adsabs/SciX_UAT_keywords huggingface dataset:
Formation of Magnetically Truncated Accretion Disks in 3D Radiation-transport Two-temperature GRMHD Simulations

Multiwavelength observations suggest that the accretion disk in the hard and intermediate states of X-ray binaries (XRBs) and active galactic nucleus transitions from a cold, thin disk at large distances into a hot, thick flow close to the black hole (BH). However, the formation, structure, and dynamics of such truncated disks are poorly constrained due to the complexity of the thermodynamic, magnetic, and radiative processes involved. We present the first radiation-transport two-temperature general relativistic magnetohydrodynamic (GRMHD) simulations of truncated disks radiating at ~35% of the Eddington luminosity with and without large-scale poloidal magnetic flux. We demonstrate that when a geometrically thin accretion disk is threaded by large-scale net poloidal magnetic flux, it self-consistently transitions at small radii into a two-phase medium of cold gas clumps floating through a hot, magnetically dominated corona. This transition occurs at a well-defined truncation radius determined by the distance out to which the disk is saturated with magnetic flux. The average ion and electron temperatures in the semiopaque corona reach, respectively, T i ≳ 1010 K and T e ≳ 5 × 108 K. The system produces radiation, powerful collimated jets, and broader winds at the total energy efficiency exceeding 90%, the highest ever energy extraction efficiency from a spinning BH by a radiatively efficient flow in a GRMHD simulation. This is consistent with jetted ejections observed during XRB outbursts. The two-phase medium may naturally lead to broadened iron line emission observed in the hard state.

Keywords: high energy astrophysics; active galactic nuclei; black hole physics; black holes; jets; plasma astrophysics
Space Weathering within C-complex Main Belt Asteroid Families

Using data from the Sloan Digital Sky Survey Moving Object Catalog, we study color as a function of size for C-complex families in the main asteroid belt to improve our understanding of space weathering of carbonaceous materials. We find two distinct spectral slope trends: Hygiea type and Themis type. The Hygiea-type families exhibit a reduction in spectral slope with increasing object size until a minimum slope value is reached and the trend reverses with increasing slope with increasing object size. The Themis family shows an increase in spectral slope with increasing object size until a maximum slope is reached and the spectral slope begins to decrease slightly or plateaus for the largest objects. Most families studied show the Hygiea-type trend. The processes responsible for these distinct changes in spectral slope affect several different taxonomic classes within the C-complex and appear to act quickly to alter the spectral slopes of the family members.

Keywords: main belt asteroids; solar system astronomy; asteroids; hirayama families
Frequency Analysis of KIC 1573174: Shedding Light on the Nature of HADS Stars

We propose that KIC 1573174 is a quadruple-mode δ Scuti star with pulsation amplitudes between those of the high-amplitude Delta Scuti star group and average low-amplitude pulsators. The radial modes detected in this star provide a unique opportunity to exploit asteroseismic techniques up to their limits. Detailed frequency analysis is given for the light curve from the Kepler mission. The variation of the light curve is dominated by the strongest mode with a frequency of F0 = 7.3975 day-1, as shown by Fourier analysis of long cadence data (Q1-Q17, spanning 1460 days), indicating that the target is a δ Scuti star. The other three independent modes with F1 = 9.4397 day-1, F2 = 12.1225 day-1, and F3 = 14.3577 day-1, have ratios of P 1/P 0, P 2/P 0, and P 3/P 0 estimated as 0.783, 0.610, and 0.515, which indicate that KIC 1573174 is a quadruple-mode δ Scuti star. A different approach has been used to determine the O - C through the study of phase modulation. The change of period (1/P)dP/dt is obtained resulting in -1.14 × 10-6 yr-1 and -4.48 × 10-6 yr-1 for F0 and F1 respectively. Based on frequency parameters (i.e., F0, F1, F2, and F3), a series of theoretical models were conducted by employing the stellar evolution code MESA. The ratio of observed f 1/f 2 is larger than that of the model, which may be caused by the rotation of the star. We suggest high-resolution spectral observation is highly desired in the future to further constrain models.

