adsabs/SciX_UAT_keywords huggingface dataset:
The Enigmatic Abundance of Atomic Hydrogen in Saturn's Upper Atmosphere

A planet's Lyα emission is sensitive to its thermospheric structure. Here we report joint Hubble Space Telescope and Cassini cross-calibration observations of the Saturn Lyα emission made 2 weeks before the Cassini grand finale. To investigate the long-term Saturn Lyα airglow observed by different ultraviolet instruments, we cross-correlate their calibration, finding that while the official Cassini/UVIS sensitivity should be lowered by ~75%, the Voyager 1/UVS sensitivities should be enhanced by ~20% at the Lyα channels. This comparison also allowed us to discover a permanent feature of the Saturn disk Lyα brightness that appears at all longitudes as a brightness excess (Lyα bulge) of ~30% (~12σ) extending over the latitude range ~5°-35° N compared to the regions at equator and ~60° N. This feature is confirmed by three distinct instruments between 1980 and 2017 in the Saturn north hemisphere. To analyze the Lyα observations, we use a radiation transfer model of resonant scattering of solar and interplanetary Lyα photons and a latitude-dependent photochemistry model of the upper atmosphere constrained by occultation and remote-sensing observations. For each latitude, we show that the Lyα observations are sensitive to the temperature profile in the upper stratosphere and lower thermosphere, thus providing useful information in a region of the atmosphere that is difficult to probe by other means. In the Saturn Lyα bulge region, at latitudes between ~5° and ~35°, the observed brightening and line broadening support seasonal effects, variation of the temperature vertical profile, and potential superthermal atoms that require confirmation.

Keywords: planetary atmospheres; upper atmosphere; atmospheric structure; radiative transfer; flux calibration; ultraviolet telescopes; space telescopes; chemical kinetics; planetary ionospheres; interplanetary medium; solar spectral irradiance; solar ultraviolet emission
Radiation Process in Relativistic MHD Waves: The Case of Circularly Polarized Alfvén Waves

Turbulence in highly magnetized plasma can be relativistic and induce an electric field comparable to the background magnetic field. Such a strong electric field can affect the emission process of nonthermal electrons. As the first step toward elucidating the emission process in relativistic turbulence, we study the radiation process of electrons in relativistic circularly polarized Alfvén waves. While the induced electric field boosts the average energy of low-energy electrons with a Larmor radius smaller than the wavelength, the emissivity for such electrons is suppressed because of the elongated gyromotion trajectory. The trajectory of high-energy electrons is shaken by the small-scale electric field, which enhances the emissivity. Since the effective Lorentz factor of E × B drift is $\simeq \sqrt{2}$ in the circularly polarized Alfvén waves, the deviation from the standard synchrotron emission is not so prominent. However, a power-law energy injection in the waves can produce a concave photon spectrum, which is similar to the GeV extra component seen in GRB spectra. If the turbulence electric field is responsible for the GeV extra component in GRBs, the estimates of the typical electron energy and magnetic field should be largely altered.

Keywords: gamma-ray bursts
Wind Mass-loss Rates of Stripped Stars Inferred from Cygnus X-1

Recent observations of the high-mass X-ray binary Cygnus X-1 have shown that both the companion star (41 solar masses) and the black hole (21 solar masses) are more massive than previously estimated. Furthermore, the black hole appears to be nearly maximally spinning. Here, we present a possible formation channel for the Cygnus X-1 system that matches the observed system properties. In this formation channel, we find that the orbital parameters of Cygnus X-1, combined with the observed metallicity of the companion, imply a significant reduction in mass loss through winds relative to commonly used prescriptions for stripped stars.

