adsabs/SciX_UAT_keywords huggingface dataset:
Near-infrared Spectral Characterization of Solar-type Stars in the Northern Hemisphere

Although solar-analog stars have been studied extensively over the past few decades, most of these studies have focused on visible wavelengths, especially those identifying solar-analog stars to be used as calibration tools for observations. As a result, there is a dearth of well-characterized solar analogs for observations in the near-infrared, a wavelength range important for studying solar system objects. We present 184 stars selected based on solar-like spectral type and V-J and V-K colors whose spectra we have observed in the 0.8-4.2 μm range for calibrating our asteroid observations. Each star has been classified into one of three ranks based on spectral resemblance to vetted solar analogs. Of our set of 184 stars, we report 145 as reliable solar-analog stars, 21 as solar analogs usable after spectral corrections with low-order polynomial fitting, and 18 as unsuitable for use as calibration standards owing to spectral shape, variability, or features at low to medium resolution. We conclude that all but five of our candidates are reliable solar analogs in the longer wavelength range from 2.5 to 4.2 μm. The average colors of the stars classified as reliable or usable solar analogs are V-J = 1.148, V-H = 1.418, and V-K = 1.491, with the entire set being distributed fairly uniformly in R.A. across the sky between -27° and +67° in decl.

Keywords: standard stars; solar analogs
Detection of Asymmetry in the Narrow Fe Kα Emission Line in MCG-5-23-16 with Chandra

Iron Kα (Fe Kα) emission is observed ubiquitously in active galactic nuclei (AGN), and it is a powerful probe of their circumnuclear environment. Examinations of the emission line play a pivotal role in understanding the disk geometry surrounding black holes. It has been suggested that the torus and the broad-line region (BLR) are the origins of emission. However, there is no universal location for the emitting region relative to the BLR. Here, we present an analysis of the narrow component of the Fe Kα line in the Seyfert AGN MCG-5-23-16, one of the brightest AGN in X-rays and in Fe Kα emission, to localize the emitting region. Spectra derived from Chandra/HETGS observations show asymmetry in the narrow Fe Kα line, which has only been confirmed before in the AGN NGC 4151. Models including relativistic Doppler broadening and gravitational redshifts are preferred over simple Gaussians and measure radii consistent with R ≃ 200–650 r g . These results are consistent with those of NGC 4151 and indicate that the narrow Fe Kα line in MCG-5-23-16 is primarily excited in the innermost part of the optical BLR, or X-ray BLR. Characterizing the properties of the narrow Fe Kα line is essential for studying the disk geometries of the AGN population and mapping their innermost regions.

Keywords: active galactic nuclei; x-ray astronomy; spectroscopy; black holes
The Behavior of Bp He-strong Stars in the far UV-Paper I: HD 37776

The analysis of thirty-two spectra of the Bp He-strong variable star HD 37776 recorded by the SWP camera on board the International Ultraviolet Explorer reveals variations of the far-ultraviolet spectral energy distribution over a time interval of about 26 hr. Variations are present shortwards of 1450 Å which can be partly attributed to variations of lines and continuum of Si II. Other lines due to C II, Si III and Si IV also contribute to the opacity in this range too. The variations suggest that silicon and possibly carbon are not distributed in a uniform manner over the surface.

Keywords: chemically peculiar stars
General Relativistic Radiation Magnetohydrodynamics Simulations of Black Hole Accretion Disks: Comparison of Methods Based on Variable Eddington Tensor and Based on M1 Closure

We perform 2.5-dimensional general relativistic radiation magnetohydrodynamics simulations of black hole accretion disks and disk winds in the range of mass accretion rate from 0.1 to 104.5 times the Eddington limit. In this paper, we compare the results of the INAZUMA code, in which the frequency-integrated time-dependent radiation transfer equation is solved in order to evaluate the Eddington tensor, with those of the first momentum (M1) approximation method. In both methods, accretion disks and disk winds appear, and there is no remarkable difference in accretion rate, outflow rate, or luminosity. However, the significant difference in the radiation field appears around the rotation axis. In the M1 method, the radial component of the radiation flux tends to be amplified owing to unphysical radiation collisions. Such an enhancement of the outward radiation flux does not appear in INAZUMA. Also, the problem of radiation not reaching the rotation axis occurs with M1, but not with INAZUMA. Our results indicate that the radiation transfer equation should be solved to obtain the accurate radiation field in the optically thin region around the rotation axis.

