adsabs/SciX_UAT_keywords huggingface dataset:
NaCl and KCl in Io's Atmosphere

We present the first comprehensive study of NaCl and KCl gases in Io's atmosphere in order to investigate their characteristics and infer properties of Io's volcanoes and subsurface magma chambers. In this work, we compile all past spectral line observations of NaCl and KCl in Io's atmosphere from the Atacama Large Millimeter/submillimeter Array and use atmospheric models to constrain the physical properties of the gases on several dates between 2012 and 2018. NaCl and KCl appear to be largely spatially confined, and for observations with high spectral resolution, the temperatures are high (~500-1000 K), implying a volcanic origin. The ratio of NaCl:KCl was found to be ~5-6 in 2015 June and ~3.5-10 in 2016 June, which is consistent with predictions based on observations of Io's extended atmosphere and less than half the Na/K ratio in chondrites. Assuming these gases are volcanic in origin, these ratios imply a magma temperature of ~1300 K, such that the magma will preferentially outgas KCl over NaCl.

Keywords: radio astronomy; galilean satellites; planetary atmospheres
A Method to Measure Photometries of Moderately Saturated UVOT Sources

For bright transients such as gamma-ray bursts (GRBs), the Ultra-Violet/Optical Telescope (UVOT) operates under event mode at early phases, which records incident positions and the arrival time for each photon. The event file is able to be screened into many exposures to study the early light curve of GRBs with a high time resolution, including the rapid brightening of the UV/optical emission in particular. Such a goal, however, is hampered for some extremely bright GRBs by the saturation in UVOT event images. For moderately saturated UVOT sources, in this work we further develop the method proposed in Jin et al. to recover their photometries. The basic idea is to assume a stable point-spread function of UVOT images, for which the counts in the core region (i.e., an aperture of a radius of 5″) and the wing region (i.e., an annulus ranging from 15″-25″) should be constant, and the intrinsic flux can be reliably inferred with data in the ring. We demonstrate that in a given band, a tight correlation does hold among the background-removed count rates in the core and the wing. With the new method, the bright limit of measuring range for UVOT V and B bands increases by ~1.7 mag, while only by ~0.7 mag for the U band due to the lack of bright calibration sources. Systematic uncertainties are ~0.2 mag for the V, B, and U bands.

Keywords: astronomical techniques; flux calibration; photometry
Lyman Continuum Emission from Active Galactic Nuclei at 2.3 ≲ z ≲ 3.7 in the UVCANDELS Fields

We present the results of our search for Lyman continuum (LyC)-emitting (weak) active galactic nuclei (AGN) at redshifts 2.3 ≲ z ≲ 4.9 from Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) F275W observations in the Ultraviolet Imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (UVCANDELS) fields. We also include LyC emission from AGN using HST WFC3 F225W, F275W, and F336W imaging found in Early Release Science (ERS) and Hubble Deep UV Legacy Survey data. We performed exhaustive queries of the Vizier database to locate AGN with high-quality spectroscopic redshifts. In total, we found 51 AGN that met our criteria within the UVCANDELS and ERS footprints. Out of these 51, we find 12 AGN that had ≥4σ detected LyC flux in the WFC3/UVIS images. Using a wide variety of space-based plus ground-based data, ranging from X-ray to radio wavelengths, we fit the multiwavelength photometric data of each AGN to a CIGALE spectral energy distribution (SED) using AGN models and correlate various SED parameters to the LyC flux. Kolmogorov–Smirnov tests of the SED parameter distributions for the LyC-detected and nondetected AGN showed they are likely not distinct samples. However, we find that the X-ray luminosity, star formation onset age, and disk luminosity show strong correlations relative to their emitted LyC flux. We also find strong correlations of the LyC flux to several dust parameters, i.e., polar and toroidal dust emission and 6 μm luminosity, and anticorrelations with metallicity and A FUV. We simulate the LyC escape fraction (f esc) using the CIGALE and intergalactic medium transmission models for the LyC-detected AGN and find an average f esc ≃ 18%, weighted by uncertainties. We stack the LyC fluxes of subsamples of AGN according to the wavelength continuum region in which they are detected and find no significant distinctions in their LyC emission, although our submillimeter-detected F336W sample (3.15 < z < 3.71) shows the brightest stacked LyC flux. These findings indicate that LyC production and escape in AGN are more complicated than the simple assumption of thermal emission and a 100% escape fraction. Further testing of AGN models with larger samples than presented here is needed.