Keywords: delta scuti variable stars; stellar evolution; asteroseismology
Statistical Study of Hard X-Ray Emitting Electrons Associated with Flare-related Coronal Jets

We present the statistical analysis of 33 flare-related coronal jets, and discuss the link between the jet and the flare properties in these events. We selected jets that were observed between 2010 and 2016 by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) that are temporally and spatially associated with flares observed by the Reuven Ramaty High Energy Solar Spectrometric Imager (RHESSI). For each jet, we calculated the jet duration and projected velocity in the plane of sky. The jet duration distribution has a median of 18.8 minutes. The projected velocities are between 31 and 456 km s-1 , with a median at 210 km s-1. For each associated flare, we performed X-ray imaging and spectroscopy and identify nonthermal emission. Nonthermal emission was detected in only 1/4 of the events considered. We did not find a clear correlation between the flare thermal energy or soft X-ray (SXR) peak flux and the jet velocity or jet duration. There is no preferential time delay between the flare and the jet. The X-ray emission is generally located at the base of the jet. The analysis presented in this paper suggests that the flare and jet are part of the same explosive event, that the jet is driven by the propagation of an Alfvénic perturbation, and that the energy partition between flare and jets varies substantially from one event to another.

Keywords: solar flares; solar energetic particles; solar x-ray flares; jets
WO-type Wolf-Rayet Stars: The Last Hurrah of Massive Star Evolution

Are WO-type Wolf-Rayet (WR) stars in the final stage of massive star evolution before core-collapse? Although WC- and WO-type WRs have very similar spectra, WOs show a much stronger O VI λλ3811,34 emission-line feature. This has usually been interpreted to mean that WOs are more oxygen rich than WCs, and thus further evolved. However, previous studies have failed to model this line, leaving the relative abundances uncertain, and the relationship between the two types unresolved. To answer this fundamental question, we modeled six WCs and two WOs in the LMC using UV, optical, and NIR spectra with the radiative transfer code CMFGEN in order to determine their physical properties. We find that WOs are not richer in oxygen; rather, the O VI feature is insensitive to the abundance. However, the WOs have a significantly higher carbon and lower helium content than the WCs, and hence are further evolved. A comparison of our results with single-star Geneva and binary BPASS evolutionary models show that, while many properties match, there is more carbon and less oxygen in the WOs than either set of evolutionary model predicts. This discrepancy may be due to the large uncertainty in the 12C+4He → 16O nuclear reaction rate; we show that if the Kunz et al. rate is decreased by a factor of 25%-50%, then there would be a good match with the observations. It would also help explain the LIGO/VIRGO detection of black holes whose masses are in the theoretical upper mass gap. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: massive stars; wolf-rayet stars; stellar evolution; wc stars
Deflection of O2 + Ion Flow by Magnetic Fields in the Martian Ionosphere

The effect of the Martian crustal magnetic field on ion escape is the focus of considerable interest. Directions of magnetic fields near Mars determined by the interaction between Mars' crustal and interplanetary magnetic fields have been suggested to play a significant role on ion transport around Mars. In this study we investigate the physical mechanism of deflection of ${{\rm{O}}}_{2}^{+}$ ion flow in two typical magnetic field orientations at the horizontal plane in the Martian ionosphere by performing 3D multifluid Hall magnetohydrodynamic simulations. Cross validation of the simulation results from two cases with the G110 crustal field model and equivalent source dipole model reveals that due to the Hall electric force, ${{\rm{O}}}_{2}^{+}$ ion flow tends to be accelerated eastwards in the region occupied by outward magnetic fields, and westwards in the region with inward magnetic fields. These results are helpful for understanding the impact of magnetic fields on the deflection of ionospheric ions in the Martian space environment.

Keywords: mars; solar-planetary interactions; magnetic anomalies; magnetohydrodynamics
ELUCID. VII. Using Constrained Hydro Simulations to Explore the Gas Component of the Cosmic Web

