adsabs/SciX_UAT_keywords huggingface dataset:
Multiepoch VLBI of L Dwarf Binary 2MASS J0746+2000AB: Precise Mass Measurements and Confirmation of Radio Emission from Both Components

Surveys have shown that up to 1/10th of all ultracool dwarfs (UCDs) are appreciable radio emitters, with their emission attributed to a combination of gyrosynchrotron radiation and the electron cyclotron maser instability. 2M J0746+2000AB is a close stellar binary comprised of an L0 and L1.5 dwarf that was previously identified as a source of 5 GHz radio emission. We used Very Long Baseline Interferometry (VLBI) to precisely track the radio emission over seven epochs in 2010-2017, and found both components to be radio emitters—the first such system identified—with the secondary component as the dominant source of emission in all epochs. The previously identified 2.07 hr periodic bursts were confirmed to originate from the secondary component, although an isolated burst was also identified from the primary component. We additionally fitted the VLBI absolute astrometric positions jointly with existing relative orbital astrometry derived from optical/infrared observations with Markov Chain Monte Carlo methods to determine the orbital parameters of the two components. We found the masses of the primary and secondary optical components to be 0.0795 ± 0.0003 M⊙, and 0.0756 ± 0.0003 M⊙, respectively, representing the most precise mass estimates of any UCDs to date. Finally, we place a 3σ upper limit of 0.9 Mjup au on the mass and separation of planets orbiting either of the two components.

Keywords: stellar magnetic fields; radio astrometry; close binary stars; low mass stars
Kepler and TESS Observations of PG 1159-035

PG 1159-035 is the prototype of the PG 1159 hot (pre-)white dwarf pulsators. This important object was observed during the Kepler satellite K2 mission for 69 days in 59 s cadence mode and by the TESS satellite for 25 days in 20 s cadence mode. We present a detailed asteroseismic analysis of those data. We identify a total of 107 frequencies representing 32 ℓ = 1 modes, 27 frequencies representing 12 ℓ = 2 modes, and eight combination frequencies. The combination frequencies and the modes with very high k values represent new detections. The multiplet structure reveals an average splitting of 4.0 ± 0.4 μHz for ℓ = 1 and 6.8 ± 0.2 μHz for ℓ = 2, indicating a rotation period of 1.4 ± 0.1 days in the region of period formation. In the Fourier transform of the light curve, we find a significant peak at 8.904 ± 0.003 μHz suggesting a surface rotation period of 1.299 ± 0.002 days. We also present evidence that the observed periods change on timescales shorter than those predicted by current evolutionary models. Our asteroseismic analysis finds an average period spacing for ℓ = 1 of 21.28 ± 0.02 s. The ℓ = 2 modes have a mean spacing of 12.97 ± 0.4 s. We performed a detailed asteroseismic fit by comparing the observed periods with those of evolutionary models. The best-fit model has T eff = 129, 600 ± 11 100 K, M * = 0.565 ± 0.024M ⊙, and $\mathrm{log}g={7.41}_{-0.54}^{+0.38}$ , within the uncertainties of the spectroscopic determinations. We argue for future improvements in the current models, e.g., on the overshooting in the He-burning stage, as the best-fit model does not predict excitation for all of the pulsations detected in PG 1159-035.

Keywords: pulsating variable stars; white dwarf stars; asteroseismology
On the Spin Period Distribution of Millisecond Pulsars

Spin period distribution provides important clues to understand the formation of millisecond pulsars (MSPs). To uncover the intrinsic period distribution, we analyze three samples of radio MSPs in the Galactic field and globular clusters. The selection bias due to pulse broadening has been corrected but turns out to be negligible. We find that all the samples can be well described by a Weibull distribution of spin frequencies. Considering MSPs in the Galactic field or globular clusters and in isolation or binary systems, we find no significant difference in the spin distribution among these subpopulations. Based on the current known population of MSPs, we find that submillisecond pulsars are unlikely to be discovered by the Square Kilometre Array, although up to ∼10 discoveries of pulsars that spin faster than the current record holder of P = 1.4 ms are expected.

