a high-resolution spectral study of Fe L-shell extinction by the diffuse interstellar medium (ISM) in the direction of the X-ray binaries Cygnus X-1 and GX 339–4, using the XMM-Newton reflection grating spectrometer. The majority of interstellar Fe is suspected to condense into dust grains in the diffuse ISM, but the compounds formed from this process are unknown. Here, we use the laboratory cross sections from Kortright & Kim (2000) and Lee et al. (2005) to model the absorption and scattering profiles of metallic Fe, and the crystalline compounds fayalite (Fe2SiO4), ferrous sulfate (FeSO4), hematite (α-Fe2O3), and lepidocrocite (γ-FeOOH), which have oxidation states ranging from Fe0 to Fe3+. We find that the observed Fe L-shell features are systematically offset in energy from the laboratory measurements. An examination of over two dozen published measurements of Fe L-shell absorption finds a 1–2 eV scatter in energy positions of the L-shell features. Motivated by this, we fit for the best energy-scale shift simultaneously with the fine structure of the Fe L-shell extinction cross sections. Hematite and lepidocrocite provide the best fits (≈ + 1.1 eV shift), followed by fayalite (≈ + 1.8 eV shift). However, fayalite is disfavored, based on the implied abundances and knowledge of ISM silicates gained by infrared astronomical observations and meteoritic studies. We conclude that iron oxides in the Fe3+ oxidation state are good candidates for Fe-bearing dust. To verify this, new absolute photoabsorption measurements are needed on an energy scale accurate to better than 0.2 eV.

Keywords: interstellar medium; dust composition; x-ray binary stars
Improving the Arrival Time Estimates of Coronal Mass Ejections by Using Magnetohydrodynamic Ensemble Modeling, Heliospheric Imager Data, and Machine Learning

The arrival time prediction of coronal mass ejections (CMEs) is an area of active research. Many methods with varying levels of complexity have been developed to predict CME arrival. However, the mean absolute error (MAE) of predictions remains above 12 hr, even with the increasing complexity of methods. In this work we develop a new method for CME arrival time prediction that uses magnetohydrodynamic simulations involving data-constrained flux-rope-based CMEs, which are introduced in a data-driven solar wind background. We found that for six CMEs studied in this work the MAE in arrival time was ~8 hr. We further improved our arrival time predictions by using ensemble modeling and comparing the ensemble solutions with STEREO-A and STEREO-B heliospheric imager data. This was done by using our simulations to create synthetic J-maps. A machine-learning (ML) method called the lasso regression was used for this comparison. Using this approach, we could reduce the MAE to ~4 hr. Another ML method based on the neural networks (NNs) made it possible to reduce the MAE to ~5 hr for the cases when HI data from both STEREO-A and STEREO-B were available. NNs are capable of providing similar MAE when only the STEREO-A data are used. Our methods also resulted in very encouraging values of standard deviation (precision) of arrival time. The methods discussed in this paper demonstrate significant improvements in the CME arrival time predictions. Our work highlights the importance of using ML techniques in combination with data-constrained magnetohydrodynamic modeling to improve space weather predictions.

Keywords: solar coronal mass ejections
Restoring Process of Sunspot Penumbra

We describe the disappearance of a sector of sunspot penumbra and its restoring process observed in the preceding sunspot of active region NOAA 12348. The evolution of the magnetic field and the plasma flows supports the idea that the penumbra forms due to a change of inclination of the magnetic field of the canopy. Moving magnetic features have been observed during the disintegration phase of that sector of sunspot penumbra. During the restoring phase we have not observed any magnetic flux emergence around the sunspot. The restoring process of the penumbra sector completed in about 72 hr and it was accompanied by the transition from the counter-Evershed flow to the classical Evershed flow. The inversion of photospheric spectropolarimetric measurements taken by the Interferometric Bidimensional Spectroscopic Instrument (IBIS) allowed us to reconstruct how the uncombed configuration of the magnetic field forms during the new settlement of the penumbra, i.e., the vertical component of the magnetic field seems to be progressively replaced by some horizontal field lines, corresponding to the intraspines.

