adsabs/SciX_UAT_keywords huggingface dataset:
An SMA Survey of Chemistry in Disks Around Herbig AeBe Stars

Protoplanetary disks around Herbig AeBe stars are exciting targets for studying the chemical environments where giant planets form. Save for a few disks, however, much of Herbig AeBe disk chemistry is an open frontier. We present a Submillimeter Array ~213-268 GHz pilot survey of millimeter continuum CO isotopologs and other small molecules in disks around five Herbig AeBe stars (HD 34282, HD 36112, HD 38120, HD 142666, and HD 144432). We detect or tentatively detect 12CO 2-1 and 13CO 2-1 from four disks, C18O 2-1 and HCO+ 3-2 from three disks, HCN 3-2, CS 5-4, and DCO+ 3-2 from two disks, and C2H 3-2 and DCN 3-2 from one disk each. H2CO 3-2 is undetected at the sensitivity of our observations. The millimeter continuum images of HD 34282 suggest a faint, unresolved source ~5.″0 away, which could arise from a distant orbital companion or an extended spiral arm. We fold our sample into a compilation of T Tauri and Herbig AeBe/F disks from the literature. Altogether, most line fluxes generally increase with millimeter continuum flux. Line flux ratios between CO 2-1 isotopologs are nearest to unity for the Herbig AeBe/F disks. This may indicate emitting layers with relatively similar, warmer temperatures and more abundant CO relative to the disk dust mass. Lower HCO+ 3-2 flux ratios may reflect lower ionization in Herbig AeBe/F disks. Lower detection rates and flux ratios for DCO+ 3-2, DCN 3-2, and H2CO 3-2 suggest smaller regimes of cold chemistry around the luminous Herbig AeBe/F stars.

Keywords: astrochemistry; protoplanetary disks; interstellar medium; interferometry
Gemini Near Infrared Spectrograph-Distant Quasar Survey: Prescriptions for Calibrating UV-based Estimates of Supermassive Black Hole Masses in High-redshift Quasars

The most reliable single-epoch supermassive black hole mass (M BH) estimates in quasars are obtained by using the velocity widths of low-ionization emission lines, typically the Hβ λ4861 line. Unfortunately, this line is redshifted out of the optical band at z ≈ 1, leaving M BH estimates to rely on proxy rest-frame ultraviolet (UV) emission lines, such as C IV λ1549 or Mg II λ2800, which contain intrinsic challenges when measuring, resulting in uncertain M BH estimates. In this work, we aim at correcting M BH estimates derived from the C IV and Mg II emission lines based on estimates derived from the Hβ emission line. We find that employing the equivalent width of C IV in deriving M BH estimates based on Mg II and C IV provides values that are closest to those obtained from Hβ. We also provide prescriptions to estimate M BH values when only C IV, only Mg II, and both C IV and Mg II are measurable. We find that utilizing both emission lines, where available, reduces the scatter of UV-based M BH estimates by ~15% when compared to previous studies. Lastly, we discuss the potential of our prescriptions to provide more accurate and precise estimates of M BH given a much larger sample of quasars at 3.20 ≲ z ≲ 3.50, where both Mg II and Hβ can be measured in the same near-infrared spectrum.

Keywords: active galactic nuclei; quasars; surveys; supermassive black holes
Aliphatics and Aromatics in the Universe: The Pre-JWST Era

The so-called "unidentified infrared emission" (UIE) features at 3.3, 6.2, 7.7, 8.6, and 11.3 μm ubiquitously seen in a wide variety of astrophysical regions are generally attributed to polycyclic aromatic hydrocarbon (PAH) molecules. Astronomical PAHs often have an aliphatic component (e.g., aliphatic sidegroups like methyl -CH3 may be attached as functional groups to PAHs) as revealed by the detection in many UIE sources of the aliphatic C-H stretching feature at 3.4 μm. With its unprecedented sensitivity and spatial resolution, and high spectral resolution, the James Webb Space Telescope (JWST) holds great promise for revolutionizing the studies of aliphatics and aromatics in the Universe. To facilitate analyzing JWST observations, we present a theoretical framework for determining the aliphatic fractions (η ali) of PAHs (the fractions of C atoms in aliphatic units) from the emission intensity ratios of the 3.4 μm aliphatic C-H feature to the 3.3 μm aromatic C-H feature. To demonstrate the effectiveness of this framework, we compile the 3.3 and 3.4 μm UIE data obtained in the pre-JWST era for an as-complete-as-possible sample, and then apply the framework to these pre-JWST data. We derive a median aliphatic fraction of <η ali> ≈ 5.4%, and find that the aliphatic fractions are the highest in protoplanetary nebulae illuminated by cool stars lacking ultraviolet radiation. Nevertheless, the "hardness" of stellar photons is not the only factor affecting the PAH aliphaticity, and other factors such as the starlight intensity may also play an important role.

