Sazuna/UAT_keywords huggingface dataset:
Variable Warm Dust around the Herbig Ae Star HD 169142: Birth of a Ring?. The Herbig Ae star HD 169142 is known to have a gaseous disk with a large inner hole, and also a photometrically variable inner dust component in the sub-astronomical-unit region. Following up on our previous analysis, we further studied the temporal evolution of inner dust around HD 169142, which may provide information on the evolution from late-stage protoplanetary disks to debris disks. We used near-infrared interferometric observations obtained with the Very Large Telescope Interferometer/PIONIER to constrain the dust distribution at three epochs spanning six years. We also studied the photometric variability of HD 169142 using our optical-infrared observations and archival data. Our results indicate that a dust ring at ∼0.3 au formed some time between 2013 and 2018, and then faded (but did not completely disappear) by 2019. The short-term variability resembles that observed in extreme debris disks, and is likely related to short-lived dust of secondary origin, though variable shadowing from the inner ring could be an alternative interpretation. If confirmed, this is the first direct detection of secondary dust production inside a protoplanetary disk. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programs 0101.C-0367 and 60.A-9135.

Keywords: Herbig Ae/Be stars, Pre-main sequence stars, Debris disks, Protoplanetary disks
Superabundance of Exoplanet Sub-Neptunes Explained by Fugacity Crisis. Transiting planets with radii 2-3 R ⊕ are much more numerous than larger planets. We propose that this drop-off is so abrupt because at R ∼ 3 R ⊕ base-of-atmosphere pressure is high enough for the atmosphere to readily dissolve into magma, and this sequestration acts as a strong brake on further growth. The viability of this idea is demonstrated using a simple model. Our results support extensive magma-atmosphere equilibration on sub-Neptunes, with numerous implications for sub-Neptune formation and atmospheric chemistry.

Keywords: Extrasolar rocky planets, Exoplanet evolution, Exoplanet atmospheres
Spectropolarimetric Insight into Plasma Sheet Dynamics of a Solar Flare. We examine spectropolarimetric data from the Coronal Multi-channel Polarimeter (CoMP) instrument, acquired during the evolution of the 2017 September 10 X8.2 solar flare on the western solar limb. CoMP captured linearly polarized light from two emission lines of Fe XIII at 1074.7 and 1079.8 nm, from 1.03 to 1.5 solar radii. We focus here on the hot plasma sheet lying above the bright flare loops and beneath the ejected coronal mass ejection. The polarization has a striking and coherent spatial structure, with unexpectedly small polarization aligned with the plasma sheet. By elimination, we find that small-scale magnetic field structure is needed to cause such significant depolarization, and suggest that plasmoid formation during reconnection (associated with the tearing-mode instability) creates magnetic structure on scales below instrument resolution of 6 Mm. We conclude that polarization measurements with new coronagraphs, such as the upcoming Daniel K. Inouye Solar Telescope, will further enhance our understanding of magnetic reconnection and development of turbulence in the solar corona.

Keywords: Solar magnetic fields, Spectropolarimetry, Solar flares, Solar magnetic reconnection
Filling the Mass Gap: How Kilonova Observations Can Unveil the Nature of the Compact Object Merging with the Neutron Star. In this Letter we focus on the peculiar case of a coalescing compact-object binary whose chirp mass is compatible both with a neutron star-neutron star and black hole-neutron star system, with the black hole in the ∼3-5 M ⊙ range defined as the “mass gap.” Some models of core-collapse supernovae predict the formation of such low-mass black holes and a recent observation seems to confirm their existence. Here we show that the nature of the companion to the neutron star can be inferred from the properties of the kilonova emission once we know the chirp mass, which is the best constrained parameter inferred from the gravitational signal in low-latency searches. In particular, we find that the kilonova in the black hole-neutron star case is far more luminous than in the neutron star-neutron star case, even when the black hole is nonspinning. The difference in the kilonovae brightness arises primarily from the mass ejected during the merger. Indeed, in the considered interval of chirp masses, the mass ejection in double neutron star mergers is at its worst as the system promptly forms a black hole. Instead mass ejection for the black hole-neutron star case is at its best as the neutron stars have low mass/large deformability. The kilonovae from black hole-neutron star systems can differ by two to three magnitudes. The outcome is only marginally dependent on the equation of state. The difference is above the systematics in the modeling.

