adsabs/SciX_UAT_keywords huggingface dataset:
TOI-3235 b: A Transiting Giant Planet around an M4 Dwarf Star

We present the discovery of TOI-3235 b, a short-period Jupiter orbiting an M dwarf with a stellar mass close to the critical mass at which stars transition from partially to fully convective. TOI-3235 b was first identified as a candidate from TESS photometry and confirmed with radial velocities from ESPRESSO and ground-based photometry from HATSouth, MEarth-South, TRAPPIST-South, LCOGT, and ExTrA. We find that the planet has a mass of 0.665 ± 0.025 M J and a radius of 1.017 ± 0.044 R J. It orbits close to its host star, with an orbital period of 2.5926 days but has an equilibrium temperature of ≈ 604 K, well below the expected threshold for radius inflation of hot Jupiters. The host star has a mass of 0.3939 ± 0.0030 M ⊙, a radius of 0.3697 ± 0.0018 R ⊙, an effective temperature of 3389 K, and a J-band magnitude of 11.706 ± 0.025. Current planet formation models do not predict the existence of gas giants such as TOI-3235 b around such low-mass stars. With a high transmission spectroscopy metric, TOI-3235 b is one of the best-suited giants orbiting M dwarfs for atmospheric characterization.

Keywords: exoplanets; transit photometry; radial velocity; m dwarf stars
Maintaining Numerical Positivity in Strong Magnetized Astrophysical Shocks

Riemann solvers play a vital role in fluid dynamics simulations. Extreme cases, however, can generate artificially negative pressures and magnetic monopoles, destabilizing the solver. Here we couple the numerical scheme of Waagan that maintains positivity with the constrained transport method to solve the magnetohydrodynamics equations. This extends the applicability of the Waagan scheme to a wider range of problems, especially with large density and pressure gradients that occur widely in astrophysical problems.

Keywords: astrophysical fluid dynamics; magnetohydrodynamics; hydrodynamics
Fine-structure Transitions of Ne+, Ar+, Ne2+, and Ar2+ Induced by Collisions with Atomic Hydrogen

We calculate cross sections for fine-structure transitions of Ne+, Ar+, Ne2+, and Ar2+ in collisions with atomic hydrogen by using quantum-mechanical methods. Relaxation rate coefficients are calculated for temperatures up to 10,000 K. The temperature-dependent critical densities for the relaxation of Ne+, Ar+, Ne2+, and Ar2+ in collisions with H have been determined and compared to the critical densities for collisions with electrons. The present calculations will be useful for studies utilizing the infrared lines [Ne II] 12.8, [Ne III] 15.6, [Ne III] 36.0, [Ar II] 6.99, [Ar III] 8.99, and [Ar III] 21.8 μm as diagnostics of, for example, planetary nebulae and star formation.

Keywords: atomic physics
Investigating the Soft X-Ray Spectra of Solar Flare Onsets

In this study, we present the analysis of six solar flare events that occurred in 2022, using new data from the third-generation Miniature X-Ray Solar Spectrometer, also known as the Dual-zone Aperture X-ray Solar Spectrometer (DAXSS). The primary focus of this study is on the flare's onset phase, which is characterized by elevated soft X-ray emissions even before the flare's impulsive phase. We analyze the temporal evolution of plasma temperature, emission measure, and elemental abundance factors during the flare onset phase by fitting the DAXSS spectra with the Astrophysical Plasma Emission Code model. The model fitting results indicate that the flaring plasma is already at a high temperature (10–15 MK) during the onset period. The temperature rises during the onset phase, followed by a decrease and subsequent increase during the impulsive phase. Elemental abundance factors show a trend of falling below preflare values during the onset phase, with some recovery before the impulsive phase. During the impulsive phase, the abundance factors decrease from elevated coronal values to about photospheric values. We also analyze images from the 193 Å channel of the Atmospheric Imaging Assembly (AIA), highlighting the formation or brightening of coronal loop structures during the onset phase. Two distinct onset loop configurations are observed, which are referred to as one-loop and two-loop onsets. Both DAXSS and AIA observations indicate that the flare onset phase exhibits hot coronal plasma properties similar to those of the impulsive phase, suggesting that the onset phase may act as a preconditioning effect for some flares.

