adsabs/SciX_UAT_keywords huggingface dataset:
Solar Wind Turbulence from 1 to 45 au. V. Data Intervals from the Voyager Observations

We have surveyed the Voyager 1 and 2 spacecraft magnetic field data from launch in 1977 through 1990 using daily spectrograms to find suitably long data intervals and to eliminate times near transients or strong gradients that might not represent homogeneous turbulence intervals. In the process, we have also omitted times when waves due to suprathermal particle populations such as interstellar pickup ions can be seen. Our goal was to construct a database of interplanetary magnetic field spectra that could be used in our companion papers to study the properties of the inertial and dissipation range of interplanetary turbulence. Here, we list those data intervals along with their heliocentric distance, latitude, and longitude as well as the angle between the mean magnetic field and the radial direction. Furthermore, we show the mean plasma parameters for the intervals listed. We invite others to use these listings in their associated studies.

Keywords: solar wind; heliosphere; magnetohydrodynamics
Hierarchical Inference of the Lensing Convergence from Photometric Catalogs with Bayesian Graph Neural Networks

We present a Bayesian graph neural network (BGNN) that can estimate the weak lensing convergence (κ) from photometric measurements of galaxies along a given line of sight (LOS). The method is of particular interest in strong gravitational time-delay cosmography (TDC), where characterizing the "external convergence" (κ ext) from the lens environment and LOS is necessary for precise Hubble constant (H 0) inference. Starting from a large-scale simulation with a κ resolution of ~1', we introduce fluctuations on galaxy-galaxy lensing scales of ~1″ and extract random sight lines to train our BGNN. We then evaluate the model on test sets with varying degrees of overlap with the training distribution. For each test set of 1000 sight lines, the BGNN infers the individual κ posteriors, which we combine in a hierarchical Bayesian model to yield constraints on the hyperparameters governing the population. For a test field well sampled by the training set, the BGNN recovers the population mean of κ precisely and without bias (within the 2σ credible interval), resulting in a contribution to the H 0 error budget well under 1%. In the tails of the training set with sparse samples, the BGNN, which can ingest all available information about each sight line, extracts a stronger κ signal compared to a simplified version of the traditional method based on matching galaxy number counts, which is limited by sample variance. Our hierarchical inference pipeline using BGNNs promises to improve the κ ext characterization for precision TDC. The code is available as a public Python package, NODE TO JOY ⏬.

Keywords: cosmology; hubble constant; hierarchical models; bayesian statistics; neural networks; weak gravitational lensing; strong gravitational lensing; astronomical simulations
Spectral Signature of Mass Outflow in the Two Component Advective Flow Paradigm

Outflows are common in many astrophysical systems. In the Two Component Advective Flow (TCAF) paradigm, which is essentially a generalized Bondi flow including rotation, viscosity, and cooling effects, the outflow originates in the hot, puffed up, post-shock region at the inner edge of the accretion disk. We consider this region to be the base of the jet carrying away matter with a high velocity. In this paper, we study the spectral properties of black holes using TCAF that includes also a jet (JeTCAF) in the vertical direction of the disk plane. Soft photons from the Keplerian disk are up-scattered by the post-shock region as well as by the base of the jet and are emitted as hard radiation. We also include the bulk motion Comptonization effect by the diverging flow of the jet. Our self-consistent accretion-ejection solution shows how the spectrum from the base of the jet varies with accretion rates, geometry of the flow, and the collimation factor of the jet. We apply the solution to a jetted candidate GS 1354-64 to estimate its mass outflow rate and the geometric configuration of the flow during the 2015 outburst observed by NuSTAR. The estimated mass outflow to mass inflow rate is {0.12}_{-0.03}^{+0.02}$ . From the model-fitted accretion rates, shock compression ratio, and the energy spectral index, we identify the presence of hard and intermediate spectral states of the outburst. Our model-fitted jet collimation factor (fcol) is found to be {0.47}_{-0.09}^{+0.09}$ .

