adsabs/SciX_UAT_keywords huggingface dataset:
AstroSat UVIT Detections of Chandra X-Ray Sources in M31

An ultraviolet (UV) survey of M31 has been carried out during 2017-19 with the Ultra-Violet Imaging Telescope (UVIT) instrument on board the AstroSat Observatory. Here we match the M31 UVIT source catalog with the Chandra source catalog. We find 67 UVIT/Chandra sources detected in a varying number of UV and X-ray bands. The UV and X-ray photometry is analyzed using power-law and blackbody models. The X-ray types include 15 low-mass X-ray binaries (LMXBs) and five active galactic nuclei. Crossmatches with catalogs of stars, clusters, and other source types yield the following: 20 of the UVIT/Chandra sources match with M31 globular clusters, and nine with foreground stars. Three more globular clusters and two more foreground stars are consistent with the UVIT source positions although outside the Chandra match radius of 1″. The UV emission of the UVIT/Chandra sources associated with globular clusters is consistent with emission from blue horizontal branch stars rather than from the X-ray source. The LMXBs in globular clusters are among the most luminous globular clusters in M31. Comparison with stellar evolutionary tracks shows that the UVIT/Chandra sources with high UV blackbody temperatures are consistent with massive (10-30 M⊙) stars in M31.

Keywords: andromeda galaxy; ultraviolet sources; x-ray sources; low-mass x-ray binary stars; globular star clusters
A Solution to Continuous RFI in Narrowband Radio SETI with FAST: The MultiBeam Point-source Scanning Strategy

Narrowband radio search for extraterrestrial intelligence (SETI) in the 21st century suffers severely from radio frequency interference (RFI), resulting in a high number of false positives, and it could be the major reason why we have not yet received any messages from space. We thereby propose a novel observation strategy, called MultiBeam Point-source Scanning (MBPS), to revolutionize the way RFI is identified in narrowband radio SETI and provide a prominent solution to the current situation. The MBPS strategy is a simple yet powerful method that sequentially scans over the target star with different beams of a telescope, creating real-time references in the time domain for cross-verification and thus potentially identifying all continuous RFI with a level of certainty never achieved in any previous attempts. By applying the MBPS strategy during the observation of TRAPPIST-1 with the Five-hundred-meter Aperture Spherical radio Telescope, we successfully identified all 6972 received signals as RFI using the solid criteria introduced by the MBPS strategy. Therefore, we present the MBPS strategy as a promising tool that should bring us much closer to the first discovery of a genuine galactic greeting.

Keywords: search for extraterrestrial intelligence; radio telescopes; astronomical instrumentation
SRGeJ045359.9+622444: A 55 Minute Period Eclipsing AM Canum Venaticorum Star Discovered from a Joint SRG/eROSITA + ZTF Search

AM Canum Venaticorum (AM CVn) systems are ultracompact binaries where a white dwarf accretes from a helium-rich degenerate or semidegenerate donor. Some AM CVn systems will be among the loudest sources of gravitational waves for the upcoming Laser Interferometer Space Antenna; yet the formation channel of AM CVns remains uncertain. We report the study and characterization of a new eclipsing AM CVn, SRGeJ045359.9+622444 (hereafter, SRGeJ0453), discovered from a joint Spektrum-Roentgen-Gamma (SRG) Extended Roentgen Survey with an Imaging Telescope Array (eROSITA) mission and Zwicky Transient Facility program to identify cataclysmic variables (CVs). We obtained optical photometry to confirm the eclipse of SRGeJ0453 and determine the orbital period to be ${P}_{\mathrm{orb}}=55.0802\pm 0.0003\,\min $ . We constrain the binary parameters by modeling the high-speed photometry and radial-velocity curves and find M donor = 0.044 ± 0.024M ⊙ and R donor = 0.078 ± 0.012R ⊙. The X-ray spectrum is approximated by a power-law model with an unusually flat photon index of Γ ~ 1 previously seen in magnetic CVs with SRG/eROSITA, but verifying that the magnetic nature of SRGeJ0453 requires further investigation. Optical spectroscopy suggests that the donor star of SRGeJ0453 could have initially been a He star or a He white dwarf. SRGeJ0453 is the ninth eclipsing AM CVn system published to date, and its lack of optical outbursts have made it elusive in previous surveys. The discovery of SRGeJ0453 using joint X-ray and optical surveys highlights the potential for discovering similar systems in the near future.