Keywords: solar corona; solar flare spectra; solar x-ray flares; solar abundances; solar x-ray emission
Carbon-grain Sublimation: A New Top-down Component of Protostellar Chemistry

Earth's carbon deficit has been an persistent problem in our understanding of the formation of our solar system. A possible solution would be the sublimation of carbon grains at the so-called soot line (∼300 K) early in the planet-formation process. Here, we argue that the most likely signatures of this process are an excess of hydrocarbons and nitriles inside the soot line, and a higher excitation temperature for these molecules compared to oxygen-bearing complex organics that desorb around the water snowline (∼100 K). Such characteristics have been reported in the literature, for example, in Orion KL, although not uniformly, potentially due to differences in the observational settings and analysis methods of different studies or the episodic nature of protostellar accretion. If this process is active, this would mean that there is a heretofore unknown component to the carbon chemistry during the protostellar phase that is acting from the top down—starting from the destruction of larger species—instead of from the bottom up from atoms. In the presence of such a top-down component, the origin of organic molecules needs to be re-explored.

Keywords: astrochemistry; protostars
CGM2 I: The Extent of the Circumgalactic Medium Traced by Neutral Hydrogen

We present initial results from the Cosmic Origins Spectrograph (COS) and Gemini Mapping the Circumgalactic Medium (CGMCGM ≡ CGM2) survey. The CGM2 survey consists of 1689 galaxies, all with high-quality Gemini-GMOS spectra, within 1 Mpc of 22 z ≲ 1 quasars, all with a signal-to-noise ratio of ∼10 Hubble Space Telescope/COS G130M+G160M spectra. For 572 of these galaxies with stellar masses 107 M⊙ < M⋆ < 1011 M⊙ and z ≲ 0.5, we show that the H I covering fraction above a threshold of NHI > 1014cm-2 is ≳0.5 within 1.5 virial radii (Rvir ∼ R200m). We examine the H I kinematics and find that the majority of absorption lies within ±250 km s-1 of the galaxy systemic velocity. We examine H I covering fractions over a range of impact parameters to infer a characteristic size of the CGM, ${R}_{\mathrm{CGM}}^{14}$ , as a function of galaxy mass. ${R}_{\mathrm{CGM}}^{14}$ is the impact parameter at which the probability of observing an absorber with NHI >1014 cm-2 is >50%. In this framework, the radial extent of the CGM of M⋆ > 109.9 M⊙ galaxies is ${R}_{\mathrm{CGM}}^{14}={346}_{-53}^{+57}$ kpc or ${R}_{\mathrm{CGM}}^{14}\simeq 1.2{R}_{\mathrm{vir}}$ . Intermediate-mass galaxies with 109.2 < M⋆/M⊙ < 109.9 have an extent of ${R}_{\mathrm{CGM}}^{14}={353}_{-50}^{+64}$ kpc or ${R}_{\mathrm{CGM}}^{14}\simeq 2.4{R}_{\mathrm{vir}}$ . Low-mass galaxies, M⋆ < 109.2 M⊙, show a smaller physical scale of ${R}_{\mathrm{CGM}}^{14}={177}_{-65}^{+70}$ kpc and extend to ${R}_{\mathrm{CGM}}^{14}\simeq 1.6{R}_{\mathrm{vir}}$ . Our analysis suggests that using Rvir as a proxy for the characteristic radius of the CGM likely underestimates its extent.

Keywords: circumgalactic medium; extragalactic astronomy; galaxy structure; quasar absorption line spectroscopy; intergalactic medium; astronomy databases; astronomy data analysis
[O IV]- and [Ne V]-weak Active Galactic Nuclei Hidden by Compton-thick Material in Late Mergers

We study "buried" active galactic nuclei (AGNs) almost fully covered by circumnuclear material in ultra/luminous infrared galaxies (U/LIRGs), which show weak ionized lines from narrow-line regions. Employing an indicator of a [O IV] 25.89 or [Ne V] 14.32 μm line to 12 μm AGN luminosity ratio, we find 17 buried AGN candidates that are [O IV]-weak (L [O IV]/L 12,AGN ≤ ‑3.0) or [Ne V]-weak (L [Ne V]/L 12,AGN ≤ ‑3.4) among 30 AGNs in local U/LIRGs. For the [O IV]-weak AGNs, we estimate their covering fractions of Compton-thick (CT; N H ≥ 1024 cm‑2) material with an X-ray clumpy torus model to be ${f}_{\mathrm{CT}}^{(\mathrm{spec})}=0.55\pm 0.19$ on average. This value is consistent with the fraction of CT AGNs ( ${f}_{\mathrm{CT}}^{(\mathrm{stat})}=53 \% \pm 12 \% $ ) among the [O IV]-weak AGNs in U/LIRGs and much larger than that in Swift/Burst Alert Telescope (BAT) AGNs (23% ± 6%). The fraction of [O IV]-weak AGNs increases from ${27}_{-10}^{+13} \% $ (early) to ${66}_{-12}^{+10} \% $ (late mergers). Similar results are obtained with the [Ne V] line. The [O IV]- or [Ne V]-weak AGNs in late mergers show larger N H and Eddington ratios (λ Edd) than those of the Swift/BAT AGNs, and the largest N H is ≳1025 cm‑2 at $\mathrm{log}{\lambda }_{\mathrm{Edd}}\sim -1$ , close to the effective Eddington limit for CT material. These suggest that (1) the circumnuclear material in buried AGNs is regulated by the radiation force from high-λ Edd AGNs on the CT obscurers, and (2) their dense material with large ${f}_{\mathrm{CT}}^{(\mathrm{spec})}$ (∼0.5 ± 0.1) in U/LIRGs is a likely cause of a unique structure of buried AGNs, whose amount of material may be maintained through merger-induced supply from their host galaxies.

