Sazuna/UAT_keywords huggingface dataset:
Splitting of Long-period Comet C/2018 F4 (PANSTARRS). Long-period comet C/2018 F4 (PANSTARRS) was observed to show duplicity of its inner region in 2020 September, suggestive of a splitting event. We here present analyses of our observations of the comet taken from the LCO Outbursting Objects Key project and the University of Hawaii 2.2 m telescope after the discovery of the splitting. The two fragments Components A and B, estimated to be ~60 m to 4 km in radius, remained highly similar to each other in terms of brightness, color, and dust morphology throughout our observing campaign from 2020 September to 2021 December. Our fragmentation model yielded that the two components split at a relative speed of 3.00 ± 0.18 m s-1 in 2020 late April, implying a specific energy change of $\left(5.3\pm 2.8\right)\times {10}^{3}$ J kg-1, and that Component B was subjected to a stronger nongravitational acceleration than Component A in both the radial and normal directions of the orbit. The obtained splitting time is broadly consistent with the result from the dust morphology analysis, which further suggested that the dominant dust grains were millimeter-sized and ejected at a speed of ~2 m s-1. We postulate that the pre-split nucleus of the comet consisted of two lobes resembling that of 67P, or that the comet used to be a binary system like main-belt comet 288P. Regardless, we highlight the possibility of using observations of split comets as a feasible manner to study the bilobate shape or binarity fraction of cometary nuclei.

Keywords: Long period comets, Comets, Small Solar System bodies
The Orbital Eccentricities of Directly Imaged Companions Using Observable-based Priors: Implications for Population-level Distributions. The eccentricity of a substellar companion is an important tracer of its formation history. Directly imaged companions often present poorly constrained eccentricities. A recently developed prior framework for orbit fitting called "observable-based priors" has the advantage of improving biases in derived orbit parameters for objects with minimal phase coverage, which is the case for the majority of directly imaged companions. We use observable-based priors to fit the orbits of 21 exoplanets and brown dwarfs in an effort to obtain the eccentricity distributions with minimized biases. We present the objects' individual posteriors compared to their previously derived distributions, showing in many cases a shift toward lower eccentricities. We analyze the companions' eccentricity distribution at a population level, and compare this to the distributions obtained with the traditional uniform priors. We fit a Beta distribution to our posteriors using observable-based priors, obtaining shape parameters α = ${1.09}_{-0.22}^{+0.30}$ and β = ${1.42}_{-0.25}^{+0.33}$ . This represents an approximately flat distribution of eccentricities. The derived α and β parameters are consistent with the values obtained using uniform priors, though uniform priors lead to a tail at high eccentricities. We find that separating the population into high- and low-mass companions yields different distributions depending on the classification of intermediate-mass objects. We also determine via simulation that the minimal orbit coverage needed to give meaningful posteriors under the assumptions made for directly imaged planets is ≈15% of the inferred period of the orbit.

Keywords: Brown dwarfs, Bayesian statistics, Orbital elements, Orbit determination, Exoplanet formation, Extrasolar gaseous giant planets
A Mini-Neptune Orbiting the Metal-poor K Dwarf BD+29 2654. We report the discovery and Doppler mass measurement of a 7.4 days 2.3 R ⊕ mini-Neptune around a metal-poor K dwarf BD+29 2654 (TOI-2018). Based on a high-resolution Keck/HIRES spectrum, the Gaia parallax, and multiwavelength photometry from the UV to the mid-infrared, we found that the host star has ${T}_{\mathrm{eff}}={4174}_{-42}^{+34}$ K, $\mathrm{log}g={4.62}_{-0.03}^{+0.02}$ , [Fe/H] = - 0.58 ± 0.18, M * = 0.57 ± 0.02 M ☉, and R * = 0.62 ± 0.01 R ☉. Precise Doppler measurements with Keck/HIRES revealed a planetary mass of M p = 9.2 ± 2.1 M ⊕ for TOI-2018 b. TOI-2018 b has a mass and radius that are consistent with an Earthlike core, with a ~1%-by-mass hydrogen/helium envelope or an ice-rock mixture. The mass of TOI-2018 b is close to the threshold for runaway accretion and hence giant planet formation. Such a threshold is predicted to be around 10M ⊕ or lower for a low-metallicity (low-opacity) environment. If TOI-2018 b is a planetary core that failed to undergo runaway accretion, it may underline the reason why giant planets are rare around low-metallicity host stars (one possibility is their shorter disk lifetimes). With a K-band magnitude of 7.1, TOI-2018 b may be a suitable target for transmission spectroscopy with the James Webb Space Telescope. The system is also amenable to metastable Helium observation; the detection of a Helium exosphere would help distinguish between a H/He-enveloped planet and a water world.