Keywords: black hole physics; high energy astrophysics; general relativity; magnetohydrodynamical simulations; radiative magnetohydrodynamics
A Luminous X-Ray Transient in SDSS J143359.16+400636.0: A Likely Tidal Disruption Event

We present the discovery of a luminous X-ray transient, serendipitously detected by Swift's X-ray Telescope on 2020 February 5, located in the nucleus of the galaxy SDSS J143359.16+400636.0 at z = 0.099 (luminosity distance DL = 456 Mpc). The transient was observed to reach a peak luminosity of ∼1044 erg s-1 in the 0.3-10 keV X-ray band, which was ∼20 times more than the peak optical/UV luminosity. Optical, UV, and X-ray light curves from the Zwicky Transient Facility and Swift show a decline in flux from the source consistent with t-5/3, and observations with NuSTAR and Chandra show a soft X-ray spectrum with photon index Γ = 2.9 ± 0.1. The X-ray/UV properties are inconsistent with well-known active galactic nucleus properties and have more in common with known X-ray tidal disruption events (TDEs), leading us to conclude that it was likely a TDE. The broadband spectral energy distribution can be described well by a disk blackbody model with an inner disk temperature of ${7.3}_{-0.8}^{+0.3}\times {10}^{5}$ K, with a large fraction (>40%) of the disk emission upscattered into the X-ray band. An optical spectrum taken with Keck/LRIS after the X-ray detection reveals LINER line ratios in the host galaxy, suggesting low-level accretion onto the supermassive black hole prior to the event, but no broad lines or other indications of a TDE were seen. The stellar velocity dispersion implies that the mass of the supermassive black hole powering the event is log(MBH/M⊙) = 7.41 ± 0.41, and we estimate that at peak the Eddington fraction of this event was ∼50%. This likely TDE was not identified by wide-field optical surveys or optical spectroscopy, indicating that more events like this would be missed without wide-field UV or X-ray surveys.

Keywords: tidal disruption; x-ray transient sources; transient sources; x-ray sources; supermassive black holes
Direct-imaging Discovery and Dynamical Mass of a Substellar Companion Orbiting an Accelerating Hyades Sun-like Star with SCExAO/CHARIS

We present the direct-imaging discovery of a substellar companion in orbit around a Sun-like star member of the Hyades open cluster. So far, no other substellar companions have been unambiguously confirmed via direct imaging around main-sequence stars in Hyades. The star HIP 21152 is an accelerating star as identified by the astrometry from the Gaia and Hipparcos satellites. We detected the companion, HIP 21152 B, in multiple epochs using the high-contrast imaging from SCExAO/CHARIS and Keck/NIRC2. We also obtained the stellar radial-velocity data from the Okayama 188 cm telescope. The CHARIS spectroscopy reveals that HIP 21152 B's spectrum is consistent with the L/T transition, best fit by an early T dwarf. Our orbit modeling determines the semimajor axis and the dynamical mass of HIP 21152 B to be 17.5 ${}_{-3.8}^{+7.2}$ au and 27.8 ${}_{-5.4}^{+8.4}$ M Jup, respectively. The mass ratio of HIP 21152 B relative to its host is ≈2%, near the planet/brown dwarf boundary suggested by recent surveys. Mass estimates inferred from luminosity-evolution models are slightly higher (33-42 M Jup). With a dynamical mass and a well-constrained age due to the system's Hyades membership, HIP 21152 B will become a critical benchmark in understanding the formation, evolution, and atmosphere of a substellar object as a function of mass and age. Our discovery is yet another key proof of concept for using precision astrometry to select direct-imaging targets. *Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Keywords: brown dwarfs; exoplanets; open star clusters; direct imaging; coronagraphic imaging; astrometry; exoplanet detection methods; astronomical instrumentation
Resolving the Peak of the Black Hole Mass Spectrum