Keywords: millisecond pulsars; neutron star cores; bayesian statistics; gravitational waves; stellar accretion
Supernova Explosions in Accretion Disks in Active Galactic Nuclei: Three-dimensional Models

Supernova (SN) explosions can potentially affect the structure and evolution of circumnuclear disks in active galactic nuclei (AGN). Some previous studies have suggested that a relatively low rate of SN explosions can provide an effective value of alpha viscosity between 0.1 and 1 in AGN accretion disks within a 1 pc scale. In order to test this possibility, we provide some analytic scalings of the evolution of an SN remnant embedded in a differentially rotating smooth disk. We calibrate our estimates using three-dimensional hydrodynamical simulations where the gas is modeled as adiabatic with index γ. Our simulations are suited to include the fact that a fraction of the momentum injected by the SN escapes from the disk into the corona. Based on these results, we calculate the contribution of SN explosions to the effective alpha viscosity, denoted by αSNe, in a model AGN accretion disk, where accretion is driven by the local viscosity α. We find that for AGN galaxies with a central black hole of $\sim {10}^{8}{M}_{\odot }$ and a disk with viscosity α = 0.1, the contribution of SN explosions may be as large as ${\alpha }_{\mathrm{SNe}}\simeq 0.02$ , provided that $\gamma \gtrsim 1.1$ . On the other hand, in the momentum conservation limit, which is valid when the push by the internal pressure of the SN remnant is negligible, we find ${\alpha }_{\mathrm{SNe}}\lesssim 6\times {10}^{-4}$ .

Keywords: accretion; galaxy accretion disks; black hole physics; hydrodynamics; active galaxies; quasars
Accretion Disk Size Measurements of Active Galactic Nuclei Monitored by the Zwicky Transient Facility

We compile a sample of 92 active galactic nuclei (AGNs) at z < 0.75 with gri photometric light curves from the archival data of the Zwicky Transient Facility and measure the accretion disk sizes via continuum reverberation mapping. We employ Monte Carlo simulation tests to assess the influences of data sampling and broad emission lines and select out the sample with adequately high sampling cadences (3 days apart in average) and minimum contaminations of broad emission lines. The interband time delays of individual AGNs are calculated using the interpolated cross-correlation function, and then these delays are fitted with a generalized accretion disk model, in which interband time delays are a power function of wavelength, black hole mass, and luminosity. A Markov Chain Monte Carlo method is adopted to determine the best parameter values. Overall the interband time delays can be fitted with the τ ∝ λ 4/3 relation as predicted from a steady-state, optically thick, geometrically thin accretion disk; however, the yielded disk size is systematically larger than expected, although the ratio of the measured to theoretical disk sizes depends on using the emissivity- or responsivity-weighted disk radius. These results are broadly consistent with previous studies, all together raising a puzzle about the "standard" accretion disk model.

Keywords: active galaxies; supermassive black holes; reverberation mapping; galaxy accretion disks
Study of the Inner Structure of the Molecular Torus in IRAS 08572+3915 NW with Velocity Decomposition of CO Rovibrational Absorption Lines

Understanding the inner structure of the clumpy molecular torus surrounding the active galactic nucleus is essential in revealing the forming mechanism. However, spatially resolving the torus is difficult because of its size of a few parsecs. Thus, to probe the clump conditions in the torus, we performed the velocity decomposition of the CO rovibrational absorption lines (Δv = 0 →1, ΔJ = ±1) at λ ~ 4.67 μm observed toward an ultraluminous infrared galaxy IRAS 08572+3915 NW with the high-resolution spectroscopy (R ~ 10,000) of Subaru Telescope. Consequently, we found that each transition had two outflowing components, i.e., (a) and (b), both at approximately ~-160 km s-1, but with broad and narrow widths, and an inflowing component, i.e., (c), at approximately ~+100 km s-1, which were attributed to the torus. The ratios of the velocity dispersions of each component led to those of the rotating radii around the black hole of Rrot,a: Rrot,b: Rrot,c ≈ 1: 5: 17, indicating the torus where clumps are outflowing in the inner regions and inflowing in the outer regions if a hydrostatic disk with ${\sigma }_{V}\propto {R}_{\mathrm{rot}}^{-0.5}$ is assumed. Based on the kinetic temperature of components (a) and (b) of ~720 and ~25 K, respectively, estimated from the level population, the temperature gradient is ${T}_{\mathrm{kin}}\propto {R}_{\mathrm{rot}}^{-2.1}$ . Magnetohydrodynamic models with large density fluctuations of two orders of magnitude or more are necessary to reproduce this gradient. * This research is based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the universe from Maunakea, which has cultural, historical, and natural significance in Hawaii.

