Sazuna/UAT_keywords huggingface dataset:
Constraints on the Spindown of Fully Convective M Dwarfs Using Wide Field Binaries. M dwarfs remain active over longer timescales than their Sunlike counterparts, with potentially devastating implications for the atmospheres of their planets. However, the age at which fully convective M dwarfs transition from active and rapidly rotating to quiescent and slowly rotating is poorly understood, as these stars remain rapidly rotating in the oldest clusters that are near enough for a large sample of low-mass M dwarfs to be studied. To constrain the spindown of these low-mass stars, we measure photometric rotation periods for field M dwarfs in wide binary systems, primarily using the Transiting Exoplanet Survey Satellite and MEarth. Our analysis includes M-M pairs, which are coeval but of unknown age, as well as M dwarfs with white dwarf or Sunlike primaries, for which we can estimate ages using techniques like white-dwarf cooling curves, gyrochronology, and lithium abundance. We find that the epoch of spindown is strongly dependent on mass. Fully convective M dwarfs initially spin down slowly, with the population of 0.2-0.3 M ☉ rapid rotators evolving from P rot &lt; 2 days at 600 Myr to 2 &lt; P rot &lt; 10 days at 1-3 Gyr before rapidly spinning down to long rotation periods at older ages. However, we also identify some variability in the spindown of fully convective M dwarfs, with a small number of stars having substantially spun down by 600 Myr. These observations are consistent with models of magnetic morphology-driven spindown, where angular momentum loss is initially inefficient until changes in the magnetic field allow spindown to progress rapidly.

Keywords: M dwarf stars, Stellar ages, Stellar activity, Wide binary stars, Stellar rotation
The Physical Properties of Low-redshift FeLoBAL Quasars. III. The Location and Geometry of the Outflows. We present continued analysis of a sample of low-redshift iron low-ionization broad-absorption-line quasars (FeLoBALQs). Choi et al. presented SimBAL spectral analysis of broad-absorption-line (BAL) outflows in 50 objects. Leighly et al. analyzed the optical emission lines of 30 of those 50 objects and found that they are characterized by either a high accretion rate (L Bol/L Edd &gt; 0.3) or low accretion rate (0.03 &lt; L Bol/L Edd &lt; 0.3). We report that the outflow velocity is inversely correlated with the BAL location among the high-accretion-rate objects, with the highest velocities observed in parsec-scale outflows. In contrast, the low-Eddington-ratio objects showed the opposite trend. We confirmed the known relationship between the outflow velocity and L Bol/L Edd and found that the scatter plausibly originates in the force multiplier (launch radius) in the low(high)-accretion-rate objects. A log volume filling factor between -6 and -4 was found in most outflows but was as high as -1 for low-velocity compact outflows. We investigated the relationship between the observed [O III] emission and that predicted from the BAL gas. We found that these could be reconciled if the emission-line covering fraction depends on the Seyfert type and BAL location. The difference between the predicted and observed [O III] luminosity is correlated with the outflow velocity, suggesting that [O III] emission in high-Eddington-ratio objects may be broad and hidden under Fe II emission. We suggest that the physical differences in the outflow properties as a function of location in the quasar and accretion rate point to different formation, acceleration, and confinement mechanisms for the two FeLoBALQ types.

Keywords: Active galactic nuclei, Quasars, Broad-absorption line quasar
Updated Photometry of the Yellow Supergiant Progenitor and Late-time Observations of the Type IIb Supernova SN 2016gkg. We present Hubble Space Telescope (HST) observations of the Type IIb supernova (SN) SN 2016gkg at 652, 1698, and 1795 days from explosion with the Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3). Comparing to pre-explosion imaging from 2001 obtained with the Wide Field Planetary Camera 2, we demonstrate that SN 2016gkg is now fainter than its candidate counterpart in the latest WFC3 imaging, implying that the counterpart has disappeared and confirming that it was the SN progenitor star. We show the latest light curve and Keck spectroscopy of SN 2016gkg, which imply that SN 2016gkg is declining more slowly than the expected rate for 56Co decay during its nebular phase. We find that this emission is too luminous to be powered by other radioisotopes and infer that SN 2016gkg is entering a new phase in its evolution where it is powered primarily by interaction with circumstellar matter. Finally, we reanalyze the progenitor star spectral energy distribution and late-time limits in the context of binary evolution models. Including emission from a potential companion star, we find that all such predicted companion stars would be fainter than our limiting magnitudes.

