adsabs/SciX_UAT_keywords huggingface dataset:
SADHANA: A Doubly Linked List-based Multidimensional Adaptive Mesh Refinement Framework for Solving Hyperbolic Conservation Laws with Application to Astrophysical Hydrodynamics and Magnetohydrodynamics

We report the development of a nested block-structured adaptive mesh framework to solve multidimensional, time-dependent hyperbolic equations encountered in astrophysics. An approach based on a tabular list is used to construct variants of Hilbert space-filling curves in an iterative fashion to maintain the connectivity of locally refined mesh configurations using a doubly linked list. Modifications are made to conventional boundaries of computational blocks to aid the adaptive mesh. We also describe a well-defined, computationally efficient data structure to hold self-similar mesh units for this purpose. The flexibility of this code is demonstrated by the performance of various Riemann solvers implemented in this computational framework.

Keywords: magnetohydrodynamics; hydrodynamics; computational methods; algorithms; astrophysical fluid dynamics
Using Neural Networks to Differentiate Newly Discovered BL Lacertae Objects and FSRQs among the 4FGL Unassociated Sources Employing Gamma-Ray, X-Ray, UV/Optical, and IR Data

Among the ~2157 unassociated sources in the third data release (DR3) of the fourth Fermi catalog, ~1200 were observed with the Neil Gehrels Swift Observatory pointed instruments. These observations yielded 238 high signal-to-noise ratio X-ray sources within the 95% Fermi uncertainty regions. Recently, Kerby et al. employed neural networks to find blazar candidates among these 238 X-ray counterparts to the 4FGL unassociated sources and found 112 likely blazar counterpart sources. A complete sample of blazars, along with their subclassification, is a necessary step to help understand the puzzle of the blazar sequence and for the overall completeness of the gamma-ray emitting blazar class in the Fermi catalog. We employed a multi-perceptron neural network classifier to identify flat spectrum radio quasars (FSRQs) and BL Lac objects among these 112 blazar candidates using the gamma-ray, X-ray, UV/optical, and IR properties. This classifier provided probability estimates for each source to be associated with one or the other category, such that P fsrq represents the probability for a source to be associated with the FSRQ subclass. Using this approach, four FSRQs and 50 BL Lac objects are classified as such with >99% confidence, while the remaining 58 blazars could not be unambiguously classified as either BL Lac objects or FSRQs.

Keywords: high energy astrophysics; active galactic nuclei; blazars; x-ray astronomy
RETRACTED: Redox Evolution of the Crystallizing Terrestrial Magma Ocean and Its Influence on the Outgassed Atmosphere

Magma oceans (MOs) are episodes of large-scale melting of the mantle of terrestrial planets. The energy delivered by the Moon-forming impact induced a deep MO on the young Earth, corresponding to the last episode of core-mantle equilibration. The crystallization of this MO led to the outgassing of volatiles initially present in the Earth's mantle, resulting in the formation of a secondary atmosphere. During outgassing, the MO acts as a chemical buffer for the atmosphere via the oxygen fugacity, set by the equilibrium between ferrous- and ferric-iron oxides in the silicate melts. By tracking the evolution of the oxygen fugacity during MO solidification, we model the evolving composition of a C-O-H atmosphere. We use the atmospheric composition to calculate its thermal structure and radiative flux. This allows us to calculate the lifetime of the terrestrial MO. We find that, upon crystallizing, the MO evolves from a mildly reducing to a highly oxidized redox state, thereby transiting from a CO- and H2-dominated atmosphere to a CO2- and H2O-dominated one. We find the overall duration of the MO crystallization to depend mostly on the bulk H content of the mantle, and to remain below 1.5 millions yr for up to nine Earth's water oceans' worth of H. Our model also suggests that reduced atmospheres emit lower infrared radiation than oxidized ones, despite of the lower greenhouse effect of reduced species, resulting in a longer MO lifetime in the former case. Although developed for a deep MO on Earth, the framework applies to all terrestrial planet and exoplanet MOs, depending on their volatile budgets.

