adsabs/SciX_UAT_keywords huggingface dataset:
R-process Rain from Binary Neutron Star Mergers in the Galactic Halo

Compact binary mergers involving at least one neutron star are promising sites for the synthesis of the r-process elements found in stars and planets. However, mergers can take place at significant offsets from their host galaxies, with many occurring several kpc from star-forming regions. It is thus important to understand the physical mechanisms involved in transporting enriched material from merger sites in the galactic halo to the star-forming disk. We investigate these processes, starting from an explosive injection event and its interaction with the halo medium. We show that the total outflow mass in compact binary mergers is too low for the material to travel to the disk in a ballistic fashion. Instead, the enriched ejecta is swept into a shell, which decelerates over ≲10 pc scales and becomes corrugated by the Rayleigh-Taylor instability. The corrugated shell is denser than the ambient medium and breaks into clouds that sink toward the disk. These sinking clouds lose thermal energy through radiative cooling, and are also ablated by shearing instabilities. We present a dynamical heuristic that models these effects to predict the delay times for delivery to the disk. However, we find that turbulent mass ablation is extremely efficient and leads to the total fragmentation of sinking r-process clouds over ≲10 pc scales. We thus predict that enriched material from halo injection events quickly assimilates into the gas medium of the halo and that enriched mass flow to the disk could only be accomplished through turbulent diffusion or large-scale inflowing mass currents.

Keywords: r-process; galaxy chemical evolution; neutron stars; chemical enrichment; nucleosynthesis
Denoising Diffusion Probabilistic Models to Predict the Density of Molecular Clouds

We introduce the state-of-the-art deep-learning denoising diffusion probabilistic model as a method to infer the volume or number density of giant molecular clouds (GMCs) from projected mass surface density maps. We adopt magnetohydrodynamic simulations with different global magnetic field strengths and large-scale dynamics, i.e., noncolliding and colliding GMCs. We train a diffusion model on both mass surface density maps and their corresponding mass-weighted number density maps from different viewing angles for all the simulations. We compare the diffusion model performance with a more traditional empirical two-component and three-component power-law fitting method and with a more traditional neural network machine-learning approach. We conclude that the diffusion model achieves an order-of-magnitude improvement on the accuracy of predicting number density compared to that by other methods. We apply the diffusion method to some example astronomical column density maps of Taurus and the infrared dark clouds G28.37+0.07 and G35.39-0.33 to produce maps of their mean volume densities.

Keywords: interstellar medium; astrostatistics; astrostatistics techniques; molecular clouds; magnetohydrodynamics; convolutional neural networks
Multifilter Observations of the Complex Periodic Variations in the M-dwarf Star RIK 90

The star RIK 90 is a member of a group of recently discovered young T Tauri stars showing complex periodic modulations of their light output, which have been difficult to explain. As one of the brightest, and having a relatively short period, RIK 90 is of particular interest. Thirty-three hours of contemporaneous BVRCIC photometry of the star are presented in this paper. An independent secondary periodicity was removed and the remainder of the data phased with the primary 0.25955 day period and smoothed to reveal the detailed structure of the light curves. The ratios of the amplitude in B to those in VRCIC are 1.2, 1.5, and 1.8. It is found that a collection of five cool starspots with temperatures in the range 2230-2550 K provides an excellent match to almost all observations, small-scale features in the IC-band light curve being the notable exception. Starspot modeling of K2 observations of RIK 90 was also attempted. The morphology of the K2 light curve is entirely different from that discussed in this paper but could be accurately modeled by four dark starspots. In order to put these results into context, 15 other distinct K2 light curves belonging to 10 similarly variable T Tauri stars were also studied. Excellent fits were obtained to some of these with models consisting of large cool starspots. The majority of the remaining light curves could be modeled with a combination of hot and cold starspots.