Gravitational-wave (GW) detections of binary black hole (BH) mergers have begun to sample the cosmic BH mass distribution. The evolution of single stellar cores predicts a gap in the BH mass distribution due to pair-instability supernovae (PISNe). Determining the upper and lower edges of the BH mass gap can be useful for interpreting GW detections of merging BHs. We use MESA to evolve single, nonrotating, massive helium cores with a metallicity of Z = 10-5, until they either collapse to form a BH or explode as a PISN, without leaving a compact remnant. We calculate the boundaries of the lower BH mass gap for S-factors in the range S(300 keV) = (77,203) keV b, corresponding to the ±3σ uncertainty in our high-resolution tabulated 12C(α,γ)16O reaction rate probability distribution function. We extensively test temporal and spatial resolutions for resolving the theoretical peak of the BH mass spectrum across the BH mass gap. We explore the convergence with respect to convective mixing and nuclear burning, finding that significant time resolution is needed to achieve convergence. We also test adopting a minimum diffusion coefficient to help lower-resolution models reach convergence. We establish a new lower edge of the upper mass gap as M lower ≃ ${60}_{-14}^{+32}$ M ⊙ from the ±3σ uncertainty in the 12C(α, γ)16O rate. We explore the effect of a larger 3α rate on the lower edge of the upper mass gap, finding M lower ≃ ${69}_{-18}^{+34}$ M ⊙. We compare our results with BHs reported in the Gravitational-Wave Transient Catalog.

Keywords: gravitational waves; black holes; nuclear astrophysics; stellar physics; core-collapse supernovae
Imaging Preflare Broadband Pulsations in the Decimetric-metric Wavelengths

Preflare activities contain critical information about the precursors and causes of solar eruptions. Here we investigate the characteristics and origin of a group of broadband pulsations (BBPs) in the decimetric-metric wavelengths that took place during the preflare stage of the M7.1 flare on 2011 September 24. The event was recorded by multiple solar instruments, including the Nançay Radioheliograh, that measure the properties of the radio source. The BBPs started ~24 minutes before the flare onset, extending from <360 to above 800 MHz without a discernible spectral drift. The BBPs consisted of two stages. During the first stage, the main source remained stationary, and during the second stage, it moved outward along with a steepening extreme-ultraviolet (EUV) wave driven by the eruption of a high-temperature structure. In both stages, we observe frequent EUV brightenings and jets originating from the flare region. During the second stage, the BBPs became more frequent and stronger in general, and the polarization level gradually increased from <20% to >60% in the right-handed sense. These observations indicate that the steepening EUV wave is important to the BBPs during the second stage, while the preflare reconnections causing the jets and EUV brightenings are important in both stages. This is the first time that such a strong association of an EUV wave with BBPs is reported. We suggest a scenario in which reconnection occurs together with a shock that sweeps across the loops as the cause of the BBPs.

Keywords: solar flares; solar activity; solar radio emission; solar corona; solar coronal mass ejections
Pyspeckit: A Spectroscopic Analysis and Plotting Package

pyspeckit is a toolkit and library for spectroscopic analysis in Python. We describe the pyspeckit package and highlight some of its capabilities, such as interactively fitting a model to data, akin to the historically widely-used splot function in IRAF. pyspeckit employs the Levenberg-Marquardt optimization method via the mpfit and lmfit implementations, and important assumptions regarding error estimation are described here. Wrappers to use pymc and emcee as optimizers are provided. A parallelized wrapper to fit lines in spectral cubes is included. As part of the astropy affiliated package ecosystem, pyspeckit is open source and open development, and welcomes input and collaboration from the community.

Keywords: astronomy software; spectroscopy
BASS. XXXIII. Swift-BAT Blazars and Their Jets through Cosmic Time

