adsabs/SciX_UAT_keywords huggingface dataset:
J0107a: A Barred Spiral Dusty Star-forming Galaxy at z = 2.467

Dusty star-forming galaxies (DSFGs) are among the most massive and active star-forming galaxies during the cosmic noon. Theoretical studies have proposed various formation mechanisms of DSFGs, including major merger-driven starbursts and secular star-forming disks. Here, we report J0107a, a bright (~8 mJy at observed-frame 888 μm) DSFG at z = 2.467 that appears to be a gas-rich massive disk and might be an extreme case of the secular disk scenario. J0107a has a stellar mass M ⋆ ~ 5 × 1011 M ⊙, molecular gas mass M mol ≳ 1011 M ⊙, and a star formation rate of ~500M ⊙ yr-1. J0107a does not have a gas-rich companion. The rest-frame 1.28 μm JWST NIRCam image of J0107a shows a grand-design spiral with a prominent stellar bar extending ~15 kpc. The Atacama Large Millimeter/submillimeter Array Band 7 continuum map reveals that the dust emission originates from both the central starburst and the stellar bar. 3D disk modeling of the CO(4-3) emission line indicates a dynamically cold disk with rotation-to-dispersion ratio ${V}_{\max }/\sigma \sim 8$ . The results suggest a bright DSFG may have a nonmerger origin, and its vigorous star formation may be triggered by the bar and/or rapid gas inflow.

Keywords: barred spiral galaxies; co line emission; galaxy formation; high-redshift galaxies; ultraluminous infrared galaxies
Uniform Forward-modeling Analysis of Ultracool Dwarfs. III. Late-M and L Dwarfs in Young Moving Groups, the Pleiades, and the Hyades

We present a uniform forward-modeling analysis of 90 late-M and L dwarfs in nearby young (~10-200 Myr) moving groups, the Pleiades, and the Hyades using low-resolution (R ≈ 150) near-infrared (0.9-2.4 μm) spectra and the BT-Settl model atmospheres. We derive the objects' effective temperatures, surface gravities, radii, and masses by comparing our spectra to the models using a Bayesian framework with nested sampling and calculate the same parameters using evolutionary models. Assuming the evolutionary-based parameters are more robust, our spectroscopically inferred parameters from BT-Settl exhibit two types of systematic behavior for objects near the M-L spectral type boundary. Several objects are clustered around T eff ≈ 1800 K and $\mathrm{log}g\approx 5.5$ dex, implying impossibly large masses (150-1400 M Jup), while others are clustered around T eff ≳ 3000 K and $\mathrm{log}g\lesssim 3.0$ dex, implying unphysically low masses and unreasonably young ages. We find the fitted BT-Settl model spectra tend to overpredict the peak J- and H-band flux for objects located near the M-L boundary, suggesting the dust content included in the model atmospheres is insufficient to match the observations. By adding an interstellar medium-like reddening law to the BT-Settl model spectra, we find the fits between models and observed spectra are greatly improved, with the largest reddening coefficients occurring at the M-L transition. This work delivers a systematic examination of the BT-Settl model atmospheres and constitutes the largest spectral analysis of benchmark late-M- and L-type brown dwarfs to date.

Keywords: brown dwarfs; l dwarfs; m dwarf stars; exoplanet atmospheres; stellar atmospheres
Prospects for Ray-tracing Light Intensity and Polarization in Models of Accreting Compact Objects Using a GPU

The Event Horizon Telescope (EHT) has recently released high-resolution images of accretion flows onto two supermassive black holes. Our physical understanding of these images depends on the accuracy and precision of numerical models of plasma and radiation around compact objects. The goal of this work is to speed up radiative-transfer simulations used to create mock images of black holes for comparison with the EHT observations. A ray-tracing code for general relativistic and fully polarized radiative transfer through plasma in strong gravity is ported onto a graphics processing unit (GPU). We describe our GPU implementation and carry out speedup tests using models of optically thin advection-dominated accretion flow onto a black hole realized semianalytically and in 3D general relativistic magnetohydrodynamic simulations, low and very high image pixel resolutions, and two different sets of CPU+GPUs. We show that a GPU with high double precision computing capability can significantly reduce the image production computational time, with a speedup factor of up to approximately 1200. The significant speedup facilitates, e.g., dynamic model fitting to the EHT data, including polarimetric data. The method extension may enable studies of emission from plasma with nonthermal particle distribution functions for which accurate approximate synchrotron emissivities are not available. The significant speedup reduces the carbon footprint of the generation of the EHT image libraries by at least an order of magnitude.

