Sazuna/UAT_keywords huggingface dataset:
SpinSpotter : An Automated Algorithm for Identifying Stellar Rotation Periods with Autocorrelation Analysis. SpinSpotter is a robust and automated algorithm designed to extract stellar rotation periods from large photometric data sets with minimal supervision. Our approach uses the autocorrelation function (ACF) to identify stellar rotation periods up to one-third the observational baseline of the data. Our algorithm also provides a suite of diagnostics that describe the features in the ACF, which allows the user to fine-tune the tolerance with which to accept a period detection. We apply it to approximately 130,000 main-sequence stars observed by the Transiting Exoplanet Survey Satellite at 2-minute cadence during Sectors 1-26 and identify rotation periods for 13,504 stars ranging from 0.4 to 14 days. We demonstrate good agreement between our sample and known values from the literature and note key differences between our population of rotators and those previously identified in the Kepler field, most notably a large population of fast-rotating M dwarfs. Our sample of rotating stars provides a data set with coverage of nearly the entire sky that can be used as a basis for future gyrochronological studies and, when combined with proper motions and distances from Gaia, to search for regions with high densities of young stars, thus identifying areas of recent star formation and undiscovered moving group members. Our algorithm is publicly available for download and use on GitHub at https://github.com/rae-holcomb/SpinSpotter.

Keywords: Stellar photometry, Light curve classification , Light curves, Stellar rotation, Algorithms
Atmospheric Thermal Emission Effect on Chandrasekhar's Finite Atmosphere Problem. The solutions of the diffuse reflection finite atmosphere problem are very useful in the astrophysical context. Chandrasekhar was the first to solve this problem analytically, by considering atmospheric scattering. These results have wide applications in the modeling of planetary atmospheres. However, they cannot be used to model an atmosphere with emission. We solved this problem by including the thermal emission effect along with scattering. Here, our aim is to provide a complete picture of the generalized finite atmosphere problem in the presence of scattering and thermal emission, and to give a physical account of the same. For that, we take an analytical approach using the invariance principle method to solve the diffuse reflection finite atmosphere problem in the presence of atmospheric thermal emission. We established general integral equations of the modified scattering function S(τ; μ, ϕ; μ 0, ϕ 0), transmission function T(τ; μ, ϕ; μ 0, ϕ 0), and their derivatives with respect to τ for a thermally emitting atmosphere. We customize these equations for the case of isotropic scattering and introduce two new functions V(μ), and W(μ), analogous to Chandrasekhar's X(μ), and Y(μ) functions, respectively. We also derive a transformation relation between the modified S and T functions and give a physical account of the V(μ) and W(μ) functions. Our final results are consistent with those of Chandrasekhar's at the low emission limit (i.e., only scattering). From the consistency of our results, we conclude that the consideration of the thermal emission effect in the diffuse reflection finite atmosphere problem gives more general and accurate results than considering only scattering.

Keywords: Diffuse radiation, Atmospheric effects, Radiative transfer equation, Radiative transfer
CLASS: Coronal Line Activity Spectroscopic Survey. We conduct the first systematic survey of a comprehensive set of the twenty optical coronal lines in the spectra of nearly 1 million galaxies observed by the Sloan Digital Sky Survey (SDSS) Data Release 8 catalog. This includes often overlooked high ionization potential lines such as [Ar X] λ5533, [S XII] λ7609, [Fe XI] λ7892, and [Fe XIV] λ5303. We find that, given the limited sensitivity of SDSS, strong coronal line emission is extremely rare, with only ~0.03% of the sample showing at least one coronal line, significantly lower than the fraction of galaxies showing optical narrow line ratios (~17%) or mid-infrared colors (~2%) indicative of nuclear activity. The coronal line luminosities exhibit a large dynamic range, with values ranging from ~1034 to 1042 erg s-1. We find that a vast majority (~80%) of coronal line emitters in dwarf galaxies (M * &lt; 9.6 × 109 M ⊙) do not display optical narrow line ratios indicative of nuclear activity, in contrast to higher mass galaxies (~17%). Moreover, we find that the highest ionization potential lines are preferentially found in lower mass galaxies. These findings are consistent with the theory that lower mass black holes found in lower mass galaxies produce a hotter accretion disk, which in turn enhances the higher ionization coronal line spectrum. Future coronal line searches with 30 m class telescopes or JWST may provide a pathway into uncovering the intermediate mass black hole population.