We derive the most up-to-date Swift-Burst Alert Telescope (BAT) blazar luminosity function in the 14-195 keV range, making use of a clean sample of 118 blazars detected in the BAT 105 month survey catalog, with newly obtained redshifts from the BAT Active Galatic Nucleus Spectroscopic Survey. We determine the best-fit X-ray luminosity function for the whole blazar population, as well as for flat-spectrum radio quasars (FSRQs) alone. The main results are: (1) at any redshift, BAT detects the most luminous blazars, above any possible break in their luminosity distribution, which means we cannot differentiate between density and luminosity evolution; (2) the whole blazar population, dominated by FSRQs, evolves positively up to redshift z ~ 4.3, confirming earlier results and implying lower number densities of blazars at higher redshifts than previously estimated. The contribution of this source class to the cosmic X-ray background at 14-195 keV can range from 5%-18%, while possibly accounting for 100% of the MeV background. We also derived the average 14 keV-10 GeV spectral energy distribution for BAT blazars, which allows us to predict the number counts of sources in the MeV range, as well as the expected number of high-energy (>100 TeV) neutrinos. A mission like COSI will detect 40 MeV blazars, of which two may have coincident neutrino detections. Finally, taking into account beaming selection effects, the distribution and properties of the parent population of these extragalactic jets are derived. We find that the distribution of viewing angles is quite narrow, with most sources aligned within <5° of the line of sight. Moreover, the average Lorentz factor, <Γ> = 8-12, is lower than previously suggested for these powerful sources.

Keywords: active galactic nuclei; blazars; cosmological evolution; x-ray active galactic nuclei; supermassive black holes; quasars; relativistic jets
Xenon Isotopes Identify Large-scale Nucleosynthetic Heterogeneities across the Solar System

Nucleosynthetic isotopic anomalies in meteorites and planetary objects contribute to our understanding of the formation of the solar system. Isotope systematics of chondrites demonstrate the existence of a physical separation between isotopic reservoirs in the solar system. The isotopic composition of atmospheric xenon (Xe) indicates that its progenitor, U-Xe, is depleted in 134Xe and 136Xe isotopes relative to solar or chondritic end-members. This deficit supports the view that nucleosynthetic heterogeneities persisted during the solar system formation. Measurements of xenon emitted from comet 67P/Churyumov-Gerasimenko (67P) identified a similar, but more extreme, deficit of cometary gas in these isotopes relative to solar gas. Here we show that the data from 67P demonstrate that two distinct sources contributed xenon isotopes associated with the r-process to the solar system. The h-process contributed at least 29% (2σ) of solar system 136Xe. Mixtures of these r-process components and the s-process that match the heavy isotope signature of cometary Xe lead to depletions of the precursor of atmospheric Xe in p-only isotopes. Only the addition of pure p-process Xe to the isotopic mixture brings 124Xe/132Xe and 126Xe/132Xe ratios back to solar-like values. No pure p-process Xe has been detected in solar system material, and variation in p-process Xe isotopes is always correlated with variation in r-process Xe isotopes. In the solar system, p-process incorporation from the interstellar medium happened before incorporation of r-process nuclides or material in the outer edge of the solar system carries a different mixture of presolar sources as have been preserved in parent bodies.

Keywords: earth atmosphere; planetary atmospheres; cosmochemistry; solar system planets; nucleosynthesis; p-process
Polarized Signatures of a Habitable World: Comparing Models of an Exoplanet Earth with Visible and Near-infrared Earthshine Spectra

In the JWST, Extremely Large Telescopes, and LUVOIR era, we expect to characterize a number of potentially habitable Earth-like exoplanets. However, the characterization of these worlds depends crucially on the accuracy of theoretical models. Validating these models against observations of planets with known properties will be key for the future characterization of terrestrial exoplanets. Due to its sensitivity to the micro- and macro-physical properties of an atmosphere, polarimetry will be an important tool that, in tandem with traditional flux-only observations, will enhance the capabilities of characterizing Earth-like planets. In this paper we benchmark two different polarization-enabled radiative-transfer codes against each other and against unique linear spectropolarimetric observations of the earthshine that cover wavelengths from ~0.4 to ~2.3 μm. We find that while the results from the two codes generally agree with each other, there is a phase dependency between the compared models. Additionally, with our current assumptions, the models from both codes underestimate the level of polarization of the earthshine. We also report an interesting discrepancy between our models and the observed 1.27 μm O2 feature in the earthshine, and provide an analysis of potential methods for matching this feature. Our results suggest that only having access to the 1.27 μm O2 feature coupled with a lack of observations of the O2 A and B bands could result in a mischaracterization of an Earth-like atmosphere. Providing these assessments is vital to aid the community in the search for life beyond the solar system.