Keywords: Neutron stars, Gamma-ray bursts, Black holes, Compact binary stars, Gravitational waves
Gravitational-wave Sources from Mergers of Binary Black Holes Catalyzed by Flyby Interactions in the Field. Several scenarios were suggested for the origins of gravitational-wave (GW) sources from mergers of stellar binary black holes (BBHs). Here we propose a novel origin through catalyzed formation of GW sources from ultra-wide binaries in the field. Such binaries experience perturbations from random stellar flybys that excite their eccentricities. Once a wide binary is driven to a sufficiently small pericenter approach, GW emission becomes significant, and the binary inspirals and merges. We derive an analytic model and verify it with numerical calculation to compute the merger rate to be ∼ 1× {f}wide} {Gpc}}-3 {{yr}}-1 (f wide is the fraction of wide BH-binaries), which is a relevant contribution to the observationally inferred rate. The observational signatures from this channel include spin-orbit misalignment; preference for high mass ratio BBH; preference for high velocity dispersion host galaxies; and a uniform delay-time distribution.

Keywords: Wide binary stars, Binary stars, Interstellar dynamics, Gravitational wave sources
The Acceleration and Confinement of Energetic Electrons by a Termination Shock in a Magnetic Trap: An Explanation for Nonthermal Loop-top Sources during Solar Flares. Nonthermal loop-top sources in solar flares are the most prominent observational signatures that suggest energy release and particle acceleration in the solar corona. Although several scenarios for particle acceleration have been proposed, the origin of the loop-top sources remains unclear. Here we present a model that combines a large-scale magnetohydrodynamic simulation of a two-ribbon flare with a particle acceleration and transport model for investigating electron acceleration by a fast-mode termination shock (TS) at the loop top. Our model provides spatially resolved electron distribution that evolves in response to the dynamic flare geometry. We find a concave-downward magnetic structure located below the flare TS, induced by the fast reconnection downflows. It acts as a magnetic trap to confine the electrons at the loop top for an extended period of time. The electrons are energized significantly as they cross the shock front, and eventually build up a power-law energy spectrum extending to hundreds of kiloelectron volts. We suggest that this particle acceleration and transport scenario driven by a flare TS is a viable interpretation for the observed nonthermal loop-top sources.

Keywords: Solar flares, Solar magnetic reconnection, Solar x-ray emission, Non-thermal radiation sources, Shocks, Solar particle emission
LBT/PEPSI Spectropolarimetry of a Magnetic Morphology Shift in Old Solar-type Stars. Solar-type stars are born with relatively rapid rotation and strong magnetic fields. Through a process known as magnetic braking, the rotation slows over time as stellar winds gradually remove angular momentum from the system. The rate of angular momentum loss depends sensitively on the magnetic morphology, with the dipole field exerting the largest torque on the star. Recent observations suggest that the efficiency of magnetic braking may decrease dramatically in stars near the middle of their main-sequence lifetimes. One hypothesis to explain this reduction in efficiency is a shift in magnetic morphology from predominantly larger to smaller spatial scales. We aim to test this hypothesis with spectropolarimetric measurements of two stars that sample chromospheric activity levels on opposite sides of the proposed magnetic transition. As predicted, the more active star (HD 100180) exhibits a significant circular polarization signature due to a nonaxisymmetric large-scale magnetic field, while the less active star (HD 143761) shows no significant signal. We identify analogs of the two stars among a sample of well-characterized Kepler targets, and we predict that the asteroseismic age of HD 143761 from future Transiting Exoplanet Survey Satellite observations will substantially exceed the age expected from gyrochronology. We conclude that a shift in magnetic morphology likely contributes to the loss of magnetic braking in middle-aged stars, which appears to coincide with the shutdown of their global dynamos. The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona Board of Regents; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, The Leibniz Institute for Astrophysics Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota and University of Virginia.