Keywords: infrared galaxies; active galactic nuclei; x-ray active galactic nuclei; infrared astronomy; supermassive black holes
Imaging Titan's Organic Haze at Atomic Scale

Titan, Saturn's largest moon, has its atmosphere filled with a thick organic photochemical haze. These suspended solid nanoparticles are one of the most complex organic materials in the Solar System. In situ measurements from the successful Cassini space mission gave first clues on the aerosol's chemical composition: pyrolysis coupled to mass spectrometry revealed a nitrogen-rich core, whereas infrared measurements highlighted poly-aromatic-hydrocarbon (PAH) signatures. The combination of these observations supports a general model of nitrogenated-polycyclic aromatic hydrocarbon (N-PAH). To constrain the generic picture and understand the formation of such macromolecules in Titan's atmosphere, we simulated the haze synthesis in the laboratory. Small (3-10 rings) N-PAH molecules composing the material were extracted, focusing on the prime aromatization and growth processes. By high-resolution atomic force microscopy (AFM), we imaged key chemical structures with atomic resolution. We resolved N-rich elongated molecules involving five-membered aromatic rings, consistent with a repetitive cata-condensation pattern via addition of C3N units. These atomic-scale observations bridge the gap between gas phase atmospheric reactants and the macroscopic structure of Titan's haze.

Keywords: pre-biotic astrochemistry
Evaluating Rotation Periods of M Dwarfs across the Ages

In this work we examine M dwarf rotation rates at a range of ages to establish benchmarks for M dwarf gyrochronology. This work includes a sample of 713 spectroscopically classified M0-M8 dwarfs with new rotation rates measured from K2 light curves. We analyze data and recover rotation rates for 179 of these objects. We add these to rotation rates for members of clusters with known ages (5-700 Myr), as well as objects assumed to have field ages (≳1 Gyr). We use Gaia DR2 parallax and $(G\mbox{--}{G}_{\mathrm{RP}})$ photometry to create color-magnitude diagrams to compare objects across samples. We use color-period plots to analyze the period distributions across age, as well as incorporate Hα equivalent width and tangential velocity where possible to further comment on age dependence. We find that the age of transition from rapid to slow rotation in clusters, which we define as an elbow in the period-color plots, depends on spectral type. Later spectral types transition at older ages: M4 for Praesepe at ≈700 Myr, one of the oldest clusters for which M dwarf rotation rates have been measured. The transition from active to inactive Hα equivalent width also occurs at this elbow, as objects transition from rapid rotation to the slowly rotating sequence. Redder or smaller stars remain active at older ages. Finally, using Gaia kinematics we find evidence for rotation stalling for late Ms in the field sample, suggesting the transition happens much later for mid- to late-type M dwarfs.

Keywords: stellar rotation; m dwarf stars; stellar kinematics; stellar associations; stellar magnetic fields; light curves
Consolidated Rotation Measure Catalog Update

We identified discrepancies between the rotation measure (RM) catalogs by Clegg et al. and Minter & Spangler and their corresponding rows in the Van Eck et al. consolidated catalog. The discrepancies, in the case of Minter & Spangler, are caused by the improper coordinate conversions between J2000 and B1950 Equatorial coordinate systems used between the catalogs. The discrepancies associated with Clegg et al. are due to differences in the number of significant figures reported between the original and consolidated catalogs, which result in overlapping points in the consolidated catalog. These errors affect studies that rely on the accuracy of the coordinate data. After proper unit conversions, we found that coordinate values differed by up to 1° between the Minter & Spangler and consolidated catalogs. Employing a combination of manual data extraction and automated coordinate conversion tools, we corrected and updated those RM coordinate values to align with the standardized format used in the Van Eck et al. consolidated catalog.

