adsabs/SciX_UAT_keywords huggingface dataset:
The Very Early Soft X-Ray Plateau of GRB 230307A: Signature of an Evolving Radiative Efficiency in Magnetar Wind Dissipation?

Very recently, a particularly long gamma-ray burst (GRB) 230307A was reported and proposed to originate from a compact binary merger based on its host galaxy property, kilonova, and heavy elements. More intriguingly, a very early plateau followed by a rapid decline in the soft X-ray band was detected in its light curve by the Lobster Eye Imager for Astronomy, indicating strong evidence of the existence of a magnetar as the merger product. This Letter explores the magnetar wind internal gradual magnetic dissipation model, in which the radiative efficiency evolves over time, and successfully fits it to the observed data. Our results reinforce the notion that the X-ray plateau serves as a powerful indicator of a magnetar and imply that an evolving efficiency is likely to be a common feature in X-ray plateaus of GRB afterglows. In addition, we also discuss the explanations for the prompt emission, GRB afterglows, as well as kilonova, and predict possible kilonova afterglows in a magnetar central engine.

Keywords: magnetars; gamma-ray bursts; compact binary stars
The Diffuse Ionized Gas Halo of the Large Magellanic Cloud

The Large Magellanic Cloud (LMC) has an extensive Hα emission halo that traces an extended, warm ionized component of its interstellar medium. Using the Wisconsin Hα Mapper telescope, we present the first kinematic Hα survey of an extensive region around the LMC, from (ℓ, b) = (264.°5, - 45.°5) to (295.°5, - 19.°5), covering +150 ≤ v LSR ≤ + 390 km s-1. We find that ionized hydrogen exists throughout the galaxy and extends several degrees beyond detected neutral hydrogen emission $(\mathrm{log}\left({N}_{{\rm{H}}\,{\rm\small{I}}/{\mathrm{cm}}^{-2}}\right)\approx 18.3)$ as traced by 21 cm in current surveys. Using the column density structure of the neutral gas and stellar line-of-sight depths as a guide, we estimate the upper limit mass of the ionized component of the LMC to be roughly M ionized ≈ (0.6-1.8) × 109 M ☉, which is comparable to the total neutral atomic gas mass in the same region (M neutral ≈ 0.76-0.85 × 109 M ☉). Considering only the atomic phases, we find M ionized/M ionized+neutral, to be 46%-68% throughout the LMC and its extended halo. Additionally, we find an ionized gas cloud that extends off of the LMC at (ℓ, b) ≈ (285°, - 28°) into a region previously identified as the Leading Arm complex. This gas is moving at a similar line-of-sight velocity as the LMC and has M ionized/M ionized+neutral = 13%-51%. This study, combined with previous studies of the SMC and extended structures of the Magellanic Clouds, continues to suggest that warm, ionized gas is as massive and dynamically important as the neutral gas in the Magellanic System.

Keywords: dwarf galaxies; large magellanic cloud; local group; galaxy kinematics; warm ionized medium; interstellar medium
Optical and Near-infrared Atmospheric Extinction Coefficients at La Silla

We used observations obtained at the Rapid Eye Mount (REM) at the La Silla Observatory between 2016 June 7 UT to determine the extinction coefficients of the REM filters currently in use. The observations were obtain on 6 nights, spanning 2016 June UT through 2016 July 4 UT, over a wide range of airmass values, to determine the mean atmospheric extinction coefficients at the La Silla Observatory site. Coefficients in the REM filter sets-Sloan g', r', i', z', and J, H and K were determined, where the REM infrared filters closely match those of the J, H, and Ks filters of the 2MASS All-Sky Survey.