Keywords: planetary science; atmospheric science; planetary atmospheres; planetary structure; planetary thermal histories; planetary theory
Discovery of a Large Population of Nitrogen-enhanced Stars in the Magellanic Clouds

We report the APOGEE-2S+ discovery of a unique collection of nitrogen-enhanced mildly metal-poor giant stars, peaking at [Fe/H] ∼ -0.89 with no carbon enrichment, toward the Small and Large Magellanic Clouds (SMC and LMC), with abundances of light- (C, N), odd-Z (Al, K), and α-elements (O, Mg, Si) that are typically found in Galactic globular clusters (GCs). Here we present 44 stars in the SMC and LMC that exhibit significantly enhanced [N/Fe] abundance ratios, well above ([N/Fe] ≳ +0.6) typical Galactic levels at similar metallicity, and a star that is very nitrogen-enhanced ([N/Fe] > +2.45). Our sample consists of luminous evolved stars on the asymptotic giant branch (AGB), eight of which are classified as bona fide semi-regular (SR) variables, as well as low-luminosity stars similar to those of stars on the tip of the red giant branch of stellar clusters in the SMC and LMC. It seems likely that whatever nucleosynthetic process is responsible for these anomalous SMC and LMC stars it is similar to that which caused the common stellar populations in GCs. We interpret these distinctive C-N patterns as observational evidence of the result of tidally shredded GCs in the SMC and LMC. These findings might explain some previous conflicting results over bulge N-rich stars, and broadly help to understand GC formation and evolution. Furthermore, the discovery of such a large population of N-rich AGB stars in the SMC and LMC suggests that multiple stellar populations might not only be exotic events from the past, but can also form at lower redshift.

Keywords: asymptotic giant branch stars; chemically peculiar stars; stellar abundances; globular star clusters; large magellanic cloud; small magellanic cloud; red giant branch; semi-regular variable stars
What Is the Nature of the HESS J1731-347 Compact Object?

Once further confirmed in future analyses, the radius and mass measurement of HESS J1731-347 with $M={0.77}_{-0.17}^{+0.20}\,{M}_{\odot }$ and $R={10.4}_{-0.78}^{+0.86}\,\mathrm{km}$ will be among the lightest and smallest compact objects ever detected. This raises many questions about its nature and opens up the window for different theories to explain such a measurement. In this article, we use the information from Doroshenko et al. on the mass, radius, and surface temperature together with the multimessenger observations of neutron stars to investigate the possibility that HESS J1731-347 is one of the lightest observed neutron star, a strange quark star, a hybrid star with an early deconfinement phase transition, or a dark matter-admixed neutron star. The nucleonic and quark matter are modeled within realistic equation of states (EOSs) with a self-consistent calculation of the pairing gaps in quark matter. By performing the joint analysis of the thermal evolution and mass-radius constraint, we find evidence that within a 1σ confidence level, HESS J1731-347 is consistent with the neutron star scenario with the soft EOS as well as with a strange and hybrid star with the early deconfinement phase transition with a strong quark pairing and neutron star admixed with dark matter.

Keywords: compact objects; neutron stars; dark matter; gravitational waves
When Does the Onset of Multiple Stellar Populations in Star Clusters Occur? III. No Evidence of Significant Chemical Variations in Main-sequence Stars of NGC 419

Recent studies have revealed that the onset age for the presence of multiple stellar populations (MPs) in star clusters seems to correspond to the disappearance of the extended main-sequence turnoff in young clusters, a pattern associated with stellar rotations. A speculative suggestion is that MPs might be caused by the magnetic brake, a stellar evolutionary effect linked to rotation. In this work, we use the young massive cluster NGC 419 as a testbed. We examined if its magnetically baked MS stars would exhibit MPs. Using the deep ultraviolet and visible images observed through the Hubble Space Telescope, combined with a specific color index that is sensitive to the nitrogen (N) abundance, we examined if its late G- and K-type MS stars are affected by N variation. Our analysis reports that the morphology of its GK-type MS is most likely a simple stellar population, and only a negligible probability, which indicates a N variation up to 0.4 dex is present. We therefore conclude that there is no significant N variation among its GK-type MS stars. The absence of a significant chemical variation among the late-type MS stars indicates that MPs might not be a specific pattern of magnetically braked stars.