Keywords: black hole physics; accretion; x-ray astronomy; shocks; hydrodynamics; radiative transfer; jets
Midsummer Atmospheric Changes in Saturn's Northern Hemisphere from the Hubble OPAL Program

Using the Hubble Space Telescope, Saturn was observed in 2018, 2019, and 2020, just after the northern hemisphere summer solstice. Analysis of multispectral imaging data reveals three years of cloud changes associated with a 70° N storm that began in 2018. Additionally, there is an increase in equatorial brightness and perhaps haze optical depth at 0° to 7° N. There are small midsummer changes at the north pole, with a thin blue feature near the polar hexagon's outer edge disappearing between 2019 and 2020 and increasingly reddish polar haze. Zonal winds at most latitudes remain close to values obtained by the Cassini mission with a slight increase of winds in the equatorial zone. Yearly cloud changes, while noticeable, are small compared with the changes observed between the Voyager (northern spring) and Cassini (southern summer to northern spring) eras, but further observations will provide a longer baseline for comparison.

Keywords: saturn; planetary atmospheres; hubble space telescope; atmospheric clouds; atmospheric variability
A Systematic Analysis of the X-Ray Emission in Optically Selected Tidal Disruption Events: Observational Evidence for the Unification of the Optically and X-Ray-selected Populations

We present a systematic analysis of the X-ray emission of a sample of 17 optically selected, X-ray-detected tidal disruption events (TDEs) discovered between 2014 and 2021. The X-ray light curves show a diverse range of temporal behaviors, with most sources not following the expected power-law decline. The X-ray spectra are mostly extremely soft and consistent with thermal emission from the innermost region of an accretion disk, which cools as the accretion rate decreases. Three sources show formation of a hard X-ray corona at late times. The spectral energy distribution shape, probed by the ratio (L BB/L X) between the UV/optical and X-ray, shows a wide range of L BB/L X ∈ (0.5, 3000) at early times and converges to disklike values of L BB/L X ∈ (0.5, 10) at late times. We estimate the fraction of optically discovered TDEs with L X ≥ 1042 erg s‑1 to be at least 40% and show that X-ray loudness is independent of black hole mass. We argue that distinct disk formation timescales are unlikely to be able to explain the diverse range of X-ray evolution. We combine our sample with X-ray-discovered ones to construct an X-ray luminosity function, best fit by a broken power law, with a break at L X ≈ 1044 erg s‑1. We show that there is no dichotomy between optically and X-ray-selected TDEs; instead, there is a continuum of early-time L BB/L X, at least as wide as L BB/L X ∈ (0.1, 3000), with optical/X-ray surveys selecting preferentially, but not exclusively, from the higher/lower end of the distribution. Our findings are consistent with unification models for the overall TDE population.

Keywords: tidal disruption; x-ray transient sources; supermassive black holes; time domain astronomy; high energy astrophysics; accretion
An Optical Overview of Blazars with LAMOST. II. Gamma-Ray Blazar Candidates and Updated Classifications

Blazars represent the dominant class of associated γ-ray sources detected by the Fermi Large Area Telescope (LAT). However, in the more recent release of the Fourth Fermi-LAT Point Source Catalog (4FGL), ~25% of the sources associated with lower-energy counterparts show a multifrequency behavior similar to that of blazars, but lacks an optical spectroscopic confirmation of their nature and are therefore classified as Blazar Candidates of Uncertain Type (BCUs). A particularly challenging task in blazar studies is to classify these BCUs and, when possible to estimate their redshifts, in particular for BL Lac objects, characterized by almost featureless optical spectra with only weak emission lines. Continuing our study of blazars with Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) optical spectral data, we perform an extensive search for optical spectra available in the LAMOST Data Release 6 archive. Our aim is confirming the blazar nature of BCUs and to test if new data can allow us to get a redshift estimate for BL Lac objects that lack measurement, as well as to search for and discover changing-look blazars. We selected sources out of the 4FGL catalog, the list of targets from our follow-up spectroscopic campaign of unidentified and/or unassociated γ-ray sources, and the Roma-BZCAT multifrequency catalog of blazars, finding a total of 42 sources with available LAMOST DR6 spectra. We confirmed the blazar-like nature of four blazar candidates . For the remaining 37 sources we confirm their previous classification.

