adsabs/SciX_UAT_keywords huggingface dataset:
Understanding Polarized Dust Emission from ρ Ophiuchi A in Light of Grain Alignment and Disruption by Radiative Torques

The alignment of dust grains with the ambient magnetic field produces polarization of starlight as well as thermal dust emission. Using the archival SOFIA/HAWC+ polarimetric data observed toward the ρ Ophiuchus (Oph) A cloud hosted by a B star at 89 and 154 μm, we find that the fractional polarization of thermal dust emission first increases with the grain temperature and then decreases once the grain temperature exceeds ≃25-32 K. The latter trend differs from the prediction of the popular RAdiative Torques (RATs) alignment theory, which implies a monotonic increase of the polarization fraction with the grain temperature. We perform numerical modeling of polarized dust emission for the ρ Oph-A cloud and calculate the degree of dust polarization by simultaneously considering the dust grain alignment and rotational disruption by RATs. Our modeling results could successfully reproduce both the rising and declining trends of the observational data. Moreover, we show that the alignment of only silicate grains or a mixture of silicate-carbon grains within a composite structure can reproduce the observational trends, assuming that all dust grains follow a power-law size distribution. Although there are a number of simplifications and limitations to our modeling, our results suggest grains in the ρ Oph-A cloud have a composite structure, and the grain size distribution has a steeper slope than the standard size distribution for the interstellar medium. Combination of SOFIA/HAWC+ data with JCMT observations 450 and 850 μm would be useful to test the proposed scenario based on grain alignment and disruption by RATs.

Keywords: interstellar radiation field; interstellar dust; interstellar medium; interstellar dust extinction; polarimetry
Hubble Space Telescope Astrometry of the Metal-poor Visual Binary μ Cassiopeiae: Dynamical Masses, Helium Content, and Age

μ Cassiopeiae is a nearby, high-velocity, metal-poor ([Fe/H] = -0.81) visual binary. We have used high-resolution imaging with the Hubble Space Telescope (HST), obtained over nearly two decades, to determine the period (21.568 yr) and precise orbital elements. Combining these with published ground- and space-based astrometry, we determined dynamical masses for both components of μ Cas: 0.7440 ± 0.0122 M⊙ for the G5 V primary and 0.1728 ± 0.0035 M⊙ for its faint dM companion. We detect no significant perturbations in the HST astrometry owing to a third body in the system. The primary aim of our program was to determine, with the aid of stellar models, the helium content and age of the metal-deficient primary star, μ Cas A. Although we now have a precise mass, there remain uncertainties about other parameters, including its effective temperature. Moreover, a reexamination of archival interferometric observations leads to a suspicion that the angular diameter was overestimated by a few percent. In the absolute magnitude versus color plane, μ Cas A lies slightly cooler and more luminous than the main sequence of the globular cluster 47 Tucanae; this may imply that the star has a lower helium content, and/or is older, and/or has a higher metallicity, than the cluster. Our best estimates for the helium content and age of μ Cas A are Y = 0.255 ± 0.014 and 12.7 ± 2.7 Gyr—making μ Cas possibly the oldest star in the sky visible to the naked eye. Improved measurements of the absolute parallax of the system, the effective temperature of μ Cas A, and its angular diameter would provide tighter constraints. * Based on observations with the NASA/ESA Hubble Space Telescope obtained at Space Telescope Science Institute, operated by Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

Keywords: binary stars; stellar evolutionary models; space astrometry; visual binary stars; stellar masses
Measuring the 8621 A Diffuse Interstellar Band in Gaia DR3 RVS Spectra: Obtaining a Clean Catalog by Marginalizing over Stellar Types

Diffuse interstellar bands (DIBs) are broad absorption features associated with interstellar dust and can serve as chemical and kinematic tracers. Conventional measurements of DIBs in stellar spectra are complicated by residuals between observations and best-fit stellar models. To overcome this, we simultaneously model the spectrum as a combination of stellar, dust, and residual components, with full posteriors on the joint distribution of the components. This decomposition is obtained by modeling each component as a draw from a high-dimensional Gaussian distribution in the data space (the observed spectrum)-a method we call "Marginalized Analytic Data-space Gaussian Inference for Component Separation" (MADGICS). We use a data-driven prior for the stellar component, which avoids missing stellar features not well modeled by synthetic spectra. This technique provides statistically rigorous uncertainties and detection thresholds, which are required to work in the low signal-to-noise regime that is commonplace for dusty lines of sight. We reprocess all public Gaia DR3 RVS spectra and present an improved 8621 Å DIB catalog, free of detectable stellar line contamination. We constrain the rest-frame wavelength to 8623.14 ± 0.087 Å (vacuum), find no significant evidence for DIBs in the Local Bubble from the 1/6th of RVS spectra that are public, and show unprecedented correlation with kinematic substructure in Galactic CO maps. We validate the catalog, its reported uncertainties, and biases using synthetic injection tests. We believe MADGICS provides a viable path forward for large-scale spectral line measurements in the presence of complex spectral contamination.