Keywords: Early stellar evolution, Core-collapse supernovae
Classical OBe Stars as Post-supernova Runaways: Confirming Binary Origins. Massive binaries play an important role in fields ranging from gravitational-wave astronomy to stellar evolution. We provide several lines of evidence that classical OBe stars in the Small Magellanic Cloud (SMC) obtain their rapid rotation from mass and angular momentum transfer in massive binaries, which predicts that the subsequent supernovae should often eject OBe stars into the field. We find that (1) OBe stars have a higher field frequency than OB stars; (2) our cumulative distribution function (CDF) of stellar distances from O stars shows that OBe stars are indeed much more isolated than ordinary OB stars of corresponding spectral types; (3) the CDFs of OBe stars approach that of high-mass X-ray binaries (HMXBs), which are confirmed post-supernova objects; and (4) Oe stars are as isolated from clusters as Be stars, implying that their final masses are relatively independent of their initial masses, consistent with major mass transfer. Lastly, we also find that the spatial distribution of supergiant OBe stars differs from that of classical OBe stars, consistent with the different mechanisms responsible for their emission-line spectra.

Keywords: Multiple star evolution, Core-collapse supernovae, Oe stars, High mass x-ray binary stars, Stellar evolutionary models, Interacting binary stars, Small Magellanic Cloud, Compact objects, Circumstellar disks, Be stars, Runaway stars, Star clusters
Characteristics of Nanoflare Heating in a Coronal Bright Point. We have obtained constraints on the nanoflare energy distribution and timing for the heating of a coronal bright point. Observations of the bright point were made using the Extreme Ultraviolet Imaging Spectrometer on Hinode in slot mode, which collects a time series of monochromatic images of the region leading to unambiguous temperature diagnostics. The Enthalpy-Based Thermal Evolution of Loops model was used to simulate nanoflare heating of the bright point and generate a time series of synthetic intensities. The nanoflare heating in the model was parameterized in terms of the power-law index α of the nanoflare energy distribution, which is ∝ E -α ; average nanoflare frequency f; and the number N of magnetic strands making up the observed loop. By comparing the synthetic and observed light curves, we inferred the region of the model parameter space (α, f, N) that was consistent with the observations. Broadly, we found that N and f are inversely correlated with one another, while α is directly correlated with either N or f. These correlations are likely a consequence of the region requiring a certain fixed energy input, which can be achieved in various ways by trading off among the different parameters. We also find that a value of α &gt; 2 generally gives the best match between the model and observations, which indicates that the heating is dominated by low-energy events. Our method of using monochromatic images, focusing on a relatively simple structure, and constraining nanoflare parameters on the basis of statistical properties of the intensity provides a versatile approach to better understand the nature of nanoflares and coronal heating.

Keywords: Solar coronal loops, Solar coronal heating, Solar coronal lines, Quiet solar corona, Spectroscopy, Active solar corona, Line intensities
Supernova Precursor Emission and the Origin of Pre-explosion Stellar Mass Loss. A growing number of core-collapse supernovae (SNe) that show evidence for interaction with dense circumstellar medium (CSM) are accompanied by "precursor" optical emission rising weeks to months prior to the explosion. The precursor luminosities greatly exceed the Eddington limit of the progenitor star, implying that they are accompanied by substantial mass loss. Here, we present a semi-analytic model for SN precursor light curves, which we apply to constrain the properties and mechanisms of the pre-explosion mass loss. We explore two limiting mass-loss scenarios: (1) an "eruption" arising from shock breakout following impulsive energy deposition below the stellar surface; and (2) a steady "wind," due to sustained heating of the progenitor envelope. The eruption model, which resembles a scaled-down version of Type IIP SNe, can explain the luminosities and timescales of well-sampled precursors, for ejecta masses ~ 0.1-1 M ⊙ and velocities ~ 100-1000 km s-1. By contrast, the steady wind scenario cannot explain the highest precursor luminosities ≳ 1041 erg s-1, under the constraint that the total ejecta mass does not exceed the entire progenitor mass (though the less luminous SN 2020tlf precursor can be explained by a mass-loss rate ~ 1 M ⊙ yr-1). However, shock interaction between the wind and pre-existing (earlier ejected) CSM may boost its radiative efficiency and mitigate this constraint. In both the eruption and wind scenarios, the precursor ejecta forms compact (≲1015 cm) optically thick CSM at the time of core collapse; though only directly observable via rapid post-explosion spectroscopy (≲ a few days before being overtaken by the SN ejecta), this material can boost the SN luminosity via shock interaction.