Keywords: blazars; gamma-ray sources; spectroscopy; optical identification; bl lacertae objects; flat-spectrum radio quasars
The Formation of Bilobate Comet Shapes through Sublimative Torques

Recent spacecraft and radar observations found that ∼70% of short-period comet nuclei, mostly Jupiter-family comets (JFCs), have bilobate shapes (two masses connected by a narrow neck). This is in stark contrast to the shapes of asteroids of similar sizes, of which ∼14% are bilobate. This suggests that a process or mechanism unique to comets is producing these shapes. Here we show that the bilobate shapes of JFC nuclei are a natural byproduct of sublimative activity during their dynamical migration from their trans-Neptunian reservoir, through the Centaur population, and into the Jupiter family. We model the torques resulting from volatile sublimation during this dynamical migration, and find that they tend to spin up these nuclei to disruption. Once disrupted, the rubble pile-like material properties of comet nuclei (tensile strengths of ∼1-10 Pa and internal friction angles of ∼35°) cause them to reform as bilobate objects. We find that JFCs likely experienced rotational disruption events prior to entering the Jupiter family, which could explain the prevalence of bilobate shapes. These results suggest that the bilobate shapes of observed comets developed recently in their history (within the past ∼1-10 Myr), rather than during solar system formation or collisions during planet migration and residency in the trans-Neptunian population.

Keywords: centaur group; short period comets; comet nuclei; comet volatiles
TOI-3785 b: A Low-density Neptune Orbiting an M2-dwarf Star

Using both ground-based transit photometry and high-precision radial velocity spectroscopy, we confirm the planetary nature of TOI-3785 b. This transiting Neptune orbits an M2-Dwarf star with a period of ~4.67 days, a planetary radius of 5.14 ± 0.16 R ⊕, a mass of ${14.95}_{-3.92}^{+4.10}$ M ⊕, and a density of $\rho ={0.61}_{-0.17}^{+0.18}$ g cm-3. TOI-3785 b belongs to a rare population of Neptunes (4 R ⊕ < R p < 7 R ⊕) orbiting cooler, smaller M-dwarf host stars, of which only ~10 have been confirmed. By increasing the number of confirmed planets, TOI-3785 b offers an opportunity to compare similar planets across varying planetary and stellar parameter spaces. Moreover, with a high-transmission spectroscopy metric of ~150 combined with a relatively cool equilibrium temperature of T eq = 582 ± 16 K and an inactive host star, TOI-3785 b is one of the more promising low-density M-dwarf Neptune targets for atmospheric follow up. Future investigation into atmospheric mass-loss rates of TOI-3785 b may yield new insights into the atmospheric evolution of these low-mass gas planets around M dwarfs.

Keywords: exoplanet astronomy; radial velocity; transits; m dwarf stars
COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-gravity T4 Benchmark around an Old White Dwarf and a Re-examination of the Surface-gravity Dependence of the L/T Transition

We present the first discovery from the COol Companions ON Ultrawide orbiTS (COCONUTS) program, a large-scale survey for wide-orbit planetary and substellar companions. We have discovered a comoving system COCONUTS-1, composed of a hydrogen-dominated white dwarf (PSO J058.9855+45.4184; d = 31.5 pc) and a T4 companion (PSO J058.9869+45.4296) at a 40"6 (1280 au) projected separation. We derive physical properties for COCONUTS-1B from (1) its near-infrared spectrum using cloudless Sonora atmospheric models, and (2) its luminosity and the white dwarf's age ({7.3}-1.6+2.8 Gyr) using Sonora evolutionary models. The two methods give consistent temperatures and radii, but atmospheric models infer a lower surface gravity and therefore an unphysically young age. Assuming evolutionary model parameters ({T}eff={1255}-8+6 K, log g={5.44}-0.03+0.02 dex, R={0.789}-0.005+0.011 {R}Jup), we find that cloudless model atmospheres have brighter Y- and J-band fluxes than the data, suggesting that condensate clouds have not fully dispersed around 1300 K. The W2 flux (4.6 μm) of COCONUTS-1B is fainter than models, suggesting non-equilibrium mixing of CO. To investigate the gravity dependence of the L/T transition, we compile all 60 known L6-T6 benchmarks and derive a homogeneous set of temperatures, surface gravities, and masses. As is well known, young, low-gravity late-L dwarfs have significantly fainter, redder near-infrared photometry and ≈200-300 K cooler temperatures than old, high-gravity objects. Our sample now reveals such gravity dependence becomes weaker for T dwarfs, with young objects having comparable near-infrared photometry and ≈100 K cooler temperatures compared to old objects. Finally, we find that young objects have a larger amplitude J-band brightening than old objects, and also brighten at H band as they cross the L/T transition.

