adsabs/SciX_UAT_keywords huggingface dataset:
Finding Substructures in Protostellar Disks in Ophiuchus

High-resolution, millimeter observations of disks at the protoplanetary stage reveal substructures such as gaps, rings, arcs, spirals, and cavities. While many protoplanetary disks host such substructures, only a few at the younger protostellar stage have shown similar features. We present a detailed search for early disk substructures in Atacama Large Millimeter/submillimeter Array 1.3 and 0.87 mm observations of ten protostellar disks in the Ophiuchus star-forming region. Of this sample, four disks have identified substructure, two appear to be smooth disks, and four are considered ambiguous. The structured disks have wide Gaussian-like rings (σ R /R disk ~ 0.26) with low contrasts (C < 0.2) above a smooth disk profile, in comparison to protoplanetary disks where rings tend to be narrow and have a wide variety of contrasts (σ R /R disk ~ 0.08 and C ranges from 0 to 1). The four protostellar disks with the identified substructures are among the brightest sources in the Ophiuchus sample, in agreement with trends observed for protoplanetary disks. These observations indicate that substructures in protostellar disks may be common in brighter disks. The presence of substructures at the earliest stages suggests an early start for dust grain growth and, subsequently, planet formation. The evolution of these protostellar substructures is hypothesized in two potential pathways: (1) the rings are the sites of early planet formation, and the later observed protoplanetary disk ring-gap pairs are secondary features, or (2) the rings evolve over the disk lifetime to become those observed at the protoplanetary disk stage.

Keywords: circumstellar disks; star formation; protostars; young stellar objects; millimeter astronomy
Unveiling the Contribution of Population III Stars in Primeval Galaxies at Redshift ≥6

Detection of the first stars has remained elusive so far but their presence may soon be unveiled by upcoming JWST observations. Previous studies have not investigated the entire possible range of halo masses and redshifts that may help in their detection. Motivated by the prospects of detecting galaxies up to z ~ 20 in the JWST early data release, we quantify the contribution of Population III stars to high-redshift galaxies from 6 ≤ z ≤ 30 by employing the semianalytical model A-SLOTH, which self-consistently models the formation of Population III and Population II stars along with their feedback. Our results suggest that the contribution of Population III stars is the highest in low-mass halos of 107-109 M ⊙. While high-mass halos ≥1010 M ⊙ contain less than 1% Population III stars, they host galaxies with stellar masses of 109 M ⊙ as early as z ~ 30. Interestingly, overall the apparent magnitude of Population III stars gets brighter toward higher redshift due to the higher stellar masses, but Population III-dominated galaxies are too faint to be directly detected with JWST. Our results predict JWST can detect galaxies up to z ~ 30, which may help in constraining the initial mass function of Population III stars and will guide observers to discern the contribution of Population III stars to high-redshift galaxies.

Keywords: population iii stars; population ii stars; high-redshift galaxies
Improved AI-generated Solar Farside Magnetograms by STEREO and SDO Data Sets and Their Release

Here we greatly improve artificial intelligence (AI)-generated solar farside magnetograms using data sets from the Solar Terrestrial Relations Observatory (STEREO) and Solar Dynamics Observatory (SDO). We modify our previous deep-learning model and configuration of input data sets to generate more realistic magnetograms than before. First, our model, which is called Pix2PixCC, uses updated objective functions, which include correlation coefficients (CCs) between the real and generated data. Second, we construct input data sets of our model: solar farside STEREO extreme-ultraviolet (EUV) observations together with nearest frontside SDO data pairs of EUV observations and magnetograms. We expect that the frontside data pairs provide historic information on magnetic field polarity distributions. We demonstrate that magnetic field distributions generated by our model are more consistent with the real ones than previously, in consideration of several metrics. The averaged pixel-to-pixel CC for full disk, active regions, and quiet regions between real and AI-generated magnetograms with 8 × 8 binning are 0.88, 0.91, and 0.70, respectively. Total unsigned magnetic flux and net magnetic flux of the AI-generated magnetograms are consistent with those of real ones for the test data sets. It is interesting to note that our farside magnetograms produce polar field strengths and magnetic field polarities consistent with those of nearby frontside magnetograms for solar cycles 24 and 25. Now we can monitor the temporal evolution of active regions using solar farside magnetograms by the model together with the frontside ones. Our AI-generated solar farside magnetograms are now publicly available at the Korean Data Center for SDO (http://sdo.kasi.re.kr).

