adsabs/SciX_UAT_keywords huggingface dataset:
Observational Kinematic Characteristics of Blobs in Solar Coronal Helmet and Pseudo Streamers

We examine two helmet and two pseudo streamers (HSs and PSs) observed on 2018 and 2019. The HSs (PSs) have dark coronal cavities and stretched loop structures (twin coronal cavities and narrow plasma sheet) at their bases, which are well observed in K-Coronagraph (K-Cor). Their outer-corona structures (top of core, cusp, and stalk) are also clearly identified in LASCO-C2. By investigating LASCO-C2 images, we find the following characteristics. (1) Blobs persistently move outward along the centers of HSs and PSs as well as their legs until the base of a stalk. We also detect outward-moving blobs along their outsides. (2) Blobs along the HS centers formed below tops of cores (~2.6 R⊙), while the other HS and PS blobs might be generated below 2.0 R⊙. (3) HS blob speeds are generally similar to or smaller than the solar wind speed based on Parker's model, while PS ones are larger. (4) HS (PS) blob speeds along the streamer centers are slightly smaller (larger) than those along the streamer legs, might be explained by the expansion-factor model. The blob speeds inside streamer structures (centers and legs) are larger than outside ones closer to solar equator, similar to typical solar wind speed distributions at solar minimum. (5) Several blobs along the HS centers only show sudden speed jumps at streamer cusps. These might be caused by sunward tension forces of overlying stretched closed fields and/or bidirectional outflows by magnetic reconnections in the cusps.

Keywords: solar coronal streamers
The Nucleus of Interstellar Comet 2I/Borisov

We present high-resolution imaging observations of interstellar comet 2I/Borisov (formerly C/2019 Q4) obtained using the Hubble Space Telescope. Scattering from the comet is dominated by a coma of large particles (characteristic size ∼0.1 mm) ejected anisotropically. Convolution modeling of the coma surface brightness profile sets a robust limit to the spherical-equivalent nucleus radius rn ≤ 0.5 km (geometric albedo 0.04 assumed). We obtain an independent constraint based on the nongravitational acceleration of the nucleus, finding rn > 0.2 km (nucleus density ρ = 500 kg m-3 assumed). The profile and the nongravitational constraints cannot be simultaneously satisfied if ρ ≤ 25 kg m-3; the nucleus of comet Borisov cannot be a low-density fractal assemblage of the type proposed elsewhere for the nucleus of 1I/'Oumuamua. We show that the spin-up timescale to outgassing torques, even at the measured low production rates, is comparable to or shorter than the residence time in the Sun's water sublimation zone. The spin angular momentum of the nucleus should be changed significantly during the current solar flyby. Lastly, we find that the differential interstellar size distribution in the 0.5 mm to 100 m size range can be represented by power laws with indices <4 and that interstellar bodies of 100 m size scale strike Earth every one to two hundred million years.

Keywords: comets; long period comets
Multiwavelength Bulge-Disk Decomposition for the Galaxy M81 (NGC 3031). I. Morphology

A panchromatic investigation of morphology for the early-type spiral galaxy M81 is presented in this paper. We perform bulge-disk decomposition in M81 images at a total of 20 wave bands from far-UV to near-IR (NIR) obtained with GALEX, Swift, Sloan Digital Sky Survey, WIYN, Two Micron All Sky Survey, Wide-field Infrared Survey Explorer, and Spitzer. Morphological parameters such as Sérsic index, effective radius, position angle, and axis ratio for the bulge and the disk are thus derived at all of the wave bands, which enables quantifying the morphological K-correction for M81 and makes it possible to reproduce images for the bulge and the disk in the galaxy at any wave band. The morphology as a function of wavelength appears as a variable-slope trend of the Sérsic index and the effective radius, in which the variations are steep at UV-optical and shallow at optical-NIR bands; the position angle and the axis ratio keep invariable at least at optical-NIR bands. It is worth noting that the Sérsic index for the bulge reaches ~4-5 at optical and NIR bands, but drops to ~1 at UV bands. This difference brings forward a caveat that a classical bulge is likely misidentified for a pseudobulge or no bulge at high redshifts where galaxies are observed through rest-frame UV channels with optical telescopes. The next work of this series is planned to study spatially resolved spectral energy distributions for the bulge and the disk, respectively, and thereby explore stellar population properties and star formation/quenching history for the galaxy composed of the subsystems.

