adsabs/SciX_UAT_keywords huggingface dataset:
Hydroxide Salts in the Clouds of Venus: Their Effect on the Sulfur Cycle and Cloud Droplet pH

The depletion of SO2 and H2O in and above the clouds of Venus (45-65 km) cannot be explained by known gas-phase chemistry and the observed composition of the atmosphere. We apply a full-atmosphere model of Venus to investigate three potential explanations for the SO2 and H2O depletion: (1) varying the below-cloud water vapor (H2O), (2) varying the below-cloud sulfur dioxide (SO2), and (3) the incorporation of chemical reactions inside the sulfuric acid cloud droplets. We find that increasing the below-cloud H2O to explain the SO2 depletion results in a cloud top that is 20 km too high, above-cloud O2 three orders of magnitude greater than observational upper limits, and no SO above 80 km. The SO2 depletion can be explained by decreasing the below-cloud SO2 to 20 ppm. The depletion of SO2 in the clouds can also be explained by the SO2 dissolving into the clouds, if the droplets contain hydroxide salts. These salts buffer the cloud pH. The amount of salts sufficient to explain the SO2 depletion entails a droplet pH of ~1 at 50 km. Because sulfuric acid is constantly condensing out into the cloud droplets, there must be a continuous and pervasive flux of salts of ≈10-13 mol cm-2 s-1 driving the cloud droplet chemistry. An atmospheric probe can test both of these explanations by measuring the pH of the cloud droplets and the concentrations of gas-phase SO2 below the clouds.

Keywords: venus; planetary atmospheres; water vapor
Study of the Spiral Structure in Galaxies with Multiple Arms: A Preliminary Analysis in NGC 1084 and NGC 3464

We performed a morphological analysis of the spiral structure in two specific galaxies: NGC 1084 and NGC 3464. The main objective of this research is to gain a deeper understanding of the distribution of the spiral structure in disk galaxies by studying their spiral patterns. We applied the two-dimensional fast Fourier transform method and conducted a detailed review of the Fourier spectra and radial density functions (RDFs) to analyze their patterns and characteristics. The initial results reveal that the main modes in the distribution of the spiral arms are m = 1 and m = 2, indicating symmetry. Additionally, specific areas in the RDF are detected where other modes, such as m = 3 and m = 4, exhibit higher relevance, indicating the presence of multiple spiral structures (bifurcations or segments).

Keywords: spiral galaxies; spiral arms
A Systematic Study of Associations between Supernova Remnants and Molecular Clouds

We universally search for evidence of kinematic and spatial correlation of supernova remnant (SNR) and molecular cloud (MC) associations for nearly all SNRs in the coverage of the Milky Way Imaging Scroll Painting CO survey, i.e., 149 SNRs, 170 SNR candidates, and 18 pure pulsar wind nebulae in 1° < l < 230° and -5.°5 < b < 5.°5. Based on high-quality and unbiased 12CO/13CO/C18O (J = 1-0) survey data, we apply automatic algorithms to identify broad lines and spatial correlations for molecular gas in each SNR region. The 91% of SNR-MC associations detected previously are identified in this paper by CO line emission. Overall, there could be as high as 80% of SNRs associated with MCs. The proportion of SNRs associated with MCs is high within the Galactic longitude less than ~50°. Kinematic distances of all SNRs that are associated with MCs are estimated based on systemic velocities of associated MCs. The radii of SNRs associated with MCs follow a lognormal distribution, which peaks at ~8.1 pc. The progenitor initial mass of these SNRs follows a power-law distribution with an index of ~-2.3 that is consistent with the Salpeter index of -2.35. We find that SNR-MC associations are mainly distributed in a thin disk along the Galactic plane, while a small number are distributed in a thick disk. With the height of these SNRs from the Galactic plane below ~45 pc, the distribution of the average radius relative to the height of them is roughly flat, and the average radius increases with the height when above ~45 pc.