Keywords: Spectropolarimetry, Solar analogs, Stellar magnetic fields, Stellar evolution
Candidate Hypervelocity Red Clump Stars in the Galactic Bulge Found Using the VVV and Gaia Surveys. We propose a new way to search for hypervelocity stars (HVS) in the Galactic bulge, by using red clump (RC) giants, that are good distance indicators. The second Gaia Data Release and the near-IR data from the VISTA Variables in the Via Lactea (VVV) Survey led to the selection of a volume limited sample of 34 bulge RC stars. A search in this combined data set leads to the discovery of seven candidate hypervelocity red clump stars in the Milky Way bulge. Based on this search we estimate the total production rate of hypervelocity RC stars from the central supermassive black hole (SMBH) to be N HVRC = 3.26 × 10-4 yr-1. This opens up the possibility of finding larger samples of HVS in the Galactic bulge using future surveys, closer to their main production site, if they originated from interactions of binaries with the central SMBH. Based on observations taken within the ESO programs 179.B-2002, and 198.B-2004.

Keywords: Stellar motion, Stellar kinematics, Galactic bulge, Stellar dynamics, Galaxy stellar content, Proper motions
Circumventing the Effects of Projection and Dust Using Inclination-independent Infrared Galaxy Structure Measurements: Method, Error Analysis, and a New Public Catalog of Near-infrared Galaxy Structures. Accurate measurements of galaxy structure are prerequisites for quantitative investigation of galaxy properties or evolution. Yet galaxy inclination, through projection and varying dust effects, strongly affects many commonly used metrics of galaxy structure. Here we demonstrate that collapsing a galaxy’s light distribution onto its major axis gives a “linear brightness profile” that is unaffected by projection. In analogy to widely used half-light radius and concentrations, we use two metrics to describe this light distribution: {x}50, the linear distance containing half of the galaxy’s luminosity, and {c}x={x}90/{x}50, the ratio between the 90% light distance and the 50% light distance. In order to minimize the effects of dust, we apply this technique to a diverse sample of galaxies with moderately deep and high-resolution K-band imaging from the UKIDSS Large Area Survey. Using simulated galaxy images, we find that while our measurements are primarily limited by the surface brightness in the outer parts of galaxies, most local galaxies have high enough surface brightnesses to result in reliable measurements. When applied to real data, our metrics vary from face-on to edge-on by typically ∼5% in {c}x and ∼12% in {x}50, representing factors of several to 10 improvement over existing optical and some infrared catalog measures of galaxy structure. We release a sample of 23,804 galaxies with inclination-independent and dust-penetrated observational proxies for stellar mass, specific star formation rate, half-light size, and concentration.

Keywords: Galaxy structure, Galaxy photometry, Interstellar dust extinction, Galaxies
General-relativistic Resistive Magnetohydrodynamics with Robust Primitive-variable Recovery for Accretion Disk Simulations. Recent advances in black hole astrophysics, particularly the first visual evidence of a supermassive black hole at the center of the galaxy M87 by the Event Horizon Telescope, and the detection of an orbiting “hot spot” nearby the event horizon of Sgr A* in the Galactic center by the Gravity Collaboration, require the development of novel numerical methods to understand the underlying plasma microphysics. Non-thermal emission related to such hot spots is conjectured to originate from plasmoids that form due to magnetic reconnection in thin current layers in the innermost accretion zone. Resistivity plays a crucial role in current sheet formation, magnetic reconnection, and plasmoid growth in black hole accretion disks and jets. We included resistivity in the three-dimensional general-relativistic magnetohydrodynamics (GRMHD) code BHAC and present the implementation of an implicit-explicit scheme to treat the stiff resistive source terms of the GRMHD equations. The algorithm is tested in combination with adaptive mesh refinement to resolve the resistive scales and a constrained transport method to keep the magnetic field solenoidal. Several novel methods for primitive-variable recovery, a key part in relativistic magnetohydrodynamics codes, are presented and compared for accuracy, robustness, and efficiency. We propose a new inversion strategy that allows for resistive-GRMHD simulations of low gas-to-magnetic pressure ratio and highly magnetized regimes as applicable for black hole accretion disks, jets, and neutron-star magnetospheres. We apply the new scheme to study the effect of resistivity on accreting black holes, accounting for dissipative effects as reconnection.