Keywords: black holes; general relativity; radiative transfer; astronomy software; computational methods; gpu computing
Laboratory and On-sky Testing of an InGaAs Detector for Infrared Imaging

We describe the results of testing a shortwave infrared CMOS camera using an indium gallium arsenide (InGaAs) detector. The new generation of InGaAs detectors offers a cost-effective alternative to mercury cadmium telluride (HgCdTe) for astronomy research, with current, off-the-shelf cameras requiring no modification before use. Testing was conducted in the laboratory and on-sky while mounted to the robotic, 2 m Liverpool Telescope using a H-band filter. The camera exhibits a dark current of 821 e- s-1 pix-1 and a bias level of 864 e- pix-1. The dark current associated shot noise is of similar size to the read noise of 32 e- pix-1 in one-second exposures. Linearity within the count region where readout noise and bit-depth saturation effects are not dominant is within a few tenths of a per cent. After field-compression by fore optics, the plate-scale yields 0.″3 pix-1, near perfect for Nyquist sampling at the La Palma site. The sky background for the H-band filter dominates the other noise sources for the instrument for one-second exposures producing sky-limited photometry. On-sky observations show that milli-magnitude precision is achieved for sources <10.7 mag and a signal-to-noise ratio of 10 is achievable for 16th magnitude with a 3 minutes total exposure time, making it an ideal follow-up instrument for sources detected in current and upcoming IR surveys.

Keywords: infrared photometry; astronomical instrumentation; astronomical detectors
Identifying Shadowing Signatures of C Ring Ringlets and Plateaus in Cassini Data from Saturn's Ionosphere

For orbits 288 and 292 of Cassini's Grand Finale, clear dips (sharp and narrow decreases) are visible in the ${{\rm{H}}}_{2}^{+}$ densities measured by the Ion and Neutral Mass Spectrometer (INMS). In 2017, the southern hemisphere of Saturn was shadowed by its rings and the substructures within. Tracing a path of the solar photons through the ring plane to Cassini's position, we can identify regions in the ionosphere that were shadowed by the individual ringlets and plateaus (with increased optical depths) of Saturn's C ring. The calculated shadowed altitudes along Cassini's trajectory line up well with the dips in the ${{\rm{H}}}_{2}^{+}$ data when adjusting the latter based on a detected evolving shift in the INMS timestamps since 2013, illustrating the potential for verification of instrument timings. We can further estimate the mean optical depths of the ringlets/plateaus by comparing the dips to inbound ${{\rm{H}}}_{2}^{+}$ densities. Our results agree well with values derived from stellar occultation measurements. No clear dips are visible for orbits 283 and 287, whose periapsides were at higher altitudes. This can be attributed to the much longer chemical lifetime of ${{\rm{H}}}_{2}^{+}$ at these higher altitudes, which in turn can be further used to estimate a lower limit for the flow speed along Cassini's trajectory. The resulting estimate of ~0.3 km s-1 at an altitude of ~3400 km is in line with prior suggestions. Finally, the ringlet and plateau shadows are not associated with obvious dips in the electron density, which is expected due to their comparatively long chemical (recombination) lifetime.

Keywords: saturn; space plasmas; planetary ionospheres; planetary rings
The Behavior of HgMn Stars in the Far UV-Paper 8: HR 7775

The analysis of 14 high resolution spectra of the chemically peculiar star HR 7775 recorded by the International Ultraviolet Explorer reveals large amplitude variations of the far and mid-ultraviolet flux (at minimum the flux is about 70% of its value at maximum) over the various observations with IUE. The lines at minimum flux are redshifted respect to their positions at maximum. These variations probably reflects an eclipse by a cooler and smaller companion of spectral type A or even early F. The absence of TESS observations prevents a search for periodic orbital and rotational variabilities.