Keywords: active galactic nuclei; ultraluminous infrared galaxies; infrared astronomy; molecular gas; high resolution spectroscopy
Nova Sagittarii 1943 (V1148 Sgr): A Luminous Red Nova?

Nova Sagittarii 1943 (V1148 Sgr) was an eighth magnitude optical transient that was unusual in having a late-type spectrum during its outburst, in striking contrast to the normal high-excitation spectra seen in classical novae. Unfortunately, only an approximate position was given in the discovery announcement, hampering follow-up attempts to observe its remnant. We have identified the nova on two photographic plates in the Harvard archive, allowing us to determine a precise astrometric position. Apart from these two plates, obtained in 1943 and 1944, none of the photographs in the Harvard collection, from 1897 to 1950, show V1148 Sgr to limits as faint as g ≃ 18.3. Modern deep images show a candidate remnant at i ≃ 19.2, lying only 0.″26 from the site of the nova. V1148 Sgr may have been a luminous red nova (LRN), only the sixth one known in the Milky Way. However, it lacks the near- and mid-infrared excesses, and millimeter-wave emission, seen in other LRNe, leaving its nature uncertain. We urge spectroscopy of the candidate remnant.

Keywords: novae; transient sources; stellar mergers; variable stars
Hidden Companions to Intermediate-mass Stars. IV. Uncovering a 1.1 M ⊙, 1.3 au Companion in the Astrometric Binary HIP 77541

There are many Hipparcos/Gaia astrometric binaries for which the nature of the companion is not known. Optical/near-infrared inteferometry is arguably the most efficient method to unambiguously identify such companions. Here we report on a VLTI/GRAVITY observation in which we detected a companion to the nearby astrometric binary HIP 77541 with a K band flux ratio of 20% at a projected separation ρ = 18 mas ↔ 1.3 au. The resulting isochrone masses 2.0 + 1.1M ⊙ imply that HIP 77541 is a potential progenitor for a close white dwarf binary within a Hubble time. *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

Keywords: multiple stars; a stars; astrometric binary stars; optical interferometry
A Search for Correlated Low-energy Electron Antineutrinos in KamLAND with Gamma-Ray Bursts

We present the results of a time-coincident event search for low-energy electron antineutrinos in the KamLAND detector with gamma-ray bursts (GRBs) from the Gamma-ray Coordinates Network and Fermi Gamma-ray Burst Monitor. Using a variable coincidence time window of ±500 s plus the duration of each GRB, no statistically significant excess above the background is observed. We place the world's most stringent 90% confidence level upper limit on the electron antineutrino fluence below 17.5 MeV. Assuming a Fermi-Dirac neutrino energy spectrum from the GRB source, we use the available redshift data to constrain the electron antineutrino luminosity and effective temperature.

Keywords: gamma-ray bursts; cosmological neutrinos
Formation of the Injection Function of Solar Energetic Particles in Gradual Events

We present a model for solar energetic particle injection into interplanetary space in gradual events, in which particle acceleration occurs in a limited region of the solar atmosphere. The distribution function of particles accelerated by the diffusion mechanism is calculated. The flux of injected solar energetic particles is determined as a function of time and energy. We provide an explanation of the characteristic properties of the injection function and their dependence on the particle energy. Comparing the calculation results with ground-based measurements in the 2001 April 15 event shows a rough agreement with the particle density as a function of time and good agreement with the spectrum of maximum intensity values.

Keywords: solar energetic particles; solar particle emission; solar coronal mass ejection shocks
Evidence for the Three Wave Interactions in the Vicinity of an Interplanetary Shock

We present the high time resolution in situ observations of coherent one-dimensional magnetic-field-aligned Langmuir wave packets with well-defined low frequency modulations (beats) in the upstream region of a coronal mass ejection driven supercritical quasi-perpendicular interplanetary (IP) shock. We show that these beat-type waveforms provide what is believed to be the first observational evidence for one of the most important three wave interactions, called the electrostatic decay instability (ESD) $L\to {L}^{{\prime} }+S$ (L is the pump Langmuir wave excited by the shock accelerated electron beam, and L' and S are the daughter Langmuir and ion sound waves, respectively). We also show that (1) the spectra of these wave packets contain the signatures of L, L', and S, which satisfy the resonance conditions required for excitation of ESD, (2) the peak intensities of these wave packets well exceed the ESD threshold values, and (3) the speed of the electron beam estimated using the resonance conditions is very close to the typical observed speeds of the IP shock accelerated electron beams. The implication of these findings is that (1) the shock accelerated electron beams probably are stabilized by the three wave interaction $L\to {L}^{{\prime} }+S$ , and (2) the second harmonic radio emission ${T}_{2{f}_{\mathrm{pe}}}$ of solar type II radio bursts probably is excited by the three wave merging $L+{L}^{{\prime} }\to {T}_{2{f}_{\mathrm{pe}}}$ .

