Sazuna/UAT_keywords huggingface dataset:
Dynamical Confirmation of a Black Hole in MAXI J1820+070. We present time-resolved 10.4 m Gran Telescopio Canarias and 4.2 m William Herschel Telescope intermediate resolution spectroscopy of the X-ray transient MAXI J1820+070 (=ASASSN-18ey) obtained during its decline to the quiescent state. Cross-correlation of the 21 individual spectra against late-type templates reveals a sinusoidal velocity modulation with a period of 0.68549 ± 0.00001 day and semi-amplitude of 417.7 ± 3.9 km s-1. We derive a mass function f(M) = 5.18 ± 0.15 M ☉, dynamically confirming the black hole (BH) nature of the compact object. Our analysis of the stellar absorption features supports a K3-5 spectral classification for the donor star, which contributes ≈20% of the total flux at 5200-6800 Å. The photometric 0.703 ± 0.003 day periodicity observed during outburst is 2.6% longer than the orbital period supporting the presence of a superhump modulation in the outburst light curves. In line with this interpretation, we constrain the binary mass ratio to be q ≃ 0.12. In addition, we observe a sharp increase in the Hα emission line equivalent width during inferior conjunction of the donor star that we interpret as a grazing eclipse of the accretion disk and allows us to constrain the binary inclination to i ≳ 69°. On the other hand, the absence of X-ray eclipses during outburst imply i ≲ 77°. These inclination limits, together with our dynamical solution, lead to a BH mass in the range 7-8 M ☉. We also measure a systemic velocity γ = -21.6 ± 2.3 km s-1, which, combined with the Gaia second data release proper motion and parallax, implies a large peculiar velocity ∼100 km s-1.

Keywords: Low-mass x-ray binary stars, Stellar accretion disks, Astrophysical black holes, X-ray binary stars
Detection of Crystalline and Fine-grained Calcic Plagioclases on Vesta. Plagioclase feldspars are among the most prevalent minerals in the solar system, and are present in many chondritic and achondritic meteorite families. Nevertheless, spectral features of plagioclases have never been unambiguously and directly observed in remote observations of asteroids. We report here the detection of an absorption band at 12.2 μm on Vesta spectra provided by ground-based spectral observations at the Subaru Telescope. This signature represents the first direct evidence of a widespread presence of crystalline Ca-rich plagioclase on Vesta and reveals that its regolith is comminuted to a very fine grain size, smaller than a few tens of microns, indicating that the mechanical brecciation process has been very effective. The crystalline nature of plagioclase strongly suggests that impacts alone cannot be the sole mechanism for regolith formation on Vesta and a milder process, such as thermal fatigue, should be invoked as an important and concomitant process Thermal fatigue should be considered a very effective process in regolith production and rejuvenation not only for near-Earth asteroids but even for large asteroids located in the main belt.

Keywords: Asteroids, Achondrites, Infrared astronomy, Main belt asteroids, Infrared telescopes, Spectroscopy, Meteorites
Discovery of a Very Hot Phase of the Milky Way Circumgalactic Medium with Non-solar Abundance Ratios. We present the discovery of a very hot gas phase of the Milky Way circumgalactic medium (CGM) at T ≈ 107 K, using deep XMM-Newton Reflection Grating Spectrometer observations of the blazar 1ES 1553+113. The hot gas, coexisting with a warm-hot phase at T ≈ 106 K is α-enhanced, with [{{O}}/{Fe}]={0.9}-0.3+0.7, indicating core-collapse supernovae enrichment. Additionally, we find [Ne/O] and [{{N}}/{{O}}]={0.7}-0.2+1.6, such that N/Ne is consistent with solar. Along with the enrichment by asymptotic giant branch stars and core-collapse supernovae, this indicates that some oxygen has depleted onto dust and/or transited to cooler gas phase(s). These results may affect previous baryonic and metallic mass estimations of the warm-hot and hot CGM from the observations of oxygen emission and absorption. Our results provide insights on the heating, mixing, and chemical enrichment of the Milky Way CGM, and provide inputs to theoretical models of galaxy evolution.