Keywords: Mini Neptunes, Ocean planets, Exoplanets
Yellow Supergiants and Post-red Supergiant Evolution in the Large Magellanic Cloud. The empirical evidence for an upper-mass limit for the red supergiant (RSG) progenitors of the Type II-P SNe at about 18 MSun, raises questions about the fate of the most luminous, most massive RSGs. These stars may evolve back to warmer temperatures to end their lives as hotter stars or collapse directly to black holes. The yellow hypergiants, many with extensive circumstellar dust and high mass loss, are excellent candidates for post-RSG evolution. We have identified six high-luminosity yellow supergiants (YSGs) in the LMC with circumstellar dust, including two of the fast yellow pulsating supergiants (FYPS). We discuss their spectral energy distributions, mass lost, and mass-loss rates. Together with three additional FYPS, these nine stars are about 1/3 of the YSGs above 105 L ⊙. We conclude that the high-luminosity YSGs with surface pulsations and circumstellar dust, distinct from other YSGs, are candidates for post-RSG evolution in the LMC.

Keywords: Massive stars
X-Ray and UV Observations of the Contact Binary KIC 9832227. We investigate the X-ray and UV emission from the contact binary star KIC 9832227, which was observed with XMM-Newton for one orbital cycle. The binary is detected with an average X-ray luminosity of 3.4 × 1030 erg s-1. The X-ray emission is restricted to energies below 3 keV and originates from a multitemperature plasma with temperatures up to 1 keV. The X-ray spectrum has at least two distinct components, a cooler, mostly steady component, and a hotter component exhibiting significant variability. The variable X-ray emission appears to originate from a compact flare near the contact region between the two stars that is being eclipsed by the secondary. We analyze the eclipse profile to constrain the location, size, and density of the flaring region. The remaining X-ray emission is not eclipsed and could originate from the polar region on the primary star or an extended corona. The UV emission exhibits the same nearly sinusoidal modulation at half the orbital period that is observed at longer wavelengths. The primary and secondary eclipses have slightly different depths, which is generally attributed to starspot activity. Using simulations of the UV light curve with stellar atmosphere models, we deduce the presence of a starspot near the polar region of the primary, and we determine the time of primary eclipse.

Keywords: Ultraviolet sources, X-ray binary stars, Stellar x-ray flares, Eclipsing binary stars, Contact binary stars
Dynamical Stability of Polar Circumbinary Orbits and Planet Formation in the Planetary Disk of 99 Herculis. A possible polar-ring debris disk, the dynamics of which can be described by the outer hierarchical restricted three-body problem, has been detected in 99 Herculis. An empirical formula for the minimum radius beyond which test particles in polar orbits can keep stable within 107 binary periods is provided through numerical fitting, applying to the binary eccentricity ${e}_{1}\in \left[0,0.8\right)$ and the mass ratio of the binary $\lambda \in \left[0.1,1\right]$ , where λ = m 0/m 1 (m 0 and m 1 represent the masses of the two binary stars). The polar planetary disk has the lowest statistical accretion efficiency and a moderate impact frequency of collisions among planetesimals (with radii of 1-10 km) compared to those in a circumbinary coplanar disk and a standard disk around the single host star. The collision timescale in the circumbinary disk (both polar and coplanar configurations) is longer than 107 yr, exceeding the dissipation timescale of the gas disk. Stochastic simulations show that successive collisions cannot make planetesimals grow, which may explain the formation of the debris disk observed in 99 Herculis.

Keywords: Exoplanet dynamics, Three-body problem, Protoplanetary disks, Planetesimals, Exoplanet formation, Debris disks
A Model Estimator for Noisy Compact Emission Recovery in Radio Synthesis Imaging. Reconstruction of a noisy compact emission must consider not only the point-spread function but also the effect of noise. However, the traditional threshold method in widely-used CLEAN-based algorithms finds it difficult to effectively prevent noise in the model image during noisy compact-emission reconstruction. This significantly limits the performance in noisy compact-emission reconstruction, such as deep field imaging. There are two major difficulties in the accurate reconstruction of a Stokes-I image of compact emission: first, the threshold method that has been used in practice is difficult to use to separate compact emission and noise; and second, over-subtraction makes it difficult for the reconstructed Stokes-I model image to remain positive. Therefore, a filter-based denoizing mechanism is introduced in the search phase of the model components to separate signal and noise so that the signal can be effectively extracted. The relatively larger loop gain for positive components means that the reconstructed model is in line with astrophysics. This will reduce the errors between the true sky image and the model image. The new model estimator is tested on a simulated JVLA observation with realistic source distributions from the VLA Low-Frequency Sky Survey project and the SKADS/SCubed simulation. The experiments show that it is very effective when used to separate signal and noise to lower the noise in the model image. This work explores the use of existing common software CASA to achieve high dynamic range imaging, which is an important step toward square kilometer array data processing.

