adsabs/SciX_UAT_keywords huggingface dataset:
A Simultaneous Dual-frequency Scintillation Arc Survey of Six Bright Canonical Pulsars Using the Upgraded Giant Metrewave Radio Telescope

We use the upgraded Giant Metrewave Radio Telescope (uGMRT) to measure scintillation arc properties in six bright canonical pulsars with simultaneous dual-frequency coverage. These observations, at frequencies from 300 to 750 MHz, allowed for detailed analysis of arc evolution across frequency and epoch. We perform more robust determinations of frequency dependence for arc curvature, scintillation bandwidth, and scintillation timescale, and comparison between arc curvature and pseudo-curvature than allowed by single-frequency-band-per-epoch measurements, which we find to agree with theory and previous literature. We find a strong correlation between arc asymmetry and arc curvature, which we have replicated using simulations, and attribute to a bias in the Hough transform approach to scintillation arc analysis. Possible evidence for an approximately week-long timescale over which a given scattering screen dominates signal propagation was found by tracking visible scintillation arcs in each epoch in PSR J1136+1551. The inclusion of a 155-minute observation allowed us to resolve the scale of scintillation variations on short timescales, which we find to be directly tied to the amount of interstellar medium sampled over the observation. Some of our pulsars showed either consistent or emerging asymmetries in arc curvature, indicating instances of refraction across their lines of sight. Significant features in various pulsars, such as multiple scintillation arcs in PSR J1136+1551 and flat arclets in PSR J1509+5531, that have been found in previous works, were also detected. The simultaneous multiple-band observing capability of the upgraded GMRT shows excellent promise for future pulsar scintillation work.

Keywords: interstellar medium; interstellar plasma; radio pulsars; pulsars; interstellar scintillation; radio astronomy
A Disk Wind Driving the Rotating Molecular Outflow in CB 26

We present the 12CO (J = 2-1) sensitive molecular line and 1.3 mm continuum observations from the Submillimeter Array (SMA) of the bipolar outflow associated with the young star located in the Bok globule known as CB 26. The SMA observations were carried out in its extended configuration allowing us to study the kinematics and structure of the outflow with about 1″ or 140 au resolution. We find that the dusty and edge-on circumstellar disk related to the outflow has a projected spatial (deconvolved) size of 196 ± 31 × 42 ± 29 au with a total (gas+dust) mass of 0.031 ± 0.015 M ⊙. We estimated a dynamical mass for the central object of 0.66 ± 0.03 M ⊙, and the mass of the molecular outflow of 5 ± 1.5 × 10-5 M ⊙. All these values are consistent with recent estimations. The observations confirm that the outflow rotation has a similar orientation to that of the edge-on disk. For the outflow, we find that the following quantities: the rotation velocity (~1-3 km s-1), specific angular momentum (~200-700 au km s-1), and launching radius (~15-35 au) decrease with the height above the midplane, as observed in other molecular rotating outflows. The radius (~180-280 au) and expansion velocity (~2-4 km s-1) also increase with the height above the disk midplane for z < 0 au; however, for z > 0 au these quantities do not exhibit this behavior. Estimations of the outflow linear momentum rate, outflow angular momentum rate, and accretion luminosity seem to be well explained by the presence of a disk wind in CB 26.

Keywords: star formation; stellar winds
The Axisymmetric Streaming Instability in Protoplanetary Disks

We reexamine the streaming instability in protoplanetary disks under the axisymmetric geometry. We identify the roles of all the relevant physical processes and clarify the clustering mechanism of dust, offering a new physical interpretation. Through back-reaction, the dust density fluctuations in combination with the mean relative drift velocity provide a source for the gas velocity, which in turn drives the velocity and divergence of the dust flow. In the limit where the dust-to-gas ratio $\bar{\epsilon }\ll 1$ , the action of the Coriolis force on the radial gradient of the azimuthal dust velocity generates the divergence of the dust. In the opposite limit $\bar{\epsilon }\gg 1$ , the vertical gradient of the vertical dust velocity makes the main contribution to the dust divergence. The different dust clustering mechanisms at $\bar{\epsilon }\ll 1$ and $\bar{\epsilon }\gg 1$ are referred to as Mode I and Mode II, respectively. In both cases, the dust divergence further enhances the dust density fluctuations, resulting in a positive feedback loop. In Mode I (or Mode II), the growth rate is contributed by the mean azimuthal (or radial) drag force in the gas equation of motion, while the mean radial (or azimuthal) drag tends to reduce it. The instability makes a transition from Mode I to Mode II when the coupling between the perturbed gas and dust velocities is stronger than the Coriolis force in the gas equations, which occurs at $\bar{\epsilon }\simeq 1$ and $\bar{\epsilon }\simeq {St}$ for Stokes numbers St < 1 and St > 1, respectively.