Keywords: chemically peculiar stars
ExoCAM: A 3D Climate Model for Exoplanet Atmospheres

The TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI) project was initiated to compare 3D climate models that are commonly used for predicting theoretical climates of habitable zone extrasolar planets. One of the core models studied as part of THAI is ExoCAM, an independently curated exoplanet branch of the National Center for Atmospheric Research Community Earth System Model (CESM), version 1.2.1. ExoCAM has been used for studying atmospheres of terrestrial extrasolar planets around a variety of stars. To accompany the THAI project and provide a primary reference, here we describe ExoCAM and what makes it unique from standard configurations of CESM. Furthermore, we also conduct a series of intramodel sensitivity tests of relevant moist physical tuning parameters while using the THAI protocol as our starting point. A common criticism of 3D climate models used for exoplanet modeling is that cloud and convection routines often contain free parameters that are tuned to the modern Earth, and thus may be a source of uncertainty in evaluating exoplanet climates. Here, we explore sensitivities to numerous configuration and parameter selections, including a recently updated radiation scheme, a different cloud and convection physics package, different cloud and precipitation tuning parameters, and a different sea ice albedo. Improvements to our radiation scheme and the modification of cloud particle sizes have the largest effects on global mean temperatures, with variations up to ~10 K, highlighting the requirement for accurate radiative transfer and the importance of cloud microphysics for simulating exoplanetary climates. However, for the vast majority of sensitivity tests, climate differences are small. For all cases studied, intramodel differences do not bias general conclusions regarding climate states and habitability.

Keywords: planetary climates; exoplanet atmospheres
On the Origin of Radio-loudness in Active Galactic Nuclei Using Far-infrared Polarimetric Observations

The dichotomy between radio-loud (RL) and radio-quiet (RQ) active galactic nuclei (AGNs) is thought to be intrinsically related to radio jet production. This difference may be explained by the presence of a strong magnetic field (B-field) that enhances, or is the cause of, the accretion activity and the jet power. Here we report the first evidence of an intrinsic difference in the polarized dust emission cores of four RL and five RQ obscured AGNs using 89 μm polarization with SOFIA/HAWC+. We find that the thermal polarized emission increases with the nuclear radio-loudness, R 20 = L 5GHz/L 20μm. The dust emission cores of RL AGNs are measured to be polarized, ~5%-11%, while RQ AGNs are unpolarized, <1%. For RQ AGNs, our results are consistent with the observed region being filled with an unmagnetized or highly turbulent disk and/or expanding outflow at scales of 5-130 pc from the AGNs. For RL AGNs, the measured 89 μm polarization arises primarily from magnetically aligned dust grains associated with a 5-130 pc scale dusty obscuring structure with a toroidal B-field orientation highly offset, 65° ± 22°, with respect to the jet axis. Our results indicate that the size and strength of the B-fields surrounding the AGNs are intrinsically related to the strength of the jet power-the stronger the jet power is, the larger and stronger the toroidal B-field is. The detection of a ≤130 pc scale ordered toroidal B-field suggests that (a) the infalling gas that fuels RL AGNs is magnetized, (b) there is a magnetohydrodynamic wind that collimates the jet, and/or (c) the jet is able to magnetize its surroundings.

Keywords: extragalactic magnetic fields; seyfert galaxies; far infrared astronomy; active galactic nuclei; magnetohydrodynamics; polarimetry; radio galaxies; astrophysical dust processes; agn host galaxies; supermassive black holes
The First Spatially Resolved Detection of 13CN in a Protoplanetary Disk and Evidence for Complex Carbon Isotope Fractionation

Recent measurements of carbon isotope ratios in both protoplanetary disks and exoplanet atmospheres have suggested a possible transfer of significant carbon isotope fractionation from disks to planets. For a clearer understanding of the isotopic link between disks and planets, it is important to measure the carbon isotope ratios in various species. In this paper, we present a detection of the 13CN N = 2 ‑ 1 hyperfine lines in the TW Hya disk with the Atacama Large Millimeter/submillimeter Array. This is the first spatially resolved detection of 13CN in disks, which enables us to measure the spatially resolved 12CN/13CN ratio for the first time. We conducted nonlocal thermal equilibrium modeling of the 13CN lines in conjunction with previously observed 12CN lines to derive the kinetic temperature, H2 volume density, and column densities of 12CN and 13CN. The H2 volume density is found to range between (4 ‑ 10) × 107 cm‑3, suggesting that CN molecules mainly reside in the disk's upper layer. The 12CN/13CN ratio is measured to be ${70}_{-6}^{+9}$ at 30 < r < 80 au from the central star, which is similar to the 12C/13C ratio in the interstellar medium. However, this value differs from the previously reported values found for other carbon-bearing molecules (CO and HCN) in the TW Hya disk. This could be self-consistently explained by different emission layer heights for different molecules combined with preferential sequestration of 12C into the solid phase toward the disk midplane. This study reveals the complexity of the carbon isotope fractionation operating in disks.