Keywords: atmospheric extinction
Extremely Metal-poor Representatives Explored by the Subaru Survey (EMPRESS). I. A Successful Machine-learning Selection of Metal-poor Galaxies and the Discovery of a Galaxy with M* < 106 M⊙ and 0.016 Z⊙

We have initiated a new survey for local extremely metal-poor galaxies (EMPGs) with Subaru/Hyper Suprime-Cam (HSC) large-area (∼500 deg2) optical images reaching a 5σ limit of ∼26 mag, about 100 times deeper than the Sloan Digital Sky Survey (SDSS). To select Z/Z⊙ < 0.1 EMPGs from ∼40 million sources detected in the Subaru images, we first develop a machine-learning (ML) classifier based on a deep neural network algorithm with a training data set consisting of optical photometry of galaxy, star, and QSO models. We test our ML classifier with SDSS objects having spectroscopic metallicity measurements and confirm that our ML classifier accomplishes 86% completeness and 46% purity EMPG classifications with photometric data. Applying our ML classifier to the photometric data of the Subaru sources, as well as faint SDSS objects with no spectroscopic data, we obtain 27 and 86 EMPG candidates from the Subaru and SDSS photometric data, respectively. We conduct optical follow-up spectroscopy for 10 of our EMPG candidates with Magellan/LDSS-3+MagE, Keck/DEIMOS, and Subaru/FOCAS and find that the 10 EMPG candidates are star-forming galaxies at z = 0.007-0.03 with large Hβ equivalent widths of 104-265 Å, stellar masses of log( ${M}_{\star }$ / ${M}_{\odot }$ ) = 5.0-7.1, and high specific star formation rates of ∼300 Gyr-1, which are similar to those of early galaxies at z ≳ 6 reported recently. We spectroscopically confirm that 3 out of 10 candidates are truly EMPGs with Z/Z⊙ < 0.1, one of which is HSC J1631+4426, the most metal-poor galaxy, with Z/Z⊙ = 0.016, ever reported. * Partly based on data obtained with the Subaru Telescope. The Subaru Telescope is operated by the National Astronomical Observatory of Japan. † The data presented herein were partly obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. ‡ This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: galaxy evolution; galaxy formation; galaxy abundances; interstellar medium; emission nebulae
The Effect of Cosmic Rays on Cometary Nuclei. I. Dose Deposition

Comets are small bodies thought to contain the most pristine material in the solar system. However, since their formation ≈4.5 Gy ago, they have been altered by different processes. While not exposed to much electromagnetic radiation, they experience intense particle radiation. Galactic cosmic rays and solar energetic particles have a broad spectrum of energies and interact with the cometary surface and subsurface; they are the main source of space weathering for a comet in the Kuiper Belt or in the Oort Cloud, and also affect the ice prior to the comet agglomeration. While low-energy particles interact only with the cometary surface, the most energetic ones deposit a significant amount of energy down to tens of meters. This interaction can modify the isotopic ratios in cometary ices and create secondary compounds through radiolysis, such as O2 and H2O2 (Paper II). In this paper, we model the energy deposition of energetic particles as a function of depth using a Geant4 application modified to account for the isotope creation process. We quantify the energy deposited in cometary nucleus by galactic cosmic rays and solar energetic particles. The consequences of the energy deposition on the isotopic and chemical composition of cometary ices and their implication on the interpretation of cometary observations, notably of 67P/Churyumov Gerasimenko by the ESA Rosetta spacecraft, will be discussed in Paper II.

Keywords: comets; galactic cosmic rays; cosmic rays; solar energetic particles; pre-biotic astrochemistry
Localizing Stellar Activity on Low-mass Stars with the Transiting Exoplanet Survey Satellite

Magnetic reconnection is the underlying cause of stellar flares which are linked to regions of high magnetic activity, like star spots. To understand trends in stellar activity, we need to study how it is heightened by rapid rotation and deep convection in young low-mass stars. We analyze light curves of such stars observed by the Transiting Exoplanet Survey Satellite to investigate trends in flare timing with starspot modulation signals. Trends in flare properties and spot modulation can provide a means to "localize" which face of a star flares more frequently and better understand their association with active regions. We present an analysis of light curves from M and K dwarfs with no companions from five nearby and young moving groups spanning ages ∼20–150 Myr. We discuss a technique to analyze the distribution of flares and star spots and describe our results, which reveal a tentative correlation.