Keywords: solar magnetic fields; convolutional neural networks; the sun; astronomy data analysis
Mass Distribution for Single-lined Hot Subdwarf Stars in LAMOST

Masses for 664 single-lined hot subdwarf stars identified in LAMOST were calculated by comparing synthetic fluxes from spectral energy distribution with observed fluxes from a Virtual Observatory service. Three groups of hot subdwarf stars were selected from the whole sample according to their parallax precision to study the mass distributions. We found that He-poor sdB/sdOB stars present a wide mass distribution from 0.1 to 1.0 M ⊙ with a sharp mass peak at around 0.46 M ⊙, which is consistent with canonical binary model prediction. He-rich sdB/sdOB/sdO stars present a much flatter mass distribution than He-poor sdB/sdOB stars and with a mass peak at around 0.42 M ⊙. By comparing the observed mass distributions to the predictions of different formation scenarios, we concluded that the binary merger channel, including two helium white dwarfs (He-WDs) and He-WD + main-sequence mergers, cannot be the only main formation channel for He-rich hot subdwarfs, and other formation channels, such as the surviving companions from Type Ia supernovae, could also make impacts on producing this special population, especially for He-rich hot subdwarfs with masses less than 0.44 M ⊙. He-poor sdO stars also present a flatter mass distribution with an inconspicuous peak mass at 0.18 M ⊙. The similar mass- ${\rm{\Delta }}{{RV}}_{\max }$ distribution between He-poor sdB/sdOB and sdO stars supports the scenario that He-poor sdO stars could be the subsequent evolution stage of He-poor sdB/sdOB stars.

Keywords: b subdwarf stars; stellar masses; spectral energy distribution
ACCESS, LRG-BEASTS, and MOPSS: Featureless Optical Transmission Spectra of WASP-25b and WASP-124b

We present new optical transmission spectra for two hot Jupiters: WASP-25b (M = 0.56 M J ; R = 1.23 R J ; P = 3.76 days) and WASP-124b (M = 0.58 M J ; R = 1.34 R J ; P = 3.37 days), with wavelength coverages of 4200-9100 Å and 4570-9940 Å, respectively. These spectra are from the ESO Faint Object Spectrograph and Camera (v.2) mounted on the New Technology Telescope and Inamori-Magellan Areal Camera & Spectrograph on Magellan Baade. No strong spectral features were found in either spectra, with the data probing 4 and 6 scale heights, respectively. Exoretrievals and PLATON retrievals favor stellar activity for WASP-25b, while the data for WASP-124b did not favor one model over another. For both planets the retrievals found a wide range in the depths where the atmosphere could be optically thick (~0.4 μ-0.2 bars for WASP-25b and 1.6 μ-32 bars for WASP-124b) and recovered a temperature that is consistent with the planets' equilibrium temperatures, but with wide uncertainties (up to ±430 K). For WASP-25b, the models also favor stellar spots that are ~500-3000 K cooler than the surrounding photosphere. The fairly weak constraints on parameters are owing to the relatively low precision of the data, with an average precision of 840 and 1240 ppm per bin for WASP-25b and WASP-124b, respectively. However, some contribution might still be due to an inherent absence of absorption or scattering in the planets' upper atmospheres, possibly because of aerosols. We attempt to fit the strength of the sodium signals to the aerosol-metallicity trend proposed by McGruder et al., and find WASP-25b and WASP-124b are consistent with the prediction, though their uncertainties are too large to confidently confirm the trend.

Keywords: exoplanet atmospheres; exoplanet astronomy; exoplanet atmospheric composition; stellar activity; hot jupiters
Dynamically Forming Extremely Low-mass White Dwarf Binaries in Wide Orbits

