adsabs/SciX_UAT_keywords huggingface dataset:
Radio Spectral Energy Distributions for Single Massive Star Winds with Free-Free and Synchrotron Emission

The mass-loss rates from single massive stars are high enough to form radio photospheres at large distances from the stellar surface, where the wind is optically thick to (thermal) free-free opacity. Here we calculate the far-infrared, millimeter, and radio band spectral energy distributions (SEDs) that can result from the combination of free-free processes and synchrotron emission, to explore the conditions for nonthermal SEDs. Simplifying assumptions are adopted in terms of scaling relations for the magnetic field strength and the spatial distribution of relativistic electrons. The wind is assumed to be spherically symmetric, and we consider the effect of Razin suppression on the synchrotron emission. Under these conditions, long-wavelength SEDs with synchrotron emission can be either more steep or more shallow than the canonical asymptotic power-law SED from a nonmagnetic wind. When nonthermal emission is present, the resultant SED shape is generally not a power law; however, the variation in the slope can change slowly with wavelength. Consequently, over a limited range of wavelengths, the SED can masquerade as approximately a power law. While most observed nonthermal long-wavelength spectra are associated with binarity, synchrotron emission can have only a mild influence on single-star SEDs, requiring finer levels of wavelength sampling for the detection of the effect.

Keywords: non-thermal radiation sources; early-type stars; stellar magnetic fields; stellar mass loss; stellar winds; radio continuum emission
Effect of H2S on the Near-infrared Spectrum of Irradiation Residue and Applications to the Kuiper Belt Object (486958) Arrokoth

On 2019 January 1, the New Horizons spacecraft flew by (486958) Arrokoth, a small body in the Kuiper Belt that is the most distant object ever visited by a spacecraft. A strong unidentified absorption band was observed in the spectrum of Arrokoth at 1.8 m. We report here experimental evidence suggesting that the near-infrared spectrum of Arrokoth is indicative of sulfur-rich, tholin-like organic residue. The spectra of organic residues produced by irradiating ice mixtures with H2S CH3OH:NH3:H2S:H2O (3:3:3:1) and without H2S CH3OH:NH3:H2O (3:3:1) were measured to study the effect of H2S. The with H2S sulfur-rich laboratory-synthesized organic residue displays an absorption band at 1.8 m that is absent in the spectrum of without H2S sample. This feature matches the Arrokoth spectrum better than any other expected material. This suggests the past presence of H2S ice on the surface of Arrokoth and a role for Kuiper Belt objects as a key S reservoir in the early solar system.

Keywords: astrochemistry; solar system; small solar system bodies; laboratory astrophysics; trans-neptunian objects; kuiper belt
The GW Vir Instability Strip in Light of New Observations of PG 1159 Stars: Discovery of Pulsations in the Central Star of A72 and Variability of RX J0122.9-7521

We present the results of new time-series photometric observations of 29 pre-white dwarf stars of PG 1159 spectral type, carried out in the years 2014-2022. For the majority of stars, a median noise level in Fourier amplitude spectra of 0.5-1.0 mmag was achieved. This allowed the detection of pulsations in the central star of planetary nebula A72 (Abell 72), consistent with g modes excited in GW Vir stars, and variability in RX J0122.9-7521 that could be due to pulsations, binarity, or rotation. For the remaining stars from the sample that were not observed to vary, we placed upper limits for variability. After combination with literature data, our results place the fraction of pulsating PG 1159 stars within the GW Vir instability strip at 36%. An updated list of all known PG 1159 stars is provided, containing astrometric measurements from the recent Gaia DR3 data, as well as information on physical parameters, variability, and nitrogen content. Those data are used to calculate luminosities for all PG 1159 stars to place the whole sample on the theoretical Hertzsprung-Russell diagram for the first time in that way. The pulsating stars are discussed as a group, and arguments are given that the traditional separation of GW Vir pulsators in "DOV" and "PNNV" stars is misleading and should not be used.