Keywords: X-ray astronomy, Quasar absorption line spectroscopy, Chemical abundances, Circumgalactic medium, Chemical enrichment, Warm ionized medium, Diffuse x-ray background
The Tidal Disruption of Sun-like Stars by Massive Black Holes. We present the first simulations of the tidal disruption of stars with realistic structures and compositions by massive black holes (BHs). We build stars in the stellar evolution code MESA and simulate their disruption in the 3D adaptive-mesh hydrodynamics code FLASH, using an extended Helmholtz equation of state and tracking 49 elements. We study the disruption of a 1M ⊙ star and 3M ⊙ star at zero-age main sequence (ZAMS), middle-age, and terminal-age main sequence (TAMS). The maximum BH mass for tidal disruption increases by a factor of ∼2 from stellar radius changes due to main-sequence (MS) evolution; this is equivalent to varying BH spin from 0 to 0.75. The shape of the mass fallback rate curves is different from the results for polytropes of Guillochon &amp; Ramirez-Ruiz. The peak timescale t peak increases with stellar age, while the peak fallback rate {\dot{M}}peak} decreases with age, and these effects diminish with increasing impact parameter β. For a β = 1 disruption of a 1M ⊙ star by a 106 M ⊙ BH, from ZAMS to TAMS, t peak increases from 30 to 54 days, while {\dot{M}}peak} decreases from 0.66 to 0.14 M ⊙ yr-1. Compositional anomalies in nitrogen, helium, and carbon can occur before the peak timescale for disruptions of MS stars, which is in contrast to predictions from the “frozen-in” model. More massive stars can show stronger anomalies at earlier times, meaning that compositional constraints can be key in determining the mass of the disrupted star. The abundance anomalies predicted by these simulations provide a natural explanation for the spectral features and varying line strengths observed in tidal disruption events.

Keywords: Black hole physics, Hydrodynamics, Gravitation, Tidal disruption, Active galaxies, Galaxy nuclei, Main sequence stars
On the Diversity of Fallback Rates from Tidal Disruption Events with Accurate Stellar Structure. The tidal disruption of stars by supermassive black holes (SMBHs) can be used to probe the SMBH mass function, the properties of individual stars, and stellar dynamics in galactic nuclei. Upcoming missions will detect thousands of tidal disruption events (TDEs), and accurate theoretical modeling is required to interpret the data with precision. Here we analyze the influence of more realistic stellar structure on the outcome of TDEs; in particular, we compare the fallback rates—being the rate at which tidally disrupted debris returns to the black hole—from progenitors generated with the stellar evolution code MESA to γ ≃ 4/3 and γ = 5/3 polytropes. We find that MESA-generated density profiles yield qualitatively different fallback rates as compared to polytropic approximations, and that only the fallback curves from low-mass (1 M ⊙ or less), zero-age main-sequence stars are well fit by either a γ ≃ 4/3 or 5/3 polytrope. Stellar age has a strong affect on the shape of the fallback curve, and can produce characteristic timescales (e.g., the time to the peak of the fallback rate) that greatly differ from the polytropic values. We use these differences to assess the degree to which the inferred black hole mass from the observed light curve can deviate from the true value, and find that the discrepancy can be at the order of magnitude level. Accurate stellar structure also leads to a substantial variation in the critical impact parameter at which the star is fully disrupted, and can increase the susceptibility of the debris stream to fragmentation under its own self-gravity. These results suggest that detailed modeling is required to accurately interpret observed light curves of TDEs.

Keywords: Tidal disruption, Hydrodynamics, Galaxy nuclei
Unprecedented Near-infrared Brightness and Variability of Sgr A*. The electromagnetic counterpart to the Galactic center supermassive black hole, Sgr A*, has been observed in the near-infrared for over 20 yr and is known to be highly variable. We report new Keck Telescope observations showing that Sgr A* reached much brighter flux levels in 2019 than ever measured at near-infrared wavelengths. In the K‧ band, Sgr A* reached flux levels of ∼6 mJy, twice the level of the previously observed peak flux from &gt;13,000 measurements over 130 nights with the Very Large Telescope and Keck Telescopes. We also observe a factor of 75 change in flux over a 2 hr time span with no obvious color changes between 1.6 and 2.1 μm. The distribution of flux variations observed this year is also significantly different than the historical distribution. Using the most comprehensive statistical model published, the probability of a single night exhibiting peak flux levels observed this year, given historical Keck observations, is less than 0.3%. The probability of observing flux levels that are similar to all four nights of data in 2019 is less than 0.05%. This increase in brightness and variability may indicate a period of heightened activity from Sgr A* or a change in its accretion state. It may also indicate that the current model is not sufficient to model Sgr A* at high flux levels and should be updated. Potential physical origins of Sgr A*'s unprecedented brightness may be from changes in the accretion flow as a result of the star S0-2's closest passage to the black hole in 2018, or from a delayed reaction to the approach of the dusty object G2 in 2014. Additional multi-wavelength observations will be necessary to both monitor Sgr A* for potential state changes and to constrain the physical processes responsible for its current variability.