Keywords: reionization; active galactic nuclei
Derivation of Instrument Requirements for Polarimetry Using Mg, Fe, and Mn Lines between 250 and 290 nm

Judge et al. recently argued that a region of the solar spectrum in the near-UV between about 250 and 290 nm is optimal for studying magnetism in the solar chromosphere, due to an abundance of Mg II, Fe II, and Fe I lines that sample various heights in the solar atmosphere. In this paper, we derive requirements for spectropolarimetric instruments to observe these lines. We derive a relationship between the desired sensitivity to magnetic field and the signal-to-noise ratio of the measurement from the weak-field approximation of the Zeeman effect. We find that many lines will exhibit observable polarization signals for both longitudinal and transverse magnetic field with reasonable amplitudes.

Keywords: solar chromosphere; spectropolarimetry; solar instruments; polarimeters
Can Carbon Fractionation Provide Evidence for Aerial Biospheres in the Atmospheres of Temperate Sub-Neptunes?

The search for signs of life on other worlds has largely focused on terrestrial planets. Recent work, however, argues that life could exist in the atmospheres of temperate sub-Neptunes. Here we evaluate the usefulness of carbon dioxide isotopologues as evidence of aerial life. Carbon isotopes are of particular interest, as metabolic processes preferentially use the lighter 12C over 13C. In principle, the upcoming James Webb Space Telescope (JWST) will be able to spectrally resolve the 12C and 13C isotopologues of CO2, but not CO and CH4. We simulated observations of CO2 isotopologues in the H2-dominated atmospheres of our nearest (<40 pc), temperate (equilibrium temperature of 250-350 K) sub-Neptunes with M-dwarf host stars. We find 13CO2 and 12CO2 distinguishable if the atmosphere is H2 dominated with a few percentage points of CO2 for the most idealized target with an Earth-like composition of the two most abundant isotopologues, 12CO2 and 13CO2. With a Neptune-like metallicity of 100× solar and a C/O of 0.55, we are unable to distinguish between 13CO2 and 12CO2 in the atmospheres of temperate sub-Neptunes. If atmospheric composition largely follows metallicity scaling, the concentration of CO2 in a H2-dominated atmosphere will be too low to distinguish CO2 isotopologues with JWST. In contrast, at higher metallicities, there will be more CO2, but the smaller atmospheric scale height makes the measurement impossible. Carbon dioxide isotopologues are unlikely to be useful biosignature gases for the JWST era. Instead, isotopologue measurements should be used to evaluate formation mechanisms of planets and exosystems.

Keywords: exoplanet atmospheres; biosignatures; astrobiology; mini neptunes
GECAM Detection of a Bright Type I X-Ray Burst from 4U 0614+09: Hint for Its Spin Frequency at 413 Hz

One month after launching the Gravitational Wave High-energy Electromagnetic Counterpart All-sky Monitor, a bright thermonuclear X-ray burst from 4U 0614+09 was observed on 2021 January 24. We report the time-resolved spectroscopy of the burst and a hint of burst oscillation at 413 Hz with a fractional amplitude ~2.0% (rms). This coincides with the burst oscillation previously discovered with Swift/Burst Alert Telescope (Strohmayer et al. 2008), and therefore supports the spin frequency of this source. This burst is a bright one in the normal bursts detected from 4U 0614+09, which leads to an upper limit of distance estimation of 3.1 kpc. The folded light curve during the burst oscillation shows a sinusoidal structure, which is consistent with previous observations.