Keywords: globular star clusters; hertzsprung russell diagram; g dwarf stars; k dwarf stars; stellar populations
Influence of Solar Wind Variations on the Shapes of Venus' Plasma Boundaries Based on Venus Express Observations

The interaction between the solar wind and Venus creates an induced magnetosphere. The regions of the induced magnetosphere are separated by plasma boundaries, where their shapes and sizes are influenced by variations in the surrounding environment. Investigations of the boundaries and their variability can help us understand the solar wind's effect on Venus and unmagnetized planets in general. In this study, the bow shock and ion composition boundary locations are investigated using, for the first time, the full data set of plasma and magnetic field measurements by Venus Express taken during 2006-2014. The locations of the boundaries are examined with respect to upstream conditions and the solar cycle. We find, in agreement with previous studies using Pioneer Venus Orbiter measurements, that the bow shock location is mostly sensitive to the solar cycle and the dynamic pressure and that it exhibits asymmetries in the terminator plane, depending on the direction of the interplanetary magnetic field. The asymmetries are mainly attributed to the asymmetry in the pickup ion distribution and thus mass loading in the magnetosheath. The ion composition boundary on the dayside is found to decrease in altitude with increasing dynamic pressure during solar maximum (2006-2011), but shows no clear trends during solar minimum (2011-2014) conditions.

Keywords: venus; planetary bow shocks; plasma physics
The Saga of M81: Global View of a Massive Stellar Halo in Formation

Recent work has shown that Milky Way-mass galaxies display an incredible range of stellar halo properties, yet the origin of this diversity is unclear. The nearby galaxy M81—currently interacting with M82 and NGC 3077—sheds unique light on this problem. We present a Subaru Hyper Suprime-Cam survey of the resolved stellar populations around M81, revealing M81's stellar halo in never-before-seen detail. We resolve the halo to unprecedented V-band equivalent surface brightnesses of 33 mag arcsec -2 and produce the first-ever global stellar mass density map for a Milky Way-mass stellar halo outside of the Local Group. Using the minor axis, we confirm M81's halo as one of the lowest mass and metal poorest known (M⋆ ≃ 1.16 × 109M⊙, [Fe/H] ≃ -1.2)—indicating a relatively quiet prior accretion history. Yet, our global halo census finds that tidally unbound material from M82 and NGC 3077 provides a substantial infusion of metal-rich material (M⋆ ≃ 5.4 × 108 M⊙, [Fe/H] ≃-0.9). We further show that, following the accretion of its massive satellite M82 (and the LMC-like NGC 3077), M81 will host one of the most massive and metal-rich stellar halos in the nearby universe. Thus, the saga of M81: following a passive history, M81's merger with M82 will completely transform its halo from a low-mass, anemic halo rivaling the Milky Way, to a metal-rich behemoth rivaled only by systems such as M31. This dramatic transformation indicates that the observed diversity in stellar halo properties is primarily driven by diversity in the largest mergers these galaxies have experienced.

Keywords: galaxy mergers; galaxy stellar halos; galaxy formation; galaxy evolution
The 50 Mpc Galaxy Catalog (50 MGC): Consistent and Homogeneous Masses, Distances, Colors, and Morphologies

We assemble a catalog of 15424 nearby galaxies within 50 Mpc with consistent and homogenized mass, distance, and morphological type measurements. Our catalog combines galaxies from HyperLeda, the NASA-Sloan Atlas, and the Catalog of Local Volume Galaxies. Distances for the galaxies combine best-estimates for flow-corrected redshift-based distances with redshift-independent distances. We also compile magnitude and color information for 11740 galaxies. We use the galaxy colors to estimate masses by creating self-consistent color—mass-to-light ratio relations in four bands; we also provide color transformations of all colors into Sloan g–i by using galaxies with overlapping color information. We compile morphology information for 13744 galaxies, and use the galaxy color information to separate early- and late-type galaxies. This catalog is widely applicable for studies of nearby galaxies and for placing these studies in the context of more distant galaxies. We present one application here: a preliminary analysis of the nuclear X-ray activity of galaxies. Out of 1506 galaxies within the sample that have available Chandra X-ray observations, we find that 291 have detected nuclear sources. Of the 291 existing Chandra detections, 249 have log(L X) > 38.3 and available stellar mass estimates. We find that the X-ray active fractions in early-type galaxies are higher than in late-type galaxies, especially for galaxy stellar masses between 109 and 1010.5 M ⊙. We show that these differences may be due at least in part to the increased astrometric uncertainties in late-type galaxies relative to early types.