Keywords: Astronomy data analysis, Astronomy data reduction
The Surface Composition of Six Newly Discovered Chemically Peculiar Stars. Comparison to the HgMn Stars mu Lep and beta Scl and the Superficially Normal B Star nu Cap. We report on a detailed abundance study of six bright, mostly southern, slowly rotating late B-stars: HD 1279 (B8III), HD 99803 (B9V), HD 123445 (B9V), HD 147550 (B9V), HD 171961 (B8III), and HD 202671 (B5II/III), hitherto reported as normal stars. We compare them to the two classical HgMn stars μ Lep and β Scl, and to the superficially normal star ν Cap. In the spectra of the six stars, the Hg II line at 3984 Å line is clearly seen and numerous lines of P, Ti, Mn, Fe, Ga, Sr, Y, and Zr appear to be strong absorbers. A comparison of newly acquired and archival spectra of these objects with a grid of synthetic spectra for selected unblended lines reveals large overabundances of P, Ti, Cr, Mn, Sr, Y, Zr, Ba, Pt, and Hg, and underabundances of He, Mg, Sc, and Ni. The effective temperatures, surface gravities, low projected rotational velocities, and the peculiar abundance patterns of the six investigated stars show that they are new chemically peculiar stars, mostly new HgMn stars, and are reclassified as such. The evolutionary status of these stars has been inferred, and their ages and masses estimated. The two most massive objects, HD 1279 and HD 202671, might have evolved away from the main sequence recently, the other stars are main-sequence objects. HD 99803A is a sharp lined HgMn star with grazing eclipses. From TESS and MASCARA photometry, we determine an orbital period of P orb = 26.12022 ± 0.00004 day.

Keywords: Eclipsing binary stars, Chemically peculiar stars
NEOMOD: A New Orbital Distribution Model for Near-Earth Objects. Near-Earth Objects (NEOs) are a transient population of small bodies with orbits near or in the terrestrial planet region. They represent a mid-stage in the dynamical cycle of asteroids and comets, which starts with their removal from the respective source regions-the main belt and trans-Neptunian scattered disk-and ends as bodies impact planets, disintegrate near the Sun, or are ejected from the solar system. Here we develop a new orbital model of NEOs by numerically integrating asteroid orbits from main-belt sources and calibrating the results on observations of the Catalina Sky Survey. The results imply a size-dependent sampling of the main belt with the ν 6 and 3:1 resonances producing ≃30% of NEOs with absolute magnitudes H = 15 and ≃80% of NEOs with H = 25. Hence, the large and small NEOs have different orbital distributions. The inferred flux of H &lt; 18 bodies into the 3:1 resonance can be sustained only if the main-belt asteroids near the resonance drift toward the resonance at the maximal Yarkovsky rate (≃2 × 10-4 au Myr-1 for diameter D = 1 km and semimajor axis a = 2.5 au). This implies obliquities θ ≃ 0° for a &lt; 2.5 au and θ ≃ 180° for a &gt; 2.5 au, both in the immediate neighborhood of the resonance (the same applies to other resonances as well). We confirm the size-dependent disruption of asteroids near the Sun found in previous studies. An interested researcher can use the publicly available NEOMOD Simulator to generate user-defined samples of NEOs from our model.

Keywords: Near-Earth objects
LAMOST J2043+3413-a Fast Disk Precession SW Sextans Candidate in Period Gap. We present follow-up photometric observations and time-series analysis of a nova-like, SW Sextans-type, cataclysmic variable (CV) candidate, LAMOST J204305.95+341340.6 (hereafter J2043+3413), with a Gaia G-band magnitude of 15.30 and a distance of 990 pc, which was identified from the LAMOST spectrum. The photometric data were collected with the Tsinghua-NAOC 0.8 m telescope (TNT), Transiting Exoplanet Survey Satellite (TESS), Zwicky Transient Facility (ZTF), and ASAS-SN. The TESS light curve reveals the presence of two prominent periods of 2.587(8) hr and 1.09(5) days, corresponding to the orbital and superorbital (precession) period, respectively. The TNT data obtained in 2020 shows a possible quasiperiodic oscillation of 1426 s. The precession period is about three times shorter than that of CVs with similar orbital periods, indicating an unusually fast precessing accretion disk. The ZTF data is found to show a sudden decline of ~0.4 mag on MJD 58979. From the intermittent behavior of the eclipse, we deduce that J2043+3413 is an intermediate inclination system of CV, similar to V795 Her, which is also situated in the period gap.