Keywords: x-ray bursters
Rotational Spectrum and First Interstellar Detection of 2-methoxyethanol Using ALMA Observations of NGC 6334I

We use both chirped-pulse Fourier transform and frequency-modulated absorption spectroscopy to study the rotational spectrum of 2-methoxyethanol (CH3OCH2CH2OH) in several frequency regions ranging from 8.7 to 500 GHz. The resulting rotational parameters permitted a search for this molecule in Atacama Large Millimeter/submillimeter Array (ALMA) observations toward the massive protocluster NGC 6334I, as well as source B of the low-mass protostellar system IRAS 16293‑2422. A total of 25 rotational transitions are observed in the ALMA Band 4 data toward NGC 6334I, resulting in the first interstellar detection of 2-methoxyethanol. A column density of ${1.3}_{-0.9}^{+1.4}\times {10}^{17}$ cm‑2 is derived at an excitation temperature of ${143}_{-39}^{+31}$ K. However, molecular signal is not observed in the Band 7 data toward IRAS 16293‑2422B, and an upper-limit column density of 2.5 × 1015 cm‑2 is determined. Various possible formation pathways—including radical recombination and insertion reactions—are discussed. We also investigate physical differences between the two interstellar sources that could result in the observed abundance variations.

Keywords: interstellar molecules; astrochemistry; rotational spectroscopy
GPCAL: A Generalized Calibration Pipeline for Instrumental Polarization in VLBI Data

We present the Generalized Polarization CALibration pipeline (GPCAL), an automated pipeline for instrumental polarization calibration of very long baseline interferometry (VLBI) data. The pipeline is designed to achieve a high calibration accuracy by means of fitting the instrumental polarization model, including the second-order terms, to data from multiple calibrator sources simultaneously. It also allows for using more accurate linear polarization models of calibrators for D-term estimation compared to the conventional way that assumes similar linear polarization and total intensity structures. This assumption has been widely used in the existing packages for instrumental polarization calibration but could be a source of significant uncertainties when there is no suitable calibrator satisfying the assumption. We demonstrate the capabilities of GPCAL by using simulated data, archival Very Long Baseline Array (VLBA) data of many active galactic nucleus (AGN) jets at 15 and 43 GHz, and our Korean VLBI Network (KVN) observations of many AGN jets at 86, 95, 130, and 142 GHz. The pipeline could reproduce the complex linear polarization structures of several sources shown in the previous studies using the same VLBA data. In addition, GPCAL reveals a complex linear polarization structure in the flat-spectrum radio quasar 3C 273 from the KVN data at all four frequencies. These results demonstrate that GPCAL can achieve a high calibration accuracy for various VLBI arrays.

Keywords: very long baseline interferometry; polarimetry; astronomy software; astronomy data analysis
Probing the Extragalactic Mid-infrared Background with HAWC

The extragalactic background light (EBL) contains all the radiation emitted by nuclear and accretion processes in stars and compact objects since the epoch of recombination. Measuring the EBL density directly is challenging, especially in the near-to-far-infrared wave band, mainly due to the zodiacal light foreground. Instead, gamma-ray astronomy offers the possibility to indirectly set limits on the EBL by studying the effects of gamma-ray absorption in the very high energy (VHE: >100 GeV) spectra of distant blazars. The High Altitude Water Cherenkov Gamma Ray Observatory (HAWC) is one of the few instruments sensitive to gamma rays with energies above 10 TeV. This offers the opportunity to probe the EBL in the near/mid-IR region: λ = 1-100 μm. In this study, we fit physically motivated emission models to Fermi-LAT gigaelectronvolt data to extrapolate the intrinsic teraelectronvolt spectra of blazars. We then simulate a large number of absorbed spectra for different randomly generated EBL model shapes and calculate Bayesian credible bands in the EBL intensity space by comparing and testing the agreement between the absorbed spectra and HAWC extragalactic observations of two blazars. The resulting bands are in agreement with current EBL lower and upper limits, showing a downward trend toward higher wavelength values λ > 10 μm also observed in previous measurements.