Keywords: low mass stars; stellar flares; optical flares; starspots; light curves; m stars; stellar astronomy; k stars
Magnetic Flux of Active Regions Determining the Eruptive Character of Large Solar Flares

We establish the largest eruptive/confined flare database to date and analyze 322 flares of Geostationary Operational Environmental Satellite class M1.0 and larger that occurred during 2010-2019, i.e., almost spanning all of solar cycle 24. We find that the total unsigned magnetic flux ( ${{\rm{\Phi }}}_{\mathrm{AR}}$ ) of active regions (ARs) is a key parameter governing the eruptive character of large flares, with the proportion of eruptive flares exhibiting a strong anticorrelation with ${{\rm{\Phi }}}_{\mathrm{AR}}$ . This means that an AR containing a large magnetic flux has a lower probability that the large flares it produces will be associated with a coronal mass ejection (CME). This finding is supported by the high positive correlation we obtained between the critical decay index height and ${{\rm{\Phi }}}_{\mathrm{AR}}$ , implying that ARs with a larger ${{\rm{\Phi }}}_{\mathrm{AR}}$ have a stronger magnetic confinement. Moreover, the confined flares originating from ARs larger than $1.0\times {10}^{23}$ Mx have several characteristics in common: stable filament, slipping magnetic reconnection, and strongly sheared post-flare loops. Our findings reveal new relations between the magnetic flux of ARs and the occurrence of CMEs in association with large flares. The relations obtained here provide quantitative criteria for forecasting CMEs and adverse space weather, and have important implications for "superflares" on solar-type stars and stellar CMEs.

Keywords: solar flares; solar activity; solar coronal mass ejections; stellar flares; solar magnetic fields; stellar coronal mass ejections
Rapidly Varying Anisotropic Methanol (CH3OH) Production in the Inner Coma of Comet 46P/Wirtanen as Revealed by the ALMA Atacama Compact Array

We report the detection of CH3OH emission in comet 46P/Wirtanen on UT 2018 December 8 and 9 using the Atacama Compact Array (ACA), part of the Atacama Large Millimeter/Submillimeter Array (ALMA). These interferometric measurements of CH3OH along with continuum emission from dust probed the inner coma (<2000 km from the nucleus) of 46P/Wirtanen approximately one week before its closest approach to Earth (Δ = 0.089-0.092 au), revealing rapidly varying and anisotropic CH3OH outgassing during five separate ACA executions between UT 23:57 December 7 and UT 04:55 December 9, with a clear progression in the spectral line profiles over a timescale of minutes. We present spectrally integrated flux maps, production rates, rotational temperatures, and spectral line profiles of CH3OH during each ACA execution. The variations in CH3OH outgassing are consistent with Wirtanen's 9 hr nucleus rotational period derived from optical and millimeter wavelength measurements and thus are likely coupled to the changing illumination of active sites on the nucleus. The consistent blue offset of the line center indicates enhanced CH3OH sublimation from the sunward hemisphere of the comet, perhaps from icy grains. These results demonstrate the exceptional capabilities of the ACA for time-resolved measurements of comets such as 46P/Wirtanen.

Keywords: molecular spectroscopy; high resolution spectroscopy; radio astronomy; comae; comets
Gender Disparity in Publishing Six Months after the KITP Workshop Probes of Transport in Stars

Conferences and workshops shape scientific discourse. The Kavli Institute for Theoretical Physics (KITP) hosts long-term workshops to stimulate scientific collaboration that would not otherwise have taken place. One goal of KITP programs is to increase diversity in the next generation of scientists. In this analysis, we examine gender trends in the authorship of papers that have been generated as a result of the KITP program Probes of Transport in Stars, which ran from 2021 October 11th to 2021 December 17th. While 38% of workshop participants were women, only 19% of publications produced between 2021 December 1st and 2022 June 3rd had female first-authors. Furthermore, of these early publications, 61% had all-male author lists. Among publications resulting from the KITP program, the proportions of both male first-author papers and papers with all-male author lists are higher than predicted by models that take into account the gender distribution of the KITP participants. These results motivate more thorough investigations of collaboration networks at scientific conferences and workshops. Importantly, they also suggest that programs, conferences, and workshops of any kind need to take steps beyond those implemented in this KITP program to enable more diverse collaborations and address gender disparities in science.