Keywords: stellar mass black holes; high mass x-ray binary stars; stellar winds
Gems of the Galaxy Zoos-A Wide-ranging Hubble Space Telescope Gap-filler Program

We describe the Gems of the Galaxy Zoos (Zoo Gems) project, a gap-filler project using short windows in the Hubble Space Telescope's schedule. As with previous snapshot programs, targets are taken from a pool based on position; we combine objects selected by volunteers in both the Galaxy Zoo and Radio Galaxy Zoo citizen-science projects. Zoo Gems uses exposures with the Advanced Camera for Surveys to address a broad range of topics in galaxy morphology, interstellar-medium content, host galaxies of active galactic nuclei, and galaxy evolution. Science cases include studying galaxy interactions, backlit dust in galaxies, post-starburst systems, rings and peculiar spiral patterns, outliers from the usual color-morphology relation, Green Pea compact starburst systems, double radio sources with spiral host galaxies, and extended emission-line regions around active galactic nuclei. For many of these science categories, final selection of targets from a larger list used public input via a voting process. Highlights to date include the prevalence of tightly wound spiral structure in blue, apparently early-type galaxies, a nearly complete Einstein ring from a group lens, redder components at lower surface brightness surrounding compact Green Pea starbursts, and high-probability examples of spiral galaxies hosting large double radio sources. *This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from 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 program 15445.

Keywords: agn host galaxies; galaxy collisions; starburst galaxies; radio galaxies; ring galaxies
Strong Carbon Features and a Red Early Color in the Underluminous Type Ia SN 2022xkq

We present optical, infrared, ultraviolet, and radio observations of SN 2022xkq, an underluminous fast-declining Type Ia supernova (SN Ia) in NGC 1784 (D ≈ 31 Mpc), from <1 to 180 days after explosion. The high-cadence observations of SN 2022xkq, a photometrically transitional and spectroscopically 91bg-like SN Ia, cover the first days and weeks following explosion, which are critical to distinguishing between explosion scenarios. The early light curve of SN 2022xkq has a red early color and exhibits a flux excess that is more prominent in redder bands; this is the first time such a feature has been seen in a transitional/91bg-like SN Ia. We also present 92 optical and 19 near-infrared (NIR) spectra, beginning 0.4 days after explosion in the optical and 2.6 days after explosion in the NIR. SN 2022xkq exhibits a long-lived C I 1.0693 μm feature that persists until 5 days post-maximum. We also detect C II λ6580 in the pre-maximum optical spectra. These lines are evidence for unburnt carbon that is difficult to reconcile with the double detonation of a sub-Chandrasekhar mass white dwarf. No existing explosion model can fully explain the photometric and spectroscopic data set of SN 2022xkq, but the considerable breadth of the observations is ideal for furthering our understanding of the processes that produce faint SNe Ia.

Keywords: supernovae; white dwarf stars; type ia supernovae
The Sun's Magnetic (Hale) Cycle and 27 Day Recurrences in the aa Geomagnetic Index

We construct a new solar cycle phase clock which maps each of the last 18 solar cycles onto a single normalized epoch for the approximately 22 yr Hale (magnetic polarity) cycle, using the Hilbert transform of daily sunspot numbers (SSNs) since 1818. The occurrences of solar maxima show almost no discernible Hale cycle dependence, consistent with the clock being synchronized to polarity reversals. We reengineer the Sargent R27 index and combine it with our epoch analysis to obtain a high time resolution parameter for 27 day recurrence in aa, ⟨acv(27)⟩. This reveals that the transition to recurrence, that is, to an ordered solar wind dominated by high-speed streams, is fast, with an upper bound of a few solar rotations. It resolves an extended late declining phase which is approximately twice as long on even Schwabe cycles as odd. Galactic cosmic ray flux rises in step with ⟨acv(27)⟩ but then stays high. Our analysis also identifies a slow-timescale trend in SSN that simply tracks the Gleissberg cycle. We find that this trend is in phase with the slow-timescale trend in the modulus of sunspot latitudes, and in antiphase with that of the R27 index.