Keywords: polycyclic aromatic hydrocarbons; astrochemistry; interstellar medium; interstellar molecules
The Kinematics of the Young Stellar Population in the W5 Region of the Cassiopeia OB6 Association: Implication for the Formation Process of Stellar Associations

The star-forming region W5 is a major part of the Cassiopeia OB6 association. Its internal structure and kinematics may provide hints of the star formation process in this region. Here, we present a kinematic study of young stars in W5 using the Gaia data and our radial velocity data. A total 490 out of 2000 young stars are confirmed as members. Their spatial distribution shows that W5 is highly substructured. We identify a total of eight groups using the k-means clustering algorithm. There are three dense groups in the cavities of H II bubbles, and the other five sparse groups are distributed at the edges of the bubbles. The three dense groups have almost the same age (5 Myr) and show a pattern of expansion. The scale of their expansion is not large enough to account for the overall structure of W5. The three northern groups are, in fact, 3 Myr younger than the dense groups, which indicates independent star formation events. Only one of these groups shows the signature of feedback-driven star formation as its members move away from the eastern dense group. The other two groups might have formed in a spontaneous way. On the other hand, the properties of two southern groups are not understood as those of a coeval population. Their origins can be explained by dynamical ejection of stars and multiple star formation. Our results suggest that the substructures in W5 formed through multiple star-forming events in a giant molecular cloud.

Keywords: star formation; stellar kinematics; stellar associations; stellar dynamics; open star clusters
Heating of Quiescent Coronal Loops Caused by Nearby Eruptions Observed with the Solar Dynamics Observatory and the Solar Upper Transition Region Imager

How structures, e.g., magnetic loops, in the upper atmosphere, i.e., the transition region and corona, are heated and sustained is one of the major unresolved issues in solar and stellar physics. Various theoretical and observational studies on the heating of coronal loops have been undertaken. The heating of quiescent loops caused by eruptions, however, is rarely observed. In this study, employing data from the Solar Dynamics Observatory (SDO) and Solar Upper Transition Region Imager (SUTRI), we report the heating of quiescent loops associated with nearby eruptions. In active regions (ARs) 13092 and 13093, a long filament and a short filament, and their overlying loops, were observed on 2022 September 4. In AR 13093, a warm channel erupted toward the northeast, whose material moved along its axis toward the northwest under the long filament, turned to the west above the long filament, and divided into two branches falling to the solar surface. Subsequently, the short filament erupted toward the southeast. Associated with these two eruptions, the quiescent loops overlying the long filament appeared in SDO/Atmospheric Imaging Assembly (AIA) high-temperature images, indicating the heating of loops. During the heating, the signature of magnetic reconnection between loops is identified, including the inflowing motions of loops, and the formation of X-type structures and newly reconnected loops. The heated loops then cooled down. They appeared sequentially in AIA and SUTRI lower-temperature images. All the results suggest that the quiescent loops are heated by reconnection between loops caused by the nearby warm channel and filament eruptions.

Keywords: solar filaments; solar radiation; plasma astrophysics; solar coronal heating; solar magnetic fields; solar magnetic reconnection
A New Class of Roche Lobe-filling Hot Subdwarf Binaries