Using reconstructed initial conditions in the Sloan Digital Sky Survey (SDSS) survey volume, we carry out constrained hydrodynamic simulations in three regions representing different types of the cosmic web: the Coma cluster of galaxies; the SDSS Great Wall; and a large low-density region at z ~ 0.05. These simulations, which include star formation and stellar feedback but no active galactic nucleus formation and feedback, are used to investigate the properties and evolution of intergalactic and intracluster media. About half of the warm-hot intergalactic gas is associated with filaments in the local cosmic web. Gas in the outskirts of massive filaments and halos can be heated significantly by accretion shocks generated by mergers of filaments and halos, respectively, and there is a tight correlation between the gas temperature and the strength of the local tidal field. The simulations also predict some discontinuities associated with shock fronts and contact edges, which can be tested using observations of the thermal Sunyaev-Zel'dovich effect and X-rays. A large fraction of the sky is covered by Lyα and O VI absorption systems, and most of the O VI systems and low-column-density H I systems are associated with filaments in the cosmic web. The constrained simulations, which follow the formation and heating history of the observed cosmic web, provide an important avenue to interpret observational data. With full information about the origin and location of the cosmic gas to be observed, such simulations can also be used to develop observational strategies.

Keywords: hydrodynamical simulations; intergalactic medium; intracluster medium; intergalactic filaments; sunyaev-zeldovich effect; x-ray photometry; quasar absorption line spectroscopy; coma cluster; cosmic web; voids; large-scale structure of the universe; warm-hot intergalactic medium
The Complex Nature of Magnetic Element Transport in the Quiet Sun: The Multiscaling Character

In recent studies the dynamic properties of small-scale magnetic fields (magnetic elements [MEs]) in the quiet Sun were used to investigate peculiar features of turbulent convection and get insights on the characteristic spatial and temporal scales of evolution of magnetic fields, from granular to supergranular. The aim of this work is to extend previous studies and show that the displacement of MEs is compatible with a multiscaling behavior consistent with a Lévy motion. We tracked over 120,000 MEs in an unprecedented and uninterrupted set of high-resolution magnetograms acquired by the Hinode mission and targeted at quiet-Sun regions in the disk center, and we applied the multifractal diffusion entropy analysis to investigate the multiscaling character of ME transport in the quiet Sun. We found that the displacement of MEs in the quiet Sun exhibits a complex multiscaling behavior that cannot be described by a unique scaling law, as scaling exponents change with the scale considered. This result adds important physical constraints on turbulent convection and diffusion of MEs in the quiet Sun that future models need to account for.

Keywords: solar convective zone; solar magnetic fields; quiet sun; space weather; solar photosphere
The First OGLE-discovered Ultracompact X-Ray Binary is an Intermediate Polar

The variable source OGLE-UCXB-01 is the first OGLE-discovered ultracompact X-ray binary (UCXB). The 12 yr long-term OGLE optical photometry of this source shows a period of $P=12.8\,\min$ and a fast period-decreasing rate $\dot{P}=-9.2\times {10}^{-11}$ s s-1. At a luminosity of ${L}_{{\rm{X}}}\approx 4\times {10}^{33}$ erg s-1, its X-ray emission is also variable and correlated with the optical variability. To determine the nature of this variable source, specifically the masses and types of its binary components, we first consider an attractive possibility that the optical variation is due to the secondary's ellipsoidal variation and a strong gravitational wave emission drives the orbital decay. However, we cannot find an allowable solution to the secondary that simultaneously satisfies the three constraints: an ultratight orbit, the bright absolute magnitude, and the large-amplitude brightness variation. Moreover, the inferred mass-transfer rate is too high. This scenario is therefore ruled out. We then find the system is fully consistent with an "intermediate polar" model, in which the optical and X-ray emission comes from a magnetized white dwarf (WD) accreting from a low-mass (≲ $0.7\,{M}_{\odot }$) main-sequence secondary. The observed period decay is the accretion-driven spin-up of the WD. The WD spin period is 12.8 minutes and the orbital period is shorter than 10 hr. The method presented here can be applied to other UCXB candidates or impostors with only time-domain data available.

Keywords: stellar accretion; white dwarf stars; magnetic variable stars; x-ray binary stars; periodic variable stars
A Low-speed Intruder Star in Hyades: A Temporary Residence

We hereby report a low-speed (about 21 km s-1 with respect to the Sun) intruder member in the Hyades cluster based on the data in the literature. The results show that the star is a nonnative member star for Hyades, with its radial velocity being smaller than the radial velocity of the Hyades cluster, even exceeding the standard deviation of the radial velocity of the cluster by a factor of 9. Furthermore, by analyzing and comparing the orbits of this star and its host, it may have intruded into its host in the past 2 Myr. If the star's current motion orbit remains unchanged, it may leave its host in the next 2 Myr. This implies that the intruder star may be temporarily residing in the cluster. This study presents the first observational evidence of a star intrusion into a cluster, which suggests that more evidence may be found.

