adsabs/SciX_UAT_keywords huggingface dataset:
Faint Active Galactic Nuclei Favor Unexpectedly Long Inter-band Time Lags

Inconsistent conclusions are obtained from recent active galactic nuclei (AGNs) accretion disk inter-band time-lag measurements. While some works show that the measured time lags are significantly larger (by a factor of ∼3) than the theoretical predictions of the Shakura & Sunyaev disk (SSD) model, others find that the time-lag measurements are consistent with (or only slightly larger than) that of the SSD model. These conflicting observational results might be symptoms of our poor understanding of AGN accretion physics. Here we show that sources with larger-than-expected time lags tend to be less luminous AGNs. Such a dependence is unexpected if the inter-band time lags are attributed to the light-travel-time delay of the illuminating variable X-ray photons to the static SSD. If, instead, the measured inter-band lags are related not only to the static SSD but also to the outer broad emission-line regions (BLRs; e.g., the blended broad emission lines and/or diffuse continua), our result indicates that the contribution of the non-disk BLR to the observed ultraviolet/optical continuum decreases with increasing luminosity (L), i.e., an anti-correlation resembling the well-known Baldwin effect. Alternatively, we argue that the observed dependence might be a result of coherent disk thermal fluctuations as the relevant thermal timescale, τTH ∝ L0.5. With future accurate measurements of inter-band time lags, the above two scenarios can be distinguished by inspecting the dependence of inter-band time lags upon either the BLR components in the variable spectra or the timescales.

Keywords: accretion; active galactic nuclei; supermassive black holes
Improved Background Model for the Large Area X-Ray Proportional Counter (LAXPC) Instrument on board AstroSat

We present an improved background model for the Large Area X-ray Proportional Counter (LAXPC) detectors on board AstroSat. Because of the large collecting area and high pressure, the LAXPC instrument has a large background count rate, which varies during the orbit. Apart from the variation with latitude and longitude during the orbit there is a prominent quasi-diurnal variation which has not been previously modeled. Using over 5 yr of background observations, we determined the period of the quasi-diurnal variation to be 84,495 s and using this period it is possible to account for the variation and also identify time intervals where the fit is not good. These lead to a significant improvement in the background model. The quasi-diurnal variation can be ascribed to the changes in charged particle flux in the near-Earth orbit.

Keywords: space vehicle instruments
Pipeline Provenance for Analysis, Evaluation, Trust or Reproducibility

Data volumes and rates of research infrastructures will continue to increase in the upcoming years and impact how we interact with their final data products. Little of the processed data can be directly investigated and most of it will be automatically processed with as little user interaction as possible. Capturing all necessary information of such processing ensures reproducibility of the final results and generates trust in the entire process. We present Pipeline pRovenance for Analysis, Evaluation, Trust Or Reproducibility (PRAETOR), a software suite that enables automated generation, modeling, and analysis of provenance information of Python pipelines. Furthermore, the evaluation of the pipeline performance, based upon a user defined quality matrix in the provenance, enables the first step of machine learning processes, where such information can be fed into dedicated optimization procedures.

Keywords: astronomy software; software documentation; interdisciplinary astronomy
Investigating the Future Potential of an Upgraded ALMA to Image Planet-forming Disks at Sub-astronomical-unit Scales

In recent years, ALMA has been able to observe large-scale substructures within protoplanetary disks. Comparison with the predictions from models of planet-disk interactions has indicated that most of these disk substructures can be explained by the presence of planets with the mass of Neptune or larger at orbital radii of ≈5-100 au. Better resolution is needed to observe structures closer to the star, where terrestrial planets are expected to form, as well as structures opened by planets with masses lower than Neptune. We investigate the capabilities of a possible extension to ALMA that would double the longest baseline lengths in the array to detect and resolve disk substructures opened by Earth-mass and super-Earth planets at orbital radii of 1-5 au. By simulating observations of a family of disk models using this extended configuration in ALMA Bands 6 and 7, we show that an upgraded ALMA would detect gaps in disks formed by super-Earths as close as 1 au, as well as Earth-mass planets down to 2-3 au from the young host stars in nearby star-forming regions.