Keywords: Supernovae, Core-collapse supernovae, Stellar mass loss
Effects of Spectral Resolution on Simple Magnetic Field Diagnostics of the Mg II H and K Lines. We study the effects of finite spectral resolution on the magnetic field values retrieved through the weak-field approximation (WFA) from the cores of the Mg II h and k lines. The retrieval of the line-of-sight component of the magnetic field, B LOS, from synthetic spectra generated in a uniformly magnetized FAL-C atmosphere is accurate when restricted to the inner lobes of Stokes V. As we degrade the spectral resolution, partial redistribution effects, which more prominently affect the outer lobes of Stokes V, are brought into the line core through spectral smearing, degrading the accuracy of the WFA and resulting in an inference bias, which is more pronounced as the resolution becomes poorer. When applied to a diverse set of spectra emerging from a sunspot simulation, we find good accuracy in the retrieved B LOS when comparing it to the model value at the height where the optical depth in the line core is unity. The accuracy is preserved up to field strengths of B ~ 1500 G. Limited spectral resolution results in a small bias toward weaker retrieved fields. The WFA for the transverse component of the magnetic field is also evaluated. Reduced spectral resolution degrades the accuracy of the inferences, because spectral mixing results in the line effectively probing deeper layers of the atmosphere.

Keywords: Solar chromosphere, Spectropolarimetry, Solar magnetic fields
Accelerated Growth of Seed Black Holes by Dust in the Early Universe. We explore the effect of dust on the growth of seed black holes (BHs) in the early universe. Previous 1D radiation-hydrodynamic (RHD) simulations show that increased radiation pressure on dust further suppresses the accretion rate than the case for the chemically pristine gas. Using the Enzo+Moray code, we perform a suite of 3D RHD simulations of accreting BHs in a dusty interstellar medium (ISM). We use the modified Grackle cooling library to consider dust physics in its nonequilibrium chemistry. The BH goes through an early evolutionary phase, where ionizing BH radiation creates an oscillating H II region as it cycles between accretion and feedback. As the simulations proceed, dense cold gas accumulates outside the ionized region where inflow from the neutral medium meets the outflow driven by radiation pressure. In the late phase, high-density gas streams develop and break the quasi-spherical symmetry of the ionized region, rapidly boosting the accretion rate. The late phase is characterized by the coexistence of strong ionized outflows and fueling high-density gas inflows. The mean accretion rate increases with metallicity reaching a peak at Z ~ 0.01-0.1 Z ☉, one order of magnitude higher than the one for pristine gas. However, as the metallicity approaches the solar abundance, the mean accretion rate drops as the radiation pressure becomes strong enough to drive out the high-density gas. Our results indicate that a dusty metal-poor ISM can accelerate the growth rate of BHs in the early universe, but can also stun its growth as the ISM is further enriched toward the solar abundance.

