adsabs/SciX_UAT_keywords huggingface dataset:
Dust Destruction by Drift-induced Sputtering in Active Galactic Nuclei

Recent mid-infrared high spatial resolution observations have revealed that active galactic nuclei (AGNs) may host a polar dust region with the size of several pc, and such dust may be carried by radiation from the central engine. The polar dust emission often exhibits very weak or absence of the silicate 10 μm emission feature. A possible explanation is that the polar dust is dominated by micron-sized large grains because these grains do not show the silicate feature, while it remains unclear how large grains are preferentially supplied to the polar region. Here, we propose a new scenario describing the prevalence of large grains at the polar region. We show that grains are accelerated to the hypersonic drift velocity by the radiation pressure from AGN, and the hypersonic drift results in dust destruction via kinetic sputtering. Sputtering destroys small grains faster than the large ones, and thus larger grains will be preferentially blown over longer distance. Although the hypersonic drift, or kinetic sputtering, tends to be suppressed for very small grains due to the Coulomb drag, they might also be disrupted by Coulomb explosion. Removal of small grains and/or survival of large grains may explain the lack of a silicate 10 μm emission feature in polar dust emission.

Keywords: active galactic nuclei; astrophysical dust processes; dust continuum emission
A Possible Extremely Fast Spinning White Dwarf in the Intermediate Polar SDSS J0932+47

We analyze the far-ultraviolet light curve of the intermediate polar (IP) candidate SDSS-J093249.57+472523.0 (J0932+47), as observed by Hubble Space Telescope/Cosmic Origins Spectrograph. The power spectrum displays two periodicities at frequencies of 2.01 and 0.462 cycles minute‑1, corresponding to periods of 29.8 and 130 s. We estimate the significance of the 29.8 s peak to be 3σ. The detection of the 130 s signal is less secure. If the 29.8 s signal is generated by a rotating white dwarf (WD), then J0932+47 would possess one of the fastest spinning WDs among known IPs. The N V/C IV and Si IV/C IV line ratios are larger than typically seen in cataclysmic variables (CVs), and anomalous line ratios are seen in several CVs with rapidly rotating WDs. Alternatively, the periodicities are in the range typical of dwarf nova oscillations.

Keywords: cataclysmic variable stars; dq herculis stars; dwarf novae; white dwarf stars
Compact Starburst Galaxies with Fast Outflows: Central Escape Velocities and Stellar Mass Surface Densities from Multiband Hubble Space Telescope Imaging

We present multiband Hubble Space Telescope imaging that spans rest-frame near-ultraviolet through near-infrared wavelengths ( ${\lambda }_{\mathrm{rest}}=0.3$ -1.1 μm) for 12 compact starburst galaxies at z = 0.4-0.8. These massive galaxies ( ${{ \mathcal M }}_{* }\sim {10}^{11}\,{{ \mathcal M }}_{\odot }$ ) are driving very fast outflows ( ${v}_{\max }=1000$ -3000 km s-1), and their light profiles are dominated by an extremely compact starburst component (half-light radius ∼ 100 pc). Our goal is to constrain the physical mechanisms responsible for launching these fast outflows by measuring the physical conditions within the central kiloparsec. Based on our stellar population analysis, the central component typically contributes ≈25% of the total stellar mass, and the central escape velocities ${v}_{\mathrm{esc},\mathrm{central}}\approx 900$ km s-1 are a factor of two smaller than the observed outflow velocities. This Requires physical mechanisms that can accelerate gas to speeds significantly beyond the central escape velocities, and it makes clear that these fast outflows are capable of traveling into the circumgalactic medium, and potentially beyond. We find central stellar densities ${{\rm{\Sigma }}}_{{\rm{e}},\mathrm{central}}\approx 3\times {10}^{11}$ ${M}_{\odot }$ kpc-2 comparable to theoretical estimates of the Eddington limit, and we estimate ${{\rm{\Sigma }}}_{1}$ surface densities within the central kiloparsec comparable to those of compact massive galaxies at $0.5\lt z\lt 3.0$ . Relative to "red nuggets" and "blue nuggets" at $z\sim 2$ , we find significantly smaller re values at a given stellar mass, which we attribute to the dominance of a young stellar component in our sample and the better physical resolution for rest-frame optical observations at $z\sim 0.6$ versus $z\sim 2$ . We compare to theoretical scenarios involving major mergers and violent disk instability, and we speculate that our galaxies are progenitors of power-law ellipticals in the local universe with prominent stellar cusps.