Keywords: starspots; pre-main sequence stars; t tauri stars; late-type dwarf stars; peculiar variable stars; variable stars
Revealing Ionization Conditions of Sz 102 with Spatially Resolved [Ne III] Microjets

Forbidden neon emission lines from small-scale microjets can probe high-energy processes in low-mass young stellar systems. We obtained spatially resolved [Ne III] spectra in the microjets from the classical T Tauri Star Sz 102 using the Hubble Space Telescope Imaging Spectrograph at a spatial resolution of ∼0"1. The blueshifted and redshifted [Ne III] emission both peak in intensity within ∼0"1 of the star and gradually decay along the flow outward to ∼0"24. The spatial distribution and extent of the [Ne III] microjet is consistent with a jet that is ionized close to the base and subsequently recombines on a longer timescale than the flow time. Ca II H and K lines are also detected from the redshifted microjet with a line full-width at half-maximum of ∼170 km s-1, consistent with those of other forbidden emission lines, atop a 300 km s-1 wide stellar component. The launching radius of the Sz 102 jet, inferred from the observed line centroids and the range of inclination angles and stellar masses from the literature, is on the order of ∼0.03 au. The possible proximity of the launching region to the star allows immediate ionization without distance dilution from the circumstellar ionization sources, most likely keV X-ray flares generated by magnetic reconnection events in the star--disk system, to sustain the observed [Ne III] flux.

Keywords: classical t tauri stars; jets; x-ray stars
Testing the High-latitude Curvature Effect of Gamma-Ray Bursts with Fermi Data: Evidence of Bulk Acceleration in Prompt Emission

When a gamma-ray burst (GRB) emitter stops emission abruptly, the observer receives rapidly fading emission from high latitudes with respect to the line of sight, known as the "curvature effect." Identifying such emission from GRB prompt-emission lightcurves would constrain the radius of prompt emission from the central engine and the composition of GRB jets. We perform a dedicated search of high-latitude emission (HLE) through spectral and temporal analyses of a sample of single-pulse bursts detected by the Gamma-ray Burst Monitor on board the Fermi satellite. We identify HLE from a subsample of bursts and constrain the emission radius to be RGRB ∼ (1015-1016) cm from the central engine. Some bursts have the HLE decay faster than predicted by a constant Lorentz factor jet, suggesting that the emission region is undergoing acceleration during prompt emission. This supports the Poynting-flux-dominated jet composition for these bursts. The conclusion is consistent with previous results drawn from spectral-lag modeling of prompt emission and HLE analysis of X-ray flares.

Keywords: gamma-ray bursts; relativistic jets; astronomy data analysis
Spectral Classification and Ionized Gas Outflows in z ∼ 2 WISE-selected Hot Dust-obscured Galaxies

We present Very Large Telescope/XSHOOTER rest-frame UV-optical spectra of 10 hot dust-obscured galaxies (Hot DOGs) at z ∼ 2 to investigate active galactic nucleus (AGN) diagnostics and assess the presence and effect of ionized gas outflows. Most Hot DOGs in this sample are narrow-line-dominated AGNs (type 1.8 or higher) and have higher Balmer decrements than typical type 2 quasars. Almost all (8/9) sources show evidence for ionized gas outflows in the form of broad and blueshifted [O III] profiles, and some sources have such profiles in Hα (5/7) or [O II] (3/6). Combined with the literature, these results support additional sources of obscuration beyond the simple torus invoked by AGN unification models. Outflow rates derived from the broad [O III] line (≳103 M⊙ yr-1) are greater than the black hole accretion and star formation rates, with feedback efficiencies (∼0.1%-1%) consistent with negative feedback to the host galaxy's star formation in merger-driven quasar activity scenarios. We find that the broad emission lines in luminous, obscured quasars are often better explained by outflows within the narrow-line region and caution that black hole mass estimates for such sources in the literature may have substantial uncertainty. Regardless, we find lower bounds on the Eddington ratio for Hot DOGs near unity.

Keywords: active galaxies
Interpreting Observations of Absorption Lines in the Circumgalactic Medium with a Turbulent Medium

Single-phase photoionization equilibrium (PIE) models are often used to infer the underlying physical properties of galaxy halos probed in absorption with ions at different ionization potentials. To incorporate the effects of turbulence, we use the Models of Agitated and Illuminated Hindering and Emitting Media (MAIHEM) code to model an isotropic turbulent medium exposed to a redshift-zero metagalactic UV background, while tracking the ionizations, recombinations, and species-by-species radiative cooling for a wide range of ions. By comparing observations and simulations over a wide range of turbulent velocities, densities, and metallicity with a Markov chain Monte Carlo technique, we find that MAIHEM models provide an equally good fit to the observed low-ionization species compared to PIE models, while reproducing at the same time high-ionization species such as Si IV and O VI. By including multiple phases, MAIHEM models favor a higher metallicity (Z/Z⊙ ≈ 40%) for the circumgalactic medium compared to PIE models. Furthermore, all of the solutions require some amount of turbulence (σ3D $\geqslant $ 26 km s-1). Correlations between turbulence, metallicity, column density, and impact parameter are discussed alongside mechanisms that drive turbulence within the halo.