Keywords: extragalactic astronomy; galaxy photometry; galaxies; galaxy structure
The Magellan-TESS Survey. I. Survey Description and Midsurvey Results

Kepler revealed that roughly one-third of Sunlike stars host planets orbiting within 100 days and between the size of Earth and Neptune. How do these planets form, what are they made of, and do they represent a continuous population or multiple populations? To help address these questions, we began the Magellan-TESS Survey (MTS), which uses Magellan II/PFS to obtain radial velocity (RV) masses of 30 TESS-detected exoplanets and develops an analysis framework that connects observed planet distributions to underlying populations. In the past, small-planet RV measurements have been challenging to obtain due to host star faintness and low RV semiamplitudes and challenging to interpret due to the potential biases in target selection and observation planning decisions. The MTS attempts to minimize these biases by focusing on bright TESS targets and employing a quantitative selection function and observing strategy. In this paper, we (1) describe our motivation and survey strategy, (2) present our first catalog of planet density constraints for 27 TESS Objects of Interest (TOIs; 22 in our population analysis sample, 12 that are members of the same systems), and (3) employ a hierarchical Bayesian model to produce preliminary constraints on the mass-radius (M-R) relation. We find that the biases causing previous M-R relations to predict fairly high masses at 1 R⊕ have been reduced. This work can inform more detailed studies of individual systems and offer a framework that can be applied to future RV surveys with the goal of population inferences. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. † Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Keywords: exoplanet astronomy; radial velocity; transit photometry; astrostatistics techniques
A "Quick Look" at All-sky Galactic Archeology with TESS: 158,000 Oscillating Red Giants from the MIT Quick-look Pipeline

We present the first near all-sky yield of oscillating red giants from the prime mission data of NASA's Transiting Exoplanet Survey Satellite (TESS). We apply machine learning toward long-cadence TESS photometry from the first data release by the MIT Quick-look Pipeline to automatically detect the presence of red giant oscillations in frequency power spectra. The detected targets are conservatively vetted to produce a total of 158,505 oscillating red giants, which is an order of magnitude increase over the yield from Kepler and K2 and a lower limit to the possible yield of oscillating giants across TESS's nominal mission. For each detected target, we report effective temperatures and radii derived from colors and Gaia parallaxes, as well as estimates of their frequency at maximum oscillation power. Using our measurements, we present the first near all-sky Gaia-asteroseismology mass map, which shows global structures consistent with the expected stellar populations of our Galaxy. To demonstrate the strong potential of TESS asteroseismology for Galactic archeology even with only one month of observations, we identify 354 new candidates for oscillating giants in the Galactic halo, display the vertical mass gradient of the Milky Way disk, and visualize correlations of stellar masses with kinematic phase-space substructures, velocity dispersions, and α-abundances.

Keywords: asteroseismology; stellar oscillations; astronomy data analysis
Bombardment of CO Ice by Cosmic Rays. I. Experimental Insights into the Microphysics of Molecule Destruction and Sputtering

We present a dedicated experimental study of microscopic mechanisms controlling radiolysis and sputtering of astrophysical ices upon bombardment by cosmic-ray ions. Such ions are slowed down owing to inelastic collisions with bound electrons, resulting in ionization and excitation of ice molecules. In experiments on CO ice irradiation, we show that the relative contribution of these two mechanisms of energy loss to molecule destruction and sputtering can be probed by selecting ion energies near the peak of the electronic stopping power. We have observed a significant asymmetry, in both the destruction cross section and the sputtering yield, for pairs of ion energies corresponding to the same values of the stopping power on either side of the peak. This implies that the stopping power does not solely control these processes, as usually assumed in the literature. Our results suggest that electronic excitations represent a significantly more efficient channel for radiolysis and, likely, for sputtering of CO ice. We also show that the charge state of incident ions and the rate for CO+ production in the ice have a negligible effect on these processes.