Keywords: pg 1159 stars; pulsating variable stars; stellar pulsations; non-radial pulsations; stellar evolution; ccd photometry; hertzsprung russell diagram; post-asymptotic giant branch stars; instability strip
MANTRA: A Machine-learning Reference Light-curve Data Set for Astronomical Transient Event Recognition

We introduce Many ANnotated TRAnsients (MANTRA), an annotated data set of 4869 transient and 71207 non-transient object light curves built from the Catalina Real-time Transient Survey. We provide public access to this data set as a plain text file to facilitate standardized quantitative comparison of astronomical transient event recognition algorithms. Some of the classes included in the data set are: supernovae, cataclysmic variables, active galactic nuclei, high proper motion stars, blazars, and flares. As an example of the tasks that can be performed on the data set we experiment with multiple data preprocessing methods, feature selection techniques, and popular machine-learning algorithms (support vector machines, random forests, and neural networks). We assess quantitative performance in two classification tasks: binary (transient/non-transient) and eight-class classification. The best-performing algorithm in both tasks is the random forest classifier. It achieves an F1 score of 96.25% in the binary classification and 52.79% in the eight-class classification. For the eight-class classification, non-transients (96.83%) is the class with the highest F1 score, while the lowest corresponds to high proper motion stars (16.79%); for supernovae it achieves a value of 54.57%, close to the average across classes. The next release of MANTRA includes images and benchmarks with deep learning models.

Keywords: astronomy databases; transient detection; astrostatistics tools
A Herschel Mapping of [{C}{II}],[{O}{I}], and [{O}{III}] Lines from the Circumnuclear Region of M31

The circumnuclear region of M31, consisting of multiphase interstellar media, provides a close-up view of the interaction of the central supermassive black hole and surrounding materials. Far-infrared (FIR) fine-structure lines and their flux ratios can be used as diagnostics of physical properties of the neutral gas in this region. Here we present the first FIR spectroscopic mapping of the circumnuclear region of M31 in [C II] 158 μm, [O I] 63 μm, and [O III] 88 μm lines with the Herschel Space Observatory, covering an ∼500 × 500 pc (2' × 2') field. Significant emissions of all three lines are detected along the so-called nuclear spiral across the central kiloparsec of M31. The velocity field under a spatial resolution of ∼50 pc of the three lines are broadly consistent and also consistent with previous CO(3-2) line observations in the central region. Combined with existing [C II] and CO(3-2) observations of five other fields targeting the disk, we derived the radial distribution of [C II]/CO(3-2) flux ratio, and found that this ratio is higher in the center than in the disk, indicating a low gas density and strong radiation field in the central region. We also found that the [C II]/FIR ratio in the central region is 5.4 (±0.8) × 10-3, which exhibits an increasing trend with the galactocentric radius, suggesting an increasing contribution from the old stellar population to dust heating toward the center.

Keywords: andromeda galaxy; interstellar medium; galaxy nuclei; interstellar atomic gas
Terrestrial- and Neptune-mass Free-Floating Planet Candidates from the MOA-II 9 yr Galactic Bulge Survey

We report the discoveries of low-mass free-floating planet (FFP) candidates from the analysis of 2006-2014 MOA-II Galactic bulge survey data. In this data set, we found 6111 microlensing candidates and identified a statistical sample consisting of 3535 high-quality single-lens events with Einstein radius crossing times in the range 0.057 < t E/days < 757, including 13 events that show clear finite-source effects with angular Einstein radii of 0.90 < θ E/μas < 332.54. Two of the 12 events with t E < 1 day have significant finite-source effects, and one event, MOA-9y-5919, with t E = 0.057 ± 0.016 days and θ E = 0.90 ± 0.14 μas, is the second terrestrial-mass FFP candidate to date. A Bayesian analysis indicates a lens mass of ${0.75}_{-0.46}^{+1.23}$ M ⊕ for this event. The low detection efficiency for short-duration events implies a large population of low-mass FFPs. The microlensing detection efficiency for low-mass planet events depends on both the Einstein radius crossing times and the angular Einstein radii, so we have used image-level simulations to determine the detection efficiency dependence on both t E and θ E. This allows us to use a Galactic model to simulate the t E and θ E distribution of events produced by the known stellar populations and models of the FFP distribution that are fit to the data. Methods like this will be needed for the more precise FFP demographics determinations from Nancy Grace Roman Space Telescope data.

