adsabs/SciX_UAT_keywords huggingface dataset:
A New Numerical Implementation for Solar Coronal Modeling by an HLL Generalized Riemann Problem Solver

In this paper, we employ a Harten-Lax-van Leer (HLL) generalized Riemann problem (HLL-GRP) solver within the framework of a finite volume method to model 3D solar coronal structures for the first time. Based on the rotational invariance of magnetohydrodynamics (MHD) equations, the HLL-GRP solver is successfully implemented into 3D MHD simulations. To constrain the divergence of the magnetic field, the locally divergence-free weighted-least-squares-based essentially nonoscillatory reconstruction and the properly discretized Godunov-Powell source term are applied. To keep density and pressure positive, a positivity-preserving limiter is added to the reconstructed polynomials of density and pressure. We first test a 3D blast wave problem to preliminarily validate the effectiveness of the proposed scheme on Cartesian structured grid. Then, we further run our code on a six-component grid to numerically study the steady-state coronal structures of Carrington rotation 2218 during the solar minimum phase. A comparison with the two-stage Runge-Kutta scheme is performed for both the 3D blast wave problem and solar coronal problem. Numerical results of large-scale solar coronal structures are basically consistent with the observational characteristics, indicating the robustness of the proposed model.

Keywords: solar coronal holes; solar coronal streamers; magnetic fields; solar wind
ACA CO(J = 2-1) Mapping of the Nearest Spiral Galaxy M33. I. Initial Results and Identification of Molecular Clouds

We present the results of ALMA-ACA 7 m array observations in 12CO(J = 2-1), 13CO(J = 2-1), and C18O(J = 2-1) line emission toward the molecular-gas disk in the Local Group spiral galaxy M33 at an angular resolution of 7.″31 × 6.″50 (30 × 26 pc). We combined the ACA 7 m array 12CO(J = 2-1) data with the IRAM 30 m data to compensate for emission from diffuse molecular-gas components. The ACA+IRAM combined 12CO(J = 2-1) map clearly depicts the cloud-scale molecular-gas structure over the M33 disk. Based on the ACA+IRAM 12CO(J = 2-1) cube data, we cataloged 848 molecular clouds with a mass range from 103-106 M ⊙. We found that high-mass clouds (≥105 M ⊙) tend to associate with the 8 μm bright sources in the spiral arm region, while low-mass clouds (<105 M ⊙) tend to be apart from such 8 μm bright sources and to exist in the inter-arm region. We compared the cataloged clouds with GMCs observed by the IRAM 30 m telescope at 49 pc resolution (IRAM GMC), and found that a small IRAM GMC is likely to be identified as a single molecular cloud even in ACA+IRAM CO data, while a large IRAM GMC can be resolved into multiple ACA+IRAM clouds. The velocity dispersion of a large IRAM GMC is mainly dominated by the line-of-sight velocity difference between small clouds inside the GMC rather than the internal cloud velocity broadening.

Keywords: triangulum galaxy; local group; molecular clouds; interstellar medium
The Orbital and Physical Properties of Five Southern Be+sdO Binary Systems

Close binary interactions may play a critical role in the formation of the rapidly rotating Be stars. Mass transfer can result in a mass gainer star spun up by the accretion of mass and angular momentum, while the mass donor is stripped of its envelope to form a hot and faint helium star. Far-UV spectroscopy has led to the detection of about 20 such binary Be+sdO systems. Here we report on a 3 yr program of high-quality spectroscopy designed to determine the orbital periods and physical properties of five Be binary systems. These binaries are long orbital period systems with P = 95-237 days and small semiamplitude K 1 < 11 km s-1. We combined the Be star velocities with prior sdO measurements to obtain mass ratios. A Doppler tomography algorithm shows the presence of the He II λ4686 line in the faint spectrum of the hot companion in four of the targets. We discuss the observed line variability and show evidence of phase-locked variations in the emission profiles of HD 157832, suggesting a possible disk spiral density wave due to the presence of the companion star. The stripped companions in HD 113120 and HD 137387 may have a mass larger than 1.4 M ⊙, indicating that they could be progenitors of Type Ib and Ic supernovae.

