adsabs/SciX_UAT_keywords huggingface dataset:
Maser Activity of Organic Molecules toward Sgr B2(N)

At centimeter wavelengths, single-dish observations have suggested that the Sagittarius (Sgr) B2 molecular cloud at the Galactic Center hosts weak maser emission from several organic molecules, including CH2NH, HNCNH, and HCOOCH3. However, the lack of spatial distribution information on these new maser species has prevented us from assessing the excitation conditions of the maser emission as well as their pumping mechanisms. Here, we present a mapping study toward Sgr B2 north (N) to locate the region where the complex maser emission originates. We report the first detection of the Class I methanol (CH3OH) maser at 84 GHz and the first interferometric map of the methanimine (CH2NH) maser at 5.29 GHz toward this region. In addition, we present a tool for modeling and fitting the unsaturated molecular maser signals with non-LTE radiative transfer models and Bayesian analysis using the Markov Chain Monte Carlo approach. These enable us to quantitatively assess the observed spectral profiles. The results suggest a two-chain-clump model for explaining the intense CH3OH Class I maser emission toward a region with low continuum background radiation. By comparing the spatial origin and extent of maser emission from several molecular species, we find that the 5.29 GHz CH2NH maser has a close spatial relationship with the 84 GHz CH3OH Class I masers. This relationship serves as observational evidence to suggest a similar collisional pumping mechanism for these maser transitions.

Keywords: interstellar masers; radiative transfer; galactic center; spectral line identification
Core-envelope Decoupling Drives Radial Shear Dynamos in Cool Stars

Differential rotation is thought to be responsible for the dynamo process in stars like our Sun, driving magnetic activity and starspots. We report that starspot measurements in the Praesepe open cluster are strongly enhanced only for stars that depart from standard models of rotational evolution. A decoupling of the spin-down history between the core and envelope explains both the activity and rotation anomalies: surface rotational evolution is stalled by interior angular momentum redistribution, and the resultant radial shears enhance starspot activity. These anomalies provide evidence for an evolving front of shear-enhanced activity affecting the magnetic and rotational evolution of cool stars and the high-energy environments of their planetary companions for hundreds of millions to billions of years on the main sequence.

Keywords: starspots; stellar activity; stellar rotation; stellar evolution; stellar magnetic fields
Comment on the Feasibility of Carbon Burning in Betelgeuse

The recent pre-print (version published to arxiv on 2023 June 3rd) by Saio et al. argues that the supergiant Betelgeuse is already undergoing carbon burning, based the assumption that all of its light variations are caused by radial pulsations. However, the angular diameter measurements of the star are in conflict with the stellar radius required by their models, as we show in this note. We discuss the feasibility that the Great Dimming was caused by constructive mode interference using long-term brightness measurements and comment on differences in modeling frameworks adopted in Saio et al. versus Joyce et al.

Keywords: pulsating variable stars
Stratified Distribution of Organic Molecules at the Planet-formation Scale in the HH 212 Disk Atmosphere

Formamide (NH2CHO) is considered an important prebiotic molecule because of its potential to form peptide bonds. It was recently detected in the atmosphere of the HH 212 protostellar disk on the solar system scale where planets will form. Here we have mapped it and its potential parent molecules HNCO and H2CO, along with other molecules CH3OH and CH3CHO, in the disk atmosphere, studying its formation mechanism. Interestingly, we find a stratified distribution of these molecules, with the outer emission radius increasing from ~24 au for NH2CHO and HNCO, to 36 au for CH3CHO, to 40 au for CH3OH, and then to 48 au for H2CO. More importantly, we find that the increasing order of the outer emission radius of NH2CHO, CH3OH, and H2CO is consistent with the decreasing order of their binding energies, supporting that they are thermally desorbed from the ice mantle on dust grains. We also find that HNCO, which has much lower binding energy than NH2CHO, has almost the same spatial distribution, kinematics, and temperature as NH2CHO, and is thus more likely a daughter species of desorbed NH2CHO. On the other hand, we find that H2CO has a more extended spatial distribution with different kinematics from NH2CHO, thus questioning whether it can be the gas-phase parent molecule of NH2CHO.

