Sazuna/UAT_keywords huggingface dataset:
Unresolved Binary Exoplanet Host Stars Fit as Single Stars: Effects on the Stellar Parameters. In this work, we quantify the effect of an unresolved companion star on the derived stellar parameters of the primary star if a blended spectrum is fit assuming the star is single. Fitting tools that determine stellar parameters from spectra typically fit for a single star, but we know that up to half of all exoplanet host stars may have one or more companion stars. We use high-resolution spectra of planet host stars in the Kepler field from the California-Kepler Survey to create simulated binaries; we select eight stellar pairs and vary the contribution of the secondary star, then determine stellar parameters with SpecMatch-Emp and compare them to the parameters derived for the primary star alone. We find that, in most cases, the effective temperature, surface gravity, metallicity, and stellar radius derived from the composite spectrum are within 2-3σ of the values determined from the unblended spectrum, but the deviations depend on the properties of the two stars. Relatively bright companion stars that are similar to the primary star have the largest effect on the derived parameters; in these cases, the stellar radii can be overestimated by up to 60%. We find that metallicities are generally underestimated, with values up to eight times smaller than the typical uncertainty in [Fe/H]. Our study shows that follow-up observations are necessary to detect or set limits on stellar companions of planetary host stars so that stellar (and planet) parameters are as accurate as possible.

Keywords: High resolution spectroscopy, Binary stars, Stellar properties, Fundamental parameters of stars, Planet hosting stars, Stellar spectral lines
On the Origin and Evolution of Curvature of the Spectral Energy Distribution of Fermi Bright Blazars. The origin and evolution of spectral curvature in blazar spectral energy distribution (SED) is still unclear. Since the observed SED curvature is related to an intrinsic curvature in emitting electron energy distribution (EED), we study this question by employing a log-parabolic EED with a curvature parameter and peak energy to model the quasi-simultaneous broadband SEDs of selected blazars in the Fermi-LAT Bright AGN Sample using synchrotron and inverse Compton (IC) processes. We find that the log-parabolic IC model can successfully explain the emission in all blazars in our sample. On average, FSRQs have higher magnetic field, Doppler factor, and curvature than BL Lac objects. The BL Lac objects show an anticorrelation between the curvature parameter of the EED and its peak energy, which is a signature of stochastic acceleration. FSRQs do not manifest such correlation and rather show a mild positive relationship between these parameters. This suggests that the evolution of spectral curvature in the BL Lac objects is dominated by a strong stochastic acceleration component, whereas the curvature in FSRQs evolves in a cooling dominated regime due to an additional external Compton component. The strong cooling in FSRQs not only restricts the electron peak energy but also adds extra curvature to the high energy tail of emitting EED. Since the curvature decreases from FSRQs toward high peak BL Lac objects (HBLs), opposite to peak energy, the curvature parameter can be considered a third parameter of the blazar sequence in addition to peak frequency and luminosity.

Keywords: BL Lacertae objects, High-luminosity active galactic nuclei, High energy astrophysics, Quasars, Blazars
Importance of Angle-dependent Partial Frequency Redistribution in Hyperfine Structure Transitions Under the Incomplete Paschen-Back Effect Regime. Angle-frequency coupling in scattering of polarized light on atoms is represented by the angle-dependent (AD) partial frequency redistribution (PRD) matrices. There are several lines in the linearly polarized solar spectrum, for which PRD combined with quantum interference between hyperfine structure states play a significant role. Here we present the solution of the polarized line transfer equation including the AD-PRD matrix for scattering on a two-level atom with hyperfine structure splitting and an unpolarized lower level. We account for the effects of arbitrary magnetic fields (including the incomplete Paschen-Back effect regime) and elastic collisions. For exploratory purposes we consider a self-emitting isothermal planar atmosphere and use atomic parameters that represent an isolated Na I D2 line. For this case we show that the AD-PRD effects are significant for field strengths below about 30 G, but that the computationally much less demanding approximation of angle-averaged PRD may be used for stronger fields.