We present the discovery of the second binary with a Roche lobe-filling hot subdwarf transferring mass to a white dwarf (WD) companion. This 56 minute binary was discovered using data from the Zwicky Transient Facility. Spectroscopic observations reveal an He-sdOB star with an effective temperature of Teff = 33,700 ± 1000 K and a surface gravity of log(g) = 5.54 ± 0.11. The GTC+HiPERCAM light curve is dominated by the ellipsoidal deformation of the He-sdOB star and shows an eclipse of the He-sdOB by an accretion disk as well as a weak eclipse of the WD. We infer a He-sdOB mass of MsdOB = 0.41 ± 0.04 M⊙ and a WD mass of MWD = 0.68 ± 0.05 M⊙. The weak eclipses imply a WD blackbody temperature of 63,000 ± 10,000 K and a radius RWD = 0.0148 ± 0.0020 R⊙ as expected for a WD of such high temperature. The He-sdOB star is likely undergoing hydrogen shell burning and will continue transferring mass for ≈1 Myr at a rate of 10-9 M⊙ yr-1, which is consistent with the high WD temperature. The hot subdwarf will then turn into a WD and the system will merge in ≈30 Myr. We suggest that Galactic reddening could bias discoveries toward preferentially finding Roche lobe-filling systems during the short-lived shell-burning phase. Studies using reddening-corrected samples should reveal a large population of helium core-burning hot subdwarfs with Teff ≈ 25,000 K in binaries of 60-90 minutes with WDs. Though not yet in contact, these binaries would eventually come into contact through gravitational-wave emission and explode as a subluminous thermonuclear supernova or evolve into a massive single WD.

Keywords: b subdwarf stars; stellar evolution; white dwarf stars; compact binary stars; stellar accretion
Evolution of an Emerging Anti-Hale Region and its Associated Eruptive Solar Flares in NOAA AR 12882

Solar active regions that violate the Hale-Nicholson rule are rare, but once formed, they tend to be flare-productive. In this letter, we investigated the evolution of an anti-Hale region newly emerging from the active region AR 12882 with a regular Hale distribution. The entire active region became very active, producing two eruptive flares within 48 hr after the emergence of the anti-Hale region. Strong photospheric shear motions appeared in this anti-Hale region, changing its tilt angle from the north-south direction to the east-west direction. The flux emergence and shearing motions continuously injected magnetic energy and negative magnetic helicity into the upper atmosphere. Meanwhile, the upper coronal structure changed from double J-shaped to reverse S-shaped, forming a magnetic flux rope lying above the anti-Hale region. This magnetic flux rope erupted successfully, then re-formed and erupted successfully again, producing a C2.7 flare and an M1.6 flare, respectively. Moreover, a large cusp structure was observed to form next to the flaring region after the M1.6 flare. Accordingly, we conclude that the evolution of the emerging anti-Hale region provides sufficient magnetic energy and helicity for the flares, and the interaction between the emerging anti-Hale region and the preexisting Hale active region eventually promotes the flares to be eruptive.

Keywords: solar active regions; solar flares; solar activity; solar coronal mass ejections
RR Lyrae Star Candidates from SDSS Databases by Cost-sensitive Random Forests

With the increase of known RR Lyrae stars, it is reliable to create classifiers of RR Lyrae stars based on their photometric data or combined photometric and spectroscopic data. Nevertheless the total number of known RR Lyrae stars is still too small compared with the large survey databases. So classification of RR Lyrae stars and other sources belongs to imbalanced learning. Based on Sloan Digital Sky Survey (SDSS) photometric and spectroscopic data, we apply cost-sensitive Random Forests fit for imbalanced learning to preselect RR Lyrae star candidates. Only with photometric data, u-g,g-r,r-I,I-z is the best input pattern. While also considering physical parameters (T eff, [Fe/H], log(g)), the optimal input pattern is T eff, [Fe/H], log(g), u-g,g-r,r-I,I-z, at this moment for cost-sensitive Random Forests, the performance metrics of completeness, contamination, and Matthews correlation coefficient are 0.975, 0.019, and 0.975, respectively. It indicates that adding stellar physical parameters is helpful for identifying RR Lyrae stars from other stars. We apply the best classifiers on the SDSS photometric data and combined photometric data with physical parameters to select RR Lyrae star candidates. Finally 11,041 photometric candidates with spectral type A and F are obtained, and then 304 candidates with physical parameters are selected out. Among the 304 candidates, a small part are HB stars, BS stars, RGB stars, and peculiar stars, and the rest are unknown in the Simbad database. These candidates may be used as the input catalog for time-series follow-up observations.