Keywords: Supermassive black holes, Low-luminosity active galactic nuclei, Galactic center, Near infrared astronomy
The First Detection of <SUP>13</SUP>C<SUP>17</SUP>O in a Protoplanetary Disk: A Robust Tracer of Disk Gas Mass. Measurements of the gas mass are necessary to determine the planet formation potential of protoplanetary disks. Observations of rare CO isotopologues are typically used to determine disk gas masses; however, if the line emission is optically thick this will result in an underestimated disk mass. With the Atacama Large Millimeter/submillimeter Array we have detected the rarest stable CO isotopologue, {}13{{{C}}}17{{O}}, in a protoplanetary disk for the first time. We compare our observations with the existing detections of {}12{CO}, {}13{CO}, {{{C}}}18{{O}}, and {{{C}}}17{{O}} in the HD 163296 disk. Radiative transfer modeling using a previously benchmarked model, and assuming interstellar isotopic abundances, significantly underestimates the integrated intensity of the {}13{{{C}}}17{{O}} J = 3-2 line. Reconciliation between the observations and the model requires a global increase in CO gas mass by a factor of 3.5. This is a factor of 2-6 larger than previous gas mass estimates using {{{C}}}18{{O}}. We find that {{{C}}}18{{O}} emission is optically thick within the snow line, while the {}13{{{C}}}17{{O}} emission is optically thin and is thus a robust tracer of the bulk disk CO gas mass.

Keywords: Submillimeter astronomy, Protoplanetary disks, Planet formation, Astrochemistry
A Kinematically Cold Structure of Candidate Young OB Stars toward the Anticenter. We combine Galaxy Evolution Explorer and Gaia DR2 catalogs to track star formation in the outskirts of our Galaxy. Using photometry, proper motions, and parallaxes we identify a structure of ∼300 OB-type candidates located between 12 and 15 kpc from the Galactic center that are kinematically cold. The structure is located between l = 120° and 200°, above the plane up to ∼700 pc and below the plane to ∼1 kpc. The bulk motion is disklike; however, we measure a mean upward vertical motion of 5.7 ± 0.4 km s-1, and a mean outward radial motion of between 8 and 16 km s-1. The velocity dispersion along the least dispersed of its proper-motion axes (perpendicular to the Galactic disk) is 6.0 ± 0.3 km s-1, confirming the young age of this structure. While spatially encompassing the outer spiral arm of the Galaxy, this structure is not a spiral arm. Its explanation as the Milky Way warp is equally unsatisfactory. The structure’s vertical extent, mean kinematics, and asymmetry with respect to the plane indicate that its origin is more akin to a wobble generated by a massive satellite perturbing the Galaxy’s disk. The mean stellar ages in this outer structure indicate the event took place some 200 Myr ago.