Keywords: planet formation; planetesimals; protoplanetary disks; astrophysical fluid dynamics
Tidally Excited Oscillations in Heartbeat Binary Stars: Pulsation Phases and Mode Identification

Tidal forces in eccentric binary stars known as heartbeat stars excite detectable oscillations that shed light on the processes of tidal synchronization and circularization. We examine the pulsation phases of tidally excited oscillations (TEOs) in heartbeat binary systems. The target list includes four published heartbeat binaries and four additional systems observed by Kepler. To the first order, the pulsation phases of TEOs can be explained by the geometric effect of the dominant l = 2, m = 0, or ±2 modes assuming pulsations are adiabatic. We found that this simple theoretical interpretation can account for more than half of the systems on the list, assuming their spin and orbit axes are aligned. We do find significant deviations from the adiabatic predictions for some other systems, especially for the misaligned binary KIC 8164262. The deviations can potentially help to probe the nonadiabaticity of pulsation modes as well as resonances in the tidal forcing.

Keywords: stellar oscillations; close binary stars; stellar interiors
Refraction of Line and Continuum Light in Exoplanet Atmospheres

Exoplanet transit spectra are calculated including the effect of atmospheric opacity and refractive lightbending. While previous studies considered the case of continuum light, here the effect of an atomic resonance line is included. The model assumes a clear atmosphere and includes H and He, which contribute static polarizability and Rayleigh scattering, as well as the Na D doublet, which contributes dynamic polarizability and a resonant cross section. The image locations and magnifications are found using the lens equation. The model including lightbending is compared to the standard model in which the light travels on straight lines. It is found that near the line center, where the polarizability is large, bending angles are nevertheless small since the optical depth τ = 1 trajectory is at such a high altitude where the particle density is low. Moving away from the line center, the Na D resonance dominates the opacity over ~400 Å, and over most of this wavelength range the polarizability is dominated by hydrogen and helium and is nearly wavelength-independent. However, the density of the τ = 1 trajectory is wavelength-dependent, and hence the bending angle increases strongly away from the line center. The wavelength-dependent flux deviation between the straight-line and lightbending models occurs at the level of ΔF λ /F 0 ~ 10-5 for a planet at orbital separation a = 10 R ⊙.

Keywords: exoplanet atmospheres; atmospheric refraction
On the Discovery Claim of a New z > 7 Quasar

Koptelova & Hwang (K22) recently claimed a new quasar discovery at z = 7.46. After careful consideration of the publicly available data underlying K22's claim, we find that the observations were contaminated by a moving solar system object, likely a main-belt asteroid. In the absence of the contaminated photometry, there is no evidence for the nearby, persistent WISE source being a high-redshift object; in fact, a detection of the source in DESI Legacy Imaging Surveys z-band rules out a redshift z > 7.3. We present our findings as a cautionary tale of the dangers of passing asteroids for photometric selections.