Keywords: diffuse interstellar bands; astronomy data reduction; catalogs
Post-outburst Evolution of Bona Fide FU Ori-type V2493 Cygnus: A Spectro-photometric Monitoring

We present here the results of 8 yr of our near-simultaneous optical-near-infrared spectro-photometric monitoring of the bona fide FU Ori (FUor)-type candidate V2493 Cygnus (V2493 Cyg) starting from 2013 September to 2021 June. During our optical monitoring period (between 2015 October 16 and 2019 December 30), the V2493 Cyg is slowly dimming with an average dimming rate of ~26.6 ± 5.6 mmag yr-1 in the V band. Our optical photometric colors show a significant reddening of the source post the second outburst pointing toward a gradual expansion of the emitting region post the second outburst. The mid-infrared colors, on the contrary, exhibit a blueing trend, which can be attributed to the brightening of the disk due to the outburst. Our spectroscopic monitoring shows a dramatic variation of the Hα line as it transitioned from absorption feature to the emission feature and back. Such transition can possibly be explained by the variation in the wind structure in combination with accretion. Combining our time evolution spectra of the Ca II infrared triplet lines with the previously published spectra of V2493 Cyg, we find that the accretion region has stabilized compared to the early days of the outburst. The evolution of the O I λ7773 Å line also points toward the stabilization of the circumstellar disk post the second outburst.

Keywords: early-type stars; eruptive variable stars; young stellar objects
Astrometric Membership Tests for the Zinn-Newell-Gibson UV-bright Stars in Galactic Globular Clusters

In 1972, Zinn, Newell, & Gibson (ZNG) published a list of 156 candidate UV-bright stars they had found in 27 Galactic globular clusters (GCs), based on photographs in the U and V bands. UV-bright stars lie above the horizontal branch (HB) and blueward of the asymptotic giant branch (AGB) and red giant branch in the clusters' color-magnitude diagrams. They are in rapid evolutionary phases—if they are members and not unrelated bright foreground stars. The ZNG list has inspired numerous follow-up studies, aimed at understanding late stages of stellar evolution. However, the ZNG candidates were presented only in finding charts, and celestial coordinates were not given. Using my own collection of CCD frames in u and V, I have identified all of the ZNG objects, and have assembled their coordinates, parallaxes, and proper motions from the recent Gaia Early Data Release 3 (EDR3). Based on the Gaia astrometry, I have determined which objects are probable cluster members (45% of the sample). For the members, using photometry from EDR3, I have assigned the stars to various evolutionary stages, including luminous post-AGB stars, and stars above the HB. I point out several ZNG stars of special interest that have still, to my knowledge, never been studied in detail. This study is an adjunct to a forthcoming survey of the Galactic GCs in the uBVI photometric system, designed for detection of low-gravity stars with large Balmer discontinuities.

Keywords: globular star clusters; late stellar evolution; post-asymptotic giant branch stars; horizontal branch stars; space astrometry
The Evolving Effect of Cosmic Web Environment on Galaxy Quenching