Keywords: The Sun, Astrophysical processes
Bremsstrahlung in GRMHD Models of Accreting Black Holes. The role of bremsstrahlung in the emission from hot accretion flows around slowly accreting supermassive black holes is not thoroughly understood. In order to appraise the importance of bremsstrahlung relative to other radiative processes, we compute spectral energy distributions (SEDs) of accretion disks around slowly accreting supermassive black holes including synchrotron radiation, inverse Compton scattering, and bremsstrahlung. We compute SEDs for (i) four axisymmetric radiative general relativistic magnetohydrodynamics (RadGRMHD) simulations of 108M⊙ black holes with accretion rates between ${10}^{-8}{\dot{M}}_{\mathrm{Edd}}$ and ${10}^{-5}{\dot{M}}_{\mathrm{Edd}}$ , (ii) four axisymmetric RadGRMHD simulations of M87* with varying dimensionless spin a* and black hole mass, and (iii) a 3D GRMHD simulation scaled for Sgr A*. At ${10}^{-8}{\dot{M}}_{\mathrm{Edd}}$ , most of the luminosity is synchrotron radiation, while at ${10}^{-5}{\dot{M}}_{\mathrm{Edd}}$ the three radiative processes have similar luminosities. In most models, bremsstrahlung dominates the SED near 512 keV. In the M87* models, bremsstrahlung dominates this part of the SED if a* = 0.5, but inverse Compton scattering dominates if a* = 0.9375. Since scattering is more variable than bremsstrahlung, this result suggests that 512 keV variability could be a diagnostic of black hole spin. In the Appendix, we compare some bremsstrahlung formulae found in the literature.

Keywords: Accretion, Supermassive black holes, Low-luminosity active galactic nuclei, Radiative transfer, Radiative processes
Influence of the Galactic Gravitational Field on the Positional Accuracy of Extragalactic Sources. II. Observational Appearances and Detectability. We consider the possibility of detecting the jitter effect of apparent celestial positions of distant sources due to local fluctuations of the Galaxy gravitational field. The observation of two samples of extragalactic sources (target and control) in different sky directions using the high-precision radio interferometry is proposed. It is shown that on a scale of ∼2 yr, it is possible to detect a systematic increase in the standard deviation of measured arc lengths of pairs of target sources compared to the control ones at the 3σ level if the accuracy of differential astrometric observations is around 10 μas. For the current state-of-the-art accuracy of 30 μas achieved at the KVN or VERA interferometers, which have shorter baselines in comparison with very long baseline interferometry, the target and control samples will differ only at the 2σ level on the scale of 10 yr. To achieve the 3σ level on this time interval, it is necessary to improve the accuracy up to ∼20 μas. Other possible effects that can also affect the arc length measurements between two sources are discussed, and an observational strategy to minimize them is suggested.

Keywords: Gravitation, Astrometry, Milky Way Galaxy
Cloud Properties and Correlations with Star Formation in Self-consistent Simulations of the Multiphase ISM. We apply gravity- and density-based methods to identify clouds in self-consistent numerical simulations of the star-forming, multiphase interstellar medium (ISM) and compare their properties and global correlation with the star formation rate (SFR) over time. The gravity-based method identifies bound objects, which have masses $M\sim {10}^{3}\mbox{--}{10}^{4}\,{M}_{\odot }$ at densities ${n}_{{\rm{H}}}\sim 100\,{\mathrm{cm}}^{-3}$ , and virial parameters αv ∼ 0.5-5. For clouds defined by a density threshold ${n}_{{\rm{H}},\min }$ , the average virial parameter decreases, and the fraction of material that is genuinely bound increases, with increasing ${n}_{{\rm{H}},\min }$ . Surprisingly, clouds defined by density thresholds can be unbound even when αv &lt; 2, and high-mass clouds ( ${10}^{4}\mbox{--}{10}^{6}\,{M}_{\odot }$ ) are generally unbound. This suggests that the traditional αv is at best an approximate measure of boundedness in the ISM. All clouds have internal turbulent motions increasing with size as $\sigma \sim 1\,\mathrm{km}\,{{\rm{s}}}^{-1}{(R/\mathrm{pc})}^{1/2}$ , similar to observed relations. Bound structures comprise a small fraction of the total simulation mass and have a star formation efficiency per freefall time ${\varepsilon }_{\mathrm{ff}}$ ∼ 0.4. For ${n}_{{\rm{H}},\min }=10\mbox{--}100\,{\mathrm{cm}}^{-3}$ , ${\varepsilon }_{\mathrm{ff}}$ ∼ 0.03-0.3, increasing with density threshold. A temporal correlation analysis between $\mathrm{SFR}(t)$ and aggregate mass $M({n}_{{\rm{H}},\min };t)$ at varying ${n}_{{\rm{H}},\min }$ shows that time delays to star formation are ${t}_{\mathrm{delay}}\sim {t}_{\mathrm{ff}}({n}_{{\rm{H}},\min })$ . The correlation between $\mathrm{SFR}(t)$ and $M({n}_{{\rm{H}},\min };t)$ systematically tightens at higher ${n}_{{\rm{H}},\min }$ . Considering moderate-density gas, selecting against high virial parameter clouds improves correlation with the SFR, consistent with previous work. Even at high ${n}_{{\rm{H}},\min }$ , the temporal dispersion in $(\mathrm{SFR}-{\varepsilon }_{\mathrm{ff}}M/{t}_{\mathrm{ff}})/\langle \mathrm{SFR}\rangle $ is ∼50%, due to the large-amplitude variations and inherent stochasticity of the system.