Keywords: interstellar medium; supernova remnants; molecular clouds; galaxy structure
Determining the Core Structure and Nuclear Equation of State of Rotating Core-collapse Supernovae with Gravitational Waves by Convolutional Neural Networks

Detecting gravitational waves from a nearby core-collapse supernova would place meaningful constraints on the supernova engine and nuclear equation of state. Here we use convolutional neural network models to identify the core rotational rates, rotation length scales, and the nuclear equation of state (EoS), using the 1824 waveforms from Richers et al. for a 12 solar mass progenitor. A high prediction accuracy for the classifications of the rotation length scales (93%) and the rotational rates (95%) can be achieved using the gravitational-wave signals from -10 to 6 ms core bounce. By including an additional 48 ms signal during the prompt convection phase, we could achieve an accuracy of 96% in the classification of the four main EoS groups. By combining the three models above, we could correctly predict the core rotational rates, rotation length scales, and the EoS at the same time with an accuracy of more than 85%. Finally, applying a transfer-learning method for an additional 74 waveforms from FLASH simulations, we show that our model using Richers' waveforms could successfully predict the rotational rates from Pan's waveforms even for a continuous value with mean absolute errors of 0.32 rad s-1 only. These results demonstrate the much broader parameter regimes to which our model can be applied to identify core-collapse supernova events through gravitational-wave signals.

Keywords: gravitational wave astronomy; core-collapse supernovae; black holes; neutron stars
The Far Side of the Galactic Bar/Bulge Revealed through Semi-regular Variables

The Galactic bulge is critical to our understanding of the Milky Way. However, due to the lack of reliable stellar distances, the structure and kinematics of the bulge/bar beyond the Galactic center have remained largely unexplored. Here, we present a method to measure distances of luminous red giants using a period-amplitude-luminosity relation anchored to the Large Magellanic Cloud, with random uncertainties of 10%-15% and systematic errors below 1%-2%. We apply this method to data from the Optical Gravitational Lensing Experiment to measure distances to 190,302 stars in the Galactic bulge and beyond out to 20 kpc. Using this sample, we measure a distance to the Galactic center of R 0 = 8108 ± 106stat ± 93sys pc, consistent with direct measurements of stars orbiting Sgr A*. We cross-match our distance catalog with Gaia DR3 and use the subset of 39,566 overlapping stars to provide the first constraints on the Milky Way's velocity field (V R , V ϕ , V z ) beyond the Galactic center. We show that the V R quadrupole from the bar's near side is reflected with respect to the Galactic center, indicating that the bar is bisymmetric and aligned with the inner disk. We also find that the vertical height V Z map has no major structure in the region of the Galactic bulge, which is inconsistent with a current episode of bar buckling. Finally, we demonstrate with N-body simulations that distance uncertainty plays a factor in the alignment of the major and kinematic axes of the bar, necessitating caution when interpreting results for distant stars.

Keywords: asteroseismology; galactic archaeology; galactic bulge
Dynamics of Photospheric Magnetic Flux Distribution and Variations in Solar RVs: A Study Using HARPS-N Solar and SDO Observations

The distribution and evolution of photospheric magnetic fields in sunspots, plages, and network, and variations in their relative flux content, play key roles in radial velocity (RV) fluctuations observed in Sun-as-a-star spectra. Differentiating and disentangling such magnetic contributions to RVs help in building models to account for stellar activity signals in high-precision RV exoplanet searches. In this work, as earlier authors, we employ high-resolution images of the solar magnetic field and continuum intensities from SDO/HMI to understand the activity contributions to RVs from HARPS-N solar observations. Using well-observed physical relationships between strengths and fluxes of photospheric magnetic fields, we show that the strong fields (spots, plages, and network) and the weak inter-network fields leave distinguishing features in their contributions to the RV variability. We also find that the fill factors and average unsigned magnetic fluxes of different features correlate differently with the RVs and hence warrant care in employing either of them as a proxy for RV variations. In addition, we examine disk-averaged UV intensities at 1600 and 1700 Å wavelength bands imaged by SDO/AIA and their performances as proxies for variations in different magnetic features. We find that the UV intensities provide a better measure of contributions of plage fields to RVs than the Ca II H-K emission indices, especially during high activity levels when the latter tend to saturate.