Keywords: Galaxy structure, Milky Way disk, Star formation, Galaxy kinematics, Catalogs
First Sub-parsec-scale Mapping of Magnetic Fields in the Vicinity of a Very-low-luminosity Object, L1521F-IRS. L1521F is found to be forming multiple cores and it is cited as an example of the densest core with an embedded VeLLO in a highly dynamical environment. We present the core-scale magnetic fields (B-fields) in the near vicinity of the VeLLO L1521F-IRS using submillimeter polarization measurements at 850 μm using JCMT POL-2. This is the first attempt to use high-sensitivity observations to map the sub-parsec-scale B-fields in a core with a VeLLO. The B-fields are ordered and very well connected to the parsec-scale field geometry seen in our earlier optical polarization observations and the large-scale structure seen in Planck dust polarization. The core-scale B-field strength estimated using the Davis-Chandrasekhar-Fermi relation is 330 ± 100 μG, which is more than 10 times the value we obtained in the envelope (the envelope in this paper is the “core envelope”). This indicates that B-fields are getting stronger on smaller scales. The magnetic energies are found to be 1 to 2 orders of magnitude higher than nonthermal kinetic energies in the envelope and core. This suggests that magnetic fields are more important than turbulence in the energy budget of L1521F. The mass-to-flux ratio of 2.3 ± 0.7 suggests that the core is magnetically supercritical. The degree of polarization is steadily decreasing toward the denser part of the core with a power-law slope of -0.86.

Keywords: Interstellar magnetic fields, Star formation, Interstellar clouds, Polarimetry
Double Neutron Star Mergers from Hierarchical Triple-star Systems. The isolated binary evolution model for merging neutron stars (NSs) involves processes such as mass transfer, common-envelope evolution, and natal kicks, all of which are poorly understood. Also, the predicted NS-NS merger rates are typically lower than the rates inferred from the LIGO GW170817 event. Here, we investigate merger rates of NS and black hole-NS binaries in hierarchical triple-star systems. In such systems, the tertiary can induce Lidov-Kozai (LK) oscillations in the inner binary, accelerating its coalescence and potentially enhancing compact object merger rates. However, because compact objects originate from massive stars, the prior evolution should also be taken into account. Natal kicks, in particular, could significantly reduce the rates by unbinding the tertiary before it can affect the inner binary through LK evolution. We carry out simulations of massive triples, taking into account stellar evolution starting from the main sequence, secular and tidal evolution, and the effects of supernovae. For large NS birth kicks ({σ }{{k}}=265 {km} {{{s}}}-1), we find that the triple NS-NS merger rate (several hundred {Gpc}}-3 {yr}}-1) is lower by a factor of ∼2-3 than the binary rate, but for no kicks ({σ }{{k}}=0 {km} {{{s}}}-1), the triple rate (several thousand {Gpc}}-3 {yr}}-1) is comparable to the binary rate. Our results indicate that a significant fraction of NS-NS mergers could originate from triples if a substantial portion of the NS population is born with low kick velocities, as indicated by other work. However, uncertainties and open questions remain because of our simplifying assumption of dynamical decoupling after inner binary interaction has been triggered.

Keywords: Neutron stars, Binary stars, Stellar dynamics, Stellar evolution
The Frequency-dependent Behavior of Subpulse Drifting. I. Carousel Geometry and Emission Heights of PSR B0031-07. The carousel model of pulsar emission attributes the phenomenon of subpulse drifting to a set of discrete sparks located very near the stellar surface rotating around the magnetic axis. Here, we investigate the subpulse drifting behavior of PSR B0031-07 in the context of the carousel model. We show that B0031-07's three drift modes (A, B, and C) can be understood in terms of a single carousel rotation rate if the number of sparks is allowed to change by an integral number, and where the different drift rates are due to (first-order) aliasing effects. This also results in harmonically related values for P 3 (the time it takes a subpulse to reappear at the same pulse phase), which we confirm for B0031-07. A representative solution has [n A, n B, n C] = [15, 14, 13] sparks and a carousel rotation period of P 4 = 16.4 P 1. We also investigate the frequency dependence of B0031-07's subpulse behavior. We extend the carousel model to include the dual effects of aberration and retardation, including the time it takes the information about the surface spark configuration to travel from the surface up to the emission point. Assuming these effects dominate at B0031-07's emission heights, we derive conservative emission height differences of ≲2000 km for mode A and ≲1000 km for modes B and C as seen between 185 and 610 MHz. This new method of measuring emission heights is independent of others that involve average profile components or the polarization position angle curve, and thus provides a potentially strong test of the carousel model.