Keywords: solar magnetic fields; solar photosphere; solar chromosphere; sunspots
ALMA Reveals a Stable Rotating Gas Disk in a Paradoxical Low-mass, Ultradusty Galaxy at z = 4.274

We report ALMA detections of [C II] and a dust continuum in Az9, a multiply imaged galaxy behind the Frontier Field cluster MACS J0717.5+3745. The bright [C II] emission line provides a spectroscopic redshift of z = 4.274. This strongly lensed (μ = 7 ± 1) galaxy has an intrinsic stellar mass of only 2 × 109 M ⊙ and a total star formation rate of 26 M ⊙ yr-1 (~80% of which is dust-obscured). Using public magnification maps, we reconstruct the [C II] emission in the source plane to reveal a stable, rotation-dominated disk with V/σ = 5.3, which is >2× higher than predicted from simulations for similarly high-redshift, low-mass galaxies. In the source plane, the [C II] disk has a half-light radius of 1.8 kpc and, along with the dust, is spatially offset from the peak of the stellar light by 1.4 kpc. Az9 is not deficient in [C II]; L [C II]/L IR = 0.0027, consistent with local and high-redshift normal star-forming galaxies. While dust-obscured star formation is expected to dominate in higher-mass galaxies, such a large reservoir of dust and gas in a lower-mass disk galaxy 1.4 Gyr after the Big Bang challenges our picture of early galaxy evolution. Furthermore, the prevalence of such low-mass dusty galaxies has important implications for the selection of the highest-redshift dropout galaxies with JWST. As one of the lowest stellar mass galaxies at z > 4 to be detected in a dust continuum and [C II], Az9 is an excellent laboratory in which to study early dust enrichment in the interstellar medium.

Keywords: galaxy evolution; galaxy kinematics; strong gravitational lensing; dust continuum emission; spectral energy distribution; luminous infrared galaxies
Thermal Effects of Ambipolar Diffusion during the Gravitational Collapse of a Radiative Cooling Filament

In this study, we consider the effects of ambipolar diffusion during the gravitational collapse of a radiative cooling filamentary molecular cloud. Two separate configurations of magnetic field, i.e., axial and toroidal, are considered in the presence of the ambipolar diffusion for a radiative cooling filament. These configurations lead to two different formulations of the problem. The filament is radiatively cooled and heated by ambipolar diffusion in both cases of magnetic field configurations. The self-similar method is used to solve the obtained equations in each case. We found that the adiabatic exponent and ambipolar diffusivity play very important roles during the gravitational collapse of a cooling filament. The results show that the ambipolar heating significantly increases the temperature in the middle regions of a cooling filament. Furthermore, we found that the ambipolar diffusion has very important effects during the collapse, so that its heating effect is dominant over its dynamical effect in the middle regions of a cooling filament. The obtained results also address some regions where the rate of star formation is more or less compared to the observational reports.

Keywords: star formation; star forming regions
A Mixture of LBG Overdensities in the Fields of Three 6 < z < 7 Quasars: Implications for the Robustness of Photometric Selection

The most luminous quasars at z > 6 are suspected to be both highly clustered and to reside in the most massive dark matter halos in the early universe, making them prime targets to search for galaxy overdensities and/or protoclusters. We search for Lyman-break dropout-selected galaxies using HST WFC3/ACS broadband imaging in the fields of three 6 < z < 7 quasars, as well as for their simultaneously observed coordinated parallel fields, and constrain their photometric redshifts using EAZY. One field, J0305-3150, shows a volume density 10× higher than the blank-field UV luminosity function (UVLF) at M UV < -20, with tentative evidence of a 3σ overdensity in its parallel field located 15 cMpc away. Another field, J2054-0005, shows an angular overdensity within 500 ckpc from the quasar, but this is still consistent with UVLF predictions within 3σ, while the last field, J2348-3054, shows no enhancement. We discuss methods for reducing uncertainty in overdensity measurements when using photometric selection and show that we can robustly select Lyman-break galaxies (LBGs) consistent with being physically associated with the quasar, corroborated by existing JWST/NIRCam WFSS data in the J0305 field. Even accounting for incompleteness, the overdensities in J0305 and J2054 are higher for brighter galaxies at short angular separations, suggesting preferential enhancement of more massive galaxies in the quasar's immediate vicinity. Finally, we compare the population of LBGs with previously identified [C II] and millimeter-continuum companions. The LBG overdensities are not accompanied by an enhanced number of dusty galaxies, suggesting that the overdense quasar fields are not in the bursty star-forming phase sometimes seen in high-redshift protoclusters.