Keywords: protoplanetary disks
GMC Collisions as Triggers of Star Formation. VII. The Effect of Magnetic Field Strength on Star Formation

We investigate the formation of stars within giant molecular clouds (GMCs) evolving in environments of different global magnetic field strength and large-scale dynamics. Building upon a series of magnetohydrodynamic simulations of noncolliding and colliding GMCs, we employ density- and magnetically regulated star formation subgrid models in clouds that range from moderately magnetically supercritical to near critical. We examine gas and star cluster morphologies, magnetic field strengths and relative orientations, prestellar core densities, temperatures, mass-to-flux ratios and velocities, star formation rates and efficiencies over time, spatial clustering of stars, and kinematics of the stars and natal gas. The large-scale magnetic criticality of the region greatly affects the overall gas evolution and star formation properties. GMC collisions enhance star formation rates and efficiencies in magnetically supercritical conditions, but may actually inhibit them in the magnetically critical case. This may have implications for star formation in different Galactic environments such as the Galactic Center and the main Galactic disk.

Keywords: star formation; molecular clouds; interstellar magnetic fields; interstellar medium
Evolution of the Deterministic Collapse Barrier of the Field Clusters as a Probe of Cosmology

The collapse barrier, δc, of the field clusters located in the low-density environment is deterministic rather than diffusive, unlike that of the wall counterparts located in the superclusters. Analyzing the data from the Mira-Titan simulations for 11 different cosmologies, including the standard ΛCDM cosmology at various redshifts, we investigate the evolution of the deterministic collapse barrier of the field clusters and explore its dependence on the background cosmology. Regardless of the background cosmology, the deterministic δc exhibits a universal behavior of having a higher value than the Einstein-de Sitter spherical collapse barrier height of δsc = 1.686, at z = 0, but gradually converging down to δsc as the dominance of dark energy diminishes with the increment of z. A significant difference among different cosmologies, however, is found in its convergence rate, as well as in the critical redshift zc, at which δc = δsc. Showing that the convergence rate and critical redshifts can distinguish even between the degenerate cosmologies, which yield almost identical linear growth factor and cluster mass functions, we suggest that the evolution of the deterministic collapse barrier of the field clusters should be a powerful complementary probe of cosmology.

Keywords: large-scale structure of the universe; cosmological models
The Small Separation A-star Companion Population: First Results with CHARA/MIRC-X

We present preliminary results from our long-baseline interferometry (LBI) survey to constrain the multiplicity properties of intermediate-mass A-type stars within 80 pc. Previous multiplicity studies of nearby stars exhibit orbital separation distributions well fitted with a lognormal with peaks >15 au, increasing with primary mass. The A-star multiplicity survey of De Rosa et al., sensitive beyond 30 au but incomplete below 100 au, found a lognormal peak around 390 au. Radial velocity surveys of slowly rotating, chemically peculiar Am stars identified a significant number of very close companions with periods ≤5 days, ~0.1 au, a result similar to surveys of O- and B-type primaries. With the improved performance of LBI techniques, we can probe these close separations for normal A-type stars where other surveys are incomplete. Our initial sample consists of 27 A-type primaries with estimated masses between 1.44 and 2.49 M ⊙ and ages 10-790 Myr, which we observed with the MIRC-X instrument at the CHARA Array. We use the open-source software CANDID to detect five companions, three of which are new, and derive a companion frequency of ${0.19}_{-0.06}^{+0.11}$ over mass ratios of 0.25-1.0 and projected separations of 0.288-5.481 au. We find a probability of 10-6 that our results are consistent with extrapolations based on previous models of the A-star companion population over the mass ratios and separations sampled. Our results show the need to explore these very close separations to inform our understanding of stellar formation and evolution processes.