We investigate how cosmic web structures affect galaxy quenching in the IllustrisTNG (TNG100) cosmological simulations by reconstructing the cosmic web within each snapshot using the DISPERSE framework. We measure the comoving distance from each galaxy with stellar mass $\mathrm{log}({M}_{* }/{M}_{\odot })\geqslant 8$ to the nearest node (d node) and the nearest filament spine (d fil) to study the dependence of both the median specific star formation rate (<sSFR>) and the median gas fraction (<f gas>) on these distances. We find that the <sSFR> of galaxies is only dependent on the cosmic web environment at z < 2, with the dependence increasing with time. At z ≤ 0.5, $8\leqslant \mathrm{log}({M}_{* }/{M}_{\odot })\lt 9$ galaxies are quenched at d node ≲ 1 Mpc, and have significantly suppressed star formation at d fil ≲ 1 Mpc, trends driven mostly by satellite galaxies. At z ≤ 1, in contrast to the monotonic drop in <sSFR> of $\mathrm{log}({M}_{* }/{M}_{\odot })\lt 10$ galaxies with decreasing d node and d fil, $\mathrm{log}({M}_{* }/{M}_{\odot })\geqslant 10$ galaxies-both centrals and satellites-experience an upturn in <sSFR> at d node ≲ 0.2 Mpc. Much of this cosmic web dependence of star formation activity can be explained by an evolution in <f gas>. Our results suggest that in the past ~10 Gyr, low-mass satellites are quenched by rapid gas stripping in dense environments near nodes and gradual gas starvation in intermediate-density environments near filaments. At earlier times, cosmic web structures efficiently channeled cold gas into most galaxies. State-of-the-art ongoing spectroscopic surveys such as the Sloan Digital Sky Survey and DESI, as well as those planned with the Subaru Prime Focus Spectrograph, JWST, and Roman, are required to test our predictions against observations.

Keywords: galaxy evolution; galaxy quenching; intergalactic filaments; cosmic web; large-scale structure of the universe; star formation; galaxy formation; hydrodynamical simulations; magnetohydrodynamical simulations
Search for Quasiperiodic Oscillations in Precursors of Short and Long Gamma-Ray Bursts

The precursors of short and long gamma-ray bursts (SGRBs and LGRBs) can serve as probes of their progenitors, as well as shedding light on the physical processes of mergers or core-collapse supernovae. Some models predict the possible existence of quasiperiodic oscillations (QPOs) in the precursors of SGRBs. Although many previous studies have performed QPO searches in the main emission of SGRBs and LGRBs, so far there were no systematic QPO searches in their precursors. In this work, we perform a detailed QPO search in the precursors of SGRBs and LGRBs detected by Fermi/Gamma-ray Burst Monitor (GBM) from 2008 to 2019 using the power density spectrum (PDS) in the frequency domain and Gaussian processes in the time domain. We do not find any convinced QPO signal with significance above 3σ, possibly due to the low fluxes of precursors. Finally, the PDS continuum properties of both the precursors and main emissions are also studied for the first time, and no significant difference is found in the distributions of the PDS slope for precursors and main emissions in both SGRBs and LGRBs.

Keywords: gamma-ray bursts
The Behavior of BpSi Stars in the Far UV-Paper II: HD 9996 (HR 465)

The analysis of IUE spectra of the B9 SiCrEu star HD 9996 recorded by the SWP and the LWP camera on board the International Ultraviolet Explorer collected at two phases of its very long rotational period (separated by Δϕ = 0.40), reveals large variations of the far and mid ultraviolet flux. The FUV flux seems to vary in opposition with the optical brightness recorded by the Fine Error Sensor near the V band. At ultraviolet maximum, the lines of Mg II, Cr II and Fe II are definitely stronger than at minimum, which suggests that these elements are distributed in a non uniform manner on the stellar disk with large horizontal gradients. However, the changing aspect of the magnetic field between the two rotational phases observed could also cause part of the ultraviolet variability.

Keywords: chemically peculiar stars; bp stars
HOPS 361-C's Jet Decelerating and Precessing through NGC 2071 IR

We present a two-epoch Hubble Space Telescope study of NGC 2071 IR highlighting HOPS 361-C, a protostar producing an arced 0.2 parsec-scale jet. The proper motions for the brightest knots decrease from 350 to 100 km s-1 with increasing distance from the source. The [Fe II] and Paβ emission line intensity ratio gives a velocity jump through each knot of 40-50 km s-1. A new [O I] 63 μm spectrum, taken with the German REciever for Astronomy at Terahertz frequencies instrument aboard Stratospheric Observatory for Infrared Astronomy, shows a low line-of-sight velocity indicative of high jet inclination. Proper motions and jump velocities then estimate 3D flow speed for knots. Subsequently, we model knot positions and speeds with a precessing jet that decelerates. The measurements are matched with a precession period of 1000-3000 yr and half opening angle of 15°. The [Fe II] 1.26-to-1.64 μm line intensity ratio determines visual extinction to each knot from 5 to 30 mag. Relative to ~14 mag of extinction through the cloud from C18O emission maps, the jet is embedded at a 1/5-4/5 fractional cloud depth. Our model suggests the jet is dissipated over a 0.2 pc arc. This short distance may result from the jet sweeping through a wide angle, allowing the cloud time to fill cavities opened by the jet. Precessing jets contrast with nearly unidirectional protostellar jets that puncture host clouds and can propagate significantly farther.