Keywords: quasars; high-redshift galaxy clusters; high-redshift galaxies; lyman-break galaxies; damped lyman-alpha systems; hubble space telescope
Broadband Selection, Spectroscopic Identification, and Physical Properties of a Population of Extreme Emission-line Galaxies at 3 < z < 3.7

We present the selection, spectroscopic identification, and physical properties of extreme emission-line galaxies (EELGs) at 3 < z < 3.7, aiming at studying physical properties of an analog population of star-forming galaxies (SFGs) at the epoch of reionization. The sample is selected based on the excess in the observed Ks broadband flux relative to the best-fit stellar continuum model flux. By applying a 0.3 mag excess as a primary criterion, we select 240 EELG candidates with intense emission lines and estimated an observed-frame equivalent width (EW) of ≳1000 Å over the UltraVISTA-DR2 ultra-deep stripe in the COSMOS field. We then carried out HK-band follow-up spectroscopy for 23 of the candidates with Subaru/MOIRCS, and we find that 19 and 2 of them are at z > 3 with intense [O III] emission and Hα emitters at z ≃ 2, respectively. These spectroscopically identified EELGs at z ≃ 3.3 show, on average, higher specific star formation rates (sSFRs) than the star-forming main sequence, low dust attenuation of E(B - V) ≲ 0.1 mag, and high [O III]/[O II]ratios of ≳3. We also find that our EELGs at z ≃ 3.3 have higher hydrogen-ionizing photon production efficiencies (ξion) than the canonical value (≃1025.2 erg-1 Hz), indicating that they are efficient in ionizing their surrounding interstellar medium. These physical properties suggest that they are low-metallicity galaxies with higher ionizing parameters and harder UV spectra than normal SFGs, which is similar to galaxies with Lyman continuum (LyC) leakage. Among our EELGs, those with the largest [O III]/[O II] and EW([O III]) values would be the most promising candidates to search for LyC leakage. * Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, with a proposal ID of S17A-049.

Keywords: high-redshift galaxies; galaxy evolution; emission line galaxies; galaxy formation; reionization; galaxy properties
Hyper Suprime-Cam Low Surface Brightness Galaxies. II. A Hubble Space Telescope Study of the Globular Cluster Systems of Ultradiffuse Galaxies in Groups

We increase the sample of ultradiffuse galaxies (UDGs) in lower-density environments with characterized globular cluster (GC) populations using new Hubble Space Telescope observations of nine UDGs in group environments. While the bulk of our UDGs have GC abundances consistent with normal dwarf galaxies, two of these UDGs have excess GC populations. These two UDGs both have GC luminosity functions consistent with higher surface brightness galaxies and cluster UDGs. We then combine our nine objects with previous studies to create a catalog of UDGs with analyzed GC populations that spans a uniquely diverse range of environments. We use this catalog to examine broader trends in the GC populations of low stellar mass galaxies. The highest GC abundances are found in cluster UDGs, but whether cluster UDGs are actually more extreme requires the study of many more UDGs in groups. We find a possible positive correlation between GC abundance and stellar mass, and between GC abundance and galaxy size at fixed stellar mass. However, we see no significant relation between stellar mass and galaxy size, over our limited stellar mass range. We consider possible origins of the correlation between GC abundance and galaxy size, including the possibility that these two galaxy properties are both dependent on the galaxy dark matter halo, or that they are related through baryonic processes like internal feedback. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO-15277.