Keywords: solar physics
Accelerating Dedispersion Using Many-core Architectures

Astrophysical radio signals are excellent probes of extreme physical processes that emit them. However, to reach Earth, electromagnetic radiation passes through the ionized interstellar medium, introducing a frequency-dependent time delay (dispersion) to the emitted signal. Removing dispersion enables searches for transient signals like fast radio bursts or repeating signals from isolated pulsars or those in orbit around other compact objects. The sheer volume and high resolution of data that next-generation radio telescopes will produce require high-performance computing solutions and algorithms to be used in time-domain data-processing pipelines to extract scientifically valuable results in real time. This paper presents a state-of-the-art implementation of brute force incoherent dedispersion on NVIDIA graphics-processing units and on Intel and AMD central-processing units. We show that our implementation is 4× faster (8-bit 8192 channels input) than other available solutions, and we demonstrate, using 11 existing telescopes, that our implementation is at least 20× faster than real time. This work is part of the AstroAccelerate package.

Keywords: gpu computing; computational methods; computational astronomy; pulsars
The Formation Height of Millimeter-wavelength Emission in the Solar Chromosphere

In the past few years, the ALMA radio telescope has become available for solar observations. ALMA diagnostics of the solar atmosphere are of high interest because of the theoretically expected linear relationship between the brightness temperature at millimeter wavelengths and the local gas temperature in the solar atmosphere. Key for the interpretation of solar ALMA observations is understanding where in the solar atmosphere the ALMA emission originates. Recent theoretical studies have suggested that ALMA bands at 1.2 (band 6) and 3 mm (band 3) form in the middle and upper chromosphere at significantly different heights. We study the formation of ALMA diagnostics using a 2.5D radiative MHD model that includes the effects of ion-neutral interactions (ambipolar diffusion) and nonequilibrium ionization of hydrogen and helium. Our results suggest that in active regions and network regions, observations at both wavelengths most often originate from similar heights in the upper chromosphere, contrary to previous results. Nonequilibrium ionization increases the opacity in the chromosphere so that ALMA mostly observes spicules and fibrils along the canopy fields. We combine these modeling results with observations from IRIS, SDO, and ALMA to suggest a new interpretation for the recently reported "dark chromospheric holes," regions of very low temperatures in the chromosphere.

Keywords: solar chromosphere; plages; solar spicules; radiative transfer; radiative magnetohydrodynamics
Quantifying the Escape of Lyα at z ≈ 5–6: A Census of Lyα Escape Fraction with Hα-emitting Galaxies Spectroscopically Confirmed by JWST and VLT/MUSE

The James Webb Space Telescope provides an unprecedented opportunity for unbiased surveys of Hα-emitting galaxies at z > 4 with the NIRCam's wide-field slitless spectroscopy (WFSS). In this work, we present a census of Lyα escape fraction (f esc,Lyα ) of 165 star-forming galaxies at z = 4.9–6.3, utilizing their Hα emission directly measured from FRESCO NIRCam/WFSS data. We search for Lyα emission of each Hα-emitting galaxy in the Very Large Telescope/MUSE data. The overall f esc,Lyα measured by stacking is 0.090 ± 0.006. We find that f esc,Lyα displays a strong dependence on the observed UV slope (β obs) and E(B ‑ V), such that the bluest galaxies (β obs ∼ ‑2.5) have the largest escape fractions (f esc,Lyα ≈ 0.6), indicative of the crucial role of dust and gas in modulating the escape of Lyα photons. f esc,Lyα is less well related to other parameters, including the UV luminosity and stellar mass, and the variation in f esc,Lyα with them can be explained by their underlying coupling with E(B ‑ V) or β obs. Our results suggest a tentative decline in f esc,Lyα at z ≳ 5, implying increasing intergalactic medium attenuation toward higher redshift. Furthermore, the dependence of f esc,Lyα on β obs is proportional to that of the ionizing photon escape fraction (f esc,LyC), indicating that the escape of Lyα and ionizing photon may be regulated by similar physical processes. With f esc,Lyα as a proxy to f esc,LyC, we infer that UV-faint (M UV > ‑16) galaxies contribute >70% of the total ionizing emissivity at z = 5–6. If these relations hold during the epoch of reionization, UV-faint galaxies can contribute the majority of UV photon budget to reionize the Universe.