Keywords: intercloud medium; interstellar emissions; dust continuum emission; interstellar plasma; protostars; nebulae; young stellar objects; herbig-haro objects; interstellar dust extinction; proper motions; jets
CN 2-1 and CS 5-4 Observations toward Arp 299 with the SMA

Dense gas is the key to understanding star formation in galaxies. We present high-resolution (~3″) observations of CN 2-1 and CS 5-4 as dense gas tracers toward Arp 299, a mid-stage major merger of galaxies, with the Submillimeter Array. The spatial distribution of CN 2-1 and CS 5-4 are generally consistent with each other, as well as HCN 1-0 in the literature. However, different line ratios of CS 5-4 and CN 2-1 are found in the A, B, and C regions, with the highest value in B. Dense gas fraction decreases from IC 694 (A) to NGC 3690 (B) and the starburst in the overlap regions (C and C'), which indicates that circumnuclear upcoming starburst in A and B will be more efficient than that in the overlap region of Arp 299.

Keywords: galaxy mergers
BVRCIC Observations and Analysis of the UV LEO-type Binary, the Pre-WUMa, V1023 Persei

V1023 Per is a polar spotted, but well-detached dwarf binary, very likely a Pre-WUMa eclipsing binary. It was observed on 11 nights in 2015 October, November, and December at Dark Sky Observatory in North Carolina with the 0.81 m reflector of Appalachian State University. The period behavior is complex and may be increasing with a cubic or quadratic ephemeris. Its odd light curves are of high amplitude but have no totality and reach maximum light just before and following the secondary eclipse, indicating that it has polar spots similar to UV Leo. The 28 yr orbital period study calls the attention of observers to further monitor this binary to understand the complex nature of the period evolution. Its presently fixed polar spot does indicate that it must have a strong magnetic field and that it is synchronously rotating. The BVRcIc simultaneous 2016 Wilson-Devinney program (W-D) solution gives fillouts of 68% and 75% for the primary and secondary components, respectively. The polar position of the spot, its radius (24°), and T-fact (0.75) indicate that a strong magnetic field is present. The small ΔT in the components (∼289 K) show that the stars are similar in spectral type despite them being well detached. The inclination is high, ∼85°19 ± 0°04, but there is not a total eclipse due to the high mass ratio (∼0.739 ± 0.001). Due to the low galactic position (longitude = 150°390, latitude = -1°023), its reddening is addressed. The primary components temperature is estimated to be 5250 ± 250 K.

Keywords: close binary stars; eclipsing binary stars; detached binary stars; w ursae majoris variable stars; rs canum venaticorum variable stars
Tying Spitzer's IRS Calibration to IRAC: Observations of IRS Standard Stars

We present 3.6 and 4.5 μm photometry for a set of 61 standard stars observed by Spitzer's Infrared Spectrograph (IRS). The photometry was obtained with the Infrared Array Camera (IRAC) on Spitzer in order to help tie the calibration of IRAC and the IRS, which had been anchored to the calibration of the Multiband Infrared Photometer for Spitzer. The wavelength range of the IRS data only slightly overlaps with the IRAC 4.5 μm band and not at all with the 3.6 μm band. Therefore, we generated synthetic spectra from spectral templates of stars with the same spectral types and luminosity classes as our sample stars, normalized to the IRS data at 6-7 μm, and compared those to the observed photometry. The new IRAC observations of IRS standard stars demonstrate that the two instruments are calibrated to within 1% of each other.

Keywords: infrared photometry; photometric standard stars; flux calibration; spectrophotometry; spectrophotometric standards
The LSST Cadence Impact on Non-time-critical Eclipsing Binary Science

The Legacy Survey of Space and Time (LSST) is slated to commence in 2025 at the Vera Rubin Observatory. One of the crucial parts of preparing the survey is the choice of observing cadence in an effort to optimize auxiliary science goals while maintaining the core project requirements. Here we look at the impact of proposed cadences, encoded in different operation simulations (opsims), on non-time-critical eclipsing binary science. This is particularly pertinent because LSST is the first large-scale survey that will provide us with color information in addition to high-precision coverage of faint targets. We study the differences between the baseline opsim v2.1 and the latest opsim v3.0 runs. We find that all runs provide sufficient data coverage to enable in-depth studies in the field of eclipsing binaries, and that there are no adverse impacts from any proposed opsim modification studied here.