Keywords: star formation; star forming regions; stellar accretion disks; astrochemistry; interstellar molecules
Blazar Variability: A Study of Nonstationarity and the Flux-Rms Relation

We analyze X-ray light curves of the blazars Mrk 421, PKS 2155-304, and 3C 273 using observations by the Soft X-ray Telescope on board AstroSat and archival XMM-Newton data. We use light curves of length 30-90 ks from three to four epochs for all three blazars. We apply the autoregressive integrated moving average model, which indicates the variability is consistent with short memory processes for most of the epochs. We show that the power spectral density (PSDs) of the X-ray variabilities of the individual blazars are consistent within uncertainties across the epochs. This implies that the construction of broadband PSD using light curves from different epochs is accurate. However, using certain properties of the variance of the light curves and its segments, we show that the blazars exhibit hints of nonstationarity beyond that due to their characteristic red-noise nature in some of those observations. We find a linear relationship between the root-mean-squared amplitude of variability at shorter timescales and the mean flux level at longer timescales for light curves of Mrk 421 across epochs separated by decades as well as light curves spanning 5 days and ∼10 yr. The presence of a flux-rms relation over very different timescales may imply that, similar to the X-ray binaries and Seyfert galaxies, longer and shorter timescale variabilities are connected in blazars.

Keywords: x-ray astronomy; blazars; x-ray active galactic nuclei
A Direct Comparison between the Use of Double Gray and Multiwavelength Radiative Transfer in a General Circulation Model with and without Radiatively Active Clouds

Inhomogeneous cloud formation and wavelength-dependent phenomena are expected to shape hot Jupiter atmospheres. We present a general circulation model with multiwavelength "picket fence" radiative transfer and radiatively active, temperature-dependent clouds, and compare the results to those of a double gray routine. The double gray method inherently fails to model polychromatic effects in hot Jupiter atmospheres, while picket fence captures these non-gray aspects and performs well compared to fully wavelength-dependent methods. We compare both methods with radiatively active clouds and cloud-free models, assessing the limitations of the double gray method. Although there are broad similarities, the picket fence models have larger dayside-nightside temperature differences, nonisothermal upper atmospheres, and multiwavelength effects in the presence of radiatively active clouds. We model the well-known hot Jupiters HD 189733 b and HD 209458 b. For the hotter HD 209458 b, the picket fence method prevents clouds from thermostating dayside temperatures, resulting in hotter upper atmospheres and the dissipation of dayside clouds. Differences in the temperature structures are then associated with nuanced differences in the circulation patterns and clouds. Models of the cooler HD 189733 b have global cloud coverage, regardless of the radiative transfer scheme, whereas there are larger differences in the models of HD 209458 b, particularly in the extent of the partial cloud coverage on its dayside. This results in minor changes to the thermal and reflected light phase curves of HD 189733 b, but more significant differences for the picket fence and double gray versions of HD 209458 b.

Keywords: exoplanet astronomy; exoplanet atmospheres; exoplanet atmospheric dynamics
BASS. XXII. The BASS DR2 AGN Catalog and Data

We present the active galactic nucleus (AGN) catalog and optical spectroscopy for the second data release of the Swift BAT AGN Spectroscopic Survey (BASS DR2). With this DR2 release we provide 1449 optical spectra, of which 1182 are released for the first time, for the 858 hard-X-ray-selected AGNs in the Swift BAT 70-month sample. The majority of the spectra (801/1449, 55%) are newly obtained from Very Large Telescope (VLT)/X-shooter or Palomar/Doublespec. Many of the spectra have both higher resolution (R > 2500, N ∼ 450) and/or very wide wavelength coverage (3200–10000 Å, N ∼ 600) that are important for a variety of AGN and host galaxy studies. We include newly revised AGN counterparts for the full sample and review important issues for population studies, with 47 AGN redshifts determined for the first time and 790 black hole mass and accretion rate estimates. This release is spectroscopically complete for all AGNs (100%, 858/858), with 99.8% having redshift measurements (857/858) and 96% completion in black hole mass estimates of unbeamed AGNs (722/752). This AGN sample represents a unique census of the brightest hard-X-ray-selected AGNs in the sky, spanning many orders of magnitude in Eddington ratio (L/L Edd = 10‑5–100), black hole mass (M BH = 105–1010 M ⊙), and AGN bolometric luminosity (L bol = 1040–1047 erg s‑1 ).