Keywords: cosmic rays; astrochemistry; laboratory astrophysics
Observations of Magnetic Fields Surrounding LkHα 101 Taken by the BISTRO Survey with JCMT-POL-2

We report the first high spatial resolution measurement of magnetic fields surrounding LkHα 101, part of the Auriga-California molecular cloud. The observations were taken with the POL-2 polarimeter on the James Clerk Maxwell Telescope within the framework of the B-fields In Star-forming Region Observations (BISTRO) survey. Observed polarization of thermal dust emission at 850 μm is found to be mostly associated with the redshifted gas component of the cloud. The magnetic field displays a relatively complex morphology. Two variants of the Davis-Chandrasekhar-Fermi method, unsharp masking and structure function, are used to calculate the strength of magnetic fields in the plane of the sky, yielding a similar result of BPOS ∼ 115 μG. The mass-to-magnetic-flux ratio in critical value units, λ ∼ 0.3, is the smallest among the values obtained for other regions surveyed by POL-2. This implies that the LkHα 101 region is subcritical, and the magnetic field is strong enough to prevent gravitational collapse. The inferred δB/B0 ∼ 0.3 implies that the large-scale component of the magnetic field dominates the turbulent one. The variation of the polarization fraction with total emission intensity can be fitted by a power law with an index of α = 0.82 ± 0.03, which lies in the range previously reported for molecular clouds. We find that the polarization fraction decreases rapidly with proximity to the only early B star (LkHα 101) in the region. Magnetic field tangling and the joint effect of grain alignment and rotational disruption by radiative torques can potentially explain such a decreasing trend.

Keywords: interstellar magnetic fields; molecular clouds; star formation
Nondetection of Helium in the Hot Jupiter WASP-48b

Hot Jupiters orbiting extremely close to their host star may experience atmospheric escape due to the large amounts of high-energy radiation they receive. Understanding the conditions under which this occurs is critical, as atmospheric escape is believed to be a driving factor in sculpting planetary populations. In recent years, the near-infrared 10833 Å helium feature has been found to be a promising spectral signature of atmospheric escape. We use transmission spectroscopy to search for excess helium absorption in the extended atmosphere of WASP-48b, a hot Jupiter orbiting a slightly evolved, rapidly rotating F star. The data were collected using the Habitable-zone Planet Finder spectrograph on the Hobby-Eberly Telescope. Observations were taken over the course of seven nights, from which we obtain three transits. No detectable helium absorption is seen, as absorption depth is measured to -0.0025 ± 0.0021, or 1.2σ from a null detection. This nondetection follows our current understanding of decreasing stellar activity (and thus high-energy radiation) with age. We use a 1D isothermal Parker wind model to compare with our observations and find that our nondetection can best be explained with a low planetary mass-loss rate and high thermosphere temperature. We explore our results within the context of the full sample of helium detections and nondetections to date. Surprisingly, comparing helium absorption with the stellar activity index $\mathrm{log}\ {R}_{\mathrm{HK}}^{{\prime} }$ reveals a large spread in the correlation between these two factors, suggesting that there are additional parameters influencing the helium absorption strength.

Keywords: exoplanet astronomy; exoplanet atmospheres; hot jupiters; high resolution spectroscopy; transmission spectroscopy
An Update on the Future Flyby of Gliese 710 to the Solar System Using Gaia EDR3: Slightly Closer and a Tad Later than Previous Estimates

Future stellar encounters with the Sun might disturb the outskirts of the solar system, for close-enough passages. Such encounters may send small bodies toward the inner regions of the solar system. In the near future and among known stars, none will pass closer to the Sun than Gliese 710. Here, we present an updated analysis of this topic using Gaia EDR3 data. Our new estimate confirms, within errors, those already published, but suggests a slightly closer in distance (at 0.051 ± 0.003 pc) and later in time (in 1.29 ± 0.04 Myr) flyby of Gliese 710 to the solar system.