Keywords: Starburst galaxies, Active galaxies, Dwarf galaxies, Galaxy accretion disks, Emission line galaxies, Infrared galaxies, Galaxy evolution, Interstellar medium
A Supercritical Accretion Disk with Radiation-driven Outflows. Outflows are inevitably driven from the disk if the vertical component of the black hole (BH) gravity cannot resist the radiation force. We derive the mass-loss rate in the outflows by solving a dynamical equation for the vertical gas motion in the disk. The structure of a supercritical accretion disk is calculated with the radial energy advection included. We find that most inflowing gas is driven into outflows if the disk is accreting at a moderate Eddington-scaled rate (up to ~100) at its outer edge, i.e., only a small fraction of gas is accreted by the BH, which is radiating at several Eddington luminosities, while it reaches around ten for extremely high accretion rate cases ( $\dot{m}\equiv \dot{M}/{\dot{M}}_{\mathrm{Edd}}\sim 1000$ ). Compared with a normal slim disk, the disk luminosity is substantially suppressed due to the mass loss in the outflows. We apply the model to the light curves of the tidal disruption events (TDEs) and find that the disk luminosity declines very slowly with time even if a typical accretion rate $\dot{m}\propto {t}^{-5/3}$ is assumed at the outer edge of the disk, which is qualitatively consistent with the observed light curves in some TDEs and helps us to understand the energy deficient phenomenon observed in the TDEs. Strong outflows from supercritical accretion disks surrounding supermassive BHs may play crucial roles in their host galaxies, which can be taken as an ingredient in the mechanical feedback models. The implications of the results on the growth of supermassive BHs are also discussed.

Keywords: Accretion, Galaxy accretion disks
The Lyα Emission in a C1.4 Solar Flare Observed by the Extreme Ultraviolet Imager aboard Solar Orbiter. The hydrogen Lyα (H I Lyα) emission during solar flares has rarely been studied in spatially resolved images, and its physical origin has not been fully understood. In this paper, we present novel Lyα images for a C1.4 solar flare (SOL2021-08-20T22:00) from the Extreme Ultraviolet Imager aboard Solar Orbiter, together with multi-wave-band and multiperspective observations from the Solar Terrestrial Relations Observatory Ahead and the Solar Dynamics Observatory spacecraft. It is found that the Lyα emission has a good temporal correlation with the thermal emissions at 1-8 Å and 5-7 keV, indicating that the flaring Lyα is mainly produced by a thermal process in this small event. However, nonthermal electrons play a minor role in generating Lyα at flare ribbons during the rise phase of the flare, as revealed by the hard X-ray imaging and spectral fitting. Besides originating from flare ribbons, the Lyα emission can come from flare loops, likely caused by plasma heating and also cooling that happen in different flare phases. It is also found that the Lyα emission shows fairly similar features to the He II λ304 emission in light curve and spatiotemporal variation, along with small differences. These observational results improve our understanding of the Lyα emission in solar flares and also provide some insights for investigating the Lyα emission in stellar flares.