Keywords: quasars; asteroids; early universe
Relation between Quiescence and Outbursting Properties of GX 339-4

Galactic black hole candidate GX 339-4 underwent several outbursting phases in the past two and a half decades at irregular intervals of 2-3 years. The nature of these outbursts in terms of the duration, number of peaks, maximum peak intensity, and so on varies. We present a possible physical reason behind the variation of the outbursts. From a physical point of view, if the supply of matter from the companion is roughly constant, the total energy released in an outburst is expected to be proportional to the quiescent period prior to the outburst when the matter is accumulated. We use archival data of RXTE/ASM from 1996 January to 2011 June and of MAXI/GSC from 2009 August to 2020 July. Five initial outbursts of GX 339-4 between 1997 and 2011 were observed by ASM and showed a good linear relation between the accumulation period and the amount of energy released in each outburst, but the outbursts after 2013 behaved quite differently. The 2013, 2017-2018, and 2018-2019 outbursts were of short duration and incomplete or "failed" in nature. We suggest that the matter accumulated during the quiescent periods prior to these outbursts was not cleared through accretion due to a lack of viscosity. The leftover matter was cleared in the very next outbursts. Our study thus sheds light on long-term accretion dynamics in outbursting sources.

Keywords: x-ray binary stars; x-ray transient sources; black holes; black hole physics; accretion
Discovery of the First Antiglitch Event in the Rotation-powered Pulsar PSR B0540-69

Using data from the Neutron star Interior Composition ExploreR observatory, we identified a permanent spin frequency decrease of Δν = ‑(1.04 ± 0.07) × 10‑7 Hz around MJD 60132 in the rotation-powered pulsar PSR B0540-69, which exhibits a periodic signal at a frequency of ν ∼ 19.6 Hz. This points to an antiglitch event, a sudden decrease of the pulsar's rotational frequency without any major alteration in the pulse profile or any significant increase of the pulsed flux. Additionally, no burst activity was observed in association with the antiglitch. To date, observations of the few known antiglitches have been made in magnetars or accreting pulsars. This is the first antiglitch detected in a rotation-powered pulsar. Given its radiatively quiet nature, this antiglitch is possibly of internal origin. Therefore, we tentatively frame this event within a proposed mechanism for antiglitches where the partial "evaporation" of the superfluid component leads to an increase in the normal component's moment of inertia and a decrease in the superfluid one.

Keywords: compact objects; rotation powered pulsars; pulsars; neutron stars
The Hawaii Infrared Parallax Program. IV. A Comprehensive Parallax Survey of L0-T8 Dwarfs with UKIRT

We present parallaxes, proper motions, and J-band photometry for 348 L and T dwarfs measured using the wide-field near-infrared camera WFCAM on the United Kingdom Infrared Telescope. This is the largest single batch of infrared parallaxes for brown dwarfs to date. Our parallaxes have a median uncertainty of 3.5 mas, similar to most previous ground-based infrared parallax surveys. Our target list was designed to complete a volume-limited parallax sample of L0-T8 dwarfs out to 25 pc spanning declinations -30° to +60° (68% of the sky). We report the first parallaxes for 165 objects, and we improve on previous measurements for another 53 objects. Our targets include 104 objects (mostly early-L dwarfs) having Gaia DR2 parallax measurements with which our parallaxes are consistent. We include an extensive comparison of previous literature parallaxes for L and T dwarfs with both our results and Gaia DR2 measurements, identifying systematic offsets for some previous surveys. Our parallaxes confirm that 14 objects previously identified as wide common proper motion companions to main-sequence stars have distances consistent with companionship. We also report new ${J}_{\mathrm{MKO}}$ photometry for our targets, including the first measurements for 193 of our targets and improvements over previously published ${J}_{\mathrm{MKO}}$ photometry for another 60 targets. Altogether, our parallaxes will enable the first population studies using a volume-limited sample spanning spectral types L0-T8 defined entirely by parallaxes.

Keywords: late-type dwarf stars; parallax; proper motions; infrared photometry; trigonometric parallax; l dwarfs; t dwarfs
Asteroseismic Inference of the Central Structure in a Subgiant Star

Asteroseismic measurements enable inferences of the underlying stellar structure, such as the density and the speed of sound at various points within the interior of the star. This provides an opportunity to test stellar evolution theory by assessing whether the predicted structure of a star agrees with the measured structure. Thus far, this kind of inverse analysis has only been applied to the Sun and three solar-like main-sequence stars. Here we extend the technique to stars on the subgiant branch, and apply it to one of the best-characterized subgiants of the Kepler mission, HR 7322. The observation of mixed oscillation modes in this star facilitates inferences of the conditions of its inert helium core, nuclear-burning hydrogen shell, and the deeper parts of its radiative envelope. We find that despite significant differences in the mode frequencies, the structure near to the center of this star does not differ significantly from the predicted structure.