Keywords: compact galaxies; starburst galaxies; galaxies; galaxy mergers; stellar feedback; galaxy formation; extragalactic astronomy
Spectroscopic Distance, Mass, and Age Estimations for APOGEE DR17

We derive distances and masses of stars from the Sloan Digital Sky Survey (SDSS) Apache Point Observatory Galactic Evolution Experiment Data Release 17 using simple neural networks. Training data for distances comes from Gaia EDR3, supplemented by literature distances for star clusters. For masses, the network is trained using asteroseismic masses for evolved stars and isochrone masses for main-sequence stars. The models are trained on effective temperature, surface gravity, metallicity, and carbon and nitrogen abundances. We found that our distance predictions have median fractional errors that range from ≈20% at low log g and ≈10% at higher log g with a standard deviation of ≈11%. The mass predictions have a standard deviation of ±12%. Using the masses, we derive ages for evolved stars based on the correspondence between mass and age for giant stars given by isochrones. The results are compiled into a Value Added Catalog called DistMass that contains distances and masses for 733,901 independent spectra, plus ages for 396,548 evolved stars.

Keywords: neural networks; stellar distance; stellar masses; stellar properties; stellar ages; abundance ratios; stellar populations
Eruptive-Impulsive Homologous M-class Flares Associated with Double-decker Flux Rope Configuration in Minisigmoid of NOAA 12673

We present a multiwavelength analysis of two homologous, short-lived, impulsive flares of GOES class M1.4 and M7.3 that occurred from a very localized minisigmoid region within the active region NOAA 12673 on 2017 September 7. Both flares were associated with initial jetlike plasma ejection that for a brief amount of time moved toward the east in a collimated manner before drastically changing direction toward the southwest. Nonlinear force-free field extrapolation reveals the presence of a compact double-decker flux rope configuration in the minisigmoid region prior to the flares. A set of open field lines originating near the active region that were most likely responsible for the anomalous dynamics of the erupted plasma gave the earliest indication of an emerging coronal hole near the active region. The horizontal field distribution suggests a rapid decay of the field above the active region, implying high proneness of the flux rope system toward eruption. In view of the low coronal double-decker flux ropes and compact extreme ultraviolet brightening beneath the filament, along with associated photospheric magnetic field changes, our analysis supports the combination of initial tether-cutting reconnection and subsequent torus instability for driving the eruption.

Keywords: solar active region filaments; solar corona; solar activity; solar x-ray flares
Gas-driven Inspiral of Binaries in Thin Accretion Disks

Numerical studies of gas accretion onto supermassive black hole binaries have generally been limited to conditions where the circumbinary disk (CBD) is 10-100 times thicker than expected for disks in active galactic nuclei. This discrepancy arises from technical limitations, and also from publication bias toward replicating fiducial numerical models. Here we present the first systematic study of how the binary's orbital evolution varies with disk scale height. We report three key results: (1) binary orbital evolution switches from outspiraling for warm disks (aspect ratio h/r ∼ 0.1), to inspiraling for more realistic cooler, thinner disks at a critical value of h/r ∼ 0.04, corresponding to orbital Mach number ${{ \mathcal M }}_{\mathrm{crit}}\approx 25$ . (2) The net torque on the binary arises from a competition between positive torque from gas orbiting close to the black holes, and negative torque from the inner edge of the CBD, which is denser for thinner disks. This leads to increasingly negative net torques on the binary for increasingly thin disks. (3) The accretion rate is modestly suppressed with increasing Mach number. We discuss how our results may influence modeling of the nano-Hz gravitational-wave background, as well as estimates of the Laser Interferometer Space Antenna merger event rate.