Keywords: x-ray active galactic nuclei; active galactic nuclei; seyfert galaxies; x-ray quasars; x-ray surveys; surveys; sky surveys; galaxy spectroscopy
Chemical Variations Across the TMC-1 Boundary: Molecular Tracers from the Translucent Phase to the Dense Phase

We investigated the chemical evolutions of gas-phase and grain-surface species across the Taurus molecular cloud-1 (TMC-1) filament from the translucent phase to the dense phase. By comparing observations with modeling results from an up-to-date chemical network, we examined the conversion processes for the carbon-, oxygen-, nitrogen-, and sulfur-bearing species, i.e., from their initial atomic form to their main molecular reservoir form both in the gas phase and on the grain surface. The conversion processes were found to depend on the species and A V . The effect of initial carbon-to-oxygen elemental abundances ratio (C/O) by varying O on the chemistry was explored, and an initial carbon elemental abundance of 2.5 × 10-4 and a C/O ratio of 0.5 could best reproduce the abundances of most observed molecules at TMC-1 CP, where more than 90 molecules have been identified. Based on the TMC-1 condition, we predicted a varied grain ice composition during the evolutions of molecular clouds, with H2O ice as the dominant ice composition at A V > 4 mag, CO2 ice as the dominant ice composition at A V <4 mag, while CO ice severely decreased at A V around 4-5 mag.

Keywords: astrochemistry; chemical abundances; interstellar medium; interstellar molecules
On the Transmission of Turbulent Structures across the Earth's Bow Shock

Collisionless shocks and plasma turbulence are crucial ingredients for a broad range of astrophysical systems. The shock-turbulence interaction, and in particular the transmission of fully developed turbulence across the quasi-perpendicular Earth's bow shock, is here addressed using a combination of spacecraft observations and local numerical simulations. An alignment between the Wind (upstream) and Magnetospheric Multiscale (downstream) spacecraft is used to study the transmission of turbulent structures across the shock, revealing an increase of their magnetic helicity content in its downstream. Local kinetic simulations, in which the dynamics of turbulent structures are followed through their transmission across a perpendicular shock, confirm this scenario, revealing that the observed magnetic helicity increase is associated with the compression of turbulent structures at the shock front.

Keywords: shocks; space plasmas; interplanetary turbulence
Magnetohydrodynamic Model of Late Accretion onto a Protoplanetary Disk: Cloudlet Encounter Event

Recent observations suggest late accretion, which is generally nonaxisymmetric, onto protoplanetary disks. We investigated nonaxisymmetric late accretion considering the effects of magnetic fields. Our model assumes a cloudlet encounter event at a few hundred astronomical units scale, where a magnetized gas clump (cloudlet) encounters a protoplanetary disk. We studied how the cloudlet size and the magnetic field strength affect the rotational velocity profile in the disk after the cloudlet encounter. The results show that a magnetic field can either decelerate or accelerate the rotational motion of the cloudlet material, primarily depending on the relative size of the cloudlet to the disk thickness. When the cloudlet size is comparable to or smaller than the disk thickness, magnetic fields only decelerate the rotation of the colliding cloudlet material. However, if the cloudlet size is larger than the disk thickness, the colliding cloudlet material can be super-Keplerian as a result of magnetic acceleration. We found that the vertical velocity shear of the cloudlet produces a magnetic tension force that increases the rotational velocity. The acceleration mechanism operates when the initial plasma β is β ≲ 2 × 101. Our study shows that magnetic fields modify the properties of spirals formed by tidal effects. These findings may be important for interpreting observations of late accretion.

Keywords: protoplanetary disks; stellar accretion disks; magnetohydrodynamical simulations
Asteroid Polarimetric Phase Behavior in the Near-infrared: S- and C-complex Objects

We present the first results of our survey of asteroid polarization phase curves in the near-infrared J and H bands using the WIRC+Pol instrument on the Palomar 200-inch telescope. We confirm through observations of standard stars that WIRC+Pol can reach the 0.1% precision needed for asteroid phase curve characterization, and we show that C-complex asteroids could act as an alternate calibration source, as they show less wavelength variation than stellar polarized standards. Initial polarization phase curve results for S-complex asteroids show a shift in behavior as a function of wavelength from visible to near-infrared bands, extending previously observed trends. Full near-infrared polarization phase curve characterization of individual asteroids will provide a unique constraint on surface composition of these objects by probing the wavelength dependence of albedo and index of refraction of the surface material.