Keywords: globular star clusters; galaxy formation; galaxy evolution
The SPOTS Models: A Grid of Theoretical Stellar Evolution Tracks and Isochrones for Testing the Effects of Starspots on Structure and Colors

One-dimensional stellar evolution models have been successful at representing the structure and evolution of stars in diverse astrophysical contexts, but complications have been noted in the context of young, magnetically active stars, as well as close binary stars with significant tidal interactions. Numerous puzzles are associated with pre-main-sequence (pre-MS) and active main sequence (MS) stars, relating to their radii, their colors, certain elemental abundances, and the coevality of young clusters, among others. A promising explanation for these puzzles is the distorting effects of magnetic activity and starspots on the structure of active stars. To assist the community in evaluating this hypothesis, we present the Stellar Parameters of Tracks with Starspots (SPOTS) models, a grid of solar-metallicity stellar evolutionary tracks and isochrones that include a treatment of the structural effects of starspots. The models range from 0.1 to 1.3 M⊙ and from spotless to a surface covering fraction of 85%, and are evolved from the pre-MS to the red giant branch (or 15 Gyr). We also produce two-temperature synthetic colors for our models using empirically calibrated color tables. We describe the physical ingredients included in the SPOTS models and compare their predictions to other modern evolution codes. Finally, we apply these models to several open questions in the field of active stars, including the radii of young eclipsing binaries, the color scale of pre-MS stars, and the existence of sub-subgiants, demonstrating that our models can explain many peculiar features of active stars.

Keywords: young star clusters; starspots; magnetic stars; stellar ages; stellar properties; early stellar evolution; stellar evolution
Space-weather-driven Variations in Lyα Absorption Signatures of Exoplanet Atmospheric Escape: MHD Simulations and the Case of AU Mic b

We simulate the space environment around AU Microscopii b and the interaction between the magnetized stellar wind and a planetary atmospheric outflow for ambient stellar wind conditions and coronal mass ejection (CME) conditions. We also calculate synthetic Lyα absorption due to neutral hydrogen in the ambient and the escaping planetary atmosphere affected by this interaction. We find that the Lyα absorption is highly variable owing to the highly varying stellar wind conditions. A strong Doppler blueshift component is observed in the Lyα profile, in contradiction to the actual escape velocity observed in the simulations themselves. This result suggests that the strong Doppler blueshift is likely attributed to the stellar wind, not the escaping neutral atmosphere, either through its advection of neutral planetary gas or through the creation of a fast neutral flow via charge exchange between the stellar wind ions and the planetary neutrals. Indeed, our CME simulations indicate a strong stripping of magnetospheric material from the planet, including some of the neutral escaping atmosphere. Our simulations show that the pressure around close-in exoplanets is not much lower, and may be even higher, than the pressure at the top of the planetary atmosphere. Thus, the neutral atmosphere is hydrodynamically escaping with a very small velocity (<15 km s-1). Moreover, our simulations show that an MHD treatment is essential in order to properly capture the coupled magnetized stellar wind and the escaping atmosphere, despite the atmosphere being neutral. This coupling should be considered when interpreting Lyα observations in the context of exoplanets' atmospheric escape.

Keywords: stellar winds; exoplanet atmospheres; magnetohydrodynamics; star-planet interactions; magnetic fields
On the Origin of the Gamma-Ray Emission toward SNR CTB 37A with Fermi-LAT

The middle-aged supernova remnant (SNR) CTB 37A is known to interact with several dense molecular clouds through the detection of shocked H2 and OH 1720 MHz maser emission. In the present work, we use eight years of Fermi-LAT Pass 8 data, with an improved point-spread function and an increased acceptance, to perform detailed morphological and spectral studies of the γ-ray emission toward CTB 37A from 200 MeV to 200 GeV. The best fit of the source extension is obtained for a very compact Gaussian model with a significance of 5.75σ and a 68% containment radius of 0°116 ± 0°014stat ± 0°017sys above 1 GeV, which is larger than the TeV emission size. The energy spectrum is modeled as a LogParabola, resulting in a spectral index α = 1.92 ± 0.19 at 1 GeV and a curvature β = 0.18 ± 0.05, which becomes softer than the TeV spectrum above 10 GeV. The SNR properties, including a dynamical age of 6000 yr, are derived assuming the Sedov phase. From the multiwavelength modeling of emission toward the remnant, we conclude that the nonthermal radio and GeV emission is mostly due to the reacceleration of preexisting cosmic rays (CRs) by radiative shocks in the adjacent clouds. Furthermore, the observational data allow us to constrain the total kinetic energy transferred to the trapped CRs in the clouds. Based on these facts, we infer a composite nature for CTB 37A to explain the broadband spectrum and to elucidate the nature of the observed γ-ray emission.