Keywords: cataclysmic variable stars; am canum venaticorum stars; x-ray identification; x-ray surveys; time domain astronomy; binary stars
The Sun's Magnetic Power Spectra over Two Solar Cycles. II. Cycle Dependence of Active Regions, a Magnetic Network, and Their Relation

The multiscaled solar magnetic field consists of two major components: active regions (ARs) and magnetic network. Unraveling the cycle-dependent properties and interrelations of these components is crucial for understanding the evolution of the solar magnetic field. In this study, we investigate these components using magnetic power spectra derived from high-resolution and continuous synoptic magnetograms since cycle 23 onward. Our results show that the size of the magnetic network ranges from 26 to 41 Mm without dependence on the solar cycle. The power of the network field (P NW) accounts for approximately 20% of the total power during any phase of solar cycles. In contrast to the AR power (P AR), P NW displays a weaker cycle dependence, as described by the relationship P NW ≈ 0.6* P AR + 40. The power-law index between AR sizes and magnetic network sizes presents a strong anticorrelation with the activity level. Additionally, our study indicates that in the absence of sunspots on the solar disc, the magnetic power spectra remain time-independent, consistently exhibiting similarity in both shape and power. This study introduces a new method to investigate the properties of the magnetic network and provides magnetic power spectra for high-resolution simulations of the solar magnetic field at the surface at various phases of solar cycles.

Keywords: solar cycle; solar magnetic fields
Accelerating and Supersonic Density Fluctuations in Coronal Hole Plumes: Signature of Nascent Solar Winds

Slow magnetoacoustic waves in a static background provide a seismological tool to probe the solar atmosphere in the analytic frame. By analyzing the spatiotemporal variation of the electron number density of plume structure in coronal holes above the limb for a given temperature, we find that the density perturbations accelerate with supersonic speeds in the distance range from 1.02 to 1.23 solar radii. We interpret them as slow magnetoacoustic waves propagating at about the sound speed with accelerating subsonic flows. The average sonic height of the subsonic flows is calculated to be 1.27 solar radii. The mass flux of the subsonic flows is estimated to be 44.1% relative to the global solar wind. Hence, the subsonic flow is likely to be the nascent solar wind. In other words, the evolution of the nascent solar wind in plumes at the low corona is quantified for the first time from imaging observations. Based on the interpretation, propagating density perturbations present in plumes could be used as a seismological probe of the gradually accelerating solar wind.

Keywords: solar coronal plumes; solar coronal seismology; solar wind
Flexible and Accurate Evaluation of Gravitational-wave Malmquist Bias with Machine Learning

Many astronomical surveys are limited by the brightness of the sources, and gravitational-wave searches are no exception. The detectability of gravitational waves from merging binaries is affected by the mass and spin of the constituent compact objects. To perform unbiased inference on the distribution of compact binaries, it is necessary to account for this selection effect, which is known as Malmquist bias. Since systematic error from selection effects grows with the number of events, it will be increasingly important over the coming years to accurately estimate the observational selection function for gravitational-wave astronomy. We employ density estimation methods to accurately and efficiently compute the compact binary coalescence selection function. We introduce a simple pre-processing method, which significantly reduces the complexity of the required machine-learning models. We demonstrate that our method has smaller statistical errors at comparable computational cost than the method currently most widely used allowing us to probe narrower distributions of spin magnitudes. The currently used method leaves 10%-50% of the interesting black hole spin models inaccessible; our new method can probe >99% of the models and has a lower uncertainty for >80% of the models.