Keywords: solar cycle; sunspot cycle; space weather
Evidence for Spin-Orbit Alignment in the TRAPPIST-1 System

In an effort to measure the Rossiter-McLaughlin effect for the TRAPPIST-1 system, we performed high-resolution spectroscopy during transits of planets e, f, and b. The spectra were obtained with the InfraRed Doppler spectrograph on the Subaru 8.2 m telescope, and were supplemented with simultaneous photometry obtained with a 1 m telescope of the Las Cumbres Observatory Global Telescope. By analyzing the anomalous radial velocities, we found the projected stellar obliquity to be λ = 1 ± 28° under the assumption that the three planets have coplanar orbits, although we caution that the radial-velocity data show correlated noise of unknown origin. We also sought evidence for the expected deformations of the stellar absorption lines, and thereby detected the "Doppler shadow" of planet b with a false-alarm probability of 1.7%. The joint analysis of the observed residual cross-correlation map including the three transits gave $\lambda ={19}_{-15}^{+13}$ °. These results indicate that the the TRAPPIST-1 star is not strongly misaligned with the common orbital plane of the planets, although further observations are encouraged to verify this conclusion.

Keywords: transit photometry; high resolution spectroscopy; extrasolar rocky planets; radial velocity
Assessing the Cosmic Infrared Background Monopole from Far-infrared to Millimeter Wavelengths

We measured the cosmic infrared background (CIB) monopole for the COBE Diffuse Infrared Background Experiment (DIRBE) and Planck High-Frequency Instrument (HFI) bands with an updated model for the Galactic dust emission. This model includes a dust excess recently observed in 25% of the sky mainly at high latitude compared to the prediction from N H I. We correlated observations from COBE/DIRBE and Planck-HFI with this model to extract the zero levels of the sky maps. We corrected for the isotropic interplanetary dust (IPD) emission and calibration gains and obtained CIB values of 1.4 ± 8.0, 24.5 ± 3.9, 15.4 ± 4.9, 6.8 ± 2.0, 3.2 ± 0.3, 1.5 ± 0.1, 0.40 ± 0.05, 0.11 ± 0.04, 0.014 ± 0.027, and 0.008 ± 0.012 nW m‑2 sr‑1 at 60, 100, 140, and 240 μm, and 857, 545, 353, 217, 143, and 100 GHz. We compared those numbers with previous direct CIB measurements and extragalactic source counts. We obtain CIB values lower than previous measurements for wavelengths above 140 μm. Below this value, the large uncertainty related to the IPD emission prevents a clear interpretation.

Keywords: interstellar thermal emission; interstellar medium; dust continuum emission
Probing Dynamics and Thermal Properties Inside Molecular Tori with CO Rovibrational Absorption Lines

A recent hydrodynamic model, the radiation-driven fountain model (Wada et al. 2016), presented a dynamical picture that active galactic nuclei (AGNs) tori sustain their geometrical thickness by gas circulation around AGNs, and previous papers have confirmed that this picture is consistent with multiwavelength observations of nearby Seyfert galaxies. Recent near-infrared observations implied that CO rovibrational absorption lines (ΔJ = ± 1, v = 0 - 1, λ ~ 4.7 μm) could probe the physical properties of the inside tori. However, the origin of the CO absorption lines has been under debate. In this paper, we investigate the origin of the absorption lines and conditions for detecting them by performing line radiative transfer calculations based on the radiation-driven fountain model. We find that CO rovibrational absorption lines are detected at inclination angles θ obs = 50°-80°. At the inclination angle θ obs = 77°, we observe multi-velocity components: inflow (v LOS = 30 km s-1), systemic (v LOS = 0 km s-1), and outflows (v LOS = -75, - 95, and -105 km s-1). The inflow and outflow components (v LOS = 30 and -95 km s-1) are collisionally excited at the excitation temperatures of 186 and 380 K up to J = 12 and 4, respectively. The inflow and outflow components originate from the accreting gas on the equatorial plane at 1.5 pc from the AGN center and the outflowing gas driven by AGN radiation pressure at 1.0 pc, respectively. These results suggest that CO rovibrational absorption lines can provide us with the velocities and kinetic temperatures of the inflow and outflow in the inner few parsec region of AGN tori, and the observations can probe the gas circulation inside the tori.