Keywords: stellar evolution; stellar physics; stellar evolutionary models; asteroseismology; stellar oscillations; stellar ages; stellar properties
TYC 3340-2437-1: A Quadruple System with a Massive Star

Hierarchical massive quadruple systems are ideal laboratories for examining the theories of star formation, dynamical evolution, and stellar evolution. The successive mergers of hierarchical quadruple systems might explain the mass gap between neutron stars and black holes. Looking for light curves of O-type binaries identified by LAMOST, we find a (2+2) quadruple system: TYC 3340-2437-1, located in the stellar bow-shock nebula (SBN). It has a probability of over 99.99% being a quadruple system derived from the surface density of the vicinity stars. Its inner orbital periods are 3.390602(89) days and 2.4378(16) days, respectively, and the total mass is about (11.47 + 5.79) + (5.2 + 2.02) = 24.48 M ⊙. The line-of-sight inclinations of the inner binaries, B1 and B2, are 55.°94 and 78.°2, respectively, indicating that they are not coplanar. Based on observations spanning 34 months and the significance of the astrometric excess noise (D > 2) in Gaia Data Release 3 data, we guess that its outer orbital period might be a few years. If it were true, the quadruple system might form through the disk fragmentation mechanism with outer eccentric greater than zero. This eccentricity could be the cause of both the arc-like feature of the SBN and the noncoplanarity of the inner orbit. The outer orbital period and outer eccentric could be determined with the release of future epoch astrometric data of Gaia.

Keywords: close binary stars; massive stars; spectroscopic binary stars; eclipsing binary stars; interstellar clouds
Variability in Proto-planetary Nebulae. VI. Multitelescope Light Curve Studies of Several Medium-bright (V = 13-15), Carbon-rich Objects

We present 10 years of new photometric monitoring of the light variability of five evolved stars with strong mid-infrared emission from surrounding dust. Three are known carbon-rich proto-planetary nebulae (PPNe) with F-G spectral types; the nature of the other two was previously unknown. For the three PPNe, we determine or refine the pulsation periods of IRAS 04296+3429 (71 days), 06530-0213 (80 days), and 23304+6147 (84 days). A secondary period was found for each, with a period ratio P 2 /P 1 of 0.9. The light variations are small, 0.1-0.2 mag. These are similar to values found in other PPNe. The other two are found to be giant stars. IRAS 09296+1159 pulsates with a period of only 47 days but reaches pulsational light variations of 0.5 mag. Supplemental spectroscopy reveals the spectrum of a CH carbon star. IRAS 08359-1644 is a G1 III star that does not display pulsational variability; rather, it shows nonperiodic decreases of brightness of up to 0.5 mag over this 10 year interval. These drops in brightness are reminiscent of the light curves of R Corona Borealis variables, but with much smaller decreases in brightness and are likely due to transient dust obscuration. Its spectral energy distribution is very similar to that of the unusual oxygen-rich giant star HDE 233517, which possesses mid-infrared hydrocarbon emission features. These two non-PPNe turn out to be members of the rare group of giant stars with large mid-infrared excesses due to dust, objects which presumably have interesting evolutionary histories.

Keywords: protoplanetary nebulae; post-asymptotic giant branch; carbon stars; stellar pulsations; pulsating variable stars; circumstellar dust; red giant stars
Active Galactic Nuclei in a Mid-infrared Selected Galaxy Sample at z > 0.13: [Ne V]λ3426 Line Emission as a Benchmark