Keywords: agn host galaxies; catalogs; x-ray sources; supermassive black holes; dwarf galaxies; galaxies
Sensitivity of the Hubble Constant Determination to Cepheid Calibration

Motivated by the large observed diversity in the properties of extragalactic extinction by dust, we reanalyze the Cepheid calibration used to infer the Hubble constant, H 0, from Type Ia supernovae, using Cepheid data in 19 Type Ia supernova host galaxies from Riess et al. and anchor data from Riess et al. Unlike the SH0ES team, we do not enforce a fixed universal color-luminosity relation to correct the Cepheid magnitudes. Instead, we focus on a data-driven method, where the optical colors and near-infrared magnitudes of the Cepheids are used to derive individual color-luminosity relations for each Type Ia supernova host and anchor galaxy. We present two different analyses, one based on Wesenheit magnitudes, resulting in H 0 = 73.2 ± 1.3 km s-1 Mpc-1, a 4.2σ tension with the value inferred from the cosmic microwave background. In the second approach, we calibrate an individual extinction law for each galaxy, with noninformative priors using color excesses, yielding H 0 = 73.9 ± 1.8 km s-1 Mpc-1, in 3.4σ tension with the Planck value. Although the two methods yield similar results, in the latter approach, the Hubble constants inferred from the individual Cepheid absolute distance calibrator galaxies range from H 0 = 68.1 ± 3.5 km s-1 Mpc-1 to H 0 = 76.7 ± 2.0 km s-1 Mpc-1. Taking the correlated nature of H 0 inferred from individual anchors into account, and allowing for individual extinction laws, the Milky Way anchor is in 2.1-3.1 σ tension with the NGC 4258 and Large Magellanic Cloud anchors, depending on prior assumptions regarding the color-luminosity relations and the method used for quantifying the tension.

Keywords: hubble constant; type ia supernovae; cepheid distance; interstellar dust extinction
The Aluminum Abundance of HD 209459 from Far Ultraviolet and Optical Spectra

The abundance of aluminum in the atmosphere of HD 209459 is measured by synthesizing selected optical and ultraviolet lines having high quality atomic data. The Al III resonance lines at 1854.12 and 1862.79 Å are reproduced by an aluminum underabundance of about 0.3 times the solar aluminum abundance. The Al II line at 4663.06 Å is properly fit by a solar aluminum abundance. This difference needs confirmation by the modeling of more lines in both spectral regions.

Keywords: chemically peculiar stars; mercury-manganese stars
Does the Gamma-Ray Binary LS I + 61°303 Harbor a Magnetar?

The high-mass X-ray binary LS I + 61°303 is also cataloged as a gamma-ray binary as a result of frequent outbursts at TeV photon energies. The system has released two soft-gamma flares in the past, suggesting a magnetar interpretation for the compact primary. This inference has recently gained significant traction following the discovery of transient radio pulses, detected in some orbital phases from the system, as the measured rotation and tentative spin-down rates imply a polar magnetic field strength of B p ≳ 1014 G if the star is decelerating via magnetic dipole braking. In this paper, we scrutinize magnetic field estimates for the primary in LS I + 61°303 by analyzing the compatibility of available data with the system's accretion dynamics, spin evolution, age limits, gamma-ray emissions, and radio pulsar activation. We find that the neutron star's age and spin evolution are theoretically difficult to reconcile unless a strong propeller torque is in operation. This torque could be responsible for the bulk of even the maximum allowed spin-down, potentially weakening the inferred magnetic field by more than an order of magnitude.

Keywords: magnetars; magnetic fields; accretion; pulsars
A Uniformly Selected Sample of Low-mass Black Holes in Seyfert 1 Galaxies. III. Radio Sources from the SKA Pathfinders and Beyond