Keywords: optical astronomy; eclipsing binary stars; optical observatories
Effective Opacity of the Intergalactic Medium from Galaxy Spectra Analysis

We measure the effective opacity ( ${\tau }_{\mathrm{eff}}$ ) of the intergalactic medium from the composite spectra of 281 Lyman-break galaxies in the redshift range 2 ≲ z ≲ 3. Our spectra are taken from the COSMOS Lyα Mapping And Tomographic Observations survey derived from the Low Resolution Imaging Spectrometer on the W.M. Keck I telescope. We generate composite spectra in two redshift intervals and fit them with spectral energy distribution (SED) models composed of simple stellar populations. Extrapolating these SED models into the Lyα forest, we measure the effective Lyα opacity ( ${\tau }_{\mathrm{eff}}$ ) in the 2.02 ≤ z ≤ 2.44 range. At z = 2.22, we estimate ${\tau }_{\mathrm{eff}}\,=0.159\pm 0.001$ from a power-law fit to the data. These measurements are consistent with estimates from quasar analyses at z < 2.5 indicating that the systematic errors associated with normalizing quasar continua are not substantial. We provide a Gaussian processes model of our results and previous ${\tau }_{\mathrm{eff}}$ measurements that describes the steep redshift evolution in ${\tau }_{\mathrm{eff}}$ from z = 1.5-4.

Keywords: intergalactic medium; intergalactic gas; lyman-break galaxies
Identification of 1RXS J165424.6-433758 as a Polar Cataclysmic Variable

We present the results of our X-ray, ultraviolet, and optical follow-up campaigns of 1RXS J165424.6-433758, an X-ray source detected with the Swift Deep Galactic Plane Survey. The source X-ray spectrum (Swift and NuSTAR) is described by thermal bremsstrahlung radiation with a temperature of kT = 10.1 ± 1.2 keV, yielding an X-ray (0.3-10 keV8) luminosity L X = (6.5 ± 0.8) × 1031 erg s-1 at a Gaia distance of 460 pc. Spectroscopy with the Southern African Large Telescope revealed a flat continuum dominated by emission features, demonstrating an inverse Balmer decrement, the λ4640 Bowen blend, almost a dozen He I lines, and He II λ4541, λ4686, and λ5411. Our high-speed photometry demonstrates a preponderance of flickering and flaring episodes, and revealed the orbital period of the system, P orb = 2.87 hr, which fell well within the cataclysmic variable (CV) period gap between 2 and 3 hr. These features classify 1RXS J165424.6-433758 as a nearby polar magnetic CV.

Keywords: am herculis stars; cataclysmic variable stars; x-ray astronomy
Initiation and Eruption of a Two-turn Helical Quiescent Filament on 2013 August 2

We investigate a quiescent filament that erupted on 2013 August 2; the eruption was observed in EUV and Hα by the Solar Dynamics Observatory and GONG. After a B9.7 flare in the nearby active region, the dark filament materials near its eastern footpoint start to move in the direction of eruption, and are followed by a counterclockwise rotation identified as the motion of a combination of dark and bright filament materials. Then the entire filament rises up and keeps rotating in a clockwise direction during the eruption. More interestingly, the filament exhibits an unusual two-helix structure near its western footpoint during the eruption, which indicates the existence of a highly twisted flux rope. This hypothesis is confirmed by magnetic field modeling using the flux rope insertion method. In the best-fit unstable model, the lower limits of the estimated maximum and average twist numbers of the erupting flux rope reach 7.5π and 4π, which suggests that kink instability plays an important role in the eruption. During these magnetically coupled sympathetic eruptions, the highly twisted filament under the western lobe of a pseudo-streamer-like structure becomes unstable and erupts due to the removal of confinement by magnetic reconnection at the overlying hyperbolic flux tube, which is initiated by the B9.7 flare in the nearby active region. The initial filament motion occurs at the more unstable eastern footpoint, where the surrounding fields are weaker and decrease with height more rapidly.

Keywords: solar filament eruptions; solar activity; quiescent solar prominence; solar magnetic fields