Keywords: stellar evolution; spectroscopic binary stars; emission line stars
Cleaning Images with Gaussian Process Regression

Many approaches to astronomical data reduction and analysis cannot tolerate missing data: corrupted pixels must first have their values imputed. This paper presents astrofix, a robust and flexible image imputation algorithm based on Gaussian process regression. Through an optimization process, astrofix chooses and applies a different interpolation kernel to each image, using a training set extracted automatically from that image. It naturally handles clusters of bad pixels and image edges and adapts to various instruments and image types. For bright pixels, the mean absolute error of astrofix is several times smaller than that of median replacement and interpolation by a Gaussian kernel. We demonstrate good performance on both imaging and spectroscopic data, including the SBIG 6303 0.4 m telescope and the FLOYDS spectrograph of Las Cumbres Observatory and the CHARIS integral-field spectrograph on the Subaru Telescope.

Keywords: gaussian processes regression; astronomical detectors
Optical Variability of Blazars in the Tomo-e Gozen Northern Sky Transient Survey

We studied the optical variability of 241 BL Lacertae (BL Lacs) and 83 flat-spectrum radio quasars (FSRQs) from the 4LAC catalog using data from the Tomo-e Gozen Northern Sky Transient Survey, with ∼50 epochs per blazar on average. We excluded blazars whose optical variability may be underestimated due to the influence of their host galaxy based on their optical luminosity (L O ). FSRQs with γ-ray photon index greater than 2.6 exhibit very low optical variability, and their distribution of standard deviation of repeated photometry is significantly different from that of the other FSRQs (Kolmogorov–Smirnov test p-value equal to 5 × 10‑6). Among a sample of blazars at any particular cosmological epoch, those with lower γ-ray luminosity (L γ ) tend to have lower optical variability, and those FSRQs with a γ-ray photon index greater than 2.6 tend to have low L γ . We also measured the structure function of optical variability and found that the amplitude of the structure function for FSRQs is higher than previously measured and higher than that of BL Lacs at multiple time lags. Additionally, the amplitude of the structure function of FSRQs with high γ-ray photon index is significantly lower than that of FSRQs with low γ-ray photon index. The structure function of FSRQs of high γ-ray photon index shows a characteristic timescale of more than 10 days, which may be the variability timescale of the accretion disk. In summary, we infer that the optical component of FSRQs with high γ-ray photon index may be dominated by the accretion disk.

Keywords: blazars; flat-spectrum radio quasars; active galactic nuclei
Deep Modeling of Quasar Variability

Quasars have long been known as intrinsically variable sources, but the physical mechanism underlying the temporal optical/UV variability is still not well understood. We propose a novel nonparametric method for modeling and forecasting the optical variability of quasars utilizing an AE neural network to gain insight into the underlying processes. The AE is trained with ∼15,000 decade-long quasar light curves obtained by the Catalina Real-time Transient Survey selected with negligible flux contamination from the host galaxy. The AE&'s performance in forecasting the temporal flux variation of quasars is superior to that of the damped random walk process. We find a temporal asymmetry in the optical variability and a novel relation—the amplitude of the variability asymmetry decreases as luminosity and/or black hole mass increases—is suggested with the help of autoencoded features. The characteristics of the variability asymmetry are in agreement with those from the self-organized disk instability model, which predicts that the magnitude of the variability asymmetry decreases as the ratio of the diffusion mass to inflow mass in the accretion disk increases.

Keywords: galaxy accretion disks; active galaxies; astrostatistics; neural networks
Deciphering the Deep Origin of Active Regions via Analysis of Magnetograms