Keywords: spectropolarimetry; exoplanets; habitable planets; polarimetry; radiative transfer; planetary atmospheres
Nonlinear Damping of Standing Kink Waves Computed With Elsässer Variables

In a previous paper, we computed the energy density and the nonlinear energy cascade rate for transverse kink waves using Elsässer variables. In this paper, we focus on the standing kink waves, which are impulsively excited in coronal loops by external perturbations. We present an analytical calculation to compute the damping time due to the nonlinear development of the Kelvin-Helmholtz instability. The main result is that the damping time is inversely proportional to the oscillation amplitude. We compare the damping times from our formula with the results of numerical simulations and observations. In both cases we find a reasonably good match. The comparison with the simulations shows that the nonlinear damping dominates in the high amplitude regime, while the low amplitude regime shows damping by resonant absorption. In the comparison with the observations, we find a power law inversely proportional to the amplitude η-1 as an outer envelope for our Monte Carlo data points.

Keywords: solar physics; solar coronal waves; solar corona; magnetohydrodynamics; solar active regions; solar coronal loops; solar coronal heating
A Radio Counterpart to a Jupiter-mass Binary Object in Orion

Using James Webb Space Telescope near-infrared data of the inner Orion Nebula, Pearson & McCaughrean detected 40 Jupiter-mass binary objects (JuMBOs). These systems are not associated with stars and their components have masses of giant Jupiter-like planets and separations in the plane of the sky of order ~100 au. The existence of these wide free-floating planetary-mass binaries was unexpected in our current theories of star and planet formation. Here we report the radio continuum (6.1 and 10.0 GHz) Karl G. Jansky Very Large Array detection of a counterpart to JuMBO 24. The radio emission appears to be steady at a level of ~50 μJy over timescales of days and years. We set an upper limit of ≃15 km s-1 to the velocity of the radio source in the plane of the sky. As in the near-infrared, the radio emission seems to be coming from both components of the binary.

Keywords: exoplanet astronomy; radio astrometry; radio continuum emission
James Webb Space Telescope Spectra of Cold Brown Dwarfs are Well-reproduced by Phosphine-free, Diabatic, ATMO2020++ Models

James Webb Space Telescope (JWST) mid-infrared spectra of cold brown dwarfs (BDs) are becoming available. In Leggett & Tremblin we demonstrated that an ATMO2020++ synthetic spectrum provided an excellent fit to the first published spectrum. Here we show that these models can reproduce the 1-14 μm spectra of BDs with a range of effective temperature: 350 ≤ T eff K ≤ 500. A grid of these models, which include disequilibrium chemistry and non-adiabatic pressure-temperature profiles, is available. In addition, a number of models without phosphine were calculated, as PH3 is absent in the JWST data. Two of the six BDs studied are particularly interesting; one appears to be a young low-mass BD, the other is best fit as a binary. More complete analyses will be possible with an extended model grid, and with additional JWST data. The ATMO2020++ models are recommended for analyses of all BD data.

Keywords: atmospheric dynamics; brown dwarfs; infrared spectroscopy
The DECam Ecliptic Exploration Project (DEEP). VI. First Multiyear Observations of Trans-Neptunian Objects

We present the first set of trans-Neptunian objects (TNOs) observed on multiple nights in data taken from the DECam Ecliptic Exploration Project. Of these 110 TNOs, 105 do not coincide with previously known TNOs and appear to be new discoveries. Each individual detection for our objects resulted from a digital tracking search at TNO rates of motion, using two-to-four-hour exposure sets, and the detections were subsequently linked across multiple observing seasons. This procedure allows us to find objects with magnitudes m VR ≈ 26. The object discovery processing also included a comprehensive population of objects injected into the images, with a recovery and linking rate of at least 94%. The final orbits were obtained using a specialized orbit-fitting procedure that accounts for the positional errors derived from the digital tracking procedure. Our results include robust orbits and magnitudes for classical TNOs with absolute magnitudes H ∼ 10, as well as a dynamically detached object found at 76 au (semimajor axis a ≈ 77 au). We find a disagreement between our population of classical TNOs and the CFEPS-L7 three-component model for the Kuiper Belt.

Keywords: kuiper belt; surveys; trans-neptunian objects