Keywords: Solar flares, Solar ultraviolet emission, Solar corona, Solar activity, Solar chromosphere
The Ultraviolet C II Lines as a Diagnostic of κ-distributed Electrons in Planetary Nebulae. Non-Maxwellian κ electron energy distributions (EEDs) have been proposed in recent years to resolve the so-called "electron temperature and abundance discrepancy problem" in the study of planetary nebulae (PNs). Thus the need to develop diagnostic tools to determine from observations the EED of PNs is raised. Arising from high-energy levels, the ultraviolet (UV) emission lines from PNs present intensities that depend sensitively on the high-energy tail of the EED. In this work, we investigate the feasibility of using the C II]λ2326/C II λ1335 intensity ratios as a diagnostic of the deviation of the EED from the Maxwellian distribution (as represented by the κ index). We use a Maxwellian decomposition approach to derive the theoretical κ-EED-based collisionally excited coefficients of C II, and then compute the C II UV intensity ratio as a function of the κ index. We analyze the archival spectra acquired by the International Ultraviolet Explorer and measure the intensities of C II UV lines from 12 PNs. By comparing the observed line ratios and the theoretical predictions, we can infer their κ values. With the Maxwellian-EED hypothesis, the observed C II]λ2326/C II λ1335 ratios are found to be generally lower than those predicted from the observed optical spectra. This discrepancy can be explained in terms of the κ EED. Our results show that the κ values inferred range from 15 to infinity, suggesting a mild or modest deviation from the Maxwellian distribution. However, the κ-distributed electrons are unlikely to exist throughout the whole nebulae. A toy model shows that if just about 1%-5% of the free electrons in a PN had a κ EED as small as κ = 3, it would be sufficient to account for the observations.

Keywords: Ultraviolet astronomy, Planetary nebulae, Non-thermal radiation sources
Exoplanet Radio Transits as a Probe for Exoplanetary Magnetic Fields-Time-dependent MHD Simulations. We perform a series of time-dependent magnetohydrodynamic simulations of the HD 189733 star-planet system in order to predict radio transit modulations due to the interaction between the stellar wind and planetary magnetic field. The simulation combines a model for the stellar corona and wind with an exoplanet that is orbiting the star in a fully dynamic, time-dependent manner. Our simulations generate synthetic radio images that enable us to obtain synthetic radio light curves in different frequencies. We find a clear evidence for the planetary motion in the radio light curves. Moreover, we find specific repeated features in the light curves that are attributed to the passage of the planetary magnetosphere in front of the star during transit. More importantly, we find a clear dependence in magnitude and phase of these light-curve features on the strength of the planetary magnetic field. Our work demonstrates that if radio transits could be observed, they could indeed provide information about the magnetic field strength of the transiting exoplanet. Future work to parameterize these light-curve features and their dependence on the planetary field strength would provide tools to search for these features in radio observation data sets. As we only consider the thermal radio emission from the host star for our study, very sensitive radio interferometers are necessary to detect these kinds of planetary transits in radio.

Keywords: Magnetohydrodynamics, Exoplanet astronomy, Stellar winds, Exoplanet detection methods, Radio astronomy, Exoplanet atmospheres, Magnetohydrodynamical simulations
A Nonlocal Magneto-curvature Instability in a Differentially Rotating Disk. A global mode is shown to be unstable to nonaxisymmetric perturbations in a differentially rotating Keplerian disk containing either vertical or azimuthal magnetic fields. In an unstratified cylindrical disk model, using both global eigenvalue stability analysis and linear global initial-value simulations, it is demonstrated that this instability dominates at strong magnetic fields where local standard magnetorotational instability (MRI) becomes stable. Unlike the standard MRI mode, which is concentrated in the high flow shear region, these distinct global modes (with low azimuthal mode numbers) are extended in the global domain and are Alfvén-continuum-driven unstable modes. As its mode structure and relative dominance over MRI are inherently determined by the global spatial curvature as well as the flow shear in the presence of a magnetic field, we call it the magneto-curvature (magneto-spatial-curvature) instability. Consistent with the linear analysis, as the field strength is increased in the nonlinear simulations, a transition from MRI-driven turbulence to a state dominated by global nonaxisymmetric modes is obtained. This global instability could therefore be a source of nonlinear transport in accretion disks at a higher magnetic field than predicted by local models.