Keywords: white dwarf stars; brown dwarfs; substellar companion stars
Orphan GRB Afterglow Searches with the Pan-STARRS1 COSMOS Survey

We present the result of a search for orphan gamma-ray burst (GRB) afterglows in the Pan-STARRS1 (PS1) COSMOS survey. There is extensive theoretical and observational evidence suggesting that GRBs are collimated jets; the direct observation of orphan GRB afterglows would further support this model. An optimal survey strategy is designed by coupling the PS1 survey with the Subaru/Hyper-Suprime-Cam (HSC) survey. The PS1 COSMOS survey, one of the survey fields in the PS1 Medium Deep Survey (PS1/MDS), searches a field of 7 deg2 from 2011 December to 2014 January, reaching a limiting magnitude R ∼ 23. The dense cadence of PS1/MDS is crucial for identifying transients, and the deep magnitude reached by the HSC survey (R ∼ 26) is important for evaluating potential GRB hosts. A transient classification method is employed to select potential orphan GRB afterglow candidates. After a thorough analysis of the transient and host galaxy properties, we conclude that there are no candidates in this survey field. The null result implies that the consideration of jet structures is essential for further orphan GRB afterglow surveys.

Keywords: gamma-ray bursts; time domain astronomy; transient sources
JWST Noise Floor. II. Systematic Error Sources in JWST NIRCam Time Series

The James Webb Space Telescope (JWST) holds great promise for characterizing atmospheres of transiting exoplanets, potentially providing insights into Earth-sized planets within the habitable zones of M-dwarf host stars if photon-limited performance can be achieved. Here, we discuss the systematic error sources that are expected to be present in grism time-series observations with the NIRCam instrument. We find that pointing jitter and high-gain antenna moves in addition to the detectors' subpixel crosshatch patterns will produce relatively small variations (less than 6 parts per million, ppm). The time-dependent aperture losses due to thermal instabilities in the optics can also be kept to below 2 ppm. To achieve these low noise values, it is important to employ a sufficiently large (more than 1"1) extraction aperture. Persistence due to charge-trapping will have a minor (less than 3 ppm) effect on the time series 20 minutes into an exposure and is expected to play a much smaller role than it does for the Hubble Space Telescope WFC3 detectors. We expect detector temperature fluctuations to contribute less than 3 ppm. In total, our estimated noise floor from known systematic error sources is only 9 ppm per visit. We urge caution, however, because unknown systematic error sources could be present in flight and will only be measurable on astrophysical sources such as quiescent stars. We find that reciprocity failure may introduce a perennial instrument offset at the 40 ppm level, so corrections may be needed when a multi-instrument multi-observatory spectrum is stitched together over wide wavelength ranges.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; red noise; astronomical detectors; space telescopes; pointing error
A Numerical Study of the Effects of a Corotating Interaction Region on Cosmic-Ray Transport. II. Features of Cosmic-Ray Composition and Rigidity