Keywords: Accretion, Black hole physics, Magnetohydrodynamics, Plasma astrophysics, Computational methods, General relativity
Detection of Hundreds of New Planet Candidates and Eclipsing Binaries in K2 Campaigns 0-8. We implement a search for exoplanets in campaigns zero through eight (C0-8) of the K2 extension of the Kepler spacecraft. We apply a modified version of the QATS planet search algorithm to K2 light curves produced by the EVEREST pipeline, carrying out the C0-8 search on 1.5 × 105 target stars with magnitudes in the range of Kp = 9-15. We detect 818 transiting planet candidates, of which 374 were undiscovered by prior searches, with {64, 15, 5, 2, 1} in {2, 3, 4, 5, 6}-planet multiplanet candidate systems, respectively. Of the new planets detected, 100 orbit M dwarfs, including one that is potentially rocky and in the habitable zone. A total of 154 of our candidates reciprocally transit with our solar system: they are geometrically aligned to see at least one solar system planet transit. We find candidates that display transit timing variations and dozens of candidates on both period extremes with single transits or ultrashort periods. We point to evidence that our candidates display similar patterns in frequency and size-period relation to confirmed planets, such as tentative evidence for the radius gap. Confirmation of these planet candidates with follow-up studies will increase the number of K2 planets by up to 50%, and characterization of their host stars will improve statistical studies of planet properties. Our sample includes many planets orbiting bright stars amenable for radial velocity follow-up and future characterization with JWST. We also list the 579 eclipsing binary systems detected as part of this search.

Keywords: Exoplanet catalogs, Exoplanets, Light curves, Exoplanet systems, Transit timing variation method, Eclipsing binary stars, Exoplanet detection methods, Transit photometry
A Search for Variable Stars in the Globular Cluster M4 with K2. We extract light curves for 4554 objects with 9 &lt; G &lt; 19 in the K2 superstamp observations of the globular cluster M4, including 3784 cluster members, and search for variability. Among cluster-member objects, we detect 66 variables, of which 52 are new discoveries. Among objects not belonging to the cluster, we detect 24 variables, of which 20 are new discoveries. We additionally discover 57 cluster-member suspected variables, 10 cluster-non-member suspected variables, and four variables with ambiguous cluster membership. Our light curves reach sub-millimagnitude precision for the cluster horizontal branch, permitting us to detect asteroseismic activity in six horizontal branch stars outside the instability strip and one inside the strip but with only ∼1 mmag amplitude variability. Nineteen additional stars along the red giant branch also have detected asteroseismic variability. Several eclipsing binaries are found in the cluster, including a 4.6 day detached eclipsing binary and an EW-class eclipsing binary, as well as an EW with uncertain cluster membership and three other candidate EWs. A 22 day detached eclipsing binary is also found outside the cluster. We identify a candidate X-ray binary that is a cluster member with quiescent and periodic ∼20 mmag optical variability. We also obtain high-precision light curves for 10 of the previously known RR Lyrae variables in the cluster and identify one as a candidate Blazhko variable with a Blazhko period in excess of 78 days. We make our light curves publicly available.