Keywords: high-redshift galaxies; reionization
Is NGC 5824 the Core of the Progenitor of the Cetus Stream?

The complicated story of the Cetus Stream (CS) is recently revealed by its newly discovered ∼150 members with 6D kinematics from the cross-matched catalog of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR5 K giants and Gaia DR2. It exhibits a very diffuse structure at heliocentric distances between 20 and 50 kpc, extending over at least 100°, and crossing the Galactic plane. Interestingly, The CS is dynamically linked to a massive globular cluster, NGC 5824. A suggestive scenario is that NGC 5824 was the nuclear star cluster of the dwarf progenitor of the CS. We explore this scenario by modeling the disruption process of a dwarf galaxy in the Milky Way potential, on the orbit of NGC 5824, using a suite of N-body simulations. Our results show that the simulated stream can marginally recover the main component of the CS, which is the densest part of the observed stream. Inspired by this mismatch, we use a dwarf progenitor following the representative orbit of the main component members, and find it can reproduce the general morphology of the CS. This gives us a more favorable scenario of the CS progenitor, in which NGC 5824 was not the core, but located off-center. Our fiducial model also predicts a vast extension of the CS in the South, surprisingly coincident with a newly discovered wide southern stream "Palca." Another more diffuse substructure, the Eridanus-Phoenix overdensity is also likely to be related to the CS progenitor.

Keywords: n-body simulations
Early Water Delivery to Terrestrial Planet Regions during the Stages of Jupiter's Formation and Migration in the Grand Tack Model

The formation and subsequent migration of gas giants could significantly affect the material mixing in the solar system. In this study, we use N-body simulations to investigate how much water is transported into the region of the terrestrial planet formation during the growth and migration phases of Jupiter in the Grand Tack model. We found that Jupiter's growth was accompanied by significant mass transport and that a substantial amount of water (about 10 times Earth's ocean mass for the initial planetesimal distribution based on the minimum-mass solar nebula) was transported into the terrestrial planet region. The total amount delivered increased further during Jupiter's migration phase (totaling about 10-40 times Earth's ocean mass), which was less dependent on simulation parameters. In addition, at these stages, terrestrial planets were not fully grown. Therefore, water supplied during these early stages could interact with metallic iron during the core formation of protoplanets and/or growing Earth. Since hydrogen in water molecules can dissolve into their cores, this could explain the density deficit observed in the current Earth core. Notably, Jupiter could play an important role as a "barrier" in explaining the dichotomy of the isotopic compositions between noncarbonaceous (NC) and carbonaceous (CC) meteorites. This study's results show that Jupiter's growth necessitates some mixing of NC and CC materials.

Keywords: planet formation; planetary dynamics; solar system
Infrared Line Emissions from Atoms and Atomic Ions in NGC 7027: Improved Wavelength Determinations for Infrared Metal Lines and a Probable Detection of Zn5+

An infrared L- and M-band spectral survey, performed toward the young planetary nebula NGC 7027 with the iSHELL instrument on NASA's Infrared Telescope Facility (IRTF), has revealed more than 20 vibrational lines of the molecules HeH+, H2, and CH+ and more than 50 spectral lines of atoms and atomic ions. The present paper focuses on the atomic line emissions, the molecular lines having been discussed in two previous publications. The atomic lines detected with high confidence in the 2.951-5.24 μm region covered (incompletely) by this survey comprise (1) six collisionally excited lines of metal ions that had previously been identified in astrophysical nebulae but for which the present observations provide the most accurate wavelength determinations obtained to date; (2) a spectral line at 4.6895 μm, not previously reported, for which the probable identification is the 4 F 7/2-4 F 9/2 fine-structure transition of [Zn VI]; (3) 39 recombination lines of H and He+, with upper states of principal quantum number up to 38 (H) or 24 (He+); (4) 10 recombination lines of the multielectron species He, C2+, and C3+.

Keywords: planetary nebulae; interstellar line emission; infrared astronomy; atomic spectroscopy