Keywords: gravitational microlensing exoplanet detection; free floating planets; exoplanets
Callisto and Europa Gravity Measurements from JUICE 3GM Experiment Simulation

The JUpiter Icy Moons Explorer is an ESA mission set for launch in 2023 April and arrival in the Jovian system in 2031 July to investigate Jupiter and its icy satellites with a suite of 10 instruments. The mission will execute several flybys of the icy moons Europa, Callisto, and Ganymede before ending the mission with a 9-month orbit around Ganymede. The 3GM experiment on board the spacecraft will exploit accurate range and Doppler (range-rate) measurements to determine the moons' orbit, gravity field, and tidal deformation. The focus of this paper is on the retrieval of Europa's and Callisto's gravity field, without delving into the modeling of their interior structures. By means of a covariance analysis of the data acquired during flybys, we assess the expected results from the 3GM gravity experiment. We find that the two Europa flybys will provide a determination of the J 2 and C 22 quadrupole gravity field coefficients with an accuracy of 3.8 × 10-6 and 5.1 × 10-7, respectively. The 21 Callisto flybys will provide a determination of the global gravity field to approximately degree and order 7, the moon ephemerides, and the time-variable component of the gravitational tide raised by Jupiter on the moon. The k 2 Love number, describing the Callisto tidal response at its orbital period, can be determined with an uncertainty σ k2 ~ 0.06, allowing us to distinguish with good confidence between a moon with or without an internal ocean. The constraints derived by 3GM gravity measurements can then be used to develop interior models of the moon.

Keywords: jovian satellites; galilean satellites; orbit determination; tides; gravitational fields
Electrostatic Solitary Waves in the Venusian Ionosphere Pervaded by the Solar Wind: A Theoretical Perspective

Electrostatic solitary waves (ESWs) in the Venusian ionosphere that are impinged by the solar wind are investigated using a homogeneous, collisionless, and magnetized multicomponent plasma consisting of Venusian H+ and O+ ions, Maxwellian Venusian electrons and streaming solar wind protons, and suprathermal electrons following κ - distribution. The model supports the propagation of positive potential slow O+ and H+ ion-acoustic solitons. The evolution and properties of the solitons occurring in two sectors, viz., dawn-dusk and noon-midnight sector of the Venus ionosphere at an altitude of (200-2000) km, are studied. The theoretical model predicts positive potential solitons with amplitude ~(0.067-56) mV, width ~(1.7-53.21) m, and velocity ~(1.48-8.33) km s-1. The bipolar soliton electric field has amplitude ~(0.03-27.67) mV m-1 with time duration ~(0.34-22) ms. These bipolar electric field pulses when Fourier transformed to the frequency domain occur as a broadband electrostatic noise, with frequency varying in the range of ~9.78 Hz-8.77 kHz. Our results can explain the observed electrostatic waves in the frequency range of 100 Hz-5.4 kHz in the Venus ionosphere by the Pioneer Venus Orbiter mission. The model can also be relevant in explaining the recent observation of ESWs in the Venus magnetosheath by the Solar Orbiter during its first gravity assist maneuver of Venus.

Keywords: venus; solar wind
Delayed Detonation Thermonuclear Supernovae with an Extended Dark Matter Component

We present spherically symmetric simulations of the thermonuclear explosion of a white dwarf admixed with an extended component of fermionic dark matter, using the deflagration model with the deflagration-detonation transition. In all the dark matter admixed models we have considered, the dark matter is left behind after the explosion as a compact dark star. The presence of dark matter lengthens the deflagration phase to produce a similar amount of iron-group elements and more thermoneutrinos. Dark matter admixed models also give dimmer but slowly declining light curves, consistent with some observed peculiar supernovae. Our results suggest a formation path for dark compact objects that mimic sub-solar-mass black holes as dark gravitational sources.