Keywords: solar photosphere; radial velocity; solar activity; solar active region magnetic fields
On Estimating the Cosmic Molecular Gas Density from CO Line Intensity Mapping Observations

The Millimeter-wave Intensity Mapping Experiment (mmIME) recently reported a detection of excess spatial fluctuations at a wavelength of 3 mm, which can be attributed to unresolved emission of several CO rotational transitions between z ~ 1 and 5. We study the implications of these data for the high-redshift interstellar medium using a suite of state-of-the-art semianalytic simulations that have successfully reproduced many other submillimeter line observations across the relevant redshift range. We find that the semianalytic predictions are mildly in tension with the mmIME result, with a predicted CO power ~3.5σ below what was observed. We explore some simple modifications to the models that could resolve this tension. Increasing the molecular gas abundance at the relevant redshifts to ~108 M ⊙ Mpc-3, a value well above that obtained from directly imaged sources, would resolve the discrepancy, as would assuming a CO-H2 conversion factor α CO of ~1.5 M ⊙ K-1 (km s-1)-1 pc2, a value somewhat lower than is commonly assumed. We go on to demonstrate that these conclusions are quite sensitive to the detailed assumptions of our simulations, highlighting the need for more careful modeling efforts as more intensity mapping data become available.

Keywords: galaxy evolution; molecular gas; co line emission; surveys
Magnetic Flux and Magnetic Nonpotentiality of Active Regions in Eruptive and Confined Solar Flares

With the aim of understanding how the magnetic properties of active regions (ARs) control the eruptive character of solar flares, we analyze 719 flares of Geostationary Operational Environmental Satellite (GOES) class ≥C5.0 during 2010-2019. We carry out the first statistical study that investigates the flare-coronal mass ejection (CME) association rate as a function of the flare intensity and the AR characteristics that produce the flare, in terms of its total unsigned magnetic flux (ΦAR). Our results show that the slope of the flare-CME association rate with flare intensity reveals a steep monotonic decrease with ΦAR. This means that flares of the same GOES class but originating from an AR of larger ΦAR, are much more likely to be confined. Based on an AR flux as high as 1.0 × 1024 Mx for solar-type stars, we estimate that the CME association rate in X100-class "superflares" is no more than 50%. For a sample of 132 flares ≥M2.0 class, we measure three nonpotential parameters including the length of steep gradient polarity-inversion line (LSGPIL), the total photospheric free magnetic energy (Efree), and the area with large shear angle (AΨ). We find that confined flares tend to have larger values of LSGPIL, Efree, and AΨ compared to eruptive flares. Each nonpotential parameter shows a moderate positive correlation with ΦAR. Our results imply that ΦAR is a decisive quantity describing the eruptive character of a flare, as it provides a global parameter relating to the strength of the background field confinement.

Keywords: solar activity; solar active region magnetic fields; solar flares; solar coronal mass ejections; stellar activity
Not That Simple: The Metallicity Dependence of the Wide Binary Fraction Changes with Separation and Stellar Mass

The metallicity dependence of the wide binary fraction (WBF) is critical for studying the formation of wide binaries. While controversial results have been found in recent years, here we combine the wide binary catalog recognized from Gaia EDR3 and stellar parameters from LAMOST to investigate this topic. Taking the bias of the stellar temperature at given separations into account, we find that the relationship between the WBF and metallicity depends on the temperature for the thin disk at s > 200 au. It changes from negative to positive as the temperature increases from 4000 to 7500 K. This temperature/mass dependence is not seen for the thick disk. Besides, the general tendency between the WBF and metallicity varies with the separation, consistent with previous results. It shows anticorrelation at small separations, s < 200 au for the thin disk and s < 600 au for the thick disk. Then it becomes an "arcuate" shape at larger separations (hundreds to thousands of astronomical units), peaking at [Fe/H] ≈0.1 for the thin disk and [Fe/H] ≈-0.5 for the thick disk. Finally it becomes roughly flat for the thin disk at 1000 < s < 10,000 au. Our work provides new observational evidence for theoretical studies on binary formation and evolution.