Keywords: astrochemistry; circumgalactic medium; markov chain monte carlo
Radiative Acceleration of Dense Circumstellar Material in Interacting Supernovae

Early-time light curves/spectra of some hydrogen-rich supernovae (SNe) provide solid evidence of the existence of confined, dense circumstellar matter (CSM) surrounding dying massive stars. We numerically and analytically study the radiative acceleration of CSM in such systems, where the radiation is mainly powered by the interaction between the SN ejecta and the CSM. We find that the acceleration of the unshocked dense CSM ahead of the shock is larger for massive and compact CSM, with velocities reaching up to ~103 km s-1 for a CSM of order 0.1 M ⊙ confined within ~1015 cm. We show that the dependence of the acceleration on the CSM density helps us explain the diversity of the CSM velocity inferred from the early spectra of some Type II SNe. For explosions in even denser CSM, radiative acceleration can affect the dissipation of strong collisionless shocks formed after the shock breakout, which would affect early nonthermal emission expected from particle acceleration.

Keywords: type ii supernovae; circumstellar matter; hydrodynamics
Pulse Timing Discovery of a Three-day Companion to the Hot Subdwarf BPM 36430

Hot subdwarf B stars are core-helium-burning objects that have undergone envelope stripping, likely by a binary companion. Using high-speed photometry from the Transiting Exoplanet Survey Satellite, we have discovered the hot subdwarf BPM 36430 is a hybrid sdBVrs pulsator exhibiting several low-amplitude g-modes and a strong p-mode pulsation. The latter shows a clear, periodic variation in its pulse arrival times. Fits to this phase oscillation imply BPM 36430 orbits a barycenter approximately 10 light-seconds away once every 3.1 days. Using the CHIRON echelle spectrograph on the CTIO 1.5 m telescope, we confirm the reflex motion by detecting a radial-velocity variation with semiamplitude, period, and phase in agreement with the pulse timings. We conclude that a white dwarf companion with minimum mass of ≈0.42 M ⊙ orbits BPM 36430. Our study represents only the second time a companion orbiting a pulsating hot subdwarf or white dwarf has been detected from pulse timings and confirmed with radial velocities.

Keywords: binary stars; stellar pulsations
CHIANTI—An Atomic Database for Emission Lines. XVI. Version 10, Further Extensions

We present version 10 of the CHIANTI package. In this release, we provide updated atomic models for several helium-like ions and for all the ions of the beryllium, carbon, and magnesium isoelectronic sequences that are abundant in astrophysical plasmas. We include rates from large-scale atomic structure and scattering calculations that are in many cases a significant improvement over the previous version, especially for the Be-like sequence, which has useful line diagnostics to measure the electron density and temperature. We have also added new ions and updated several of them with new atomic rates and line identifications. Also, we have added several improvements to the IDL software, to speed up the calculations and to estimate the suppression of dielectronic recombination.

Keywords: atomic spectroscopy; line intensities; atomic data benchmarking; atomic physics
Transit Search for Exoplanets around Alpha Centauri A and B with ASTERIA

Alpha Centauri is a triple star system with two Sun-like stars, α Cen A (V = 0.01) and B (V = 1.33), and a third fainter red dwarf star, Proxima Centauri. Most current transit missions cannot produce precision photometry of α Cen A and B as their detectors saturate for these very bright stars. The Arcsecond Space Telescope Enabling Research in Astrophysics (ASTERIA) was a technology demonstration mission that successfully demonstrated two key technologies necessary for precision photometry achieving line-of-sight fine-pointing stability of 0.5″ rms and focal plane temperature control of ±0.01 K over a period of 20 minutes. The payload consisted of a 6.7 cm aperture diameter refractive camera and used a scientific complementary metal-oxide semiconductor detector that enabled monitoring of the brightest stars without saturating. We obtained spatially unresolved (blended) observations of α Cen A and B during opportunistic science campaigns as part of ASTERIA's extended mission. The resulting 1σ photometric precision for the blended α Cen A and B data is 250 ppm (parts per million) per 9 s exposure. We do not find evidence of transits in the blended data. We establish limits for transiting exoplanets around both α Cen A and B using transit signal injection and recovery tests. We find that ASTERIA is sensitive to planets with radii as small as 3.0 R⊕ around α Cen A and 3.7 R⊕ around α Cen B, corresponding to signals of ∼500 ppm (signal-to-noise ratio = 5.0) in the blended data, with periods ranging from 0.5 to 6 days.