Keywords: interstellar medium; interstellar magnetic fields; catalogs; radio source catalogs; radio astronomy
Distillation of 56Fe in Ultramassive O-Ne White Dwarfs

When white dwarfs freeze, the plasma mixtures inside them undergo separation processes that can produce radical changes in the composition profile of the star. The abundance of neutron-rich elements, such as 22Ne or 56Fe, determines whether or not the first crystals are more or less dense than the surrounding fluid and thus whether they sink or float. These processes have now been studied for C-O-Ne and C-O-Fe mixtures, finding that distillation and precipitation processes are possible in white dwarfs. In this work, we calculate the phase diagram of more complicated O-Ne-Fe mixtures and make predictions for the internal structure of the separated white dwarf. There are two possible outcomes determined by a complicated interplay between the Ne abundance, the 22Ne fraction, and the 56Fe abundance. Either Fe distills to form an inner core because the first O-Ne solids are buoyant, or an O-Ne inner core forms and Fe accumulates in the liquid until Fe distillation begins and forms an Fe shell. In the case of an Fe shell, a Rayleigh-Taylor instability may arise and overturn the core. In either case, Fe distillation may only produce a cooling delay of order 0.1 Gyr, as these processes occur early at high white dwarf luminosities. Fe inner cores and shells may be detectable through asteroseismology and could enhance the yield of neutron-rich elements such as 55Mn and 58Ni in supernovae.

Keywords: white dwarf stars; stellar evolution; stellar interiors; plasma physics; computational methods
Blind H I and OH Absorption Line Search: First Results with MALS and uGMRT Processed Using ARTIP

We present details of the Automated Radio Telescope Imaging Pipeline (ARTIP) and the results of a sensitive blind search for H I and OH absorbers at z < 0.4 and z < 0.7, respectively. ARTIP is written in Python 3.6, extensively uses the Common Astronomy Software Application tools and tasks, and is designed to enable the geographically distributed MeerKAT Absorption Line Survey (MALS) team to collaboratively process large volumes of radio interferometric data. We apply it to the first MALS data set obtained using the 64-dish MeerKAT radio telescope and 32 K channel mode of the correlator. With merely 40 minutes on target, we present the most sensitive spectrum of PKS 1830-211 ever obtained and characterize the known H I (z = 0.19) and OH (z = 0.89) absorbers. We further demonstrate ARTIP's capabilities to handle realistic observing scenarios by applying it to a sample of 72 bright radio sources observed with the upgraded Giant Metrewave Radio Telescope (uGMRT) to blindly search for H I and OH absorbers. We estimate the numbers of H I and OH absorbers per unit redshift to be n21(z ∼ 0.18) < 0.14 and nOH(z ∼ 0.40) < 0.12, respectively, and constrain the cold gas covering factor of galaxies at large impact parameters (50 kpc < ρ < 150 kpc) to be less than 0.022. Due to the small redshift path, Δz ∼ 13 for H I with column density >5.4 × 1019 cm-2, the survey has probed only the outskirts of star-forming galaxies at ρ > 30 kpc. MALS with the expected Δz ∼ 103-4 will overcome this limitation and provide stringent constraints on the cold gas fraction of galaxies in diverse environments over 0 < z < 1.5.

Keywords: quasar absorption line spectroscopy; radio loud quasars
A Rapidly Fading Star as a Type II Obscuring Intermediate Luminosity Optical Transient (ILOT) in a Triple-star System

We propose a triple-star scenario where the merger of two pre-main-sequence low-mass stars, ≲0.5 M ⊙, ejects a dusty equatorial outflow that obscures and temporarily causes the disappearance of a massive star, ≳8 M ⊙. The merger of the low-mass inner binary powers a faint outburst, i.e., a faint intermediate luminosity optical transient (ILOT), but its main effect that can last for decades is to (almost) disappear the luminous massive star of the triple system. The typical orbital period of the triple system is about 1 yr. The merger process proceeds as the more-massive star of the two low-mass pre-main-sequence stars starts to transfer mass to the least-massive star in the triple system and as a result of that expands. This type II obscuring ILOT scenario in a triple-star system might account for the fading, rebrightening, and then refading of the massive post-main-sequence star M101-OC1. It might recover in about 20-100 yr. Our study strengthens the claim that there are alternative scenarios to account for the (almost) disappearing of massive stars, removing the need for failed supernovae. In these scenarios the disappearing is temporary, lasting from months to decades, and therefore at a later time the massive star explodes as a core collapse supernova, even if it forms a black hole.