Keywords: supermassive black holes; hydrodynamical simulations; galaxy accretion disks; accretion; gravitational waves; compact objects
Examining Neutrino-Matter Interactions in the Cassiopeia A Supernova

Neutrino interactions with stellar material are widely believed to be fundamental to the explosion of massive stars. However, this important process has remained difficult to confirm observationally. We propose a new method to verify it using X-ray observations of the supernova remnant Cassiopeia A. The elemental composition in its Fe-rich ejecta that could have been produced at the innermost region of the supernova, where neutrinos are expected to interact, allows us to examine the presence of neutrino interactions. Here we demonstrate that the amount of Mn produced without neutrino nucleosynthesis processes (i.e., the ν- and νp-processes) is too small to explain the Mn/Fe mass ratio we measure (0.14%-0.67%). This result supports the operation of significant neutrino interactions in the Cassiopeia A supernova. If the observed Mn/Fe mass ratio purely reflects the production at the innermost region of the supernova, this would be the first robust confirmation of neutrino-matter interactions in an individual supernova. We further show that the Mn/Fe mass ratio has the potential to constrain supernova neutrino parameters (i.e., total neutrino luminosity, neutrino temperature). Future spatially resolved, high-resolution X-ray spectroscopy will allow us to investigate the details of neutrino-supernova astrophysics through its signatures in elemental composition not only in Cassiopeia A but also in other remnants.

Keywords: supernova neutrinos; interstellar medium; supernova remnants; explosive nucleosynthesis; nucleosynthesis; x-ray astronomy
Spiral Arm Pattern Motion in the SAO 206462 Protoplanetary Disk

Spiral arms have been observed in more than a dozen protoplanetary disks, yet the origin of nearly all systems is under debate. Multi-epoch monitoring of spiral arm morphology offers a dynamical way to distinguish two leading arm formation mechanisms: companion-driven and gravitational instability induction, since these mechanisms predict distinct motion patterns. By analyzing multi-epoch J-band observations of the SAO 206462 system using the SPHERE instrument on the Very Large Telescope in 2015 and 2016, we measure the pattern motion for its two prominent spiral arms in polarized light. On one hand, if both arms are comoving, they can be driven by a planet at ${86}_{-13}^{+18}$ au on a circular orbit, with gravitational instability motion ruled out. On the other hand, they can be driven by two planets at ${120}_{-30}^{+30}$ au and ${49}_{-5}^{+6}$ au, offering tentative evidence (3.0σ) that the two spirals are moving independently. The independent arm motion is possibly supported by our analysis of a re-reduction of archival observations using the NICMOS instrument on board the Hubble Space Telescope (HST) in 1998 and 2005, yet artifacts including shadows can manifest spurious arm motion in HST observations. We expect future re-observations to better constrain the motion mechanism for the SAO 206462 spiral arms.

Keywords: protoplanetary disks; coronagraphic imaging; orbital motion; planetary system formation
The Impact and Mechanism of the Magnetic Inclination Angle on O+ Escape from Mars

Ion escape from the atmosphere to space is one of the most likely reasons to account for the evolution of the Martian climate. Based on three-dimensional multifluid magnetohydrodynamic simulations, we investigated the impact of the magnetic inclination angle on O+ escape at low altitudes of 275-1000 km under the typical solar wind conditions. Numerical results showed that an outward ion velocity in the direction opposite to the electromagnetic (EM) force results in weak outward flux and leads to ions becoming trapped by the horizontal magnetic field lines at the local horizontal magnetic equator. Much of the EM force can be attributed to the Hall electric force. In the region of high absolute magnetic inclination angle, the outward ion velocity has the same direction as the EM force, which increases the outward flux and causes ions to diffuse upward along open magnetic field lines to higher altitude. In addition, the EM force is mainly provided by the electron pressure gradient force and the motional electric force. Global results for the magnetic inclination angle indicate that the strong crustal field regions in the southern hemisphere are mainly occupied by magnetic field lines with high absolute magnetic inclination angle, while horizontal field lines are dominant in the northern hemisphere, which leads to a higher O+ escape rate in the Martian southern hemisphere than in the northern, from altitudes of 275 to 1000 km. This is a significant advance in understanding the impact and mechanism of the Martian magnetic field directions on ion escape.