Keywords: rr lyrae variable stars; stellar types; astronomy databases; metallicity; random forests; astrostatistics; astronomy data analysis
Kinematic Signatures of Reverberation Mapping of Close Binaries of Supermassive Black Holes in Active Galactic Nuclei. II. Atlas of Two-dimensional Transfer Functions

Most large galaxies harbor supermassive black holes (SMBHs) in their centers, and galaxies merge. Consequently, binary SMBHs should be common in galactic nuclei. However, close binaries of SMBH (CB-SMBHs) with subparsec separation cannot be imaged directly using current facilities. Some indirect signatures, such as periodic signals in light curves and double peaks in the emission-line profile, have been used to find CB-SMBH candidates, but ambiguities still exist and no definitive conclusions can be made. We have recently proposed a new method focusing on kinematic signatures that can be derived from reverberation mapping of CB-SMBHs, one that offers a promising avenue to address this important problem. In this paper, we calculated models for a wide range of parameters, but broad-line regions of two BHs are close but still not merged. The purpose of this supplementary paper is to provide an atlas of two-dimensional transfer functions of CB-SMBHs with a wide range of orbital and geometrical parameters to aid more efficient identification of CB-SMBH candidates in reverberation mapping data.

Keywords: supermassive black holes; reverberation mapping; active galactic nuclei
The High-resolution Fe K Spectrum of Cygnus X-3

We analyze features of the Fe K spectrum of the high-mass X-ray binary Cygnus X-3. The spectrum was obtained with the Chandra High Energy Transmission Grating Spectrometer in the third diffraction order. The increased energy resolution of the third order enables us to fully resolve the Fe XXV Heα complex and the Fe XXVI Lyα lines. The emission-line spectrum shows the expected features of photoionization equilibrium, excited in the dense stellar wind of the companion star. We detect discrete emission from inner-shell transitions, in addition to absorption likely due to multiple unresolved transitions in lower ionization states. The emission-line intensity ratios observed in the range of the spectrum occupied by the Fe XXV n = 1–2 forbidden and intercombination lines suggest that there is a substantial contribution from resonantly scattered inner-shell emission from the Li- and Be-like ionization states. The Fe XXV forbidden and intercombination lines arise in the ionization zone closest to the compact object, and since they are not subject to radiative-transfer effects, we can use them in principle to constrain the radial velocity amplitude of the compact object. We infer that the results indicate a compact object mass of the order of the mass of the Wolf–Rayet companion star, but we note that the presence of resonantly scattered radiation from Li-like ions may complicate the interpretation of the He-like emission spectrum, and specifically of the radial velocity curve of the Fe XXV forbidden line.

Keywords: high mass x-ray binary stars; compact objects; high resolution spectroscopy; black holes
The Formation of Blue Large-amplitude Pulsators from White-dwarf Main-sequence Star Mergers

Blue large-amplitude pulsators (BLAPs) are hot low-mass stars that show large-amplitude light variations likely due to radial oscillations driven by iron group opacities. Period changes provide evidence of both secular contraction and expansion among the class. Various formation histories have been proposed, but none are completely satisfactory. Zhang et al. proposed that the merger of a helium-core white dwarf with a low-mass main-sequence star (HeWD+MS) can lead to the formation of some classes of hot subdwarfs. We have analyzed these HeWD+MS merger models in more detail. Between helium-shell ignition and full helium-core burning, the models pass through the volume of luminosity-gravity-temperature space occupied by BLAPs. Periods of expansion and contraction associated with helium-shell flashes can account for the observed rates of period change. We argue that the HeWD+MS merger model provides at least one BLAP formation channel.

Keywords: stellar evolution; stellar evolutionary models; binary stars; stellar abundances; blue large-amplitude pulsators; stellar mergers; white dwarf stars; extreme horizontal branch stars; asteroseismology; stellar oscillations
The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). III. A Young Molecular Outflow Driven by a Decelerating Jet

We present a spatio-kinematical analysis of the CO (J = 2 → 1) line emission, observed with the Atacama Large Millimeter/submillimeter Array (ALMA), of the outflow associated with the most massive core, ALMA1, in the 70 μm dark clump G010.991-00.082. The position-velocity (PV) diagram of the molecular outflow exhibits a peculiar S-shaped morphology that has not been seen in any other star-forming region. We propose a spatio-kinematical model for the bipolar molecular outflow that consists of a decelerating high-velocity component surrounded by a slower component whose velocity increases with distance from the central source. The physical interpretation of the model is in terms of a jet that decelerates as it entrains material from the ambient medium, which has been predicted by calculations and numerical simulations of molecular outflows in the past. One side of the outflow is shorter and shows a stronger deceleration, suggesting that the medium through which the jet moves is significantly inhomogeneous. The age of the outflow is estimated to be τ ≈ 1300 yr, after correction for a mean inclination of the system of ≈57°.