Keywords: gravitational waves; gravitational wave astronomy; gravitational wave sources
A Hubble Space Telescope Imaging Survey of Low-redshift Swift-BAT Active Galaxies

We present initial results from a Hubble Space Telescope snapshot imaging survey of the host galaxies of Swift-BAT active galactic nuclei (AGN) at z < 0.1. The hard X-ray selection makes this sample relatively unbiased in terms of obscuration, compared to optical AGN selection methods. The high-resolution images of 154 target AGN enable us to investigate the detailed photometric structure of the host galaxies, such as the Hubble type and merging features. We find 48% and 44% of the sample to be hosted by early-type and late-type galaxies, respectively. The host galaxies of the remaining 8% of the sample are classified as peculiar galaxies because they are heavily disturbed. Only a minor fraction of host galaxies (18%-25%) exhibit merging features (e.g., tidal tails, shells, or major disturbance). The merging fraction increases strongly as a function of bolometric AGN luminosity, revealing that merging plays an important role in triggering luminous AGN in this sample. However, the merging fraction is weakly correlated with the Eddington ratio, suggesting that merging does not necessarily lead to an enhanced Eddington ratio. Type 1 and Type 2 AGN are almost indistinguishable in terms of their Hubble type distribution and merging fraction. However, the merging fraction of Type 2 AGN peaks at a lower bolometric luminosity compared with those of Type 1 AGN. This result may imply that the triggering mechanism and evolutionary stages of Type 1 and Type 2 AGN are not identical. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program #15444.

Keywords: active galaxies
Outbursts in Global Protoplanetary Disk Simulations

While accreting through a circumstellar disk, young stellar objects are observed to undergo sudden and powerful accretion events known as FUor or EXor outbursts. Although such episodic accretion is considered to be an integral part of the star formation process, the triggers and mechanisms behind them remain uncertain. We conducted global numerical hydrodynamics simulations of protoplanetary disk formation and evolution in the thin-disk limit, assuming both magnetically layered and fully magnetorotational instability (MRI)-active disk structure. In this paper, we characterize the nature of the outbursts occurring in these simulations. The instability in the dead zone of a typical layered disk results in "MRI outbursts." We explore their progression and their dependence on the layered disk parameters as well as cloud core mass. The simulations of fully MRI-active disks showed an instability analogous to the classical thermal instability. This instability manifested at two temperatures—above approximately 1400 K and 3500 K—due to the steep dependence of Rosseland opacity on the temperature. The origin of these thermally unstable regions is related to the bump in opacity resulting from molecular absorption by water vapor and may be viewed as a novel mechanism behind some of the shorter duration accretion events. Although we demonstrated local thermal instability in the disk, more investigations are needed to confirm that a large-scale global instability will ensue. We conclude that the magnetic structure of a disk, its composition, as well as the stellar mass, can significantly affect the nature of episodic accretion in young stellar objects.

Keywords: protoplanetary disks; t tauri stars; young stellar objects; hydrodynamical simulations; circumstellar disks
The Potential of Detecting Nearby Terrestrial Planets in the HZ with Different Methods

Terrestrial planets in the habitable zone (hereafter HZ) around nearby stars are of great interest and provide a good sample to characterize their habitability. In this paper, we collect a nearby star catalog within 20 pc according to the Gaia Catalog of Nearby Stars, complete the physical parameters of the stars, and select stars that are not brown or white dwarfs. After selection, a sample of 2234 main-sequence stars is used to estimate the extended HZ. Then we inject Earth-like planets into the extended HZ around each star and calculate the signals with four methods, i.e., velocity amplitude for radial velocity, transit probability and depth for transit, stellar displacements for astrometry, and contrast and angular separation for imaging. Considering a typical noise model based on classic instruments, e.g., ESPRESSO, Kepler, Gaia, HabEx, and LIFE, we predict the highest possible detection number of Earth-like planets via different methods in the best-case hypothetical scenario. According to this, we conclude that both astrometry and imaging have the potential to detect nearby Earth-like planets around G-type stars, while radial velocity has the potential to detect 2% of nearby Earth-like planets around M stars with a precision of 0.2 m s-1. Our work also provides the precision requirements for future missions to reveal the nearby Earth-like planet in the HZ.