Keywords: mars; solar-planetary interactions; magnetic anomalies; magnetohydrodynamics
Magnetic Field Dropouts at Near-Sun Switchback Boundaries: A Superposed Epoch Analysis

During Parker Solar Probe's first close encounter with the Sun in early 2018 November, a large number of impulsive rotations in the magnetic field were detected within 50 Rs; these also occurred in association with short-lived impulsive solar wind bursts in speed. These impulsive features are now called "switchback" events. We examined a set of these switchbacks where the boundary transition into and out of the switchback was abrupt, with fast B rotations and simultaneous solar wind speed changes occurring on timescales of less than ∼10 s; these thus appear as step function-like changes in the radial component of B and V. Our objective was to search for any diamagnetic effects that might occur especially if the boundaries are associated with quick changes in density (i.e., a steep spatial density gradient at the switchback boundary). We identified 25 switchback entries where the radial component of B, Br, quickly transitioned from large negative to positive values and Vr simultaneously abruptly increased (i.e., step-up transitions) and 28 switchback exits where Br quickly transitioned from large positive to negative values and Vr simultaneously abruptly decreased (i.e., step-down transitions). We then performed a superposed epoch analysis on each of these sets of events. We found these fast-transitioning events typically had a clear and distinct decrease in the magnetic field magnitude by 7%-8% detected exactly at the boundary. The presence of the $| B| $ dropout suggests there is a diamagnetic current present at the boundary.

Keywords: the sun; solar wind; solar physics
Critical Metallicity of Cool Supergiant Formation. I. Effects on Stellar-mass Loss and Feedback

This paper systematically studies the relation between metallicity and mass loss of massive stars. We perform one-dimensional stellar evolution simulations and build a grid of ~2000 models with initial masses ranging between 11 and 60 M ⊙ and absolute metallicities Z between 0.00001 and 0.02. Steady-state winds, comprising hot main-sequence winds and cool supergiant winds, are the main drivers of the mass loss of massive stars in our models. We calculate the total mass loss over the stellar lifetime for each model. Our results reveal the existence of a critical metallicity Z c at Z ~ 10-3, where the mass loss exhibits a dramatic jump. If Z > Z c, massive stars tend to evolve into cool supergiants, and a robust cool wind is operational. In contrast, if Z < Z c, massive stars usually remain as blue supergiants, wherein the cool wind is not activated and the mass loss is generally weak. Moreover, we calculate the wind feedback in a 105 M ⊙ star cluster with the Salpeter initial mass function. The kinetic energy released by winds does not exhibit any significant transition at Z c because the wind velocity of a cool supergiant wind is low and contributes little to the kinetic energy. The effects of critical metallicity provide implications for the fates of metal-poor stars in the early universe.

Keywords: stellar mass loss; massive stars; late-type supergiant stars; metallicity
Observation of a Lunar Eclipse at 89, 150, and 183 GHz

We describe the measurement of the brightness temperature of the Moon from space during a total lunar eclipse by using a microwave sounder aboard a weather satellite. Previous observations of lunar eclipses were inconsistent and did not cover the frequency range between 100 and 200 GHz. In this work, we seek to establish a reliable relationship between frequency and drop in brightness temperature during a total eclipse for millimeter wavelengths. For this purpose, we chose the eclipse on 2004 October 28, because it coincided with appearances of the Moon in the deep space view of the Advanced Microwave Sounding Unit-B on NOAA-15. It was therefore possible to measure its disk-integrated radiance at 89, 150, and 183 GHz at 100 minutes intervals. Our observations are, to the best of our knowledge, the only ones between 100 and 200 GHz, and demonstrate the nearly linear dependency on frequency of the maximum relative drop in effective temperature during an eclipse. The slope of this function is m = 0.00114 ± 0.00017 GHz-1 in the range 88-300 GHz. The good agreement between the variations of the effective lunar temperature and a new radiative-transfer model suggests that the Moon is suitable as a flux standard for microwave observations with beam sizes larger than 0.5°.

Keywords: lunar eclipses; total eclipses; the moon; millimeter astronomy
GW190521 May Be an Intermediate-mass Ratio Inspiral