Keywords: Accretion, Black hole physics, Interstellar dust, Intermediate-mass black holes, Hydrodynamics, Radiative transfer simulations
The Rate and Spatial Distribution of Novae in M31 as Determined by a 20 Year Survey. A long-term (1995-2016) survey for novae in the nearby Andromeda galaxy (M31) was conducted as part of the Research-Based Science Education initiative. During the course of the survey 180 nights of observation were completed at Kitt Peak, Arizona. A total of 262 novae were either discovered or confirmed, 40 of which have not been previously reported. Of these, 203 novae form a spatially complete sample detected by the KPNO/WIYN 0.9 m telescope within a $20^{\prime} \times 20^{\prime} $ field centered on the nucleus of M31. An additional 50 novae are part of a spatially complete sample detected by the KPNO 4 m telescope within a larger $36^{\prime} \times 36^{\prime} $ field. Consistent with previous studies, it is found that the spatial distribution of novae in both surveys follows the bulge light of M31 somewhat more closely than the overall background light of the galaxy. After correcting for the limiting magnitude and the spatial and temporal coverage of the surveys, a final nova rate in M31 is found to be $R={40}_{-4}^{+5}$ yr-1, which is considerably lower than recent estimates. When normalized to the K-band luminosity of M31, this value yields a luminosity-specific nova rate, ν  K  = 3.3 ± 0.4 yr ${}^{-1}\,{[{10}^{10}\,{L}_{\odot ,K}]}^{-1}$ . By scaling the M31 nova rate using the relative infrared luminosities of M31 and our Galaxy, a nova rate of ${R}_{{\rm{G}}}={28}_{-4}^{+5}$ yr-1 is found for the Milky Way.

Keywords: Novae, Time domain astronomy, Cataclysmic variable stars, Galaxies, Classical novae
Origin and Evolution of Dust-obscured Galaxies in Galaxy Mergers. Dust-obscured galaxies (DOGs), which are observationally characterized as faint in the optical and bright in the infrared, are the final stage of galaxy mergers and are essential objects in the evolution of galaxies and active galactic nuclei (AGNs). However, the relationship between the torus-scale gas dynamics around AGNs and the DOGs' lifetime remains unclear. We obtained the evolution of the spectral energy distributions (SEDs) of a galaxy merger system with AGN feedback from postprocessed pseudo-observations based on an N-body/smoothed particle hydrodynamics (SPH) simulation. We focused on a late-stage merger of two identical galaxies with a supermassive black hole (SMBH) of 108 M ⊙. We found that the infrared luminosity of the system reaches ultra- and hyperluminous infrared galaxy classes (1012 and 1013 L ⊙, respectively). The DOG phase corresponds to a state in which the AGNs are buried in dense gas and dust, with the infrared luminosity exceeding 3.3 × 1012 L ⊙. We also identified subcategories of DOGs, namely bump and power-law DOGs, from the SEDs and their evolution. The bump DOGs tend to evolve to power-law DOGs over several Myrs. We found that contribution from the hot dust around the nucleus in the infrared radiation is essential for identifying the system as a power-law DOG; the gas and dust are distributed nonspherically around the nucleus, therefore, the observed properties of DOGs depend on the viewing angle. In our model, the lifetime of merger-driven DOGs is less than 4 Myr, suggesting that the observed DOG phase is a brief aspect of galaxy mergers.

Keywords: Supermassive black holes, Hydrodynamical simulations, Active galaxies, Active galactic nuclei, Galaxy mergers, Radiative transfer simulations, N-body simulations
Merger Effects on the Spin and Shape Alignments of Galaxy Stellar, Cold Gas, Hot Gas, and Dark Matter Components. We present a numerical evidence supporting the scenario that the peculiar alignments of the galaxy stellar spins with the major principal axes of the local tidal tensors are produced during the quiescent evolution period when the galaxies experience no recent merger events. Analyzing the merger tree from the TNG300-1 simulation of the IllustrisTNG project, we find the latest merger epochs, a(z  m ), of the galaxies, and create four a(z  m )-selected samples that are controlled to share the identical mass and density distributions. For each sample, we determine the spin and shape vectors of the galaxy stellar, cold and hot gas, and dark matter components separately, and compute the average strengths of their alignments with the principal directions of the local tidal fields as well as their mutual alignment tendencies. It is found that the stellar (cold gas) spin axes of the galaxies whose latest merger events occur at earlier epochs are more strongly aligned (weakly antialigned) with the major principal axes of the tidal fields. It is also shown that, although the mass-dependent transition of the galaxy DM spins have little connection with the merger events, the morphologies, spin-shape, and shape-shear alignment strengths of the four components of the galaxies sensitively depend on a(z  m ). Noting that the stellar components of the galaxies that undergo long quiescent evolution have distinctively oblate shapes and very strong spin-shape alignments, we suggest that the local tidal field might be traced by using the stellar shapes of galaxies without signatures of mergers as a proxy of their stellar spins.