Keywords: sociology of astronomy
r-process Viable Outflows are Suppressed in Global Alpha-viscosity Models of Collapsar Disks

Collapsar disks have been proposed to be rich factories of heavy elements, but the major question of whether their outflows are neutron rich and could therefore represent significant sites of the rapid neutron-capture (r-) process or dominated by iron-group elements remains unresolved. We present the first global models of collapsars that start from a stellar progenitor and self-consistently describe the evolution of the disk, its composition, and its outflows in response to the imploding stellar mantle, using energy-dependent M1 neutrino transport and an α-viscosity to approximate turbulent angular-momentum transport. We find that a neutron-rich, neutrino-dominated accretion flow (NDAF) is established only marginally-either for short times or relatively low viscosities-because the disk tends to disintegrate into an advective disk already at relatively high mass-accretion rates, launching powerful outflows but preventing it from developing a hot, dense, and therefore neutron-rich core. Viscous outflows disrupt the star within ~100 s with explosion energies close to that of hypernovae. If viscosity is ignored, a stable NDAF with disk mass of about 1 M ☉ is formed but is unable to release neutron-rich ejecta, while it produces a relatively mild explosion powered by a neutrino-driven wind blown off its surface. With ejecta electron fractions close to 0.5, all models presumably produce large amounts of 56Ni. Our results suggest that collapsar models based on the α-viscosity are inefficient r-process sites and that genuinely magnetohydrodynamic effects may be required to generate neutron-rich outflows. A relatively weak effective viscosity generated by magnetohydrodynamic turbulence would improve the prospects for obtaining neutron-rich ejecta.

Keywords: core-collapse supernovae; explosive nucleosynthesis; r-process; gamma-ray bursts; black holes
Identifying Multiple Populations in M71 Using CN

We have observed the CN features at ∼3800 and 4120 Å as well as the CH band at ∼4300 Å for 145 evolved stars in the Galactic globular cluster M71 using the multi-object spectrograph, Hydra, on the Wisconsin-Indiana-Yale-NOAO-3.5 m telescope. We use these measurements to create two δCN indices finding that both distributions are best fit by two populations: a CN-enhanced and CN-normal. We find that 42% ± 4% of the red giant branch stars in our sample are CN-enhanced. The percentage of CN-enhanced is 40% ± 13% for the asymptotic giant branch and 33% ± 9% for the horizontal-branch stars (HB stars), which suggests there are no missing second generation stars at these stages of stellar evolution. The two generations also separate in magnitude and color on the HB, which allows us to find the difference in He abundance between the two populations by fitting appropriate zero-age horizontal branches. The broad range of distances from the cluster’s center covered by our sample allows us to study the dependence of the ratio of the number of first to second population stars on the distance from the cluster’s center, and we find that this ratio does not vary radially and that the two populations are spatially mixed. Finally, we compare our identification of multiple populations with the classification based on the Na-O anti-correlation and the Hubble Space Telescope UV photometry, and we find good agreement with both methods.

Keywords: globular star clusters; stellar astronomy; spectroscopy
A Novel Solution for Resonant Scattering Using Self-consistent Boundary Conditions

We present two novel additions to the semianalytic solution of Lyα radiative transfer in spherical geometry: (1) implementation of the correct boundary condition for a steady source, and (2) solution of the time-dependent problem for an impulsive source. For the steady-state problem, the solution can be represented as a sum of two terms: a previously known analytic solution of the equation with mean intensity J = 0 at the surface, and a novel, semianalytic solution which enforces the correct boundary condition of zero-ingoing intensity at the surface. This solution is compared to that of the Monte Carlo method, which is valid at arbitrary optical depth. It is shown that the size of the correction is of order unity when the spectral peaks approach the Doppler core and decreases slowly with line center optical depth, specifically as ${(a{\tau }_{0})}^{-1/3}$ , which may explain discrepancies seen in previous studies. For the impulsive problem, the time, spatial, and frequency dependence of the solution are expressed using an eigenfunction expansion in order to characterize the escape time distribution and emergent spectra of photons. It is shown that the lowest-order eigenfrequency agrees well with the decay rate found in the Monte Carlo escape time distribution at sufficiently large line center optical depths. The characterization of the escape time distribution highlights the potential for a Monte Carlo acceleration method, which would sample photon escape properties from distributions rather than calculating every photon scattering, thereby reducing computational demand.