Keywords: dark matter; type ia supernovae; hydrodynamical simulations; supernova neutrinos; light curves
Infrared Color Separation between Thin-shelled Oxygen-rich and Carbon-rich AGB Stars

We present 43 GHz VLA spectra for 51 AGB sources with the goal of verifying an infrared (IR) color cut intended to separate carbon-rich (C) and oxygen-rich (O) AGB sources throughout the Galaxy. The color cut is a simple line in the [Ks] - [A] versus [A] - [E] color-color diagram based on 2MASS and MSX photometry, and was originally derived from SiO detection rates in the Bulge Asymmetries and Dynamical Evolution (BAaDE) sample. The division is fully supported by the spectra presented here, which show that SiO maser detections lie on the O-rich side, and SiO nondetections and a single HC3N detection are found on the C-rich side of the division. We further compare the color cut with classifications of the sources based on Low-Resolution Spectra from the Infrared Astronomical Satellite, and find good agreement, verifying that the division is a reliable and efficient method for differentiating O- and C-rich AGB sources. These observations also demonstrate that single lines detected in the BAaDE survey around 42.9 GHz are almost certainly the 29SiO v = 0 line. SiO maser sources where this rare isotopologue transition is brighter than the dominant 28SiO lines have not been reported before, and our observations show that these sources can reverse their behavior such that the typical ratios of 28SiO and 29SiO are restored within a few years.

Keywords: circumstellar masers; silicon monoxide masers; asymptotic giant branch stars; carbon stars; radio spectroscopy
The Kullback–Leibler Divergence and the Convergence Rate of Fast Covariance Matrix Estimators in Galaxy Clustering Analysis

We present a method to quantify the convergence rate of the fast estimators of the covariance matrices in the large-scale structure analysis. Our method is based on the Kullback–Leibler (KL) divergence, which describes the relative entropy of two probability distributions. As a case study, we analyze the delete-d jackknife estimator for the covariance matrix of the galaxy correlation function. We introduce the information factor or the normalized KL divergence with the help of a set of baseline covariance matrices to diagnose the information contained in the jackknife covariance matrix. Using a set of quick particle mesh mock catalogs designed for the Baryon Oscillation Spectroscopic Survey DR11 CMASS galaxy survey, we find that the jackknife resampling method succeeds in recovering the covariance matrix with 10 times fewer simulation mocks than that of the baseline method at small scales (s ≤ 40 h ‑1 Mpc). However, the ability to reduce the number of mock catalogs is degraded at larger scales due to the increasing bias on the jackknife covariance matrix. Note that the analysis in this paper can be applied to any fast estimator of the covariance matrix for galaxy clustering measurements.

Keywords: large-scale structure of the universe; astrostatistics
Time Variability of FUV Emission from Cool Stars on Multi-year Timescales

The physical and chemical properties of planetary atmospheres are affected by temporal evolution of ultraviolet (UV) radiation inputs from their host stars at all time scales. While studies of X-ray/UV flare properties and long-term stellar evolution of exoplanet host stars have provided new constraints regarding stellar inputs to exoplanetary systems, the UV temporal variability of cool stars on the timescale of stellar cycles remains largely unexplored. To address this gap in our understanding of the UV temporal variability of cool stars, we analyze far-ultraviolet (FUV) emission lines of ions that trace the chromosphere and transition region of nearby stars (C II, Si III, Si IV, and N V; formation temperatures ∼ 20–150 kK) using data from the Hubble Space Telescope (HST) and International Ultraviolet Explorer (IUE) archives spanning temporal baselines of months to years. We select 33 unique stars of spectral types F-M with observing campaigns spanning over a year, and create ionic light curves to evaluate the characteristic variability of cool stars on such timescales. Screening for large flare events, we observe that the relative variability of FUV light curves decreases with increasing stellar effective temperature, from 30% to 70% variability for M-type stars to <30% variability for F and G-type stars. We also observe a weak trend in the temporal variability with the Ca II ${R}_{\mathrm{HK}}^{{\prime} }$ stellar activity indicator, suggesting that stars with lower Ca II activity exhibit a smaller range of FUV flux variability. Screening for data sets with optimal temporal spread, and a sufficient number of individual observations, we select 5 data sets for further periodicity analysis (HST α Centauri A, HST α Centauri B, IUE α Centauri B, IUE ϵ Eri, IUE ξ Boo). Various periodic structures within the FUV flux were detected, with most significant being a 79 days frequency present within the IUE observations of ξ Boo, with a significance of 6σ, and a periodic signal in the FUV observations of α Centauri B, for both HST and IUE measurements, at ≈210 days frequency with significance of 3σ and 3.7σ, respectively. Our results suggest that extreme ultraviolet flux from cool stars varies by less than a factor of two on decade timescales, significantly smaller than variations on flare or stellar evolutionary timescales.