Keywords: Galaxy evolution, Large-scale structure of the universe
A Novel RID Algorithm of Muon Trajectory Reconstruction in Water Cherenkov Detectors. Cosmic rays that strike the top of the Earth's atmosphere generate a shower of secondary particles that move toward the surface with relativistic speeds. Water Cherenkov detectors (WCDs) on the ground can detect charged muons, which are one of the many particles generated in the shower, with the Cherenkov imaging technique. A large number of these muons travel in WCD tanks near the speed of light in a vacuum, faster than the speed of light in water, and so trigger isotropic Cherenkov radiation, which is detected by the photomultiplier tubes (PMTs) placed inside the tanks. When the radial component of the speed of the muon toward a PMT drops from superluminal to subluminal, the PMT records Cherenkov light from an optical phenomenon known as relativistic image doubling (RID), which causes two Cherenkov images of the same muon to appear suddenly, with both images moving in geometrically opposite directions on the original muon track. The quantities associated with the RID effect can be measured experimentally with a variety of detector types and can be used to find various points on the original trajectory of the muon. In this paper, a detailed study of reconstructing the trajectory of a muon entering a WCD using the RID technique has been presented. It is found that the measurements of standard RID observables enables a complete reconstruction of the trajectory of the muon to a high degree of accuracy with less than 1% error.

Keywords: Cosmic ray showers, Special relativity, Astronomical optics
A Magnetogram-matching Method for Energizing Magnetic Flux Ropes Toward Eruption. We propose a new "helicity-pumping" method for energizing coronal equilibria that contain a magnetic flux rope (MFR) toward an eruption. We achieve this in a sequence of magnetohydrodynamics relaxations of small line-tied pulses of magnetic helicity, each of which is simulated by a suitable rescaling of the current-carrying part of the field. The whole procedure is "magnetogram-matching" because it involves no changes to the normal component of the field at the photospheric boundary. The method is illustrated by applying it to an observed force-free configuration whose MFR is modeled with our regularized Biot-Savart law method. We find that, in spite of the bipolar character of the external field, the MFR eruption is sustained by two reconnection processes. The first, which we refer to as breakthrough reconnection, is analogous to breakout reconnection in quadrupolar configurations. It occurs at a quasi-separator inside a current layer that wraps around the erupting MFR and is caused by the photospheric line-tying effect. The second process is the classical flare reconnection, which develops at the second quasi-separator inside a vertical current layer that is formed below the erupting MFR. Both reconnection processes work in tandem with the magnetic forces of the unstable MFR to propel it through the overlying ambient field, and their interplay may also be relevant for the thermal processes occurring in the plasma of solar flares. The considered example suggests that our method will be beneficial for both the modeling of observed eruptive events and theoretical studies of eruptions in idealized magnetic configurations.

Keywords: Solar flares, Solar prominences, Solar physics, Solar filaments, Solar magnetic fields, Solar coronal mass ejections, Solar activity
Effect of the Heliospheric State on CME Evolution. The culmination of solar cycle 24 by the end of 2019 has created the opportunity to compare the differing properties of coronal mass ejections (CMEs) between two whole solar cycles: solar cycle 23 (SC 23) and solar cycle 24 (SC 24). We report on the width evolution of limb CMEs in SCs 23 and 24 in order to test the suggestion by Gopalswamy et al. that CME flux ropes attain pressure balance at larger heliocentric distances in SC 24. We measure CME width as a function of heliocentric distance for a significantly large number of limb CMEs (~1000) and determine the distances where the CMEs reach constant width in each cycle. We introduced a new parameter, the transition height (hc) of a CME, defined as the critical heliocentric distance beyond which the CME width stabilizes to a quasi-constant value. Cycle and phase-to-phase comparisons are based on this new parameter. We find that the average value of hc in SC 24 is 62% higher than that in SC 23. SC 24 CMEs attain their peak width at larger distances from the Sun than SC 23 CMEs do. The enhanced transition height in SC 24 is new observational ratification of the anomalous expansion. The anomalous expansion of SC 24 CMEs, which is caused by the weak state of the heliosphere, accounts for the larger heliocentric distance where the pressure balance between CME flux rope and the ambient medium is attained.

Keywords: Solar cycle, Solar flares, Heliosphere, Active sun, Solar coronal mass ejections, Solar x-ray flares