Keywords: variable stars; close binary stars; trinary stars; transient sources
The Study of Mode-switching Behavior of PSR J0614+2229 Using the Parkes Ultra–wide-bandwidth Receiver Observations

In this paper we present a detailed single-pulse and polarization study of PSR J0614+2229 based on the archived data observed on 2019 August 15 (MJD 58710) and 2019 September 12 (MJD 58738) using the ultra‑wide-bandwidth low-frequency receiver on the Parkes radio telescope. The single-pulse sequences show that this pulsar switches between two emission states, in which the emission of state A occurs earlier than that of state B in pulse longitude. We found that the variation in relative brightness between the two states varies temporally and both states follow a simple power law very well. Based on the phase-aligned multifrequency profiles, we found that there is a significant difference in the distributions of spectral index across the emission regions of the two states. Furthermore, we obtained the emission height evolution for the two emission states and found that, at a fixed frequency, the emission height of state A is higher than that of state B. What is even more interesting is that the emission heights of both states A and B do not change with frequency. Our results suggest that the mode switching of this pulsar is possibly caused by changes in the emission heights that alter the distributions of spectral index across the emission regions of states A and B, resulting in frequency-dependent behaviors, i.e., intensity and pulse width.

Keywords: radio pulsars; pulsars
Starspot Modulation Detected in the Detached Eclipsing Binary KIC 8301013

We investigate a short-period (P ≈ 4.4 days) eclipsing binary KIC 8301013 using high-quality Kepler photometry and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectroscopic data. Through the light-curve and radial-velocity synthesis using the Wilson-Devinney method, it reveals that the binary is an almost circular (e ≈ 0.001), detached system composed of two late F-type main-sequence stars, with masses and radii of ${M}_{1}=1.29\pm 0.02{M}_{\odot }$ , R1 = 1.45 ± 0.01R⊙ and M2 = 1.11 ± 0.05M⊙, R2 = 1.20 ± 0.01R⊙ for the primary and secondary, respectively. Besides the light variations due to the eclipses, the light curve shows quasi-sinusoidal variations that could be ascribed to starspot modulation. After removing the synthetic binary light curve from the detrended Kepler data, we measure the periods of the active region rotation by using the autocorrelation function (ACF) and Lomb-Scargle periodograms, the decay timescale of the active region by fitting the ACF of out-of-eclipse residuals, and the size of the active region represented by the rms scatter of the out-of-eclipse residuals. The activity level on the binary is significantly stronger than the Sun and has a better agreement with individual F-type stars. No periodic changes are detected in the active region evolution. Thus, KIC 8301013 is an interesting sample for the study of starspot modulation.

Keywords: eclipsing binary stars; starspots; stellar rotation
Nitrogen as a Tracer of Giant Planet Formation. I. A Universal Deep Adiabatic Profile and Semianalytical Predictions of Disequilibrium Ammonia Abundances in Warm Exoplanetary Atmospheres

A major motivation of spectroscopic observations of giant exoplanets is to unveil planet formation processes from atmospheric compositions. Several recent studies suggested that atmospheric nitrogen, like carbon and oxygen, can provide important constraints on planetary formation environments. Since nitrogen chemistry can be far from thermochemical equilibrium in warm atmospheres, we extensively investigate under what conditions, and with what assumptions, the observable NH3 abundances can diagnose an atmosphere's bulk nitrogen abundance. In the first paper of this series, we investigate atmospheric T-P profiles across equilibrium temperature, surface gravity, intrinsic temperature, atmospheric metallicity, and C/O ratio using a 1D radiative-convective equilibrium model. Models with the same intrinsic temperature and surface gravity coincide with a shared "universal" adiabat in the deep atmosphere, across a wide equilibrium temperature range (250-1200 K), which is not seen in hotter or cooler models. We explain this behavior in terms of the classic "radiative zero solution" and then establish a semianalytical T-P profile of the deep atmospheres of warm exoplanets. This profile is then used to predict vertically quenched NH3 abundances. At solar metallicity, our results show that the quenched NH3 abundance only coincides with the bulk nitrogen abundance (within 10%) at low intrinsic temperature, corresponding to a planet with a sub-Jupiter mass (≲1 M J) and old age (≳1 Gyr). If a planet has a high-metallicity (≳10× solar) atmosphere, the quenched NH3 abundance significantly underestimates the bulk nitrogen abundance at almost all planetary masses and ages. We suggest modeling and observational strategies to improve the assessment of bulk nitrogen from NH3.

Keywords: exoplanet atmospheres; exoplanet atmospheric structure; exoplanet atmospheric composition; chemical abundances