Keywords: Globular star clusters, Eclipses, X-ray binary stars, Binary stars, Close binary stars, W Ursae Majoris variable stars, Algol variable stars, RR Lyrae variable stars, Detached binary stars, Semi-detached binary stars, Eclipsing binary stars, Variable stars
The SDO/EVE Solar Irradiance Coronal Dimming Index Catalog. I. Methods and Algorithms. When a coronal mass ejection departs, it leaves behind a temporary void. That void is known as coronal dimming, and it contains information about the mass ejection that caused it. Other physical processes can cause parts of the corona to have transient dimmings, but mass ejections are particularly interesting because of their influence in space weather. Prior work has established that dimmings are detectable even in disk-integrated irradiance observations, i.e., Sun-as-a-star measurements. The present work evaluates four years of continuous Solar Dynamics Observatory Extreme Ultraviolet Experiment (EVE) observations to greatly expand the number of dimmings we may detect and characterize, and collects that information into James’s EVE Dimming Index catalog. This paper details the algorithms used to produce the catalog, provides statistics on it, and compares it with prior work. The catalog contains 5051 potential events (rows), which correspond to all robustly detected solar eruptive events in this time period as defined by &gt;C1 flares. Each row has a corresponding 27,349 elements of metadata and parameterizations (columns). In total, this catalog is the result of analyzing 7.6 million solar ultraviolet light curves.

Keywords: Stellar coronal dimming, Light curve classification , Solar extreme ultraviolet emission, Active sun, Solar coronal mass ejections, Solar electromagnetic emission, Support vector machine
Bright Southern Variable Stars in the bRing Survey. In addition to monitoring the bright star β Pic during the near-transit event for its giant exoplanet, the β Pictoris b Ring (bRing) observatories at Siding Springs Observatory, Australia and Sutherland, South Africa have monitored the brightnesses of bright stars (V ≃ 4-8 mag) centered on the south celestial pole (δ ≤ -30°) for approximately two years. Here we present a comprehensive study of the bRing time-series photometry for bright southern stars monitored between 2017 June and 2019 January. Of the 16,762 stars monitored by bRing, 353 were found to be variable. Of the variable stars, 80% had previously known variability and 20% were new variables. Each of the new variables was classified, including three new eclipsing binaries (HD 77669, HD 142049, HD 155781), 26 δ Scutis, 4 slowly pulsating B stars, and others. This survey also reclassified four stars based on their period of pulsation, light curve, spectral classification, and color-magnitude information. The survey data were searched for new examples of transiting circumsecondary disk systems, but no candidates were found.

Keywords: Short period variable stars, Ellipsoidal variable stars, Long period variable stars, Variable stars, Eclipsing binary stars, Multi-periodic variable stars
The Massive Star-forming Regions Omnibus X-ray Catalog, Third Installment. We offer to the star formation community the third installment of the Massive Star-forming Regions (MSFRs) Omnibus X-ray Catalog (MOXC3), a compilation of X-ray point sources detected in 50 archival Chandra Advanced CCD Imaging Spectrometer observations of 14 Galactic MSFRs and surrounding fields. The MOXC3 MSFRs are NGC 2264, NGC 6193, RCW 108-IR, Aur OB1, DR15, NGC 6231, Berkeley 87, NGC 6357, AFGL 4029, h Per (NGC 869), NGC 281, Onsala 2S, G305, and RCW 49 (Wd 2); they have distances of 0.7-4.2 kpc. Most exhibit clumped or clustered young stellar populations; several contain at least two distinct massive young stellar clusters. The total MOXC3 catalog includes 27,923 X-ray point sources. We take great care to identify even the faintest X-ray point sources across these fields. This allows us to remove this point source light, revealing diffuse X-ray structures that pervade and surround MSFRs, often generated by hot plasmas from massive star feedback. As we found in MOXC1 and MOXC2, diffuse X-ray emission is traceable in all MOXC3 MSFRs; here we perform spectral fitting to investigate the origins of selected diffuse regions. Once again, MOXC3 shows the value of high spatial resolution X-ray studies of MSFRs enabled by Chandra.

Keywords: Star formation, Early-type stars, H II regions, X-ray stars