Keywords: asteroids; asteroid surfaces; polarimetry
Automatic Detection of Plateau Phases in Light Curves of Variable Stars

Modern astronomical surveys produce millions of light curves of variable sources. These massive data sets challenge the community to create automatic light-curve processing methods for detection, classification, and characterization of variable stars. In this paper, we present a novel method for extracting the variable components of a light curve based on Otsu's thresholding method. To validate the effectiveness of this method, we apply it to the light curves of detached eclipsing binaries and dwarf novae, sourced from Optical Gravitational Lensing Experiment catalogs.

Keywords: time series analysis
GRB 231115A: A Nearby Magnetar Giant Flare or a Cosmic Short Gamma-Ray Burst?

There are two classes of gamma-ray transients with a duration shorter than 2 s. One consists of cosmic short gamma-ray bursts (GRBs) taking place in the deep Universe via the neutron star mergers, and the other is the magnetar giant flares (GFs) with energies of ∼1044 ‑ 1046 erg from "nearby" galaxies. Though the magnetar GFs and the short GRBs have rather similar temporal and spectral properties, their energies (E γ,iso) are different by quite a few orders of magnitude and hence can be distinguished supposing the host galaxies have been robustly identified. The newly observed GRB 231115A has been widely discussed as a new GF event for its high probability of being associated with M82. Here we conduct a detailed analysis of its prompt emission observed by Fermi-GBM and compare the parameters with existing observations. The prompt gamma-ray emission properties of GRB 231115A, if associated with M82, nicely follow the E p,z–E γ,iso relation of the GFs, where E p,z is the peak energy of the gamma-ray spectrum after the redshift (z) correction. To be a short GRB, the redshift needs to be ∼1. Though such a chance is low, the available X-ray/GeV observation upper limits are not stringent enough to further rule out this possibility. We have also discussed the prospect of convincingly establishing the magnetar origin of GRB 231115A-like events in the future.

Keywords: gamma-ray bursts; magnetars
SN 1961V: A Pulsational Pair-instability Supernova

We explore a variety of models in which SN 1961V, one of the most enigmatic supernovae (SNe) ever observed, was a pulsational pair-instability supernova (PPISN). Successful models reproduce the bolometric light curve of the principal outburst and, in some cases, the emission 1 yr before and several years afterward. All models have helium-rich ejecta, bulk hydrogenic velocities near 2000 km s-1, and total kinetic energies of (4-8) × 1050 erg. Each eventually leaves behind a black hole remnant. Three subclasses of PPISN models are explored, each with two different choices of carbon abundance following helium burning. Carbon is an important parameter because shell carbon burning can weaken the explosion. The three subclasses correspond to situations where SN 1961V and its immediate afterglow were (a) a single event, (b) the first of two or more pulsational events separated by decades or centuries, or (c) the latter stages of a complex explosion that had already been going on for a year or more. For the low-carbon case, the main-sequence mass for SN 1961V's progenitor would have been 100-115 M ⊙, its pre-SN helium core mass was 45-52 M ⊙, and the final black hole mass was 40-45 M ⊙. For the high-carbon case, these values are increased by roughly 20%-25%. In some PPISN models, a ~1040 erg s-1 star-like object could still be shining at the site of SN 1961V, but it has more likely been replaced by a massive accreting black hole.

Keywords: supernovae; type ii supernovae; supernova dynamics; stellar mass black holes; massive stars; core-collapse supernovae
Very Local Interstellar Medium Revealed by a Complete Solar Cycle of Interstellar Neutral Helium Observations with IBEX