Keywords: Giant molecular clouds, Star forming regions, Star formation, Interstellar medium
Toward the Detection of Relativistic Image Doubling in Water Cerenkov Detectors. When a gamma or cosmic ray strikes the top of Earth's atmosphere, a shower of secondary particles moves toward the surface. Some of these secondary particles are charged muons that subsequently enter water Cerenkov detectors (WCDs) on the ground. Many of these muons, traveling near the speed of light in vacuum, are moving faster than the speed of light in water and so trigger isotropic Cerenkov radiation in the WCDs. Inside many WCDs are photomultiplier tubes (PMTs) that detect this Cerenkov radiation. When the radial component of the speed of a muon toward a PMT drops from superluminal to subluminal, the PMT will record Cerenkov light from a little-known optical phenomenon called Relativistic Image Doubling (RID). Were the RID-detecting PMTs replaced by high resolution video recorders, they would see two Cerenkov images of the muon suddenly appear inside the tank, with one image moving with a velocity component toward the recorders, the other away. Even without a video, the RID phenomenon will cause different PMTs to record markedly different light curves for the same muon. In this paper, we present a study hoping to inspire the explicit detection and reporting of RID effects in WCDs. We consider three example cases of muon RIDs in High-Altitude Water Cerenkov (HAWC)-like systems: vertical, horizontal, and oblique. Monte Carlo simulations show that RID effects in HAWC-like systems are not rare—they occur for over 85% of all muon tracks.

Keywords: Cosmic ray showers, Special relativity, Astronomical optics
Chemical Composition in the IRAS 16562-3959 High-mass Star-forming Region. We have analyzed the Atacama Large Millimeter/submillimeter Array cycle 2 data of band 6 toward the G345.4938+01.4677 massive young protostellar object (G345.5+1.47 MYSO) in the IRAS 16562-3959 high-mass star-forming region with an angular resolution of ∼0"3, corresponding to ∼760 au. We spatially resolve the central region, which consists of three prominent molecular emission cores. A hypercompact H II region (Core A) and two molecule-rich cores (Core B and Core C) are identified using the moment zero images of the H30α line and a CH3OH line, respectively. Various oxygen-bearing complex organic molecules, such as (CH3)2CO and CH3OCHO, have been detected toward the positions of Core B and Core C, while nitrogen-bearing species, CH3CN, HC3N, and its 13C isotopologues, have been detected toward all of the cores. We discuss the formation mechanisms of H2CO by comparing the spatial distribution of C18O with that of H2CO. The 33SO emission, on the other hand, shows a ring-like structure surrounding Core A, and it peaks on the outer edge of the H30α emission region. These results imply that SO is enhanced in a shock produced by the expanding motion of the ionized region.

Keywords: Interstellar molecules, Massive stars, Astrochemistry
Multiband GPI Imaging of the HR 4796A Debris Disk. We have obtained Gemini Planet Imager (GPI) J-, H-, K1-, and K2-Spec observations of the iconic debris ring around the young, main-sequence star HR 4796A. We applied several point-spread function (PSF) subtraction techniques to the observations (Mask-and-Interpolate, RDI-NMF, RDI-KLIP, and ADI-KLIP) to measure the geometric parameters and the scattering phase function for the disk. To understand the systematic errors associated with PSF subtraction, we also forward-modeled the observations using a Markov Chain Monte Carlo framework and a simple model for the disk. We found that measurements of the disk geometric parameters were robust, with all of our analyses yielding consistent results; however, measurements of the scattering phase function were challenging to reconstruct from PSF-subtracted images, despite extensive testing. As a result, we estimated the scattering phase function using disk modeling. We searched for a dependence of the scattering phase function with respect to the GPI filters but found none. We compared the H-band scattering phase function with that measured by Hubble Space Telescope STIS at visual wavelengths and discovered a blue color at small scattering angles and a red color at large scattering angles, consistent with predictions and laboratory measurements of large grains. Finally, we successfully modeled the SPHERE H2 HR 4796A scattered phase function using a distribution of hollow spheres composed of silicates, carbon, and metallic iron.