Keywords: Relativistic aberration, Radio pulsars, Pulsars
Metal Abundances and Star Formation Rates of Emission-line Galaxies in and around the Boötes Void. We explore the possible dependencies of galaxy metal abundance and star formation rate (SFR) on local environment, focusing on the volume of space in and around the Boötes Void. Our sample of star-forming galaxies comes from the second catalog of the Hα-selected KPNO International Spectroscopic Survey (KISS), which overlaps the void. This sample represents a statistically complete, line-flux-limited ensemble of 820 star-forming galaxies, all of which possess metallicity and SFR estimates. We carry out two distinct analyses of the KISS galaxies: one that probes the properties of the entire sample as a function of local density, and a second that details the properties of 33 KISS star-forming galaxies located within the Boötes Void. In both cases, we find no evidence that either the metallicity of the KISS galaxies or their SFRs depend on the environments within which the galaxies are located. Our global analysis does show weak trends for decreasing stellar mass, decreasing metallicity, and decreasing SFRs with decreasing local densities. However, we argue that the metallicity and SFR trends are artifacts of the stellar mass—local density trend. In particular, the change in metallicity with density is precisely what one would predict from the mass-metallicity relation, given the observed drop in stellar mass with decreasing metallicity. Likewise, the SFR trend with density disappears when one instead considers the mass-normalized specific SFR. The KISS galaxies dwelling in the Boötes Void are found to have metallicity and SFR properties nearly identical to those of a matched comparison sample, despite the fact that the former are located in density environments that are, on average, more than 16 times lower.

Keywords: Galaxy environments, Emission line galaxies, Star formation, Voids, Metallicity
A Search for Cosmic-Ray Proton Anisotropy with the Fermi Large Area Telescope. The Fermi Large Area Telescope (LAT) has amassed a large data set of primary cosmic-ray protons throughout its mission. In fact, it is the largest set of identified cosmic-ray protons ever collected at this energy. The LAT’s wide field of view and full-sky survey capabilities make it an excellent instrument for studying cosmic-ray anisotropy. As a space-based survey instrument, the LAT is sensitive to anisotropy in both R.A. and decl., while ground-based observations only measure the anisotropy in R.A. We present the results of the first-ever proton anisotropy search using Fermi LAT. The data set was collected over eight years and consists of approximately 179 million protons above 78 GeV, enabling it to probe dipole anisotropy below an amplitude of 10-3, resulting in the most stringent limits on the decl. dependence of the dipole to date. We measure a dipole amplitude δ = 3.9 ± 1.5 × 10-4 with a p-value of 0.01 (pretrials) for protons with energy greater than 78 GeV. We discuss various systematic effects that could give rise to a dipole excess and calculate upper limits on the dipole amplitude as a function of minimum energy. The 95% confidence level upper limit on the dipole amplitude is δ UL = 1.3 × 10-3 for protons with energy greater than 78 GeV and δ UL = 1.2 × 10-3 for protons with energy greater than 251 GeV.

Keywords: Galactic cosmic rays, High energy astrophysics
Variations in α-element Ratios Trace the Chemical Evolution of the Disk. It is well established that the chemical structure of the Milky Way exhibits a bimodality with respect to the α-enhancement of stars at a given [Fe/H]. This has been studied largely based on a bulk α abundance, computed as a summary of several individual α-elements. Inspired by the expected subtle differences in their nucleosynthetic origins, here we probe the higher level of granularity encoded in the inter-family [Mg/Si] abundance ratio. Using a large sample of stars with APOGEE abundance measurements, we first demonstrate that there is additional information in this ratio beyond what is already apparent in [α/Fe] and [Fe/H] alone. We then consider Gaia astrometry and stellar age estimates to empirically characterize the relationships between [Mg/Si] and various stellar properties. We find small but significant trends between this ratio and α-enhancement, age, [Fe/H], location in the Galaxy, and orbital actions. To connect these observed [Mg/Si] variations to a physical origin, we attempt to predict the Mg and Si abundances of stars with the galactic chemical evolution model Chempy. We find that we are unable to reproduce abundances for the stars that we fit, which highlights tensions between the yield tables, the chemical evolution model, and the data. We conclude that a more data-driven approach to nucleosynthetic yield tables and chemical evolution modeling is necessary to maximize insights from large spectroscopic surveys.

Keywords: Milky Way formation, Galaxy chemical evolution, Stellar abundances, Astronomy data analysis, Milky Way disk, Milky Way evolution