Keywords: active galactic nuclei; infrared astronomy; radiative transfer simulations
Photometric Masses of Eclipsing Binary Components

Eclipsing binaries allow the study of physical stellar parameters in a model-independent way, when photometric and spectroscopic data are combined. However, when spectroscopic data are not available, purely photometric methods can be adopted to first estimate stellar properties, especially for large samples. Cruz et al. have then characterized components of detached EB systems from photometric colors and light curves from the literature, with the purpose of estimating trends from statistical values. An inflation trend of around 20% was estimated, which is in agreement with several results from the literature. As a response to MacDonald & Mullan, the obtained values for individual systems should not be analyzed separately, since they could mislead the results. We encourage further spectroscopic measurements to verify the values estimated from the photometric method.

Keywords: photometry; eclipsing binary stars
Characterization of Population III Stars with Stellar Atmosphere and Evolutionary Modeling and Predictions of their Observability with the JWST

Population III stars were the first stars to form after the Big Bang and are believed to have made the earliest contribution to the metal content of the universe beyond the products of the Big Bang nucleosynthesis. These stars are theorized to have had extremely short life spans and therefore would only be observable at high redshifts (z ≥ 3-17) and faint apparent magnitudes (m AB ≳ 40). The direct detection of Population III stars therefore remains elusive. However, the recently launched James Webb Space Telescope (JWST) may be capable of detecting stars in the relevant magnitude range in the event of favorable gravitational lensing. Theoretical models are required to interpret these future observations. In this study, new evolutionary models and nonequilibrium model atmospheres were used to characterize the observable properties of zero-age main-sequence Population III stars. The calculated models cover a wide range of possible Population III stellar masses, from the minimum mass predicted by star formation studies to the maximum mass capable of maintaining hydrostatic equilibrium. Synthetic photometry and theoretical color-magnitude diagrams were calculated for the bands of the Near-Infrared Camera (NIRCam) on the JWST. The final results are compared to the scales of known lensing events and JWST magnitude limits. The purpose of this study is to calculate the observable parameters of Population III stars in the most optimal JWST bands in order to provide a theoretical foundation for anticipated future observations of this stellar population.

Keywords: gravitational lensing; theoretical models; limiting magnitude; population iii stars; proton-proton reaction; carbon-nitrogen cycle
Reprocessing Models for the Optical Light Curves of Hypervariable Quasars from the Sloan Digital Sky Survey Reverberation Mapping Project

We explore reprocessing models for a sample of 17 hypervariable quasars, taken from the Sloan Digital Sky Survey Reverberation Mapping project, which all show coordinated optical luminosity hypervariability with amplitudes of factors ≳2 between 2014 and 2020. We develop and apply reprocessing models for quasar light curves in simple geometries that are likely to be representative of quasar inner environments. In addition to the commonly investigated thin-disk model, we include the thick-disk and hemisphere geometries. The thick-disk geometry could, for instance, represent a magnetically elevated disk, whereas the hemisphere model can be interpreted as a first-order approximation for any optically thick out-of-plane material caused by outflows/winds, warped/tilted disks, and so on. Of the 17 quasars in our sample, 11 are best-fitted by a hemisphere geometry, five are classified as thick disks, and both models fail for just one object. We highlight the successes and shortcomings of our thermal reprocessing models in case studies of four quasars that are representative of the sample. While reprocessing is unlikely to explain all of the variability that we observe in quasars, we present our classification scheme as a starting point for revealing the likely geometries of reprocessing for quasars in our sample and hypervariable quasars in general.