Keywords: exoplanet detection methods; habitable zone; extrasolar rocky planets; star counts; exoplanets
Detection of a 0.1c Radio Knot in M81* Associated with a Moderate X-Ray Flare

Through very long baseline interferometry observations of one of the closest low-luminosity active galactic nuclei, M81*, at multiple frequencies of 8.8, 22, and 44 GHz, a bright discrete knot with an unusual low apparent speed ~0.1c was detected. Combined with the contemporaneous monitoring of X-ray data at 2-10 keV, our data indicate that a moderate X-ray flare happened when the knot was launched from the core region. Three possible origins of the knot are proposed to explain our observational results. They are an episodic jet ejection, a low-speed shock wave, and a possible secondary black hole in a binary system. Future intensive multiwavelength monitoring can help to understand the discrete knot as well as the central black hole better.

Keywords: low-luminosity active galactic nuclei; relativistic jets; very long baseline interferometry
Statistical Results for Solar Energetic Electron Spectra Observed over 12 yr with STEREO/SEPT

This work presents a statistical analysis of near-relativistic solar energetic electron event spectra near 1 au. We use measurements of the Solar Electron and Proton Telescope (SEPT) on board STEREO in the energy range of 45-425 keV and utilize the SEPT electron event list containing all electron events observed by STEREO A and STEREO B from 2007 through 2018. We select 781 events with significant signal-to-noise ratios for our analysis and fit the spectra with single or broken-power-law functions of energy. We find 437 events showing broken power laws and 344 events only showing a single power law in the energy range of SEPT. For those events with broken power laws, we find a mean break energy of about 120 keV. We analyze the dependence of the spectral index on the rise times and peak intensities of the events as well as on the presence of relativistic electrons. The results show a relation between the power law spectral index and the rise times of the events with softer spectra belonging to rather impulsive events. Long rise-time events are associated with hard spectra as well as with the presence of higher-energy (>0.7 MeV) electrons. This group of events cannot be explained by a pure flare scenario but suggests an additional acceleration mechanism, involving a prolonged acceleration and/or injection of the particles. A dependence of the spectral index on the longitudinal separation from the parent solar source region was not found. A statistical analysis of the spectral indices during impulsively rising events where the rise times are below 20 minutes is also shown.

Keywords: heliosphere; interplanetary particle acceleration; solar flares; spectral index; solar energetic particles; radio bursts; solar coronal mass ejection shocks
Dark Matter Distribution of Four Low-z Clusters of Galaxies

We present here the weak gravitational lensing detection of four nearby galaxy clusters in the southern sky: A2029, A85, A1606, and A2457. The weak lensing detections of A1606 and A2457 are the first in the literature. This work capitalizes on the wide field of view of the Dark Energy Camera at the Cerro Tololo Inter-American Observatory, which we use to obtain deep, multiwavelength imaging of all targets. We publish maps of the clusters' projected mass distributions and obtain the M200 of their clusters through Navarro-Frenk-White profile fits to the 2D tangential ellipticity signal.

Keywords: abell clusters; galaxy clusters; weak gravitational lensing
Photometry of the Didymos System across the DART Impact Apparition