Keywords: gamma-ray astronomy; diffuse radiation; blazars
Octofitter: Fast, Flexible, and Accurate Orbit Modeling to Detect Exoplanets

As next-generation imaging instruments and interferometers search for planets closer to their stars, they must contend with increasing orbital motion and longer integration times. These compounding effects make it difficult to detect faint planets but also present an opportunity. Increased orbital motion makes it possible to move the search for planets into the orbital domain, where direct images can be freely combined with the radial velocity and proper motion anomaly, even without a confirmed detection in any single epoch. In this paper, we present a fast and differentiable multimethod orbit-modeling and planet detection code called Octofitter. This code is designed to be highly modular and allows users to easily adjust priors, change parameterizations, and specify arbitrary function relations between the parameters of one or more planets. Octofitter further supplies tools for examining model outputs including prior and posterior predictive checks and simulation-based calibration. We demonstrate the capabilities of Octofitter on real and simulated data from different instruments and methods, including HD 91312, simulated JWST/NIRISS aperture masking interferometry observations, radial velocity curves, and grids of images from the Gemini Planet Imager. We show that Octofitter can reliably recover faint planets in long sequences of images with arbitrary orbital motion. This publicly available tool will enable the broad application of multiepoch and multimethod exoplanet detection, which could improve how future targeted ground- and space-based surveys are performed. Finally, its rapid convergence makes it a useful addition to the existing ecosystem of tools for modeling the orbits of directly imaged planets.

Keywords: exoplanet detection methods; bayesian statistics; direct imaging
The Variation in the Galaxy-wide Initial Mass Function for Low-mass Stars: Modeling and Observational Insights

The stellar initial mass function (IMF) characterizes the mass distribution of newly formed stars in various cosmic environments, serving as a fundamental assumption in astrophysical research. Recent findings challenge the prevalent notion of a universal and static IMF, proposing instead that the IMF's shape is contingent upon the star formation environment. In this study, we analyze the galaxy-wide variation in the IMF for low-mass stars in both dwarf and massive galaxies with diverse observational methods. Despite systematic discrepancies between different approaches, an IMF model with a metallicity-dependent slope for the low-mass stars aligns with the majority of observations, indicating a high degree of uniformity in the star formation processes across the Universe. We also emphasize the need for a more comprehensive understanding of the variation in the low-mass IMF, considering measurement biases and factors beyond metallicity.

Keywords: stellar populations; initial mass function; galaxy stellar content; early-type galaxies; star counts; galaxy chemical evolution; galaxy evolution; galaxy spectroscopy; metallicity; star formation
A Global Numerical Model of the Prompt Emission in Short Gamma-ray Bursts

We present the first global model of prompt emission from a short gamma-ray burst (GRB) that consistently describes the evolution of the central black hole (BH) torus system, the propagation of the jet through multicomponent merger ejecta, the transition into free expansion, and the photospheric emission from the relativistic jet. To this end, we perform a special relativistic neutrino-hydrodynamics simulation of a viscous BH-torus system, which is formed about 500 ms after the merger and is surrounded by dynamical ejecta as well as neutron star winds, along with a jet that is injected in the vicinity of the central BH. In a postprocessing step, we compute the photospheric emission using a relativistic Monte Carlo radiative transfer code. It is found that the wind from the torus leaves a strong imprint on the jet as well as on the emission, causing narrow collimation and rapid time variability. The dependence of the emission on viewing angle gives rise to correlations among the spectral peak energy, Ep, isotropic energy, Eiso, and peak luminosity, Lp, which may provide natural explanations for the Amati and Yonetoku relations. We also find that the degree of polarization is small for emission from the jet core (≲2%), while it tends to increase with viewing angle outside the core and can become as high as ~10%-40% for energies larger than the peak energy. Finally, the comparison of our model with GRB 170817A strongly disfavors the photospheric emission scenario and therefore supports alternative scenarios, such as cocoon shock breakout.

Keywords: gamma-ray bursts; radiative transfer simulations
A Multiplanet System's Sole Super-puff: Exploring Allowable Physical Parameters for the Cold Super-puff HIP 41378 f

The census of known exoplanets exhibits a variety of physical parameters, including densities that are measured to span the range from less dense than Styrofoam to more dense than iron. These densities represent a large diversity of interior structures. Despite this staggering diversity, recent analyses have shown that the densities of planets that orbit a common star exhibit remarkable uniformity. A fascinating exception to this is the system HIP 41378 (also known as K2-93), which contains a super-puff planet, HIP 41378 f, as well as several planets with more typical bulk densities. The range of densities in this system begs the question of what physical processes are responsible for the disparate planetary structures in this system. In this paper, we consider how the densities of the planets in the HIP 41378 system would have changed over time as the host star evolved and the planets' atmospheres were subsequently affected by the evolving insolation level. We also present a range of allowable core masses for HIP 41378 f based on the measured planet parameters, and we comment on the feasibility of the proposed existence of planetary rings around HIP 41378 f as an explanation for its current low density.