Keywords: open star clusters; a stars
Accretion Disk Luminosity for Black Holes Surrounded by Dark Matter with Tangential Pressure

We study the motion of test particles in the gravitational field of a Schwarzschild black hole surrounded by a spherical dark matter cloud with nonzero tangential pressure, and compute the luminosity of the accretion disk. The presence of nonvanishing tangential pressure allows us to mimic the dark matter's angular momentum, while still considering a static model, which simplifies the mathematical framework. We compare the numerical results of the influence of dark matter on the luminosity of the accretion disks around static supermassive black holes with the previously studied cases of isotropic and anisotropic pressures. We show that the flux and luminosity of the accretion disk in the presence of dark matter are different from the case of a Schwarzschild black hole in a vacuum, and highlight the impact of the presence of tangential pressures.

Keywords: black holes; dark matter; stellar accretion disks; schwarzschild black holes; dark matter distribution
Are High-Σ1 Massive Blue Spiral Galaxies Rejuvenated Systems?

Quiescent galaxies generally possess denser cores than star-forming galaxies with similar mass. As a measurement of the core density, the central stellar mass surface density within a radius of 1 kpc (Σ1) was thus suggested to be closely related to galaxy quenching. Massive star-forming galaxies with high Σ1 do not fit into this picture. To understand the origin of such galaxies, we compare the spatially resolved stellar population and star formation properties of massive (>1010.5 M ⊙) blue spiral galaxies with high and low Σ1, divided by Σ1 = 109.4 M ⊙ kpc‑2, based on the final release of MaNGA integral field unit data. We find that both high-Σ1 and low-Σ1 blue spirals show large diversities in stellar population and star formation properties. Despite the diversities, high-Σ1 blue spirals are statistically different from the low-Σ1 ones. Specifically, the radial profiles of the luminosity-weighted age and Mgb/<Fe> show that high-Σ1 blue spirals consist of a larger fraction of galaxies with younger and less α-element-enhanced centers than their low-Σ1 counterparts, ∼55% versus ∼30%. The galaxies with younger centers mostly have higher central specific star formation rates, which still follow the spaxel-based star formation main-sequence relation. Examinations of the Hα velocity field and the optical structures suggest that galactic bars or galaxy interactions should be responsible for the rejuvenation of these galaxies. The remaining ∼45% of high-Σ1 blue spirals are consistent with the inside-out growth scenario.

Keywords: galaxy evolution; galaxy formation; galaxy ages; spiral galaxies; galaxy spectroscopy
Absolute Dimensions of the Unevolved F-type Eclipsing Binary BT Vulpeculae

We report extensive differential V-band photometry and high-resolution spectroscopy for the 1.14 day, detached, double-lined eclipsing binary BT Vul (F0+F7). Our radial-velocity monitoring and light-curve analysis lead to absolute masses and radii of ${M}_{1}=1.5439\pm 0.0098\,{{ \mathcal M }}_{\odot }^{{\rm{N}}}$ and ${R}_{1}=1.536\pm 0.018\,{{ \mathcal R }}_{\odot }^{{\rm{N}}}$ for the primary, and ${M}_{2}=1.2196\pm 0.0080\,{{ \mathcal M }}_{\odot }^{{\rm{N}}}$ and ${R}_{2}=1.151\pm 0.029\,{{ \mathcal R }}_{\odot }^{{\rm{N}}}$ for the secondary. The effective temperatures are 7270 ± 150 K and 6260 ± 180 K, respectively. Both stars are rapid rotators, and the orbit is circular. A comparison with stellar evolution models from the MESA Isochrones and Stellar Tracks series shows excellent agreement with these determinations, for a composition of $[\mathrm{Fe}/{\rm{H}}]=+0.08$ and an age of 350 Myr. The two components of BT Vul are very near the zero-age main sequence.