Keywords: exoplanets; transit photometry; space telescopes
Low-mass Quiescent Galaxies Are Small in Isolated Environments: Environmental Dependence of the Mass-Size Relation of Low-mass Quiescent Galaxies

We study the mass-size relation of quiescent galaxies across various environments, with a particular focus on its environmental dependence at the low-mass part of $\mathrm{log}({M}_{\mathrm{star}}/{M}_{\odot })\lesssim 10.0$ . Our sample consists of 13,667 quiescent galaxies with $\mathrm{log}({M}_{\mathrm{star}}/{M}_{\odot })\geqslant 9.4$ and 0.01 < z < 0.04 from the Sloan Digital Sky Survey. We discover that the mass-size relation of low-mass quiescent galaxies (LQGs) with $\mathrm{log}({M}_{\mathrm{star}}/{M}_{\odot })\lesssim 10.0$ depends on their environment, with LQGs in the highest-density environments exhibiting an average size ~70% larger than those in isolated environments. Moreover, the slope of the mass-size relation for LQGs in high-density environments is significantly shallower than that of their counterparts in isolated environments. This is in contrast with high-mass quiescent galaxies with $\mathrm{log}({M}_{\mathrm{star}}/{M}_{\odot })\gtrsim 10.5$ that show a nearly identical mass-size relation across all environments. Combined with additional discoveries that the mass-size relation slopes of LQGs and star-forming galaxies are similar to each other in high-density environments, and that LQGs in higher-density environments exhibit more disk-like structures, our results support the idea that LQGs in high-density environments have evolved from star-forming galaxies through environmental effects, which are capable of causing their quenching and transformation into quiescent galaxies. With the aid of an analysis of merger rates for simulated galaxies from a cosmological galaxy formation simulation, we suggest that the steep slope and low normalization of the mass-size relation of LQGs in the lowest-density environments may originate from recent gas-rich mergers, which occur over 10-30 times more frequently in the progenitors of LQGs in the lowest-density environments than in their counterparts in high-density environments at low redshifts.

Keywords: early-type galaxies; galaxy environments; galaxy evolution; galaxy formation; galaxy structure; quenched galaxies; galaxy mergers
Skeletal Kinetics Reduction for Astrophysical Reaction Networks

A novel methodology is developed to extract accurate skeletal reaction models for nuclear combustion. Local sensitivities of isotope mass fractions with respect to reaction rates are modeled based on the forced optimally time-dependent (f-OTD) scheme. These sensitivities are then analyzed temporally to generate skeletal models. The methodology is demonstrated by conducting skeletal reduction of constant density and temperature burning of carbon and oxygen relevant to Type Ia supernovae (SNe Ia). The 495-isotopes Torch model is chosen as the detailed reaction network. A map of maximum production of 56Ni in SNe Ia is produced for different temperatures, densities, and proton-to-neutron ratios. The f-OTD simulations and the sensitivity analyses are then performed with initial conditions from this map. A series of skeletal models are derived and their performances are assessed by comparison against currently existing skeletal models. Previous models have been constructed intuitively by assuming the dominance of α-chain reactions. The comparison of the newly generated skeletal models against previous models is based on the predicted energy release and 44Ti and 56Ni abundances by each model. The consequences of y e ≠ 0.5 in the initial composition are also explored where y e is the electron fraction. The simulated results show that 56Ni production decreases by decreasing y e as expected, and that the 43Sc is a key isotope in proton and neutron channels toward 56Ni production. It is shown that an f-OTD skeletal model with 150 isotopes can accurately predict the 56Ni abundance in SNe Ia for y e ≲ 0.5 initial conditions.