Occupying the intermediate-mass regime of the accretion-jet parameter space, radio continuum emission from active galactic nuclei (AGNs) with black hole mass M BH ≲ 106 M ⊙ (low-mass AGNs) is a valuable probe to the physics of relativistic jets. Yet the number of low-mass AGNs with radio detection is rather limited so far (≈40 in total). In this work, we make two efforts to search for radio counterparts for the largest sample of optically selected low-mass AGNs. First, we collect counterparts from the recent data releases of Square Kilometre Array (SKA) pathfinders such as LOFAR Two-meter Sky Survey (LoTSS). Additionally, we deeply mine in Faint Images of the Radio Sky at Twenty-Centimeters (FIRST), fitting the FIRST images of the optical AGNs with an elaborate procedure optimized to detect faint radio sources. We have obtained 151 radio sources (mainly from the SKA pathfinders), including 102 new reliable sources (signal-to-noise ratio, hereafter S/N, ≥ 5) and 23 new candidates (3.5 ≤ S/N < 5). The majority of these new sources (119 of 125) have flux densities lower than the threshold of the official FIRST catalog. The new sources have rest-frame 20 cm power (P 20 cm) from 1.98 × 1020 to 1.29 × 1023 W Hz‑1. For low-z Seyfert galaxies, P 20 cm correlates with M BH intrinsically and positively, yet only marginally with Eddington ratio L/L Edd. In terms of the log N–log S relation for the expanding Universe, the limiting flux density for the completeness of our LoTSS sources turns out to be 0.45 mJy at 1.4 GHz; i.e., complete to such a flux-density level that is 4 times deeper than the official FIRST catalog.

Keywords: active galactic nuclei; accretion; intermediate-mass black holes; seyfert galaxies; radio continuum emission; relativistic jets
Rapid Optical Flares in the Blazar OJ 287 on Intraday Timescales with TESS

We have analyzed the optical light curves of the blazar OJ 287 obtained with the Transiting Exoplanet Survey Satellite over about 80 days from 2021 October 13 to December 31, with an unprecedented sampling of 2 minutes. Although significant variability has been found during the entire period, we have detected two exceptional flares with flux nearly doubling and then nearly tripling over 2 days in the middle of 2021 November. We went through the light-curve analysis using the excess variance, generalized Lomb-Scargle periodogram, and continuous autoregressive moving average methods and estimated the flux halving/doubling timescales. The most probable shortest variability timescale was found to be 0.38 days in the rising phase of the first flare. We briefly discuss some emission models for the variability in radio-loud active galactic nuclei that could be capable of producing such fast flares.

Keywords: blazars; active galactic nuclei; bl lacertae objects; jets
Reconstructing Functions and Estimating Parameters with Artificial Neural Networks: A Test with a Hubble Parameter and SNe Ia

In this work, we propose a new nonparametric approach for reconstructing a function from observational data using an Artificial Neural Network (ANN), which has no assumptions about the data and is a completely data-driven approach. We test the ANN method by reconstructing functions of the Hubble parameter measurements H(z) and the distance-redshift relation DL(z) of Type Ia supernovae. We find that both H(z) and DL(z) can be reconstructed with high accuracy. Furthermore, we estimate cosmological parameters using the reconstructed functions of H(z) and DL(z) and find the results are consistent with those obtained using the observational data directly. Therefore, we propose that the function reconstructed by ANN can represent the actual distribution of observational data and can be used for parameter estimation in further cosmological research. In addition, we present a new strategy for training and evaluating the neural network, and a code for reconstructing functions using ANN has been developed and will be available.

Keywords: observational cosmology; computational methods; astronomy data analysis; cosmological models; neural networks; cosmological parameters
Molecules with ALMA at Planet-forming Scales (MAPS). VI. Distribution of the Small Organics HCN, C2H, and H2CO

Small organic molecules, such as C2H, HCN, and H2CO, are tracers of the C, N, and O budget in protoplanetary disks. We present high-angular-resolution (10-50 au) observations of C2H, HCN, and H2CO lines in five protoplanetary disks from the Molecules with ALMA at Planet-forming Scales (MAPS) ALMA Large Program. We derive column density and excitation temperature profiles for HCN and C2H, and find that the HCN emission arises in a temperate (20-30 K) layer in the disk, while C2H is present in relatively warmer (20-60 K) layers. In the case of HD 163296, we find a decrease in column density for HCN and C2H inside one of the dust gaps near ~83 au, where a planet has been proposed to be located. We derive H2CO column density profiles assuming temperatures between 20 and 50 K, and find slightly higher column densities in the colder disks around T Tauri stars than around Herbig Ae stars. The H2CO column densities rise near the location of the CO snowline and/or millimeter dust edge, suggesting an efficient release of H2CO ices in the outer disk. Finally, we find that the inner 50 au of these disks are rich in organic species, with abundances relative to water that are similar to cometary values. Comets could therefore deliver water and key organics to future planets in these disks, similar to what might have happened here on Earth. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.

Keywords: protoplanetary disks