Keywords: intermediate-type stars; multiple stars; binary stars; star formation; long baseline interferometry; close binary stars; stellar types; chemically peculiar stars
K2 Photometry on Oscillation Mode Variability: The New Pulsating Hot B Subdwarf Star EPIC 220422705

We present an analysis of oscillation mode variability in the hot B subdwarf star EPIC 220422705, a new pulsator discovered from ~78 days of K2 photometry. The high-quality light curves provide a detection of 66 significant independent frequencies, from which we identified nine incomplete potential triplets and three quintuplets. Those g- and p-multiplets give rotation periods of ~36 and 29 days in the core and at the surface, respectively, potentially suggesting a slightly differential rotation. We derived a period spacing of 268.5 s and 159.4 s for the sequence of dipole and quadrupole modes, respectively. We characterized the precise patterns of amplitude and frequency modulations (AM and FM) of 22 frequencies with high enough amplitude for our science. Many of them exhibit intrinsic and periodic patterns of AM and FM, with periods on a timescale of months as derived by the best fitting and Markov Chain Monte Carlo test. The nonlinear resonant mode interactions could be a natural interpretation for such AMs and FMs after other mechanisms are ruled out. Our results are the first step to building a bridge between mode variability from K2 photometry and the nonlinear perturbation theory of stellar oscillation.

Keywords: b subdwarf stars; stellar oscillations; photometry; pulsation frequency method; pulsation modes; multi-periodic pulsation
Refined Mass and Geometric Measurements of the High-mass PSR J0740+6620

We report results from continued timing observations of PSR J0740+6620, a high-mass, 2.8 ms radio pulsar in orbit with a likely ultracool white dwarf companion. Our data set consists of combined pulse arrival-time measurements made with the 100 m Green Bank Telescope and the Canadian Hydrogen Intensity Mapping Experiment telescope. We explore the significance of timing-based phenomena arising from general relativistic dynamics and variations in pulse dispersion. When using various statistical methods, we find that combining ~1.5 yr of additional, high-cadence timing data with previous measurements confirms and improves on previous estimates of relativistic effects within the PSR J0740+6620 system, with the pulsar mass ${m}_{p}=\,{2.08}_{-0.07}^{+0.07}\ {M}_{\odot }$ (68.3% credibility) determined by the relativistic Shapiro time delay. For the first time, we measure secular variation in the orbital period and argue that this effect arises from apparent acceleration due to significant transverse motion. After incorporating contributions from Galactic differential rotation and off-plane acceleration in the Galactic potential, we obtain a model-dependent distance of $d\,=\,{1.14}_{-0.15}^{+0.17}$ kpc (68.3% credibility). This improved distance confirms the ultracool nature of the white dwarf companion determined from recent optical observations. We discuss the prospects for future observations with next-generation facilities, which will likely improve the precision on mp for J0740+6620 by an order of magnitude within the next few years.

Keywords: neutron stars; pulsars; general relativity; compact objects; binary pulsars
Spectral Analysis of Gravity Waves in the Martian Thermosphere during Low Solar Activity Based on MAVEN/NGIMS Observations

Gravity waves (GWs) are important for vertical coupling between the lower and upper atmosphere on Mars. Saturated GWs will promote the acceleration of mean flow and turbulence generation, causing diffuse transport of energy and momentum. We analyze the spectral characteristics of GWs in the thermosphere on Mars during the low solar activity of Martian Year (MY) 35, based on CO2 density measured by the Neutral Gas and Ion Mass Spectrometer (NGIMS) on board Mars Atmosphere and Volatile EvolutioN (MAVEN). The results are compared with those of MY33 at the higher solar activity. The vertical wavenumber spectral density obtained in the Martian thermosphere is similar to the semi-empirically predicted saturation spectrum in the Earth's atmosphere, with a logarithmic spectral slope around -3. The average spectral density of GWs shows saturation between 160 and 200 km and decreases with increasing altitude. Compared to MY33, GW activity is larger and less attenuated in MY35 as it propagates upward, implying that waves experience more favorable propagation conditions during low solar activity. Also, the dependence of GW activity on local time during this period is found to be different from previous studies, with the strongest GWs in the spring of MY35 occurring within 6-12 hr on the dayside, suggesting that the amplitude of the GWs in the Martian thermosphere during low solar activity is less controlled by the background temperature and is subject to dissipative effects of other factors, such as molecular viscosity and thermal conduction.