Keywords: Accretion, Magnetohydrodynamics, Magnetic fields
Variability Signatures of a Burst Process in Flaring Gamma-Ray Blazars. Blazars exhibit stochastic flux variability across the electromagnetic spectrum, often exhibiting heavy-tailed flux distributions, commonly modeled as lognormal. However, Tavecchio et al. and Adams et al. found that the high-energy gamma-ray flux distributions of several of the brightest flaring Fermi-LAT flat-spectrum radio quasars (FSRQs) are well modeled by an even heavier-tailed distribution, which we show is the inverse gamma distribution. We propose an autoregressive inverse gamma variability model in which an inverse gamma flux distribution arises as a consequence of a shot-noise process. In this model, discrete bursts are individually unresolved and averaged over within time bins, as in the analysis of Fermi-LAT data. Stochastic variability on timescales longer than the time-bin duration is modeled using first-order autoregressive structure. The flux distribution becomes approximately lognormal in the limiting case of many weak bursts. The fractional variability is predicted to decrease as the time-bin duration increases. Using simulated light curves, we show that the proposed model is consistent with the typical gamma-ray variability properties of FSRQs and BL Lac objects. The model parameters can be physically interpreted as the average burst rate, the burst fluence, and the timescale of long-term stochastic fluctuations.

Keywords: BL Lacertae objects, Blazars, Flat-spectrum radio quasars, Active galactic nuclei, Time domain astronomy, Gamma-ray astronomy, Time series analysis
Deep Two-phase, Hemispherical Magma Oceans on Lava Planets. Astronomers have discovered a handful of exoplanets with rocky bulk compositions but orbiting that orbit so close to their host star that the surface of the planet must be at least partially molten. It is expected that the dayside of such "lava planets" harbors a rock-vapor atmosphere that flows quickly toward the airless nightside-this partial atmosphere is critical to the interpretation of lava planet observations, but transports negligible heat toward the nightside. As a result, the surface temperature of the magma ocean may range from 3000 K near the substellar point down to 1500 K near the day-night terminator. We use simple models incorporating the thermodynamics and geochemistry of partial melt to predict the physical and chemical properties of the magma ocean as a function of the distance from the substellar point. Our principal findings are that: (1) the dayside magma ocean is much deeper than previously thought, probably extending down to the core-mantle boundary below the substellar point of an Earth-sized planet; (2) much of the dayside is only partially molten, leading to gradients in the surface chemistry of the magma ocean; and (3) the temperature at the base of the silicate mantle is as important as the surface temperature. In the most extreme cases, lava planet interiors could be cold enough such that thermal stratification below the substellar point is gravitationally stable. These findings have important implications for the dynamics of the magma ocean, as well as the composition and dynamics of the atmosphere.

Keywords: Exoplanet dynamics, Exoplanets, Exoplanet atmospheres, Extrasolar rocky planets
A Multiepoch X-Ray Study of the Nearby Seyfert 2 Galaxy NGC 7479: Linking Column Density Variability to the Torus Geometry. Active galactic nuclei are powered by accreting supermassive black holes, surrounded by a torus of obscuring material. Recent studies have shown how the torus structure, formerly thought to be homogeneous, appears to be "patchy": the detection of variability in the line-of-sight hydrogen column density, in fact, matches the description of an obscurer with a complex structure made of clouds with different column density. In this work, we perform a multiepoch analysis of the X-ray spectra of the Seyfert 2 galaxy NGC 7479 in order to estimate its torus properties, such as the average column density and the covering factor. The measurement of the line-of-sight hydrogen column density variability of the torus allows us to obtain an upper limit on the cloud distance from the central engine. In addition, using the X-ray luminosity of the source, we estimate the Eddington ratio to be in a range of λ Edd = 0.04-0.05 over all epochs.

Keywords: Supermassive black holes, Seyfert galaxies, X-ray active galactic nuclei
Characterization of the Fireballs Detected by All-sky Cameras in Romania. Some of the fields of research that have captured the persistent interest of both scientists and the general public are meteor phenomena. The main goal in the study of meteoroid impacts into Earth's atmosphere is the recovery of the remnant matter after the ablation in the form of meteorites. This is a complementary approach, yet cheap alternative, to a sample return mission. Meteoroids are messengers since the time of the formation of the solar system due to the fact that they have preserved the same composition. The study of meteorites provides information regarding the chemical composition from which the planets formed. The increasing number of all-sky camera networks in recent years has resulted in a large set of events available for study. Thus, it is very important to use a method that determines whether the meteoroid could produce a meteorite or not. In this paper we study the meteors detected by the FRIPON network in Romania with the use of all-sky cameras. We focus on the events with noticeable deceleration (V  f /V 0 &lt; 0.8). We determine the ballistic coefficient α and the mass-loss parameter β for the selected sample. Based on this analysis the events are classified in three categories: (1) meteoroids that are likely to produce meteorites; (2) meteoroids that can possibly produce meteorites; (3) meteoroids that are unlikely to produce meteorites. The entry and final mass are determined for each event. From the recorded fireballs, we identified one possible meteorite dropper, and we analyzed its dynamical evolution.