Keywords: wide binary stars; stellar abundances; stellar physics
A Spectroscopic Study of Supernova Remnants with the Infrared Space Observatory

We present far-infrared (FIR) spectroscopy of supernova remnants (SNRs) based on the archival data of the Infrared Space Observatory taken with the Long Wavelength Spectrometer (LWS). Our sample includes previously unpublished profiles of line and continuum spectra for 20 SNRs in the Galaxy and Magellanic Clouds. In several SNRs including G21.5-0.9, G29.7-0.3, the Crab Nebula, and G320.4-1.2, we find evidence for broad [O I], [O III], [N II], and [C II] lines with velocity dispersions up to a few 103 km s-1, indicating that they are associated with high-velocity SN ejecta. Our detection of Doppler-broadened atomic emission lines and a bright FIR continuum hints at the presence of newly formed dust in SN ejecta. For G320.4-1.2, we present the first estimate of an ejecta-dust mass of 0.1-0.2 M⊙, which spatially coincides with the broad-line emission, by applying a blackbody model fit with components of the SNR and background emission. Our sample includes raster maps of 63 μm, 145 μm [O I], and 158 μm [C II] lines toward SNRs Kes 79, CTB 109, and IC 443. Based on these line intensities, we suggest interacting shock types in these SNRs. Finally, we compare our LWS spectra of our sample SNRs with the spectra of several H II regions, and discuss their FIR line intensity ratios and continuum properties. Follow-up observations with modern instruments (e.g., JWST and SOFIA) with higher spatial and spectral resolution are encouraged for an extensive study of the SN ejecta and the SN dust. * Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands, and the United Kingdom) and with the participation of ISAS and NASA.

Keywords: far infrared astronomy; supernova remnants; interstellar medium; astrophysical dust processes; shocks
Evidence of a Nonorthogonal X-line in Guide-field Magnetic Reconnection

We present observations that suggest the X-line of guide-field magnetic reconnection is not necessarily orthogonal to the plane in which magnetic reconnection is occurring. The plane of magnetic reconnection is often referred to as the L-N plane, where L is the direction of the reversing and reconnecting magnetic field and N is normal to the current sheet. The X-line is often assumed to be orthogonal to the L-N plane (defined as the M-direction) in the majority of theoretical studies and numerical simulations. The four-satellite Magnetospheric Multiscale (MMS) mission, however, observes a guide-field magnetic reconnection event in Earth's magnetotail in which the X-line may be oblique to the L-N plane. This finding is somewhat opportune as two of the MMS satellites at the same N location report nearly identical observations with no significant time delays in the electron diffusion region (EDR) even though they have substantial separation in L. A minimum directional derivative analysis suggests that the X-line is between 40° and 60° from M, adding support that the X-line is oblique. Furthermore, the measured ion velocity is inconsistent with the apparent motion of the MMS spacecraft in the L-direction through the EDR, which can be resolved if one assumes a shear in the L-N plane and motion in the M-direction. A nonorthogonal X-line, if somewhat common, would call for revisiting theory and simulations of guide-field magnetic reconnection, reexamination of how the reconnection electric field is supported in the EDR, and reconsidering the large-scale geometry of the X-line.

Keywords: space plasmas; planetary magnetospheres; plasma astrophysics; plasma physics
AT 2021loi: A Bowen Fluorescence Flare with a Rebrightening Episode Occurring in a Previously Known AGN

The optical-ultraviolet transient AT 2021loi is located at the center of its host galaxy. Its spectral features identify it as a member of the Bowen fluorescence flare (BFF) class. The first member of this class was considered to be related to a tidal disruption event, but enhanced accretion onto an already active supermassive black hole was suggested as an alternative explanation. Having occurred in a previously known unobscured active galactic nucleus, AT 2021loi strengthens the latter interpretation. Its light curve is similar to those of previous BFFs, showing a rebrightening approximately 1 yr after the main peak (which was not explicitly identified but might be the case in all previous BFFs). An emission feature around 4680 Å, seen in the preflare spectrum, strengthens by a factor of ~2 around the optical peak of the flare and is clearly seen as a double-peaked feature then, suggesting a blend of N III λ4640 with He II λ4686 as its origin. The appearance of O III λ3133 and possible N III λλ4097, 4103 (blended with Hδ) during the flare further support a Bowen fluorescence classification. Here we present ZTF, ATLAS, Keck, Las Cumbres Observatory, NEOWISE-R, Swift AMI, and Very Large Array observations of AT 2021loi, making it one of the best-observed BFFs to date. It thus provides some clarity on the nature of BFFs but also further demonstrates the diversity of nuclear transients.