Keywords: mars; internal waves; thermosphere; solar activity
Assessment of the Roche and the Darwin-Radau Approximations for Rotating Astrophysical Objects

Assessment of two of the frequently used approximations for rotating astrophysical objects, the Roche and the Darwin-Radau approximations, is performed by comparing the rotational frequencies computed by these approximations with those of self-consistent numerical hydrostatic solutions. Overall, the Darwin-Radau approximation performs better, though the error increases as the rotational oblateness increases. It should be also remarked that the Darwin-Radau approximation does not provide a closed-form formula of the frequency as a function of the oblateness.

Keywords: stellar rotation
Electron Vorticity at Dipolarization Fronts

Using magnetospheric multiscale high-resolution measurements, we present the first comprehensive investigation of electron vorticity developing at earthward-propagating dipolarization fronts (DFs). Superposed epoch analysis reveals that electron vorticity increases at and behind the DFs, with its average magnitude slightly larger than lower hybrid frequency, indicating that vorticity is related to Hall dynamics at the DFs. Vorticity at the DFs exhibits clear anisotropy, ω⊥ > ω∥, where ω⊥, ω∥ are the components perpendicular and parallel to local magnetic field, respectively. Parametric dependence analysis shows that electron vorticity is well anticorrelated with electron density. We find that in a statistical sense, vorticity-induced magnetic field perturbations are not significant, although in a few cases vorticity can generate intense magnetic field perturbations. This study can improve our current understanding of the DF dynamics.

Keywords: solar magnetic reconnection; space plasmas; plasma physics
Constraining the Cosmic Baryon Distribution with Fast Radio Burst Foreground Mapping

The dispersion measure of fast radio bursts (FRBs) encodes the integrated electron density along the line of sight, which is typically dominated by the intergalactic medium contribution in the case of extragalactic FRBs. In this paper, we show that incorporating wide-field spectroscopic galaxy survey data in the foreground of localized FRBs can significantly improve constraints on the partition of diffuse cosmic baryons. Using mock dispersion measures and realistic light-cone galaxy catalogs derived from the Millennium simulation, we define spectroscopic surveys that can be carried out with 4 and 8 m class wide-field spectroscopic facilities. On these simulated surveys, we carry out Bayesian density reconstructions in order to estimate the foreground matter density field. In comparison with the "true" matter density field, we show that these can help reduce the uncertainties in the foreground structures by ~2-3× compared to cosmic variance. We calculate the Fisher matrix to forecast that N = 30 (96) localized FRBs should be able to constrain the diffuse cosmic baryon fraction to ~10% (~5%) and parameters governing the size and baryon fraction of galaxy circumgalactic halos to within ~20%-25% (~8%-12%). From the Fisher analysis, we show that the foreground data increase the sensitivity of localized FRBs toward our parameters of interest by ~25×. We briefly introduce FLIMFLAM, an ongoing galaxy redshift survey that aims to obtain foreground data on ~30 localized FRB fields.

Keywords: missing mass; intergalactic gas; circumgalactic medium; cosmic web; redshift surveys
Dimorphos Orbit Determination from Mutual Events Photometry

The NASA Double Asteroid Redirection Test spacecraft successfully impacted the Didymos–Dimorphos binary asteroid system on 2022 September 26 UTC. We provide an update to its preimpact mutual orbit and estimate the postimpact physical and orbital parameters, derived using ground-based photometric observations taken from 2022 July to 2023 February. We found that the total change of the orbital period was ‑33.240 ± 0.072 minutes (all uncertainties are 3σ). We obtained the eccentricity of the postimpact orbit to be 0.028 ± 0.016 and the apsidal precession rate was 7.3 ± 2.0 degrees day‑1 from the impact to 2022 December 2. The data taken later in 2022 December to 2023 February suggest that the eccentricity dropped close to zero or the orbit became chaotic approximately 70 days after the impact. Most of the period change took place immediately after the impact, but in the few weeks following the impact it was followed by an additional change of $-{27}_{-58}^{+19}$ s or ‑19 ± 18 s (the two values depend on the approach we used to describe the evolution of the orbital period after the impact—an exponentially decreasing angular acceleration or the assumption of a constant orbital period, which changed abruptly some time after the impact, respectively). We estimate the preimpact Dimorphos–Didymos size ratio was 0.223 ± 0.012 and the postimpact is 0.202 ± 0.018, which indicate a marginally significant reduction of Dimorphos' volume by (9 ± 9)% as the result of the impact.