Keywords: exoplanet atmospheres; exoplanet evolution; exoplanet structure
Three-dimensional Magnetic and Thermodynamic Structures of Solar Microflares

Microflares, one of the small-scale solar activities, are believed to be caused by magnetic reconnection. Nevertheless, their three-dimensional (3D) magnetic structures, thermodynamic structures, and physical links to reconnection are unclear. In this Letter, based on a high-resolution 3D radiative magnetohydrodynamic simulation of the quiet Sun spanning from the upper convection zone to the corona, we investigate the 3D magnetic and thermodynamic structures of three homologous microflares. It is found that they originate from localized hot plasma embedded in the chromospheric environment at the height of 2-10 Mm above the photosphere and last for 3-10 minutes with released magnetic energy in the range of 1027-1028 erg. The heated plasma is almost cospatial with the regions where the heating rate per particle is maximal. The 3D velocity field reveals a pair of converging flows with velocities of tens of km s-1 moving toward and outflows with velocities of about 100 km s-1 moving away from the hot plasma. These features support magnetic reconnection playing a critical role in heating the localized chromospheric plasma to coronal temperature, giving rise to the observed microflares. The magnetic topology analysis further discloses that the reconnection region is located near quasi-separators where both current density and squashing factors are maximal although the specific topology may vary from a tether-cutting to fan-spine-like structure.

Keywords: solar flares; solar magnetic reconnection; solar coronal heating
Ultra-relativistic Electron Acceleration during High-intensity Long-duration Continuous Auroral Electrojet Activity Events

Magnetospheric relativistic electrons are accelerated during substorms and strong convection events that occur during high-intensity long-duration continuous auroral electrojet activity (HILDCAA) events, associated with solar wind high-speed streams (coming from coronal holes). From an analysis of ∼2–20 MeV electrons at L ∼ 2–7 measured by the Van Allen Probe satellite, it is shown that ∼3.4–4.1 days long HILDCAA events are characterized by ∼7.2 MeV electron acceleration in the L ∼ 4.0–6.0 region, which occurs ∼2.9–3.4 days after the onset of HILDCAA. The dominant acceleration process is due to wave–particle interactions between magnetospheric electromagnetic chorus waves and substorm-injected ∼100 keV electrons. The longer the HILDCAA and chorus last, the higher the maximum energy of the accelerated relativistic electrons. The acceleration to higher and higher energies is due to a bootstrap mechanism.

Keywords: van allen radiation belts; interplanetary magnetic fields; interplanetary medium; solar storm; solar coronal mass ejections; solar activity
The Structure and Origin of Switchbacks: Parker Solar Probe Observations

Switchbacks are rapid magnetic field reversals that last from seconds to hours. Current Parker Solar Probe (PSP) observations pose many open questions in regard to the nature of switchbacks. For example, are they stable as they propagate through the inner heliosphere, and how are they formed? In this work, we aim to investigate the structure and origin of switchbacks. In order to study the stability of switchbacks, we suppose the small-scale current sheets therein are generated by magnetic braiding, and they should work to stabilize the switchbacks. With more than 1000 switchbacks identified with PSP observations in seven encounters, we find many more current sheets inside than outside switchbacks, indicating that these microstructures should work to stabilize the S-shape structures of switchbacks. Additionally, we study the helium variations to trace the switchbacks to their origins. We find both helium-rich and helium-poor populations in switchbacks, implying that the switchbacks could originate from both closed and open magnetic field regions in the Sun. Moreover, we observe that the alpha-proton differential speeds also show complex variations as compared to the local Alfvén speed. The joint distributions of both parameters show that low helium abundance together with low differential speed is the dominant state in switchbacks. The presence of small-scale current sheets in switchbacks along with the helium features are in line with the hypothesis that switchbacks could originate from the Sun via interchange reconnection process. However, other formation mechanisms are not excluded.

Keywords: solar wind; interplanetary magnetic fields