The detection of a 0.2 M ⊙ extremely low-mass white dwarf (EW) in a wide orbit (P orb ≈ 450 days) with a 1.1 M ⊙ main-sequence companion, KIC 8145411, challenges our current understanding of how EWs form. The traditional channel for EW formation, via mass transfer from the EW's progenitor, is expected to form EW binaries in tight orbits. Indeed, the majority of known EWs are found in tight binaries with a median P orb ≈ 5.4 hr. Using numerical scattering experiments, we find that binary-binary strong encounters in star clusters can sufficiently widen the orbit of a typical EW binary, to explain the observed wide orbit of the KIC 8145411 system. The P orb distribution for EW binaries produced through binary-binary encounters is bimodal: one mode corresponds to the initial orbital period of the EW binary, while the other is near P orb ~ few 102 days, similar to the orbital period of the KIC 8145411 system. We find that the production of wide EW binaries that are also ejected from the cluster peaks at a star cluster mass of ~105 M ⊙ with a rate of ~10-3 Gyr-1. Assuming that 50% of all stars form in star clusters and an initial cluster mass function ∝m -2, we estimate a galactic formation rate of ~4.16 × 103 Gyr-1 for wide EW binaries.

Keywords: white dwarf stars; computational methods; interacting binary stars; stellar dynamics
Two New Rapidly Rotating ON Stars Found with LAMOST

The ON stars are a rare subtype of O stars of uncertain origin. We report two new, rapidly rotating ON stars found in data acquired with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope. LS I +61 28 is an ON8.5 Vn dwarf with a projected equatorial rotational velocity of {V}{{e}}\sin I≃ 298 {km} {{{s}}}-1, while HDE 236672 is an ON9 IVn subgiant with {V}{{e}}\sin I≃ 253 {km} {{{s}}}-1. The former is the first rapidly rotating ON dwarf to be found, and the latter is only the third ON subgiant. The luminosity classes of non-supergiant ON stars appear to be influenced by the axial inclination angle I: the rapidly rotating giants are close to equator-on, while ON dwarfs with lower {V}{{e}}\sin I values are viewed more nearly pole-on. Combining parallaxes and proper motions from Gaia Data Release 2 with radial-velocity measurements, we investigate the kinematics of non-supergiant ON stars and infer that the dynamics, rapid rotation, and surface nitrogen characteristics may all be consequences of binary interaction.

Keywords: stellar rotation; o stars
Chondrule Survivability in the Solar Nebula

The lifetime of millimeter-sized dust grains, such as chondrules, in the nominal solar nebula model is limited to ∼105 yr, due to an inward drift driven by gas drag. However, isotopic and petrological studies of primitive meteorites indicate a discrepancy of ≳106 yr between the formation time of chondrules and that of chondritic parent bodies. Therefore, chondrules should survive for ≳106 yr in the solar nebula against the inward drift without subsequent growth (i.e., planetesimal formation). Here, we investigate the conditions of the solar nebula that are suitable for the long lifetime of chondrule-sized dust particles. We take the turbulent strength, the radial pressure gradient force, and the disk metallicity of the solar nebula as free parameters. For 1 mm radius chondrules to survive and keep their size for ≳106 yr, the suitable condition is a weak turbulence (α ∼ 10‑6), a flat radial profile (η ≲ 10‑3), and a high metallicity (Z ∼ 0.1). This condition is qualitatively consistent with the characteristics of protoplanetary disks suggested by recent observations. We eventually propose that planetesimal formation may be induced by disk evolution, e.g., the inside-out dispersal of the gas component due to the disk wind.

Keywords: chondrules; solar nebulae; planetesimals; planetary system formation; protoplanetary disks; carbonaceous chondrites
ArtPop: A Stellar Population and Image Simulation Python Package

We present Artificial Stellar Populations (ArtPop), an open-source Python package for synthesizing stellar populations and generating artificial images of stellar systems, populated star by star. The code is designed to be intuitive to use and as modular as possible, making it possible to use each of its functionalities independently or together. ArtPop has a wide range of scientific and pedagogical use cases, including the measurement of detection efficiencies in current and future imaging surveys, the calculation of integrated stellar population parameters, quantitative comparisons of isochrone models, and the development and validation of astronomical image-processing algorithms. In this paper, we give an overview of the ArtPop package, provide simple coding examples to demonstrate its implementation, and present results from some potential applications of the code. We provide links to the source code that created each example and figure throughout the paper. ArtPop is under active development, and we welcome bug reports, feature requests, and code contributions from the community. https://artpop.readthedocs.io/en/latest/ https://github.com/ArtificialStellarPopulations/ArtPop/ https://artpop.readthedocs.io/en/latest/tutorials/quickstart.html https://github.com/ArtificialStellarPopulations/artpop-paper-figures/blob/main/scripts/