Keywords: asteroid dynamics; asteroid satellites; near-earth objects
Impact of Magnetorotational Instability on Grain Growth in Protoplanetary Disks. II. Increased Grain Collisional Velocities

Turbulence is the dominant source of collisional velocities for grains with a wide range of sizes in protoplanetary disks. So far, only Kolmogorov turbulence has been considered for calculating grain collisional velocities, despite the evidence that turbulence in protoplanetary disks may be non-Kolmogorov. In this work, we present calculations of grain collisional velocities for arbitrary turbulence models characterized by power-law spectra and determined by three dimensionless parameters: the slope of the kinetic energy spectrum, the slope of the autocorrelation time, and the Reynolds number. The implications of our results are illustrated by numerical simulations of the grain size evolution for different turbulence models. We find that for the modeled cases of the Iroshnikov-Kraichnan turbulence and the turbulence induced by the magnetorotational instabilities, collisional velocities of small grains are much larger than those for the standard Kolmogorov turbulence. This leads to faster grain coagulation in the outer regions of protoplanetary disks, resulting in rapid increase of dust opacity in millimeter wavelength and possibly promoting planet formation in very young disks.

Keywords: interstellar dust; protoplanetary disks
An Extreme Black Hole in the Recurrent X-Ray Transient XTE J2012+381

The black hole (BH) candidate XTE J2012+381 underwent an outburst at the end of 2022. We analyzed 105 NICER observations and two NuSTAR observations of the source during the outburst. The NuSTAR observations of the M ~ 10 M ⊙ BH indicate clear signs of relativistic disk reflection, which we modeled to measure a BH spin of $a={0.988}_{-0.030}^{+0.008}$ and an inclination of $\theta ={68}_{-11}^{+6}$ deg (1σ statistical errors). In our analysis, we test an array of models and examine the effect of fitting NuSTAR spectra alone versus fitting simultaneously with NICER. We find that when the underlying continuum emission is properly accounted for, the reflected emission is similarly characterized by multiple models. We combined 52 NICER spectra to obtain a spectrum with an effective exposure of 190 ks in order to probe the presence of absorption lines that would be suggestive of disk winds, but the resulting features were not statistically significant. We discuss the implications of this measurement in relation to the overall BH spin distribution in X-ray binary systems.

Keywords: black holes; astrophysical black holes; high energy astrophysics; accretion; x-ray binary stars
The Three Regimes of Atmospheric Evaporation for Super-Earths and Sub-Neptunes

A significant fraction of super-Earths and sub-Neptunes are thought to experience an extreme loss of volatiles because of atmospheric evaporation in the early stages of their life. Though the mechanisms behind the extreme mass loss are not fully understood, two contenders have been widely discussed: photoevaporation from X-ray and ultraviolet irradiation and core-powered mass loss. Here, it is shown that both mechanisms occur, but with different timescales, and that atmospheric loss can take place over three regimes. In the first regime, a planet has very high internal temperatures arising from its high-energy formation processes. These high temperatures give rise to a fully convecting atmosphere that efficiently loses mass without much internal cooling. The second regime applies to planets with lower internal temperatures, so a radiative region forms, but the photosphere still remains outside the Bondi radius. Hence, mass loss continues to depend only on the internal temperatures. Planets with the lowest internal temperatures are in the third regime, when the photosphere forms below the Bondi radius and mass is lost primarily because of X-ray and ultraviolet irradiation. This paper provides the first unifying framework for modeling atmospheric evaporation through the life span of a planet.

Keywords: mini neptunes; super earths; star-planet interactions; exoplanet evolution; exoplanet atmospheres; planetary interior