Keywords: Planetary system formation, Coronagraphic imaging, Debris disks, Circumstellar matter
The Spectacular Ultraviolet Flash from the Peculiar Type Ia Supernova 2019yvq. Early observations of Type Ia supernovae (SNe Ia) provide essential clues for understanding the progenitor system that gave rise to the terminal thermonuclear explosion. We present exquisite observations of SN 2019yvq, the second observed SN Ia, after iPTF 14atg, to display an early flash of emission in the ultraviolet (UV) and optical. Our analysis finds that SN 2019yvq was unusual, even when ignoring the initial flash, in that it was moderately underluminous for an SN Ia ( ${M}_{g}\approx -18.5$ mag at peak) yet featured very high absorption velocities ( $v\approx 15{\rm{,0}}00$ km s-1 for Si II λ6355 at peak). We find that many of the observational features of SN 2019yvq, aside from the flash, can be explained if the explosive yield of radioactive 56Ni is relatively low (we measure ${M}_{{56}_{\mathrm{Ni}}}=0.31\pm 0.05\,{M}_{\odot }$ ) and it and other iron-group elements are concentrated in the innermost layers of the ejecta. To explain both the UV/optical flash and peak properties of SN 2019yvq we consider four different models: interaction between the SN ejecta and a nondegenerate companion, extended clumps of 56Ni in the outer ejecta, a double-detonation explosion, and the violent merger of two white dwarfs. Each of these models has shortcomings when compared to the observations; it is clear additional tuning is required to better match SN 2019yvq. In closing, we predict that the nebular spectra of SN 2019yvq will feature either H or He emission, if the ejecta collided with a companion, strong [Ca II] emission, if it was a double detonation, or narrow [O I] emission, if it was due to a violent merger.

Keywords: Observational astronomy, Surveys, White dwarf stars, Type Ia supernovae, Supernovae
MCR-TRGB: A Multiwavelength-covariant, Robust Tip of the Red Giant Branch Measurement Method. We present a new method to measure colors and magnitudes of the tip of the red giant branch (TGRB) in multiple bandpasses simultaneously by fitting an n-dimensional Gaussian to photometry of candidate tip stars. We demonstrate that this method has several advantages over traditional edge detection, particularly in regimes where the TRGB magnitude is strongly color dependent, as is the case in the near-infrared (NIR). We apply this method to a re-reduction of a set of optical and NIR Hubble Space Telescope data originally presented in Dalcanton et al. (D12). The re-reduction takes advantage of the increased depth and accuracy in the NIR photometry enabled by simultaneous reduction with higher-resolution optical data in crowded fields. We compare three possible absolute calibrations of the resulting apparent TRGB measurements, one adopting the same distance moduli as in D12 and two based on predicted TRGB absolute magnitudes from two widely used, modern sets of model isochrones. We find systematic offsets among the model absolute calibrations at the ∼0.15 mag level, in line with previous investigations. The models also have difficulty reproducing the optical-NIR color-magnitude behavior of our measurements, making these observations a useful benchmark for future improvements. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Keywords: Near infrared astronomy, Red giant tip, Distance indicators
Abundances in the Milky Way across Five Nucleosynthetic Channels from 4 Million LAMOST Stars. Large stellar surveys are revealing the chemodynamical structure of the Galaxy across a vast spatial extent. However, the many millions of low-resolution spectra observed to date are yet to be fully exploited. We employ The Cannon, a data-driven approach for estimating chemical abundances, to obtain detailed abundances from low-resolution (R = 1800) LAMOST spectra, using the GALAH survey as our reference. We deliver five (for dwarfs) or six (for giants) estimated abundances representing five different nucleosynthetic channels, for 3.9 million stars, to a precision of 0.05-0.23 dex. Using wide binary pairs, we demonstrate that our abundance estimates provide chemical discriminating power beyond metallicity alone. We show the coverage of our catalog with radial, azimuthal and dynamical abundance maps and examine the neutron capture abundances across the disk and halo, which indicate different origins for the in situ and accreted halo populations. LAMOST has near-complete Gaia coverage and provides an unprecedented perspective on chemistry across the Milky Way.