On 2022 September 26, the Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos. This demonstrated the efficacy of a kinetic impactor for planetary defense by changing the orbital period of Dimorphos by 33 minutes. Measuring the period change relied heavily on a coordinated campaign of lightcurve photometry designed to detect mutual events (occultations and eclipses) as a direct probe of the satellite's orbital period. A total of 28 telescopes contributed 224 individual lightcurves during the impact apparition from 2022 July to 2023 February. We focus here on decomposable lightcurves, i.e., those from which mutual events could be extracted. We describe our process of lightcurve decomposition and use that to release the full data set for future analysis. We leverage these data to place constraints on the postimpact evolution of ejecta. The measured depths of mutual events relative to models showed that the ejecta became optically thin within the first ∼1 day after impact and then faded with a decay time of about 25 days. The bulk magnitude of the system showed that ejecta no longer contributed measurable brightness enhancement after about 20 days postimpact. This bulk photometric behavior was not well represented by an HG photometric model. An HG 1 G 2 model did fit the data well across a wide range of phase angles. Lastly, we note the presence of an ejecta tail through at least 2023 March. Its persistence implied ongoing escape of ejecta from the system many months after DART impact.

Keywords: near-earth objects; asteroids; small solar system bodies
The Kepler Peas in a Pod Pattern is Astrophysical

Kepler planets around a given star have similar sizes to each other and regular orbital spacing, like "peas in a pod." Several studies have tested whether detection bias could produce this apparent pattern by resampling planet radii at random and applying a sensitivity function analogous to that of the Kepler spacecraft. However, Zhu argues that this pattern is not astrophysical but an artifact of Kepler's discovery efficiency at the detection threshold. To support this claim, their new analysis samples the transit signal-to-noise ratio (S/N) to derive a synthetic population of bootstrapped planet radii. Here, we examine the procedure of sampling transit S/N and demonstrate it is not applicable. Sampling transit S/N does not set up random, independent planet radii, and so it is unsuitable for corroborating (or falsifying) detection bias as the origin of apparent patterns in planet radius. By sampling the planet radii directly and using a simple model for Kepler's sensitivity, we rule out detection bias as the source of the peas-in-a-pod pattern with >10σ confidence.

Keywords: exoplanets; exoplanet systems; exoplanet astronomy; exoplanet formation; exoplanet detection methods; planetary system formation; planet formation
A Self-similar Solution of Hot Accretion Flow: The Role of the Kinematic Viscosity Coefficient

We investigate the dependency of the inflow-wind structure of a hot accretion flow on the kinematic viscosity coefficient. In this regard, we propose a model for the kinematic viscosity coefficient to mimic the behavior of the magnetorotational instability that would be maximal at the rotation axis. Then, we compare our model with two other prescriptions from numerical simulations of the accretion flow. We solve two-dimensional hydrodynamic equations of hot accretion flows in the presence of thermal conduction. The self-similar approach is also adopted in the radial direction. We calculate the properties of the inflow and the wind such as velocity, density, and angular momentum for three models of the kinematic viscosity prescription. On inspection, we find that in our suggested model the wind is less efficient at extracting the angular momentum outward where the self-similar solutions are applied than it is in two other models. The solutions obtained in this paper might be applicable to hydrodynamical numerical simulations of hot accretion flows.

Keywords: accretion; hydrodynamics; low-luminosity active galactic nuclei
Morphological Classification of the Convective Regimes in Rotating Stars

We present a set of numerical simulations that model the convection zones of solar-like stars. With this suite of numerical experiments, we explore how the nature of the convective structures transitions through a series of morphological regimes as the reduced Rayleigh number increases. Convection first manifests as a belt of rotationally aligned, convective, Taylor columns that circumscribes the equator. As the supercriticality increases, the poles begin to convect, initially in a cellular form, but eventually a plumy form emerges. Finally, at extremely high values of the Rayleigh number, a weakly rotating regime is achieved with antisolar differential rotation, i.e., the equator rotates more slowly than the poles. For all of these regimes, we provide theoretical and empirical scaling relations that summarize how global quantities—such as the bulk Rossby number and Reynolds number—scale with the Rayleigh and Ekman numbers. We demonstrate that a Rossby number based on the properties of the thermal boundary layer that clings to the outer surface of the convection zone works particularly well to predict the transition to antisolar differential rotation.

Keywords: stellar physics; stellar dynamics; solar physics; stellar convective zones; stellar interiors; stellar rotation; solar rotation; solar interior; solar differential rotation