In this work, we derive magnetic toroids from surface magnetograms by employing a novel optimization method, based on the trust region reflective algorithm. The toroids obtained in this way are combinations of Fourier modes (amplitudes and phases) with low longitudinal wavenumbers. The optimization also estimates the latitudinal width of the toroids. We validate the method using synthetic data, generated as random numbers along a specified toroid. We compute the shapes and latitudinal widths of the toroids via magnetograms, generally requiring several m's to minimize residuals. A threshold field strength is chosen to include all active regions in the magnetograms for toroid derivation, while avoiding non-contributing weaker fields. Higher thresholds yield narrower toroids, with an m = 1 dominant pattern. We determine the spatiotemporal evolution of toroids by optimally weighting the amplitudes and phases of each Fourier mode for a sequence of five Carrington Rotations (CRs) to achieve the best amplitude and phases for the middle CR in the sequence. Taking more than five causes "smearing" or degradation of the toroid structure. While this method applies no matter the depth at which the toroids actually reside inside the Sun, by comparing their global shape and width with analogous patterns derived from magnetohydrodynamic (MHD) tachocline shallow water model simulations, we infer that their origin is at/near the convection zone base. By analyzing the "Halloween" storms as an example, we describe features of toroids that may have caused the series of space weather events in 2003 October-November. Calculations of toroids for several sunspot cycles will enable us to find similarities/differences in toroids for different major space weather events.

Keywords: solar activity; solar storm; solar active regions; solar active region magnetic fields; solar interior; magnetohydrodynamics; magnetohydrodynamical simulations
Rover-mounted Hydrated Mineral Detector for Mars Exploration: A Preliminary Report

The rover-mounted hydrated mineral detector (HMD) is based on a dielectric spectrometer (tuned frequency range of 0.8-4 MHz) that will detect bulk subsurface hydrated minerals in local scale. The HMD is a compact, low-mass (1.5 kg), and low-power instrument (5 W) suitable for Mars application. Compared with orbiter-based instruments with low horizontal resolution (5-10 km), the HMD will offer high resolution (2 m) that can identify optimal sampling sites for the presence of hydrated minerals. From field testing with reduced radio frequency (RF) power (P rf = 10 mW), the HMD demonstrated detection of shallow buried gypsum samples. When developed with full RF power, the HMD could potentially detect hydrates down to depths of 2 m (P rf = 1 W) or 4 m (P rf = 36 W) in Martian soil. Unlike conventional dielectric spectrometers, which require small amounts of the sample (5-10 g) to be placed inside sample cells, the HMD will detect hydrated minerals by scanning over the Mars surface mounted on a rover platform (<1 m above ground) without any sample preparation. This capability will allow future rovers to rapidly assess the scientific potential of field sites. Compared with optical techniques that are limited to surface exposed mineralogical features that could be obscured by dust and weathering products, the HMD will detect bulk subsurface hydrated minerals along the rover traverse irrespective of surface obscuration. The HMD (TRL 4) is a proof-of-concept instrument that can be developed and matured for future Mars rover missions.

Keywords: space vehicle instruments
HCN Production in Titan's Atmosphere: Coupling Quantum Chemistry and Disequilibrium Atmospheric Modeling

Hydrogen cyanide (HCN) is a critical reactive source of nitrogen for building key biomolecules relevant for the origin of life. Still, many HCN reactions remain uncharacterized by experiments and theory, and the complete picture of HCN production in planetary atmospheres is not fully understood. To improve this situation, we develop a novel technique making use of computational quantum chemistry, experimental data, and atmospheric numerical simulations. First, we use quantum chemistry simulations to explore the entire field of possible reactions for a list of primary species in N2-, CH4-, and H2-dominated atmospheres. In this process, we discover 33 new reactions with no previously known rate coefficients. From here, we develop a consistent reduced atmospheric hybrid chemical network (CRAHCN) containing experimental values when available and our calculated rate coefficients otherwise. Next, we couple CRAHCN to a 1D chemical kinetic model (ChemKM) to compute the HCN abundance as a function of atmospheric depth on Titan. Our simulated atmospheric HCN profile agrees very well with the Cassini observations. CRAHCN contains 104 reactions; however, nearly all of the simulated atmospheric HCN profile can be obtained using a scaled-down network of only 19 dominant reactions. From here, we form a complete picture of HCN chemistry in Titan's atmosphere, from the dissociation of the main atmospheric species, down to the direct production of HCN along four major channels. One of these channels was first discovered and characterized in Pearce et al. and this work.