Keywords: solar neighborhood; stellar kinematics; solar system
Exploring the Evolution of a Dwarf Spheroidal Galaxy with Smoothed-particle Hydrodynamics Simulations. I. Stellar Feedback

A fundamental question regarding the evolution of dwarf spheroidal galaxies is the identification of the key physical mechanisms responsible for gas depletion. Here, we focus on the study of stellar feedback in isolated dwarf spheroidal galaxies by performing numerical simulations using a modified version of the smoothed-particle hydrodynamics code GADGET-3. The Milky Way satellite Leo II (PGC 34176) in the Local Group was considered as our default model dwarf galaxy. The parameter space for the stellar feedback models was explored to match observational constraints of Leo II, such as residual gas mass, total mass within the tidal radius, star formation history, final stellar mass, stellar ages, and metallicity. Additionally, we examined the impact of the binary fraction of stars, initial mass function, dark matter halo mass, and initial gas reservoir. Many simulations revealed recent star formation quenching due to stellar feedback. In general, the gas depletion, expected star formation history, total mass of stars, and total mass within the tidal radius were adequately reproduced in the simulations when compared to observational estimates. However, there were discrepancies in the distribution of stellar ages and metallicities, which suggested that the cosmic gas infall would play a more complex role in our dwarf spheroidal galaxy than captured by a monolithic infall scenario. Our results suggest that currently quenched dwarf galaxies may not necessarily need to evolve within clusters or groups and that stellar feedback alone could be a sufficient factor in shaping at least some of these galaxies as we observe them today.

Keywords: dwarf spheroidal galaxies; hydrodynamical simulations; stellar feedback
Bulk Flow Motion Detection in the Local Universe with Pantheon+ Type Ia Supernovae

The bulk flow in the Local Universe is a collective phenomenon due to the peculiar motions of matter structures, which, instead of moving in random directions, appears to follow an approximate dipole velocity flow. We apply a directional analysis to investigate, through the Hubble-Lemaître diagram, the angular dependence of the Hubble constant H 0 of a sample of Type Ia supernovae from the Pantheon+ catalog in the Local Universe (0.015 ≤ z ≤ 0.06). We perform a directional analysis that reveals a statistically significant dipole variation of H 0, at more than 99.9% confidence level, showing that matter structures follow a dipole bulk flow motion toward (l, b) = (326.°1 ± 11.°2, 27.°8 ± 11.°2), close to the Shapley supercluster (l Shapley, b Shapley) = (311.°5, 32.°3), with velocity 132.14 ± 109.3 km s‑1 at the effective distance 102.83 ± 10.2 Mpc. Interestingly, the antipodal direction of this dipole points close to the Dipole Repeller structure. Our analyses confirm that the gravitational dipole system Shapley-Dipole Repeller explains well the observed bulk flow velocity field in the Local Universe. Furthermore, we performed robustness tests that support our results. Additionally, our approach provides a measurement of the Hubble constant H 0 = 70.39 ± 1.4 km s‑1 Mpc‑1, at the effective distance 102.8 Mpc, z ≃ 0.025.

Keywords: large-scale structure of the universe; observational cosmology; type ia supernovae
Concerning the Verity of the MMRD Relation for Novae

It has long been claimed that novae reaching the highest luminosity at the peak of their eruptions appear to fade the fastest from maximum light. The relationship between peak brightness and fade rate is known as the Maximum-Magnitude, Rate-of-Decline (MMRD) relation. Lightcurve parameters for the most recent sample of M31 recurrent novae are presented and used to buttress the case that the observed MMRD relation can be explained as a consequence of observational selection effects coupled with expectations from standard nova models.

Keywords: cataclysmic variable stars; novae; recurrent novae
Revealing the Physical Conditions around Sgr A* Using Bayesian Inference. I. Observations and Radiative Transfer