Keywords: quasars; active galactic nuclei; supermassive black holes; accretion
Patchy Forsterite Clouds in the Atmospheres of Two Highly Variable Exoplanet Analogs

We present an atmospheric retrieval analysis of a pair of highly variable, ~200 Myr old, early T type planetary-mass exoplanet analogs SIMP J01365662+0933473 and 2MASS J21392676+0220226 using the Brewster retrieval framework. Our analysis, which makes use of archival 1-15 μm spectra, finds almost identical atmospheres for both objects. For both targets, we find that the data is best described by a patchy, high-altitude forsterite (Mg2SiO4) cloud above a deeper, optically thick iron (Fe) cloud. Our model constrains the cloud properties well, including the cloud locations and cloud particle sizes. We find that the patchy forsterite slab cloud inferred from our retrieval may be responsible for the spectral behavior of the observed variability. Our retrieved cloud structure is consistent with the atmospheric structure previously inferred from spectroscopic variability measurements, but clarifies this picture significantly. We find consistent C/O ratios for both objects, which supports their formation within the same molecular cloud in the Carina-Near moving group. Finally, we note some differences in the constrained abundances of H2O and CO, which may be caused by data quality and/or astrophysical processes such as auroral activity and their differing rotation rates. The results presented in this work provide a promising preview of the detail with which we will characterize extrasolar atmospheres with JWST, which will yield higher-quality spectra across a wider wavelength range.

Keywords: brown dwarfs; t dwarfs; exoplanet atmospheres; exoplanet atmospheric composition; exoplanet astronomy; exoplanet atmospheric variability
A Tempered Fractional Kinetic Transport Theory for Energetic Particle Interaction with Quasi-two-dimensional Turbulence in the Large-scale Solar Wind

Observational evidence is accumulating that turbulence in the solar wind is intermittent (non-Gaussian) because of the strong presence of a quasi-two-dimensional (quasi-2D), low-frequency turbulence component containing nonpropagating, closed, small-scale magnetic flux ropes with open meandering field lines in between. le Roux & Zank showed how one can derive fractional focused and Parker-type transport equations that model large-scale anomalous transport in the solar wind as the outcome of energetic particle interaction with quasi-2D turbulence. In this follow-up paper this theory is developed further to address certain limitations. (i) The second moment of the Lévy probability distribution function (PDF) specified in the theory for the particle step size is infinite, indicating unphysical transport. (ii) The expected transition of energetic particle transport from anomalous to normal diffusion beyond a certain critical transport distance was not included. (iii) The competition between anomalous diffusion and advection is not properly sustained at late times. Shortcomings (i) and (ii) are addressed by introducing an exponentially truncated Lévy PDF for the energetic particle step size in the theory, resulting in revised tempered fractional focused and Parker-type transport equations featuring tempered fractional derivatives that enable modeling of tempered Lévy flights. Furthermore, these equations are cast in a tempered fractional telegrapher form to investigate whether the fractional wave equation part of the equation can restore causality in unscattered particle transport during early times and in Lévy flights during intermediate times (Lévy walks). They are also transformed into a tempered fractional Fokker–Planck form to overcome limitation (iii).

Keywords: solar wind; interplanetary turbulence; solar energetic particles; interplanetary particle acceleration
The Trigger Mechanism of Recurrent Solar Active Region Jets Revealed by the Magnetic Properties of a Coronal Geyser Site

Solar active region jets are small-scale collimated plasma eruptions that are triggered from magnetic sites embedded in sunspot penumbral regions. Multiple trigger mechanisms for recurrent jets are under debate. Vector magnetic field data from Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) observations are used to analyze a prolific photospheric configuration, identified in extreme ultraviolet observations as a "coronal geyser," that triggered a set of at least 10 recurrent solar active region jets. We focus on interpreting the magnetic fields of small-scale flaring sites aiming to understand the processes that govern recurrent jet eruptions. We perform a custom reprocessing of the SDO-HMI products, including disambiguation and uncertainty estimation. We scrutinized the configuration and dynamics of the photospheric magnetic structures. The magnetic configuration is described, via the analysis of the photospheric magnetic vertical fields, to identify the process that is responsible for driving the jet eruptions. We report that the two widely debated magnetic trigger processes, namely magnetic flux cancellation and magnetic flux emergence, appear to be responsible on a case by case basis for generating each eruption in our set. We find that 4 out of 10 jets were due to flux cancellation, while the rest were clearly not and were more likely due to flux emergence.

Keywords: solar photosphere; solar activity; solar magnetic reconnection; solar magnetic fields; astronomy data analysis; solar magnetic flux emergence