Keywords: radio astronomy; submillimeter astronomy
The Host Galaxies and Progenitors of Fast Radio Bursts Localized with the Australian Square Kilometre Array Pathfinder

The Australian SKA Pathfinder (ASKAP) telescope has started to localize fast radio bursts (FRBs) to arcsecond accuracy from the detection of a single pulse, allowing their host galaxies to be reliably identified. We discuss the global properties of the host galaxies of the first four FRBs localized by ASKAP, which lie in the redshift range 0.11 < z < 0.48. All four are massive galaxies (log(M*/M⊙) ∼ 9.4-10.4) with modest star formation rates of up to 2 M⊙ yr-1—very different to the host galaxy of the first repeating FRB 121102, which is a dwarf galaxy with a high specific star formation rate. The FRBs localized by ASKAP typically lie in the outskirts of their host galaxies, which appears to rule out FRB progenitor models that invoke active galactic nuclei or free-floating cosmic strings. The stellar population seen in these host galaxies also disfavors models in which all FRBs arise from young magnetars produced by superluminous supernovae, as proposed for the progenitor of FRB 121102. A range of other progenitor models (including compact-object mergers and magnetars arising from normal core-collapse supernovae) remain plausible.

Keywords: galaxies; radio continuum emission; radio bursts; star formation
Robotic Reverberation Mapping of the Southern Seyfert NGC 3783

We present spectroscopic and photometric monitoring of NGC 3783 conducted throughout the first half of 2020. Time delays between the continuum variations and the response of the broad optical emission lines were clearly detected, and we report reverberation measurements for Hβ, He II λ4686, Hγ, and Hδ. From the time delay in the broad Hβ emission line and the line width in the variable portion of the spectrum, we derive a black hole mass of ${M}_{\mathrm{BH}}={2.34}_{-0.43}^{+0.43}\times {10}^{7}$ M⊙. This is slightly smaller than, but consistent with, previous determinations. However, our significantly improved time sampling (Tmed = 1.7 days compared to Tmed = 4.0 days) has reduced the uncertainties on both the time delay and the derived mass by ∼50%. We also detect clear velocity-resolved time delays across the broad Hβ profile, with shorter lags in the line wings and a longer lag in the line core. Future modeling of the full velocity-resolved time-delay response will further improve the reverberation-based mass for NGC 3783, adding it to the small but growing sample of active galactic nuclei for which we have constrained the black hole mass as well as the geometry and kinematics of the broad-ine region. Upcoming MUSE observations at the Very Large Telescope will also allow NGC 3783 to join the smaller sample of black holes where reverberation masses and masses from stellar dynamical modeling may be directly compared.

Keywords: supermassive black holes; seyfert galaxies; reverberation mapping
On the Spectral Evolution of Hot White Dwarf Stars. IV. The Diffusion and Mixing of Residual Hydrogen in Helium-rich White Dwarfs

In the framework of our extensive modeling study of the spectral evolution of white dwarfs, we present here a new set of detailed calculations of the transport of residual hydrogen in helium-rich white dwarfs. First, we investigate the so-called float-up process at high effective temperatures, whereby the upward diffusion of trace hydrogen leads to the formation of a hydrogen atmosphere. We examine the dependence of this phenomenon on the initial hydrogen abundance and on the strength of the radiative wind that opposes gravitational settling. Combined with our empirical knowledge of spectral evolution, our simulations provide new quantitative constraints on the hydrogen content of the hot helium-dominated white dwarf population. Then, we study the outcome of the so-called convective dilution process at low effective temperatures, whereby the superficial hydrogen layer is mixed within the underlying helium-rich envelope. In stark contrast with previous works on convective dilution, we demonstrate that, under reasonable assumptions, our models successfully reproduce the observed atmospheric composition of cool DBA stars, thereby solving one of the most important problems of the theory of spectral evolution. This major improvement is due to our self-consistent modeling of the earlier float-up process, which predicts the existence of a massive hydrogen reservoir underneath the thin superficial layer. We argue that the trace hydrogen detected at the surface of DBA white dwarfs is, in most cases, of primordial origin rather than the result of external accretion.

Keywords: white dwarf stars; da stars; db stars; do stars; stellar evolutionary models; atmospheric composition; stellar diffusion; stellar convection envelopes; stellar winds