The IBEX-Lo instrument on board the Interstellar Boundary Explorer (IBEX) mission samples interstellar neutral (ISN) helium atoms penetrating the heliosphere from the very local interstellar medium (VLISM). In this study, we analyze the IBEX-Lo ISN helium observations covering a complete solar cycle, from 2009 through 2020 using a comprehensive uncertainty analysis including statistical and systematic sources. We employ the Warsaw Test Particle Model to simulate ISN helium fluxes at IBEX, which are subsequently compared with the observed count rate in the three lowest energy steps of IBEX-Lo. The χ 2 analysis shows that the ISN helium flows from ecliptic $\left(\lambda ,\beta \right)=(255\buildrel{\circ}\over{.} 59\pm 0\buildrel{\circ}\over{.} 23,5\buildrel{\circ}\over{.} 14\pm 0\buildrel{\circ}\over{.} 08)$ , with speed v HP = 25.86 ± 0.21 km s-1 and temperature T HP = 7450 ±140 K at the heliopause. Accounting for gravitational attraction and elastic collisions, the ISN helium speed and temperature in the pristine VLISM far from the heliopause are v VLISM = 25.9 km s-1 and T VLISM = 6150 K, respectively. The time evolution of the ISN helium fluxes at 1 au over 12 yr suggests significant changes in the IBEX-Lo detection efficiency, higher ionization rates of ISN helium atoms in the heliosphere than assumed in the model, or an additional unaccounted for signal source in the analyzed observations. Nevertheless, we do not find any indication of the evolution of the derived parameters of ISN helium over the period analyzed. Finally, we argue that the continued operation of IBEX-Lo to overlap with the Interstellar Mapping and Acceleration Probe will be pivotal in tracking possible physical changes in the VLISM.

Keywords: heliosphere; interstellar atomic gas; interstellar medium; heliopause; interstellar clouds; photoionization; ionization; interstellar medium wind; solar cycle; solar activity
Moving Corona and the Line Profile of the Relativistic Broad Iron Emission Line

Iron fluorescence emission lines from X-ray binaries and active galactic nuclei are important diagnostic tools for studying the physical processes near the event horizon of both the stellar-mass black holes in X-ray binaries and the supermassive black holes in active galactic nuclei. In this work, we investigate the line profile of the relativistic broad iron lines from the cool accretion disk of a black hole due to the asymmetric illumination of a moving corona, which moves away from the disk with a relativistic velocity. Both the off-axis location and the radial velocity of the moving corona are considered. Our results clearly show that the illumination and the line profile are dependent on the position and velocity of the corona, since the disk region below the corona receives more flux, which is the most important factor affecting the line profiles. As expected, if the corona is close to the receding part of the rotating disk, the red peak is enhanced, while the blue peak is weakened in the broad line profile, and the central energy of the emission line is low. Conversely, if the corona is close to the approaching part of the disk, the blue peak is strong and the central energy of the emission line is high, even higher than the intrinsic energy of the emission line. Due to the beaming effect of the moving corona, the corona with high velocity illuminates the outer region of the disk, which leads to the red peak disappearing and there being only one blue peak in the profile of the emission line.

Keywords: x-ray binary stars; black hole physics; high energy astrophysics
ALMA Data Cubes and Continuum Maps of the Irradiated Western Wall in Carina

We present Atacama Large Millimeter/submillimeter Array observations of the continuum and line emission of 12CO, 13CO, C18O, and [C I] for a portion of the G287.38-0.62 (Car 1-E) region in the Carina star-forming complex. The new data record how a molecular cloud responds on subarcsecond scales when subjected to a powerful radiation front, and provide insights into the overall process of star formation within regions that contain the most-massive young stars. The maps show several molecular clouds superpose upon the line of sight, including a portion of the Western Wall, a highly irradiated cloud situated near the young star cluster Trumpler 14. In agreement with theory, there is a clear progression from fluoresced H2, to [C I], to C18O with distance into the photodissociation region (PDR) front. Emission from optically thick 12CO extends across the region, while 13CO, [C I] and especially C18O are more optically thin, and concentrate into clumps and filaments closer to the PDR interface. Within the Western Wall cloud itself we identify 254 distinct core-sized clumps in our data cube of C18O. The mass distribution of these objects is similar to that of the stellar initial mass function. Aside from a large-scale velocity gradient, the clump radial velocities lack any spatial coherence size. There is no direct evidence for triggering of star formation in the Western Wall in that its C18O clumps and continuum cores appear starless, with no pillars present. However, the densest portion of the cloud lies closest to the PDR, and the C18O emission is flattened along the radiation front.

Keywords: star forming regions; molecular clouds; photodissociation regions; young massive clusters