GW190521 is the first confident observation of a binary black hole merger with total mass $M\gt 100\,{M}_{\odot }$ . Given the lack of observational constraints at these masses, we analyze GW190521 considering two different priors for the binary's masses: uniform in mass ratio and source-frame total mass, and uniform in source-frame component masses. For the uniform in mass-ratio prior, we find that the component masses are ${m}_{1}^{\mathrm{src}}={168}_{-61}^{+15}\,{M}_{\odot }$ and ${m}_{2}^{\mathrm{src}}={16}_{-3}^{+33}\,{M}_{\odot }$ . The uniform in component-mass prior yields a bimodal posterior distribution. There is a low-mass-ratio mode ( $q\lt 4$ ) with ${m}_{1}^{\mathrm{src}}={100}_{-18}^{+17}\,{M}_{\odot }$ and ${m}_{2}^{\mathrm{src}}={57}_{-16}^{+17}\,{M}_{\odot }$ and a high-mass-ratio mode ( $q\geqslant 4$ ) with ${m}_{1}^{\mathrm{src}}={166}_{-35}^{+16}\,{M}_{\odot }$ and ${m}_{2}^{\mathrm{src}}={16}_{-3}^{+14}\,{M}_{\odot }$ . Although the two modes have nearly equal posterior probability, the maximum-likelihood parameters are in the high-mass-ratio mode, with ${m}_{1}^{\mathrm{src}}=171\,{M}_{\odot }$ and ${m}_{2}^{\mathrm{src}}=16\,{M}_{\odot }$ , and a signal-to-noise ratio of 16. These results are consistent with the proposed "mass gap" produced by pair-instability in supernovae. Our results differ from those published in Abbott et al. We find that a combination of the prior used and the constraints applied may have prevented that analysis from sampling the high-mass-ratio mode. An accretion flare in AGN J124942.3+344929 was observed in possible coincidence with GW190521 by the Zwicky Transient Facility. We report parameters assuming a common origin; however, the spatial agreement of GW190521 and the electromagnetic flare alone does not provide convincing evidence for the association ( $\mathrm{ln}{ \mathcal B }\gtrsim -4$ ).

Keywords: gravitational waves
Pulsations of the Rapidly Oscillating Ap Star KIC 10685175 Revisited by TESS

KIC 10685175 (TIC 264509538) was discovered to be a rapidly oscillating Ap star from Kepler long-cadence data using super-Nyquist frequency analysis. It was reobserved by the Transiting Exoplanet Survey Satellite (TESS) with 2 minute cadence data in Sectors 14 and 15. We analyzed the TESS light curves, finding that the previously determined frequency is a Nyquist alias. The revised pulsation frequency is 191.5151 ± 0.0005 day-1 (P = 7.52 minutes) and the rotation frequency is 0.32229 ± 0.00005 day-1 (Prot = 3.1028 days). The star is an oblique pulsator with a pulsation amplitude modulated by the rotation, reaching a maximum pulsation amplitude at the time of the rotational light minimum. The oblique pulsation generates a frequency quintuplet split by exactly the rotation frequency. The phases of sidelobes, the pulsation phase modulation, and a spherical harmonic decomposition all show this star to be pulsating in a distorted quadrupole mode. Following the oblique pulsator model, we calculated the rotation inclination i and magnetic oblique β of this star, which provide detailed information of pulsation geometry. The i and β derived by the best fit of pulsation amplitude and phase modulation through a theoretical model differ from those calculated for a pure quadrupole, indicating the existence of strong magnetic distortion. The model also predicts the polar magnetic field strength is as high as about 6 kG which is predicted to be observed in a high-resolution spectrum of this star.

Keywords: rapidly oscillating ap star; oblique rotators; asteroseismology
Constraints on the Binarity of the WN3/O3 Class of Wolf-Rayet Stars

The WN3/O3 Wolf-Rayet (WR) stars were discovered as part of our survey for WRs in the Magellanic Clouds. The WN3/O3s show the emission lines of a high-excitation WN star and the absorption lines of a hot O-type star, but our prior work has shown that the absorption spectrum is intrinsic to the WR star. Their place in the evolution of massive stars remains unclear. Here we investigate the possibility that they are the products of binary evolution. Although these are not WN3+O3 V binaries, they could still harbor unseen companions. To address this possibility, we have conducted a multiyear radial velocity study of six of the nine known WN3/O3s. Our study finds no evidence of statistically significant radial velocity variations, and allows us to set stringent upper limits on the mass of any hypothetical companion star: for probable orbital inclinations, any companion with a period less than 100 days must have a mass <2M ⊙. For periods less than 10 days, any companion would have to have a mass <1M ⊙. We argue that scenarios where any such companion is a compact object are unlikely. The absorption lines indicate a normal projected rotational velocity, making it unlikely that these stars evolved with the aid of a companion star that has since merged. The modest rotation also suggests that these stars are not the result of homogenous evolution. Thus it is likely that these stars are a normal but short-lived stage in the evolution of massive stars. * 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