We present a 24 μm-selected spectroscopic sample z > 0.13 (median <z> = 0.41) in the Lockman Hole field, consisting of 4035 spectra. Our aim is to identify active galactic nuclei (AGNs) and determine their fraction in this mid-infrared-selected sample. In this work, we use the [Ne V]λ3426 emission line to spectroscopically identify AGNs. Combined with broad-line Type I AGNs selected in our previous study, our sample consists of 887 (∼22%) spectroscopically confirmed AGNs. We perform a stacking analysis on the remaining spectra and find that in various mid-infrared (MIR) wedge-selected AGN candidates, the stacked spectra still show significant [Ne V]λ3426 emission. In contrast, no clear [Ne V]λ3426 signal is detected in non-AGN candidates falling outside the wedges. Assuming a range of AGN MIR spectral energy distribution (SED) slope of ‑0.3 <α < 0.7, and an average star-forming relation derived from 65 star-forming templates, we develop a robust method to separate the AGN and star-forming contributions to the MIR SEDs using the rest-frame L 12/L 1.6 versus L 4.5/L 1.6 diagram. We separate the objects into bins of L 12 and find that the AGN fraction increases with increasing L 12. We also find that the stacked [Ne V]λ3426 strength scales with L 12. The pure AGN luminosity at 12 μm exhibits a positive correlation with the star formation rates, indicating possible coevolution and common gas supply between the AGNs and their host galaxies. Varying population properties across the redshift range explored contribute to the observed correlation.

Keywords: active galactic nuclei; galaxy spectroscopy; infrared galaxies; agn host galaxies
CALET Search for Electromagnetic Counterparts of Gravitational Waves during the LIGO/Virgo O3 Run

The CALorimetric Electron Telescope (CALET) on the International Space Station consists of a high-energy cosmic-ray CALorimeter (CAL) and a lower-energy CALET Gamma-ray Burst Monitor (CGBM). CAL is sensitive to electrons up to 20 TeV, cosmic-ray nuclei from Z = 1 through Z ~ 40, and gamma rays over the range 1 GeV-10 TeV. CGBM observes gamma rays from 7 keV to 20 MeV. The combined CAL-CGBM instrument has conducted a search for gamma-ray bursts (GRBs) since 2015 October. We report here on the results of a search for X-ray/gamma-ray counterparts to gravitational-wave events reported during the LIGO/Virgo observing run O3. No events have been detected that pass all acceptance criteria. We describe the components, performance, and triggering algorithms of the CGBM-the two Hard X-ray Monitors consisting of LaBr3(Ce) scintillators sensitive to 7 keV-1 MeV gamma rays and a Soft Gamma-ray Monitor BGO scintillator sensitive to 40 keV-20 MeV-and the high-energy CAL consisting of a charge detection module, imaging calorimeter, and the fully active total absorption calorimeter. The analysis procedure is described and upper limits to the time-averaged fluxes are presented.

Keywords: gamma-ray astronomy; gamma-ray bursts; gravitational wave sources; gamma-ray transient sources
Space Weathering Affects the Remote Near-IR Identification of Phyllosilicates

Near-infrared (NIR) spectrometers on board current sample return missions Hayabusa2 and the Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer (OSIRIS-REx) from primitive bodies detected the presence of hydrated silicates on the surface of asteroids Ryugu and Bennu, respectively. These detections relied upon the study of the 2.7 μm OH-stretching spectral feature, whose peak position is related to the composition and structure of minerals. However, space weathering might alter the band profile, depth and position, thus complicating the interpretation of remote sensing data. In order to better understand these processes and provide support to space missions, we performed ion bombardment experiments on serpentine and saponite analogs. These two phyllosilicates are among the dominant mineral phases found in hydrated carbonaceous chondrites, which are possible analogs to surface materials observed on these primitive asteroids. We studied the behavior of the 2.7 μm band as a function of ion fluence and found that the evolution of the phyllosilicate depends on its nature. For the saponite sample, the band is only slightly affected by ion bombardment, while for both serpentine samples it shifts toward longer wavelengths. For both samples, peak intensity and width is not strongly affected. The band shift for serpentine indicates that space weathering introduces a bias in the interpretation of NIR remote sensing observations of phyllosilicates. The shift observed in our experiments can be detected by instruments on board Hayabusa2 and OSIRIS-REx, depending on the geometry of observation. Our findings provide support to the interpretation of such data.

Keywords: space weather; spectroscopy; near infrared astronomy; infrared astronomy; laboratory astrophysics; small solar system bodies; surface composition; surface processes