Keywords: radiative transfer equation; radiative transfer; exoplanet atmospheres
The Implications of Thermal Hydrodynamic Atmospheric Escape on the TRAPPIST-1 Planets

JWST observations of the seven-planet TRAPPIST-1 system will provide an excellent opportunity to test outcomes of stellar-driven evolution of terrestrial planetary atmospheres, including atmospheric escape, ocean loss, and abiotic oxygen production. While most previous studies use a single luminosity evolution for the host star, we incorporate observational uncertainties in stellar mass, luminosity evolution, system age, and planetary parameters to statistically explore the plausible range of planetary atmospheric escape outcomes. We present probabilistic distributions of total water loss and oxygen production as a function of initial water content, for planets with initially pure water atmospheres and no interior–atmosphere exchange. We find that the interior planets are desiccated for initial water contents below 50 Earth oceans. For TRAPPIST-1e, f, g, and h, we report maximum water-loss ranges of , , , and Earth oceans, respectively, with corresponding maximum oxygen retention of , , , and bars. We explore statistical constraints on initial water content imposed by current water content, which could inform evolutionary history and planet formation. If TRAPPIST-1b is airless while TRAPPIST-1c possesses a tenuous oxygen atmosphere, as initial JWST observations suggest, then our models predict an initial surface water content of 8.2 Earth oceans for these worlds, leading to the outer planets retaining >1.5 Earth oceans after entering the habitable zone. Even if TRAPPIST-1c is airless, surface water on the outer planets would not be precluded.

Keywords: exoplanets; extrasolar rocky planets; exoplanet atmospheres; exoplanet atmospheric evolution
Nondetection of Helium in the Upper Atmospheres of Three Sub-Neptune Exoplanets

We present a search for helium in the upper atmospheres of three sub-Neptune-sized planets to investigate the origins of these ubiquitous objects. The detection of helium for a low-density planet would be strong evidence for the presence of a primary atmosphere accreted from the protoplanetary nebula because large amounts of helium are not expected in the secondary atmospheres of rocky planets. We used Keck+NIRSPEC to obtain high-resolution transit spectroscopy of the planets GJ 1214b, GJ 9827d, and HD 97658b around the 10833 Å He triplet feature. We did not detect helium absorption for any of the planets despite achieving a high level of sensitivity. We used the nondetections to set limits on the planets' thermosphere temperatures and atmospheric loss rates by comparing grids of 1D models to the data. We also performed coupled interior structure and atmospheric loss calculations, which suggest that the bulk atmospheres (winds) of the planets would be at most modestly enhanced (depleted) in helium relative to their primordial composition. Our lack of detections of the helium triplet for GJ 1214b and GJ 9827d is highly inconsistent with the predictions of models for the present-day mass loss on these planets. Higher signal-to-noise data would be needed to detect the helium feature predicted for HD 97658b. We identify uncertainties in the extreme-ultraviolet fluxes of the host stars and the lack of detailed mass-loss models specifically for cool and metal-enhanced atmospheres as the main limitations to the interpretation of our results. Ultimately, our results suggest that the upper atmospheres of sub-Neptune planets are fundamentally different from those of gas giant planets.

Keywords: exoplanet atmospheres; super earths; exoplanets; mini neptunes; exoplanet atmospheric composition
Magnetic Energy Balance in the Quiet Sun on Supergranular Spatial and Temporal Scales

Small-scale magnetic fields are ubiquitous in the quiet solar photosphere and may store and transfer huge amounts of energy to the upper atmospheric layers. For this reason, it is fundamental to constrain the energetics of the quiet Sun. By taking advantage of a 24 hr long magnetogram time series acquired by the Hinode mission without interruption, we computed, for the first time, the average rate of change of magnetic energy density on supergranular spatial and temporal scales. We found that the regions where this quantity is positive correspond with the longest magnetic field decorrelation times, with the latter being consistent with the timescales of magnetic energy density variation. This suggests that, on average, the energy provided by photospheric electric and magnetic fields and current density is effective in sustaining the magnetic fields in the network.

Keywords: solar photosphere; supergranulation; quiet sun; solar magnetic fields; space weather