Keywords: eclipsing binary stars; stellar evolution; fundamental parameters of stars; ccd photometry; radial velocity; spectroscopy
JWST Peers into the Class I Protostar TMC1A: Atomic Jet and Spatially Resolved Dissociative Shock Region

Outflows and winds launched from young stars play a crucial role in the evolution of protostars and the early stages of planet formation. However, the specific details of the mechanism behind these phenomena, including how they affect the protoplanetary disk structure, are still debated. We present JWST NIRSpec integral field unit observations of atomic and H2 lines from 1 to 5.1 μm toward the low-mass protostar TMC1A. For the first time, a collimated atomic jet is detected from TMC1A in the [Fe II] line at 1.644 μm along with corresponding extended H2 2.12 μm emission. Toward the protostar, we detected spectrally broad H I and He I emissions with velocities up to 300 km s-1 that can be explained by a combination of protostellar accretion and a wide-angle wind. The 2 μm continuum dust emission, H I, He I, and O I all show emission from the illuminated outflow cavity wall and scattered line emission. These observations demonstrate the potential of JWST to characterize and reveal new information about the hot inner regions of nearby protostars; in this case, a previously undetected atomic wind and ionized jet in a well-known outflow.

Keywords: jets; h i line emission; young stellar objects; protostars
Bridging High-density Electron Beam Coronal Transport and Deep Chromospheric Heating in Stellar Flares

The optical and near-ultraviolet (NUV) continuum radiation in M-dwarf flares is thought to be the impulsive response of the lower stellar atmosphere to magnetic energy release and electron acceleration at coronal altitudes. This radiation is sometimes interpreted as evidence of a thermal photospheric spectrum with T ≈ 104 K. However, calculations show that standard solar flare coronal electron beams lose their energy in a thick target of gas in the upper and middle chromosphere (log10 column mass/[g cm-2] ≲ -3). At larger beam injection fluxes, electric fields and instabilities are expected to further inhibit propagation to low altitudes. We show that recent numerical solutions of the time-dependent equations governing the power-law electrons and background coronal plasma (Langmuir and ion-acoustic) waves from Kontar et al. produce order-of-magnitude larger heating rates than those that occur in the deep chromosphere through standard solar flare electron beam power-law distributions. We demonstrate that the redistribution of beam energy above E ≳ 100 keV in this theory results in a local heating maximum that is similar to a radiative-hydrodynamic model with a large, low-energy cutoff and a hard power-law index. We use this semiempirical forward-modeling approach to produce opaque NUV and optical continua at gas temperatures T ≳ 12,000 K over the deep chromosphere with log10 column mass/[g cm-2] of -1.2 to -2.3. These models explain the color temperatures and Balmer jump strengths in high-cadence M-dwarf flare observations, and they clarify the relation among atmospheric, radiation, and optical color temperatures in stellar flares.

Keywords: stellar flares
Unified Astronomy Thesaurus: Usage Stats and Release Cycle

The Unified Astronomy Thesaurus (UAT) is an open and community-supported thesaurus that was formally adopted by the American Astronomical Society on 2019 June 3. This article examines the usage of UAT concepts across AAS journals since its adoption and summarizes information about the variety of concepts used, the most commonly used concepts, and frequent concept co-occurrences. Finally, it provides an update on the documentation governing the release cycle for future versions of the UAT.

Keywords: interdisciplinary astronomy
Fine Structures of Radio Bursts from Flare Star AD Leo with FAST Observations

Radio bursts from nearby active M-dwarfs have been frequently reported and extensively studied in solar or planetary paradigms. Whereas, their substructures or fine structures remain rarely explored despite their potential significance in diagnosing the plasma and magnetic field properties of the star. Such studies in the past have been limited by the sensitivity of radio telescopes. Here we report the inspiring results from the high time-resolution observations of a known flare star AD Leo with the Five-hundred-meter Aperture Spherical radio Telescope. We detected many radio bursts in the 2 days of observations with fine structures in the form of numerous millisecond-scale sub-bursts. Sub-bursts on the first day display stripe-like shapes with nearly uniform frequency drift rates, which are possibly stellar analogs to Jovian S-bursts. Sub-bursts on the second day, however, reveal a different blob-like shape with random occurrence patterns and are akin to solar radio spikes. The new observational results suggest that the intense emission from AD Leo is driven by electron cyclotron maser instability, which may be related to stellar flares or interactions with a planetary companion.

Keywords: radio bursts; flare stars; star-planet interactions; stellar flares; stellar magnetic fields