Keywords: dwarf galaxies; star clusters; stellar populations; astronomy software; open source software
Eccentric Minidisks in Accreting Binaries

We show that gas disks around the components of an orbiting binary system (so-called minidisks) may be susceptible to a resonant instability that causes the minidisks to become significantly eccentric. Eccentricity is injected by, and also induces, regular impacts between the minidisks at roughly the orbital period of the binary. Such eccentric minidisks are seen in vertically integrated, two-dimensional simulations of a circular, equal-mass binary accreting from a circumbinary gas disk with a Γ-law equation of state. Minidisk eccentricity is suppressed by the use of an isothermal equation of state. However, the instability still operates and can be revealed in a minimal disk-binary simulation by removing the circumbinary disk and feeding the minidisks from the component positions. Minidisk eccentricity is also suppressed when the gravitational softening length is large (≳4% of the binary semimajor axis), suggesting that its absence could be an artifact of widely adopted numerical approximations; a follow-up study in three dimensions with well-resolved, geometrically thin minidisks (aspect ratios ≲0.02) may be needed to assess whether eccentric minidisks can occur in real astrophysical environments. If they can, the electromagnetic signature may be important for discriminating between binary and single black hole scenarios for quasiperiodic oscillations in active galactic nuclei; in turn, this might aid in targeted searches with pulsar timing arrays for individual supermassive black hole binary sources of low-frequency gravitational waves.

Keywords: eccentricity; binary stars; astrophysical black holes; gravitational wave sources; hydrodynamical simulations
Large-scale Gravitational Lens Modeling with Bayesian Neural Networks for Accurate and Precise Inference of the Hubble Constant

We investigate the use of approximate Bayesian neural networks (BNNs) in modeling hundreds of time delay gravitational lenses for Hubble constant (H0) determination. Our BNN was trained on synthetic Hubble Space Telescope quality images of strongly lensed active galactic nuclei with lens galaxy light included. The BNN can accurately characterize the posterior probability density functions (PDFs) of model parameters governing the elliptical power-law mass profile in an external shear field. We then propagate the BNN-inferred posterior PDFs into an ensemble H0 inference, using simulated time delay measurements from a plausible dedicated monitoring campaign. Assuming well-measured time delays and a reasonable set of priors on the environment of the lens, we achieve a median precision of 9.3% per lens in the inferred H0. A simple combination of a set of 200 test lenses results in a precision of 0.5 km s-1 Mpc-1 (0.7%), with no detectable bias in this H0 recovery test. The computation time for the entire pipeline—including the generation of the training set, BNN training and H0 inference—translates to 9 minutes per lens on average for 200 lenses and converges to 6 minutes per lens as the sample size is increased. Being fully automated and efficient, our pipeline is a promising tool for exploring ensemble-level systematics in lens modeling for H0 inference.

Keywords: hubble constant; cosmology; bayesian statistics; hierarchical models; strong gravitational lensing; publicly available software
Three-dimensional Atmospheric Dynamics of Jupiter from Ground-based Doppler Imaging Spectroscopy in the Visible

We present three-dimensional (3D) maps of Jupiter's atmospheric circulation at cloud-top level from Doppler-imaging data obtained in the visible domain with JIVE, the second node of the JOVIAL network, which is mounted on the Dunn Solar Telescope at Sunspot, New Mexico. We report on 12 nights of observations between 2018 May 4 and May 30, representing a total of about 80 hr. First, the average zonal wind profile derived from our data is compatible with that derived from cloud-tracking measurements performed on Hubble Space Telescope images obtained in 2018 April from the Outer Planet Atmospheres Legacy program. Second, we present the first ever 2D maps of Jupiter's atmospheric circulation from Doppler measurements. The zonal velocity map highlights well-known atmospheric features, such as the equatorial hot spots and the Great Red Spot (GRS). In addition to zonal winds, we derive meridional and vertical velocity fields from the Doppler data. The motions attributed to vertical flows are mainly located at the boundary between the equatorial belts and tropical zones, which could indicate active motion in theses regions. Qualitatively, these results compare well to recent Juno data that have unveiled the 3D structure of Jupiter's wind field. To the contrary, the motions attributed to meridional circulation are very different from what is obtained by cloud tracking, except at the GRS. Because of limitations with data resolution and processing techniques, we acknowledge that our measurements of the vertical or meridional flows of Jupiter are still to be confirmed.