Keywords: supernova remnants; galactic cosmic rays; non-thermal radiation sources
Minima Epoches of BF Draconis Observed by the TESS Satellite

The epochs of 80 minima from 2019 to 2022 of the eclipsing binary BF Dra have been measured from photometric fluxes obtained by the TESS satellite with uncertainties of 3 s and 6 s for primary and secondary minima, respectively. There is a clear negative linear trend of the interval length between primary and secondary minima, which confirms previous analyses that the system's orbit has an apsidal motion. It is found that the periastron advances 1.43 ± 0.03 deg/century, i.e., the apsidal period is U = 25,200 ± 500 yr. These values agree with previous estimates within the combined uncertainties but the present uncertainties are lower by a factor of eight. It is also confirmed that the residuals of the TESS-minima have a significant trend relative to a mean long-term apsidal motion signature due to a systematic influence of unknown origin.

Keywords: stellar astronomy
ethraid: A Simple Method for Characterizing Long-period Companions Using Doppler, Astrometric, and Imaging Constraints

We present ethraid, an open-source Python package designed to measure the mass (m c ) and separation (a) of a bound companion from measurements covering a fraction of the orbital period. ethraid constrains m c and a by jointly modeling radial velocity, astrometric, and/or direct imaging data in a Bayesian framework. Partial orbit data sets, especially those with highly limited phase coverage, are represented well by a few method-specific summary statistics. By modeling these statistics rather than the original data, ethraid optimizes computational efficiency with minimal reduction in accuracy. ethraid uses importance sampling to efficiently explore the often broad posteriors that arise from partial orbits. The core computations of ethraid are implemented in Cython for speed. We validate ethraid's performance by using it to constrain the masses and separations of the planetary companions to HD 117207 and TOI-1694. We designed ethraid to be both fast and simple, as well as to give broad, "quick look" constraints on companion parameters using minimal data. ethraid is pip installable and available on Zenodo and GitHub.

Keywords: exoplanets; bayesian statistics; brown dwarfs; radial velocity; astrometry; gaia; direct imaging
Detection of Rydberg Lines from the Atmosphere of Betelgeuse

Emission lines from Rydberg transitions are detected for the first time from a region close to the surface of Betelgeuse. The H30α line is observed at 231.905 GHz, with an FWHM ∼42 km s‑1 and extended wings. A second line at 232.025 GHz (FWHM ∼21 km s‑1 ), is modeled as a combination of Rydberg transitions of abundant low first ionization potential metals. Both H30α and the Rydberg combined line X30α are fitted by Voigt profiles, and collisional broadening with electrons may be partly responsible for the Lorentzian contribution, indicating electron densities of a few 108 cm‑3. X30α is located in a relatively smooth ring at a projected radius of 0.9× the optical photospheric radius R ⋆, whereas H30α is more clumpy, reaching a peak at ∼1.4 R ⋆. We use a semiempirical thermodynamic atmospheric model of Betelgeuse to compute the 232 GHz (1.29 mm) continuum and line profiles making simple assumptions. Photoionized abundant metals dominate the electron density, and the predicted surface of continuum optical depth unity at 232 GHz occurs at ∼1.3 R ⋆, in good agreement with observations. Assuming a Saha–Boltzmann distribution for the level populations of Mg, Si, and Fe, the model predicts that the X30α emission arises in a region of radially increasing temperature and turbulence. Inclusion of ionized C and non-LTE effects could modify the integrated fluxes and location of emission. These simulations confirm the identity of the Rydberg transition lines observed toward Betelgeuse and reveal that such diagnostics can improve future atmospheric models.

Keywords: red supergiant stars; stellar atmospheres; radio interferometry