Keywords: protoplanetary disks; astrochemistry; isotopic abundances
WOCS 4540: Detailed Analysis of a very Long Orbital Period Blue Straggler

WOCS 4540 is the longest orbital period (P orb = 3030 days) blue straggler star (BSS)-white dwarf (WD) pair in the old open cluster NGC 188. It also contains one of the most luminous BSS in the cluster. Prior Hubble Space Telescope Cosmic Origins Spectrograph spectroscopy measured a WD mass of 0.53 M ⊙, indicative of a carbon-oxygen WD and suggesting previous mass transfer from an asymptotic giant branch (AGB) star. Detailed modeling of the system evolution, including red giant branch phase wind mass transfer, AGB wind Roche-lobe overflow, and regular Roche-lobe overflow, is done with Modules for Experiments in Stellar Astrophysics. The best-fit model produces excellent agreement with a wide array of observational constraints on the BSS, the WD, and the binary system. To produce the observed luminosity and effective temperature of the BSS, all three donor mass-transfer mechanisms contribute similarly to build a 1.5 M ⊙ BSS. The overall mass-transfer efficiency is 55%. Regular Roche-lobe overflow occurs only during the largest AGB thermal pulse, but yields a very high accretion rate at 75% efficiency and briefly (less than 1 Myr) a very high luminosity boost from the accretor.

Keywords: blue straggler stars; binary stars; close binary stars; open star clusters; stellar evolution; white dwarf stars
A Jupiter Analog Orbiting The Nearby M Dwarf GJ 463

We report the detection of a long-period giant planetary companion to the nearby M3V star GJ 463 (=Ross 690). The detection is based on over ten years of highly-precise radial velocity measurements with the High Resolution Spectrograph at the Hobby-Eberly Telescope and the HIRES spectrograph at Keck. With an orbital period of 10 yr and a minimum mass of 1.55 ± 0.15 M Jup, GJ 463 b has a comparable orbital period to Jupiter and hence qualifies as a Jupiter analog around a low-mass star. We demonstrate that the radial velocity signal is not produced by a magnetic activity cycle of the host star. GJ 463 was observed with TESS, and we searched the light curve for any possible signals of stellar or planetary origin, but detected none. This planet is a candidate for possible direct detection with the coronagraph of the upcoming Nancy Grace Roman Space Telescope. We compared Gaia EDR3 with Hipparcos astrometry and detected a significant acceleration, which is likely caused by this long-period planetary companion at a = 3.53 ± 0.07 au.

Keywords: exoplanets; extrasolar gaseous planets
Stellar Evolution in the Disks of Active Galactic Nuclei Produces Rapidly Rotating Massive Stars

Stars can either be formed in or captured by the accretion disks in active galactic nuclei (AGNs). These AGN stars are irradiated and subject to extreme levels of accretion, which can turn even low-mass stars into very massive ones (M > 100M⊙) whose evolution may result in the formation of massive compact objects (M > 10M⊙). Here we explore the spins of these AGN stars and the remnants they leave behind. We find that AGN stars rapidly spin up via accretion, eventually reaching near-critical rotation rates. They further maintain near-critical rotation even as they shed their envelopes, become compact, and undergo late stages of burning. This makes them good candidates to produce high-spin massive black holes, such as the ones seen by LIGO-Virgo in GW 190521g, as well as long gamma-ray bursts and the associated chemical pollution of the AGN disk.