Keywords: jupiter; planetary atmospheres; doppler imaging
Can the Cosmological Dilation Explain the Skewness in the Gamma-Ray Burst Duration Distribution?

In order to explain the origin of skewness in the gamma-ray burst (GRB) duration distribution, a statistical model, based on the cosmological time dilation and taking into account the GRB formation rate and instrumental effects, is examined. It is concluded that the considered effects are able to account for only a small fraction of the observed skewness. Therefore, its origin needs to be searched for in the processes governing the progenitors of GRBs​.

Keywords: astrostatistics; astronomy data analysis; gamma-ray bursts; cosmology
Lyα Absorption in a "Croissant-like" Heliosphere

Lyα absorption profiles have been used to detect astrospheres and heliospheric absorption from the hydrogen wall and heliotail. Using magnetohydrodynamic models of the heliosphere, we can compare simulated to observed Lyα profiles to probe the neutral hydrogen within and near the heliosphere. There is an ongoing controversy whether the heliosphere has a long "comet-like" tail or a short "croissant-like" tail. Here we present the first Lyα absorption investigation using a croissant-like heliosphere. With identical boundary conditions we compare the BU model, which presents a croissant-like tail, and the Moscow model, which presents a comet-like tail. The BU and Moscow models present nearly identical Lyα profiles toward nose targets (α Cen and 36 Oph). Differences in Lyα profiles are shown toward the tail target (HD 35296). Despite the shortened heliotail of the croissant model, significant downwind heliosheath absorption is seen, just 5% shallower and shifted by 4 km s‑1. This implies that an extended tail model is not required to reproduce the heliosheath Lyα absorption observations. Finer observation gratings may be able to resolve this shift. Additionally, when using higher interstellar medium (ISM) neutral and plasma densities and lower magnetic field (∣B LISM∣ = 3.2 μG, α BV ≈ 40°) than in the Moscow model, we find better agreement with observed Lyα profiles. None of the models presented show agreement in all directions simultaneously. Furthermore, we show that for the ISM conditions with the least certainty (n p,LISM, n H,LISM, T LISM, B LISM), B LISM has the most significant effect on the structure of the hydrogen wall and Lyα profiles.

Keywords: heliosphere; heliosheath; interstellar medium; solar wind; heliopause
Living with a Red Dwarf: X-Ray, UV, and Ca II Activity-Age Relationships of M Dwarfs

The vast majority of stars in the nearby stellar neighborhood are M dwarfs. Their low masses and luminosities result in slow rates of nuclear evolution and minimal changes to the stars' observable properties, even along astronomical timescales. However, they possess relatively powerful magnetic dynamos and resulting X-ray to UV (X-UV) activity, compared to their bolometric luminosities. This magnetic activity does undergo an observable decline over time, potentially making it a key age determinant for M dwarfs. Observing this activity is important for studying the outer atmospheres of these stars, but also for comparing the behaviors of different spectral type subsets of M dwarfs; e.g., those with partially versus fully convective interiors. Beyond stellar astrophysics, understanding the X-UV activity of M dwarfs over time is a key component when studying the atmospheres and habitability of any hosted exoplanets. Earth-sized exoplanets, in particular, are more commonly found orbiting M dwarfs than any other stellar type, and thermal escape (driven by the M dwarf X-UV activity) is believed to be the dominant atmospheric loss mechanism for these planets. Utilizing recently calibrated M dwarf age-rotation relationships, also constructed as part of the Living with a Red Dwarf program, we have analyzed the evolution of M dwarf activity over time, in terms of coronal (X-ray), chromospheric (Lyα, and Ca II), and overall X-UV (5-1700 Å) emissions. The activity-age relationships presented here will be useful for studying exoplanet habitability and atmospheric loss, and also for studying the different dynamo and outer atmospheric heating mechanisms at work in M dwarfs.

Keywords: stellar ages; stellar atmospheres; stellar coronae; stellar chromospheres; stellar evolution; stellar rotation; x-ray astronomy; ultraviolet astronomy; low mass stars; late-type dwarf stars; m dwarf stars