Keywords: astrobiology; pre-biotic astrochemistry; atmospheric science; reaction rates
Potential Subpopulations and Assembling Tendency of the Merging Black Holes

The origins of coalescing binary black holes (BBHs) detected by the advanced LIGO/Virgo are still under debate, and clues may be present in the joint mass-spin distribution of these merger events. Here we construct phenomenological models containing two subpopulations to investigate the BBH population detected in gravitational-wave observations. We find that our models can explain the GWTC-3 data rather well, and several constraints to our model are required by the data: first, the maximum mass for the component with a stellar-origin, ${m}_{\max }$ , is ${39.1}_{-2.7}^{+2.4}\,{M}_{\odot }$ at 90% credibility; second, about 15% of the mergers happen in dynamical environments, in which 7%-16% of events are hierarchical mergers, and these BHs have an average spin magnitude significantly larger than the first-generation mergers, with d μ a > 0.4 at 99% credibility; third, the dynamical component BHs tend to pair with each other with larger total mass and higher mass ratio. An independent analysis focusing on spins is also carried out, and we find that the spin amplitude of component BHs can be divided into two groups according to a division mass ${m}_{{\rm{d}}}={46.1}_{-5.1}^{+5.6}\,{M}_{\odot }$ . These constraints can be naturally explained by current formation channels, and our results suggest that some of the observed events were likely from active galactic nucleus disks.

Keywords: ligo; stellar mass black holes; gravitational waves; stellar evolution; bayesian statistics
Investigating Stellar Variability in the Open Cluster Region NGC 381

We study variable stars in the field of the open cluster NGC 381 using photometric data observed over 27 nights and identify a total of 57 variable stars, six of which are member stars. The variable stars are classified based on their periods, amplitudes, light-curve shapes, and locations in the H-R diagram. We found a rich variety of variable stars in the cluster. We identified a total of 10 eclipsing binaries, of which two are of Algol type while eight are of W UMa type (EW). The estimated ages of these EW binaries are greater than 0.6 Gyr, which is in agreement with the formation time constraint of ≥0.6 Gyr on short-period eclipsing binaries. The physical parameters of the two EW-type binaries are estimated using PHOEBE model-fitting software. The pulsating variable stars include one each from the δ Scuti and γ Dor variability classes. We determined the pulsation modes of pulsating variables with the help of the FAMIAS package. We obtained 15 rotational variable stars comprising four dwarf stars identified on the basis of their log(g) versus log(T eff) diagram. These dwarf stars are found to have generally longer periods than the remaining rotational variables.

Keywords: open star clusters; variable stars; eclipsing binary stars; photometry
Improving White Dwarfs as Chronometers with Gaia Parallaxes and Spectroscopic Metallicities

White dwarfs (WDs) offer unrealized potential in solving two problems in astrophysics: stellar age accuracy and precision. WD cooling ages can be inferred from surface temperatures and radii, which can be constrained with precision by high-quality photometry and parallaxes. Accurate and precise Gaia parallaxes along with photometric surveys provide information to derive cooling and total ages for vast numbers of WDs. Here we analyze 1372 WDs found in wide binaries with main-sequence (MS) companions and report on the cooling and total age precision attainable in these WD+MS systems. The total age of a WD can be further constrained if its original metallicity is known because the MS lifetime depends on metallicity at fixed mass, yet metallicity is unavailable via spectroscopy of the WD. We show that incorporating spectroscopic metallicity constraints from 38 wide binary MS companions substantially decreases internal uncertainties in WD total ages compared to a uniform constraint. Averaged over the 38 stars in our sample, the total (internal) age uncertainty improves from 21.04% to 16.77% when incorporating the spectroscopic constraint. Higher mass WDs yield better total age precision; for eight WDs with zero-age MS masses ≥2.0 M ⊙, the mean uncertainty in total ages improves from 8.61% to 4.54% when incorporating spectroscopic metallicities. We find that it is often possible to achieve 5% total age precision for WDs with progenitor masses above 2.0 M ⊙ if parallaxes with ≤1% precision and Pan-STARRS g, r, and i photometry with ≤0.01 mag precision are available.