Keywords: supermassive black holes; active galactic nuclei; transient sources
Spatially Resolved Velocity Structures in Jets of DF Tau and UY Aur A

Young stars accrete mass and angular momentum from their circumstellar disks. Some of them also drive outflows, which can be distinguished in optical forbidden emission lines. We analyze a sample of binary T Tauri stars observed with long-slit spectroscopy by the Hubble Space Telescope between 1998 and 2000, searching for spatially resolved outflows. We detect resolved [O I] emission in 2 cases out of 21. In DF Tau we resolve high- and medium-velocity outflows in a jet and counterjet out to 60 au. The outflows are accelerated within the inner 12 au and retain a constant speed thereafter. In UY Aur, we detect a blue- and a redshifted outflow from UY Aur A, as well as a blueshifted jet from UY Aur B. All of these features have been seen in [Fe II] with data taken 10 years apart indicating that the underlying outflow pattern is stable on these timescales.

Keywords: circumstellar gas; stellar jets; star formation; classical t tauri stars
A Comprehensive Power Spectral Density Analysis of Astronomical Time Series. II. The Swift/BAT Long Gamma-Ray Bursts

We have investigated the prompt light curves of long gamma-ray bursts (GRBs) from the Swift/BAT catalog. We aimed to characterize their power spectral densities (PSDs), search for quasiperiodic oscillations (QPOs), and conduct novel analyses directly in the time domain. We analyzed the PSDs using Lomb-Scargle periodograms, and searched for QPOs using wavelet scalograms. We also attempted to classify the GRBs using the Hurst exponent, H, and the ${ \mathcal A }\mbox{--}{ \mathcal T }$ plane. The PSDs fall into three categories: power law (PL; P(f) ∝ 1/fβ) with index β ∈ (0, 2), PL with a non-negligible Poisson noise level (PLC) with β ∈ (1, 3), and a smoothly broken PL (with Poisson noise level) yielding high-frequency index β2 ∈ (2, 6). The latter yields break timescales of the order of 1-100 s. The PL and PLC models are broadly consistent with fully developed turbulence, β = 5/3. For an overwhelming majority of GRBs (93%), H > 0.5, implying ubiquity of the long-term memory. We find no convincing substructure in the ${ \mathcal A }\mbox{--}{ \mathcal T }$ plane. Finally, we report on 34 new QPOs, with one or more constant leading periods, as well as several chirping signals. The presence of breaks and QPOs suggests the existence of characteristic timescales that in at least some GRBs might be related to the dynamical properties of plasma trajectories in the accretion disks powering the relativistic jets.

Keywords: gamma-ray bursts; astrostatistics; astronomy data analysis; light curves
eDIG-CHANGES. II. Project Design and Initial Results on NGC 3556

The extraplanar diffuse ionized gas (eDIG) represents ionized gases traced by optical/UV lines beyond the stellar extent of galaxies. We herein introduce a novel multislit narrow-band spectroscopy method to conduct spatially resolved spectroscopy of the eDIG around a sample of nearby edge-on disk galaxies (eDIG-CHANGES). In this paper, we introduce the project design and major scientific goals, as well as a pilot study of NGC 3556 (M108). The eDIG is detected to a vertical extent of a few kiloparsecs above the disk, comparable to the X-ray and radio images. We do not see significant vertical variation of the [N II]/Hα line ratio. A rough examination of the pressure balance between different circumgalactic medium phases indicates the magnetic field is in a rough pressure balance with the X-ray emitting hot gas and may play an important role in the global motion of both the eDIG and the hot gas in the lower halo. At the location of an Hubble Space Telescope/Cosmic Origins Spectrograph observed UV bright background active galactic nucleus ∼29 kpc from the center of NGC 3556, the magnetic pressure is much lower than that of the hot gas and the ionized gas traced by UV absorption lines, although the extrapolation of the pressure profiles may cause some biases in this comparison. By comparing the position–velocity diagrams of the optical and CO lines, we also find the dynamics of the two gas phases are consistent with each other, with no evidence of a global inflow/outflow and a maximum rotation velocity of ∼150 km s‑1.

Keywords: interstellar medium; circumgalactic medium; spiral galaxies; warm ionized medium; galaxy rotation curves; radio continuum emission; extragalactic magnetic fields