Keywords: stellar physics; stellar evolutionary models; massive stars; quasars
Imaging Spectroscopy of CME-associated Solar Radio Bursts using OVRO-LWA

We present the first results of a solar radio event observed with the Owens Valley Radio Observatory Long Wavelength Array at metric wavelengths. We examine a complex event consisting of multiple radio sources/bursts associated with a fast coronal mass ejection (CME) and an M2.1 GOES soft X-ray flare from 2015 September 20. Images of 9 s cadence are used to analyze the event over a 120 minute period, and solar emission is observed out to a distance of ≈3.5 R⊙, with an instantaneous bandwidth covering 22 MHz within the frequency range of 40-70 MHz. We present our results from the investigation of the radio event, focusing particularly on one burst source that exhibits outward motion, which we classify as a moving type IV burst. We image the event at multiple frequencies and use the source centroids to obtain the velocity for the outward motion. Spatial and temporal comparison with observations of the CME in white light from the C2 coronagraph of the Large Angle and Spectrometric COronagraph, indicates an association of the outward motion with the core of the CME. By performing graduated-cylindrical-shell reconstruction of the CME, we constrain the density in the volume. The electron plasma frequency obtained from the density estimates do not allow us to completely dismiss plasma emission as the underlying mechanism. However, based on source height and smoothness of the emission in frequency and time, we argue that gyrosynchrotron is the more plausible mechanism. We use gyrosynchrotron spectral-fitting techniques to estimate the evolving physical conditions during the outward motion of this burst source.

Keywords: radio continuum emission; solar radio emission; solar coronal mass ejections; solar radio flares
A Triple Scenario for the Formation of Wide Black Hole Binaries Such as Gaia BH1

Recently, several noninteracting black hole–stellar binaries have been identified in Gaia data—for example, Gaia BH1, where a Sun-like star is in a moderately eccentric (e = 0.44) 185 days orbit around a black hole. This orbit is difficult to explain through binary evolution. The present-day separation suggests the progenitor system would have undergone an episode of common-envelope evolution, but a common envelope should shrink the period below the observed one. Since the majority of massive stars form in higher-multiplicity systems, a triple evolution scenario is more likely for the progenitors of BH binaries. Here we show that such systems can indeed be more easily explained via evolution in hierarchical triple systems. von Zeipel–Lidov–Kozai oscillations or instabilities can delay the onset of the common-envelope phase in the inner binary of the triple, so that the black hole progenitor and low-mass star are more widely separated when it begins, leading to the formation of wider binaries. There are also systems with similar periods but larger eccentricities, where the BH progenitor is a merger product of the inner binary in the triple. Such mergers lead to a more top-heavy black hole mass function.

Keywords: multiple star evolution; astrophysical black holes; common envelope binary stars
Choked Accretion onto a Schwarzschild Black Hole: A Hydrodynamical Jet-launching Mechanism

We present a novel, relativistic accretion model for accretion onto a Schwarzschild black hole. This consists of a purely hydrodynamical mechanism in which, by breaking spherical symmetry, a radially accreting flow transitions into an inflow-outflow configuration. The spherical symmetry is broken by considering that the accreted material is more concentrated on an equatorial belt, leaving the polar regions relatively under-dense. What we have found is a flux-limited accretion regime in which, for a sufficiently large accretion rate, the incoming material chokes at a gravitational bottleneck and the excess flux is redirected by the density gradient as a bipolar outflow. The threshold value at which the accreting material chokes is of the order of the mass-accretion rate found in the spherically symmetric case studied by Bondi and Michel. We describe the choked accretion mechanism first in terms of a general relativistic, analytic toy model based on the assumption of an ultrarelativistic stiff fluid. We then relax this approximation and, by means of numerical simulations, show that this mechanism can operate also for general polytropic fluids. Interestingly, the qualitative inflow-outflow morphology obtained appears as a generic result of the proposed symmetry break, across analytic and numeric results covering both the Newtonian and relativistic regimes. The qualitative change in the resulting steady-state flow configuration appears even for a very small equatorial-to-polar-density contrast (∼0.1%) in the accretion profile. Finally, we discuss the applicability of this model as a jet-launching mechanism in different astrophysical settings.

Keywords: black hole physics; astrophysical black holes; accretion; bondi accretion; hydrodynamical simulations; analytical mathematics; relativistic fluid dynamics; general relativity; jets