Keywords: Chemical abundances, Milky Way Galaxy
Intrinsic Properties of the Engine and Jet that Powered the Short Gamma-Ray Burst Associated with GW170817. GRB 170817A was a subluminous short gamma-ray burst detected about 1.74 s after the gravitational wave signal GW170817 from a binary neutron star (BNS) merger. It is now understood as an off-axis event powered by the cocoon of a relativistic jet pointing 15°-30° away from the direction of observation. The cocoon was energized by the interaction of the incipient jet with the non-relativistic baryon wind from the merger remnant, resulting in a structured outflow with a narrow core and broad wings. In this paper, we couple the observational constraints on the structured outflow with a model for the jet-wind interaction to constrain the intrinsic properties with which the jet was launched by the central engine, including its time delay from the merger event. Using wind prescriptions inspired by magnetized BNS merger simulations, we find that the jet was launched within about 0.4 s from the merger, implying that the 1.74 s observed delay was dominated by the fireball propagation up to the photospheric radius. We also constrain, for the first time for any gamma-ray burst, the jet opening angle at injection and set a lower limit to its asymptotic Lorentz factor. These findings suggest an initially Poynting-flux dominated jet, launched via electromagnetic processes. If the jet was powered by an accreting black hole, they also provide a significant constraint on the survival time of the metastable neutron star remnant.

Keywords: Gamma-ray bursts, Gravitational wave sources, Stellar mergers
A Simple, Entropy-based Dissipation Trigger for SPH. Smoothed particle hydrodynamics (SPH) schemes need to be enhanced by dissipation mechanisms to handle shocks. Most SPH formulations rely on artificial viscosity and, while this works well in pure shocks, attention must be paid to avoid dissipation where it is not wanted. Commonly used approaches include limiters and time-dependent dissipation parameters. The former try to distinguish shocks from other types of flows that do not require dissipation while in the latter approach the dissipation parameters are steered by some source term ("trigger") and, if not triggered, they decay to a predescribed floor value. The commonly used source terms trigger on either compression, $-{\rm{\nabla }}\cdot {\boldsymbol{v}}$ , or its time derivative. Here we explore a novel way to trigger SPH-dissipation: since an ideal fluid conserves entropy exactly, its numerical nonconservation can be used to identify "troubled particles" that need dissipation because they either pass through a shock or become noisy for other reasons. Our new scheme is implemented into the Lagrangian hydrodynamics code MAGMA2 and is scrutinized in a number of shock and fluid instability tests. We find excellent results in shocks and only a very moderate (and desired) switch-on in instability tests. The new scheme is robust, trivial to implement into existing SPH codes, and does not add any computational overhead.

Keywords: Hydrodynamical simulations
Circumnuclear Molecular Gas in Low-redshift Quasars and Matched Star-forming Galaxies. A series of gravitational instabilities in a circumnuclear gas disk (CND) are required to trigger gas transport to a central supermassive black hole and ignite active galactic nuclei (AGNs). A test of this scenario is to investigate whether an enhanced molecular gas mass surface density (Σmol) is found in the CND-scale of quasars relative to a comparison sample of inactive galaxies. Here we performed subkiloparsec resolution CO(2-1) observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of four low-redshift (z ∼ 0.06), luminous (∼1045 erg s-1) quasars with each matched to a different star-forming galaxy, having similar redshift, stellar mass, and star formation rate. We detected CO(2-1) emission from all quasars, which show diverse morphologies. Contrary to expectations, Σmol of the quasar sample, computed from the CO(2-1) luminosity, tends to be smaller than the comparison sample at r &lt; 500 pc; there is no systematic enhancement of Σmol in our quasars. We discuss four possible scenarios that would explain the lower molecular gas content (or CO(2-1) luminosity as an actual observable) at the CND-scale of quasars, i.e., AGN-driven outflows, gas-rich minor mergers, time-delay between the onsets of a starburst-phase and a quasar-phase, and X-ray-dominated region (XDR) effects on the gas chemical abundance and excitation. While not extensively discussed in the literature, XDR effects can have an impact on molecular mass measurements particularly in the vicinity of luminous quasar nuclei; therefore higher resolution molecular gas observations, which are now viable using ALMA, need to be considered.

Keywords: Supermassive black holes, Molecular gas, Quasars, Active galactic nuclei, Star formation, Submillimeter astronomy