Keywords: white dwarf stars; stellar evolution
First Impressions: Early-time Classification of Supernovae Using Host-galaxy Information and Shallow Learning

Substantial effort has been devoted to the characterization of transient phenomena from photometric information. Automated approaches to this problem have taken advantage of complete phase coverage of an event, limiting their use for triggering rapid follow-up of ongoing phenomena. In this work, we introduce a neural network with a single recurrent layer designed explicitly for early photometric classification of supernovae (SNe). Our algorithm leverages transfer learning to account for model misspecification, host-galaxy photometry to solve the data-scarcity problem soon after discovery, and a custom weighted loss to prioritize accurate early classification. We first train our algorithm using state-of-the-art transient and host-galaxy simulations, then adapt its weights and validate it on the spectroscopically confirmed SNe Ia, SNe II, and SNe Ib/c from the Zwicky Transient Facility Bright Transient Survey. On observed data, our method achieves an overall accuracy of 82% ± 2% within 3 days of an event's discovery, and an accuracy of 87% ± 5% within 30 days of discovery. At both early and late phases, our method achieves comparable or superior results to the leading classification algorithms with a simpler network architecture. These results help pave the way for rapid photometric and spectroscopic follow-up of scientifically valuable transients discovered in massive synoptic surveys.

Keywords: supernovae; light curve classification; neural networks; classification
Clustering of LRGs in the DECaLS DR8 Footprint: Distance Constraints from Baryon Acoustic Oscillations Using Photometric Redshifts

A photometric redshift sample of luminous red galaxies (LRGs) obtained from the DECam Legacy Survey (DECaLS) is analyzed to probe cosmic distances by exploiting the wedge approach of the two-point correlation function. Although the cosmological information is highly contaminated by the uncertainties existing in the photometric redshifts from the galaxy map, an angular diameter distance can be probed at the perpendicular configuration in which the measured correlation function is minimally contaminated. An ensemble of wedged correlation functions selected up to a given threshold based on having the least contamination was studied in previous work (Sridhar & Song 2019) using simulations, and the extracted cosmological information was unbiased within this threshold. We apply the same methodology for analyzing the LRG sample from DECaLS, which will provide the optical imaging for targeting two-thirds of the Dark Energy Spectroscopic Instrument footprint and measure the angular diameter distances at z = 0.69 and z = 0.87 to be ${D}_{A}(0.697)=(1529\pm 73\,\mathrm{Mpc})({r}_{d}/{r}_{d,\mathrm{fid}})$ and ${D}_{A}(0.874)=(1674\pm 102\,\mathrm{Mpc})({r}_{d}/{r}_{d,\mathrm{fid}})$ with a fractional error of 4.77% and 6.09%, respectively. We obtain a value of H0 = 66.58 ± 5.31 km s-1 Mpc-1, which supports the H0 measured by all other baryon acoustic oscillation results and is consistent with the ΛCDM model.

Keywords: large-scale structure of the universe; distance measure; cosmology; high-redshift galaxies; photometry
Clouds will Likely Prevent the Detection of Water Vapor in JWST Transmission Spectra of Terrestrial Exoplanets

We are on the verge of characterizing the atmospheres of terrestrial exoplanets in the habitable zones of M dwarf stars. Due to their large planet-to-star radius ratios and higher frequency of transits, terrestrial exoplanets orbiting M dwarf stars are favorable for transmission spectroscopy. In this work, we quantify the effect that water clouds have on the amplitude of water vapor transmission spectral features of terrestrial exoplanets orbiting M dwarf stars. To do so, we make synthetic transmission spectra from general circulation model (GCM) experiments of tidally locked planets. We improve upon previous work by considering how varying a broad range of planetary parameters affects transmission spectra. We find that clouds lead to a 10-100 times increase in the number of transits required to detect water features with the James Webb Space Telescope (JWST) with varying rotation period, incident stellar flux, surface pressure, planetary radius, and surface gravity. We also find that there is a strong increase in the dayside cloud coverage in our GCM simulations with rotation periods ≳12 days for planets with Earth’s radius. This increase in cloud coverage leads to even stronger muting of spectral features for slowly rotating exoplanets orbiting M dwarf stars. We predict that it will be extremely challenging to detect water transmission features in the atmospheres of terrestrial exoplanets in the habitable zone of M dwarf stars with JWST. However, species that are well-mixed above the cloud deck (e.g., CO2 and CH4) may still be detectable on these planets with JWST.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; extrasolar rocky planets; habitable planets; planetary atmospheres; water vapor