Keywords: stellar nucleosynthesis; reaction rate equations; stellar physics; astrophysical fluid dynamics; nuclear astrophysics
Testing Velocity-field Lensing on IllustrisTNG Galaxies

Weak gravitational lensing shear could be measured far more precisely if information about unlensed attributes of source galaxies were available. Disk galaxy velocity fields supply such information, at least in principle, with idealized models predicting orders of magnitude more Fisher information when velocity-field observations are used to complement images. To test the level at which realistic features of disk galaxies (warps, bars, spiral arms, and other substructure) inject noise or bias into such shear measurements, we fit an idealized disk model, including shear, to unsheared galaxies in the Illustris TNG100 simulation. The inferred shear thus indicates the extent to which unmodeled galaxy features inject noise and bias. We find that γ +, the component of shear parallel to the galaxy's first principal axis, is highly biased and noisy because disks violate the assumption of face-on circularity, displaying a range of intrinsic axis ratios (0.85 ± 0.11). The other shear component, γ ×, shows little bias and is well-described by a double Gaussian distribution with central core scatter σ core ≈ 0.03, with low-amplitude, broad wings. This is the first measurement of the natural noise floor in the proposed velocity-field lensing technique. We conclude that the technique will achieve impressive precision gains for measurements of γ ×, but little gain for measurements of γ +.

Keywords: gravitational lensing; gravitational lensing shear; weak gravitational lensing; galaxy kinematics; magnetohydrodynamical simulations
Cross-match between the Latest Swift-BAT and Fermi-LAT Catalogs

We report the results of a cross-match study between the hard X-ray and GeV gamma-ray catalogs, by making use of the latest 105 month Swift-Burst Alert Telescope (BAT) and 10 yr Fermi-Large Area Telescope (LAT) catalogs, respectively. The spatial cross-matching between the two catalogs results in the matching of 132 point-like sources, including ~5% of false-match sources. Additionally, 24 sources that have been identified as the same identifications are matched. Among the 75 extended sources in the Fermi-LAT catalog, 31 sources have spatial coincidences with at least one Swift-BAT source inside their extent. All the matched sources consist of blazars (>60%), pulsars and pulsar wind nebulae (~13%), radio galaxies (~7%), binaries (~5%), and others. Compared to the original catalogs, the matched sources are characterized by a double-peaked photon index distribution, higher flux, and larger gamma-ray variability index. This difference arises from the different populations of sources, particularly the large proportion of blazars (i.e., flat-spectrum radio quasar and BL Lac). We also report 13 cross-matched and unidentified sources. The matched sources in this study would be promising in the intermediate energy band between the hard X-ray and GeV gamma-ray observations, that is the unexplored MeV gamma-ray domain.

Keywords: catalogs; x-ray sources; gamma-ray sources; active galactic nuclei
Electron Density Reconstruction of Solar Coronal Mass Ejections Based on a Genetic Algorithm: Method and Application

We present a new method to reconstruct the three-dimensional electron density of coronal mass ejections (CMEs) based on a genetic algorithm, namely the genetic reconstruction method (GRM). GRM is first applied to model CMEs with different orientations and shapes. A set of analytic model CMEs from Gibson and Low is employed to produce synthetic CME images for GRM reconstruction. Model CMEs with longitudes of 0°, 45°, 90°, 135°, and 180° and latitudes of 0°, 15°, 30°, and 45° are used to test the performance of GRM. The model CMEs are obscured with a simulated occulter of a coronagraph to determine the influence of CME brightness incompleteness. We add random noise to some synthetic CME images to test the performance of GRM. The CME reconstructions are carried out using synthetic data from Solar Terrestrial Relations Observatory (STEREO) A and B with a separation angle of 90° and from STEREO A and the Solar and Heliospheric Observatory (SOHO) with a separation angle of 73°. The Pearson correlation coefficient and the mean relative absolute deviation are calculated to analyze the similarities in brightness and electron density between the model and reconstructed CMEs. Comparisons based on the similarity analysis under various conditions stated above give us valuable insights into the advantages and limitations of GRM reconstruction. The method is then applied to real coronagraph data from STEREO A and B, and SOHO on 2013 September 30.

Keywords: solar coronal mass ejections; solar activity; line of sight; field of view