Keywords: Meteorites, Meteors, Meteoroids
Identification and Parameter Determination of F-type Herbig Stars from LAMOST DR8. We identify 20 F-type Herbig stars and provide a list of 22 pre-main-sequence candidates from LAMOST DR8. The effective temperature, distance, extinction, stellar luminosity, mass, age, and radius are derived for each Herbig star based on optical spectra, photometry, Gaia EDR3 parallaxes, and pre-main-sequence evolutionary tracks. According to spectral energy distribution, 19 F-type Herbig stars belong to Class II YSOs, and one belongs to the flat-spectrum class. Four have Spitzer IRS spectra, of which three show extremely weak polycyclic aromatic hydrocarbon emissions, and three with both amorphous and crystalline silicate emissions share similar parameters and are at the same evolutionary stage. We detect a solar-nearby outbursting EXor Herbig star J034344.48+314309.3, a possible precursor of a Herbig Ae star. Intense emission lines of H I, He I, O I, Na I, and Ca II originating from the rapid accretion during the outbursts are detected in its optical spectra, and silicate emission features are detected in its infrared spectrum. We also conduct a statistical analysis of the disk properties of all known Herbig stars using the defined infrared spectral indices ( ${\alpha }_{J-{K}_{{\rm{S}}}}$ and ${\alpha }_{{K}_{{\rm{S}}}-W3}$ ). The proportion of Herbig stars with moderate infrared excesses decreases as effective temperature increases. The majority of the precursors (F, G, or K type) have moderate infrared excesses. Hotter Herbig stars tend to have a larger proportion with large infrared excesses. The trends may be due to the fact that hotter stars have larger areas of re-emitting dust, although there is some scatter due to the particularities of each disk.

Keywords: Herbig Ae/Be stars, Young stellar objects, Pre-main sequence stars, Star formation
Diagnosing FU Ori-like Sources: The Parameter Space of Viscously Heated Disks in the Optical and Near-infrared. FU Ori-type objects (FUors) are decades-long outbursts of accretion onto young stars that are strong enough to viscously heat disks so that the disk outshines the central star. We construct models for FUor objects by calculating emission components from a steady-state viscous accretion disk, a passively-heated dusty disk, magnetospheric accretion columns, and the stellar photosphere. We explore the parameter space of the accretion rate $\dot{M}$ and stellar mass M * to investigate implications on the optical and near-infrared spectral energy distribution and spectral lines. The models are validated by fitting to multiwavelength photometry of three confirmed FUor objects, FU Ori, V883 Ori, and HBC 722, and then comparing the predicted spectra to the observed optical and infrared spectra. The brightness ratio between the viscous disk and the stellar photosphere, η, provides an important guide for identifying viscous accretion disks, with η = 1 ("transition line") and η = 5 ("sufficient dominance line") marking turning points in diagnostics, evaluated here in the near-infrared. These turning points indicate the emergence and complete development of FUor-characteristic strong CO absorption, weak metallic absorption, the triangular spectral continuum shape in the H band, and location in color-magnitude diagrams. Lower M * and higher $\dot{M}$ imply larger η; for M * = 0.3 M ☉, η = 1 corresponds to $\dot{M}=2\,\times \,{10}^{-7}\,{M}_{\odot }$ yr-1 and η = 5 to $\dot{M}=6\,\times \,{10}^{-7}\,{M}_{\odot }$ yr-1. The "sufficient dominance line" also coincides with the expected accretion rate where accreting material directly reaches the star. We discuss implications of the models on extinction diagnostics, FUor brightening timescales, viscous disks during initial protostellar growth, and eruptive young stellar objects associated with FUors.

Keywords: Stellar accretion disks, Protoplanetary disks