Keywords: ultraviolet telescopes; stellar activity; stellar chromospheres
Multiphase Circumnuclear Gas in a Low-β Disk: Turbulence and Magnetic Field Reversals

We studied the magnetic field structures and dynamics of magnetized multiphase gas on parsec scales around supermassive black holes by using global 3D magnetohydrodynamics (MHD) simulations. We considered the effect of radiative cooling and X-ray heating due to active galactic nuclei (AGNs). The gas disk consists of a multiphase gas with (1) cold (≤103 K) and thin, and (2) warm (∼104 K) and thick components with a wide range of number densities. The turbulent magnetic energy at maximum is comparable to the thermal and turbulent kinetic energies in the turbulent motion. We confirmed that the turbulent velocity of the warm gas in the ambient cold gas is caused by magnetoconvective instability. The turbulent magnetic field due to magnetorotational instability (MRI) is developed in the disk, but the mean toroidal magnetic field dominates and supports in a quasi-steady state, where the plasma-β, the ratio between gas pressure and magnetic pressure, is low (β < 1). As often seen in adiabatic MHD simulations of rotating disks, the direction of the mean toroidal field periodically reverses with time even in multiphase gas structures. The direction reversal is caused by magnetic flux vertically escaping from the disk and by the combination of the MRI and the Parker instability.

Keywords: active galactic nuclei; galaxy circumnuclear disk; magnetohydrodynamics; galaxy nuclei
The Effect of a Dark Matter Core on the Structure of a Rotating Neutron Star

Neutron stars represent unique laboratories, offering insights into the physics of supranuclear-density matter and serving as potential hosts for dark matter. This study explores the impact of dark matter cores on rapidly rotating neutron stars through the two-fluid approximation, assuming minimal interaction between baryonic matter and dark matter. The investigation employs phenomenological models for fermionic and bosonic dark matter, revealing that universal relations governing mass and radius changes due to rotation remain largely unaffected in the presence of a dark matter core. Specifically, for a 5% dark matter mass fraction, the percent deviations in total mass (M tot), the baryonic equatorial radius (R Be), and polar-to-equatorial baryonic radius ratio (R ratioB) are within 3.9%, 1.8%, and 1.4%, respectively. These findings suggest that the universal relations governing neutron star shape can be utilized to infer constraints on the properties of dark matter cores even in cases where the dark matter significantly softens the neutron star's equation of state.

Keywords: neutron stars; relativistic stars; pulsars; stellar rotation; compact objects; millisecond pulsars; dark matter
One, Two, Three ... An Explosive Outflow in IRAS 12326-6245 Revealed by ALMA

In the last years there has been a substantial increase in the number of the reported massive and luminous star-forming regions with related explosive outflows thanks to the superb sensitivity and angular resolution provided by the new radio, infrared, and optical facilities. Here, we report one more explosive outflow related with the massive and bright star-forming region IRAS 12326-6245 using Band 6 sensitive and high-angular-resolution (~0.″2) Atacama Large Millimeter/Submillimeter Array observations. We find over 10 molecular and collimated well-defined streamers, with Hubble-Lemaitre-like expansion motions, and pointing right to the center of a dusty and molecular shell (reported for the first time here) localized in the northern part of the UC H II region known as G301.1A. The estimated kinematic age and energy for the explosion are ~700 yr and 1048 erg, respectively. Taking into account the recently reported explosive outflows together with IRAS 12326-6245, we estimate an event rate of once every 90 yr in our Galaxy, similar to the formation rate of massive stars.

Keywords: star formation