We continue the numerical modeling of a corotating interaction region (CIR) and the effects it has on solar-rotational recurrent variations of galactic cosmic rays (GCRs). A magnetohydrodynamic model is adapted to simulate the background solar wind plasma with a CIR structure in the inner heliosphere, which is incorporated into a comprehensive Parker-type transport model. The focus is on the simulation of the effects of a CIR on GCR protons and the two helium isotopes as a function of heliolongitude. This is to establish whether the difference in composition affects how they are modulated by the CIR in terms of their distribution in longitude. It is demonstrated that particle diffusion and drift influence the effects of the CIR with increasing rigidity from 100 MV up to 15 GV. It is found that protons and helium isotopes are modulated differently with longitude by the CIR and that particle drift influences the modulation effects in longitude. These differences dissipate with increasing rigidity. The final results are focused on the simulated amplitude of these GCR flux variations as a function of rigidity. The amplitude displays a power-law behavior above ~1 GV with an index similar to the power index of the rigidity dependence of the assumed diffusion coefficients. The simulations further show that below this rigidity, the amplitude at first flattens off, displaying a plateau-like profile, but it then increases systematically with decreasing rigidity below ~0.3 GV. Again, a power-law behavior is displayed, but it is completely different from that above 1 GV.

Keywords: galactic cosmic rays; heliosphere; solar activity; solar wind
Black Hole Encircled by a Thin Disk: Fully Relativistic Solution

We give a full metric describing the gravitational field of a static and axisymmetric thin disk without radial pressure encircling a Schwarzschild black hole. The disk density profiles are astrophysically realistic, stretching from the horizon to radial infinity, yet falling off quickly at both these locations. The metric functions are expressed as finite series of Legendre polynomials. The main advantages of the solution are that (i) the disks have no edges, so their fields are regular everywhere (outside the horizon), and (ii) all nontrivial metric functions are provided analytically and in closed forms. We examine and illustrate basic properties of the black hole-disk spacetimes. * Dedicated to our teacher, colleague, and friend, Professor Oldřich Semerák, on the occasion of his 60th orbit around the Sun. Oldřich's well-known lectures-famous not only among us (former) students of "math-phys" in Prague-were the first impulse that led us to devote our studies to general relativity.

Keywords: relativistic disks; black holes
Dwarfs in Void Environments (DIVE): The Stellar Kinematics of Void Dwarf Galaxies Using the Keck Cosmic Web Imager

Dwarf galaxies located in extremely underdense cosmic voids are excellent test beds for disentangling the effects of large-scale environments on galaxy formation and evolution. We present the first results of the Dwarfs in Void Environments Survey, which has obtained integral field spectroscopy for low-mass galaxies (M ⋆ = 107-109 M ⊙) located inside (N = 21) and outside (N = 9) cosmic voids using the Keck Cosmic Web Imager. Using measurements of stellar line-of-sight rotational velocity v rot and velocity dispersion σ ⋆, we test the tidal stirring hypothesis, which posits that dwarf spheroidal galaxies are formed through tidal interactions with more massive host galaxies. We measure low values of v rot/σ ⋆ ≲ 2 for our sample of isolated dwarf galaxies, and we find no trend between v rot/σ ⋆ and the distance from a massive galaxy ${d}_{{L}^{\star }}$ out to ${d}_{{L}^{\star }}\sim 10$ Mpc. These suggest that dwarf galaxies can become dispersion-supported, "puffy" systems even in the absence of environmental effects like tidal interactions. We also find indications of an upward trend between v rot/σ ⋆ and galaxy stellar mass, perhaps implying that stellar disk formation depends on mass rather than environment. Although some of our conclusions may be slightly modified by systematic effects, our main result still holds: that isolated low-mass galaxies may form and remain as puffy systems rather than the dynamically cold disks predicted by classical galaxy formation theory.

Keywords: dwarf galaxies; galaxy kinematics; stellar kinematics; galaxy environments
OH and H2O Maser Activities Among Long-period Variables

The distribution within an infrared color–magnitude diagram of variable red giants known to have circumstellar masers is reported. Stars with H2O-maser sources occur within a color and period domain of (J ‑ K s ) > 1.15 and P > 199 days, respectively, often in the absence of OH masers. By contrast, OH masers are mostly detected among cooler red giants with (J ‑ K s ) > 1.35 and P > 316 days, and can coexist with H2O-maser sources. The results suggest that red giants must evolve to absolute magnitudes brighter than prior to enabling H2O-maser emission, and possibly expand beyond a certain size before triggering OH masers.

Keywords: long period variable stars; mira variable stars; semi-regular variable stars; pulsating variable stars; circumstellar masers