We report subarcsecond Atacama Large Millimeter/submillimeter Array (ALMA) observations between 272 and 375 GHz toward Sgr A*'s circumnuclear disk (CND). Our data comprise eight individual pointings, with significant SiO (87-76) and SO (7-6) emission detected toward 98 positions within these pointings. Additionally, we identify H2CS (91,9-81,8), OCS (25-24), and CH3OH (21,1-20,2) toward a smaller subset of positions. By using the observed peak line flux density, together with a Bayesian inference technique informed by radiative transfer models, we systematically recover the physical gas conditions toward each of these positions. We estimate that the bulk of the surveyed gas has temperature Tkin < 500 K and density nH ⪅ 106 cm-3, consistent with previous studies of similar positions as traced by HCN clumps. However, we identify an uncharacteristically hot (Tkin ≈ 600 K) and dense (nH ≈ 106 cm-3) source in the Northeastern Arm. This position is found to be approximately consistent with a gravitationally bound region dominated by turbulence. We also identify a nearby cold (Tkin ≈ 60 K) and extremely dense (nH ≈ 107 cm-3) position that is again potentially bound and dominated by turbulence. We also determine that the total gas mass contained within the CND is MCND ≲ 4 × 104 M⊙. Furthermore, we qualitatively note that the observed chemical enrichment across large scales within the CND is consistent with bulk grain processing, though multiple desorption mechanisms are plausibly responsible. Further chemical modeling is required to identify the physical origin of the grain processing, as well as the localized H2CS and OCS emission.

Keywords: interstellar medium; molecular clouds; star formation; astrochemistry; radiative transfer; bayesian statistics; observational astronomy; spectral line identification
Hunting Distant BL Lacertae Objects with the Photometric Technique Using Swift and SARA

BL Lacertae objects represent a large fraction (22%) of γ-ray sources in the Third Fermi Large Area Telescope catalog (3FGL). Nearly half of the BL Lac object population remains without a redshift because of their featureless optical spectra. We aim to increase the number of BL Lac objects with a redshift measurement by using the photometric technique. For this work, we have used six Swift-UVOT filters and SDSS g', r', i', and z' optical filters mounted on the 0.65 m SARA-CTIO located in Chile and the 1.0 m SARA-ORM in the Canary Islands. A sample of 45 sources was selected from the 3FGL catalog for which photometry was performed in 10 optical and UV filters to obtain redshift measurements. We found three sources with z > 1.3, while reliable upper limits have been provided for 17 sources. The results presented here bring the total number of high-z (z > 1.3) BL Lac objects to 29.

Keywords: active galactic nuclei; active galaxies; blazars; high energy astrophysics; high-redshift galaxies
A New Sample of Transient Ultraluminous X-Ray Sources Serendipitously Discovered by Swift/XRT

Ultraluminous X-ray sources (ULXs) are our best laboratories for studying extreme super-Eddington accretion. Most studies of these objects are of relatively persistent sources; however, there is growing evidence to suggest a large fraction of these sources are transient. Here we present a sample of five newly reported transient ULXs in the galaxies NGC 4945, NGC 7793, and M81 serendipitously discovered in Swift/XRT observations. Swift monitoring of these sources have provided well-sampled lightcurves, allowing for us to model the lightcurves with the disk-instability model of Hameury & Lasota, which implies durations of 60-400 days and that the mass-accretion rate through the disk is close to or greater than the Eddington rate. Of the three source regions with prior Hubble Space Telescope imaging, color-magnitude diagrams of the potential stellar counterparts show varying ages of the possible stellar counterparts. Our estimation of the rates of these sources in these three galaxies is 0.4-1.3 yr-1. We find that, while persistent ULXs dominate the high end of galaxy luminosity functions, the number of systems that produce ULX luminosities are likely dominated by transient sources.

Keywords: x-ray transient sources; transient sources; x-ray sources; ultraluminous x-ray sources
Hydrodynamical Simulations of Black Hole Binary Formation in AGN Disks

We study close encounters between two single black holes (BHs) embedded in an AGN disk using a series of global 2D hydrodynamics simulations. We find that when the disk density is sufficiently high, bound BH binaries can be formed by the collision of their circum-single disks. Our analysis demonstrates that, after a BH pair passes the pericenter of their relative trajectory, post-collision gas drag may slow down the BHs, possibly forcing the two BHs to stay tightly bound. A binary formed by a close encounter can have a compact semimajor axis, large eccentricity, and retrograde orbital angular momentum. We provide a fitting formula that can accurately predict whether a close encounter can form a binary based on the gas mass and the incoming energy of the encounter. This fitting formula can be easily implemented in other long-term simulations that study the dynamical evolution of BHs in active galactic nucleus disks.

Keywords: active galactic nuclei; black holes; galaxy accretion disks; gravitational wave sources; hydrodynamical simulations; orbital evolution