Keywords: Stellar accretion disks, Nova-like variable stars, Cataclysmic variable stars, Eclipsing binary stars
Exploring the Extremes: Characterizing a New Population of Old and Cold Brown Dwarfs. Mapping out the populations of thick disk and halo brown dwarfs is important for understanding the metallicity dependence of low-temperature atmospheres and the substellar mass function. Recently, a new population of cold and metal-poor brown dwarfs has been discovered, with T eff ≲ 1400 K and metallicity ≲−1 dex. This population includes what may be the first known "extreme T-type subdwarfs" and possibly the first Y-type subdwarf, WISEA J153429.75−104303.3. We have conducted a Gemini YJHK/Ks photometric follow-up campaign targeting potentially metal-poor T and Y dwarfs, utilizing the GNIRS and Flamingos-2 instruments. We present 14 near-infrared photometric detections of eight unique targets: six T subdwarf candidates, one moderately metal-poor Y dwarf candidate, and one Y subdwarf candidate. We have obtained the first-ever ground-based detection of the highly anomalous object WISEA J153429.75−104303.3. The F110W − J color of WISEA J153429.75−104303.3 is significantly bluer than that of other late T and Y dwarfs, indicating that WISEA J153429.75−104303.3 has an unusual spectrum in the 0.9─1.4 μm wavelength range which encompasses the J-band peak. Our J-band detection of WISEA J153429.75−104303.3 and corresponding model comparisons suggest a subsolar metallicity and temperature of 400─550 K for this object. JWST spectroscopic follow-up at near-infrared and mid-infrared wavelengths would allow us to better understand the spectral peculiarities of WISEA J153429.75−104303.3, assess its physical properties, and conclusively determine whether or not it is the first Y-type subdwarf.

Keywords: Brown dwarfs, Y dwarfs, Metallicity, Infrared photometry, T dwarfs
Confirming Resonance in Three Transiting Systems. Although resonant planets have orbital periods near commensurability, resonance is also dictated by other factors, such as the planets' eccentricities and masses, and therefore must be confirmed through a study of the system's dynamics. Here, we perform such a study for five multiplanet systems: Kepler-226, Kepler-254, Kepler-363, Kepler-1542, and K2-32. For each system, we run a suite of N-body simulations that span the full parameter space that is consistent with the constrained orbital and planetary properties. We study the stability of each system and look for resonances based on the libration of the critical resonant angles. We find strong evidence for a two-body resonance in each system; we confirm a 3:2 resonance between Kepler-226c and Kepler-226d, confirm a 3:2 resonance between Kepler-254c and Kepler-254d, and confirm a three-body 1:2:3 resonant chain between the three planets of Kepler-363. We explore the dynamical history of two of these systems and find that these resonances most likely formed without migration. Migration leads to the libration of the three-body resonant angle, but these angles circulate in both Kepler-254 and Kepler-363. Applying our methods to additional near-resonant systems could help us identify which systems are truly resonant or nonresonant and which systems require additional follow-up analysis.

Keywords: Exoplanet dynamics, Exoplanet migration, N-body simulations
Satellite Optical Brightness. The apparent brightness of satellites is calculated as a function of satellite position as seen by a ground-based observer in darkness. Both direct illumination of the satellite by the Sun as well as indirect illumination due to reflection from the Earth are included. The reflecting properties of the satellite components and of the Earth must first be estimated (the Bidirectional Reflectance Distribution Function, or BRDF). The reflecting properties of the satellite components can be found directly using lab measurements or accurately inferred from multiple observations of a satellite at various solar angles. Integrating over all scattering surfaces leads to the angular pattern of flux from the satellite. Finally, the apparent brightness of the satellite as seen by an observer at a given location is calculated as a function of satellite position. We develop an improved model for reflection of light from Earth's surface using aircraft data. We find that indirectly reflected light from Earth's surface contributes significant increases in apparent satellite brightness. This effect is particularly strong during civil twilight. We validate our approach by comparing our calculations to multiple observations of selected Starlink satellites and show significant improvement on previous satellite brightness models. Similar methodology for predicting satellite brightness has already informed mitigation strategies for next-generation Starlink satellites. Measurements of satellite brightness over a variety of solar angles widens the effectiveness of our approach to virtually all satellites. We demonstrate that an empirical model in which reflecting functions of the chassis and the solar panels are fit to observed satellite data performs very well. This work finds application in satellite design and operations, and in planning observatory data acquisition and analysis.

Keywords: Artificial satellites
Lithium in Kepler Red Giants: Defining Normal and Anomalous. The orders-of-magnitude variations in the lithium abundances of evolved stars have long been a puzzle. Diluted signals, ambiguous evolutionary states, and unknown masses have made it challenging to both map the expected lithium signals and explain the anomalously lithium-rich stars. Using a set of asteroseismically characterized evolved stars, we show here that the base lithium abundance in red giant stars is mass-dependent, with higher-mass stars having higher "normal" lithium abundances, while highly lithium-enhanced stars may cluster around 0.8 or 1.8 M ☉. We confirm previous studies that have shown that lithium enhancement and rapid rotation are often coincident but find that the actual correlation between lithium abundance and rotation rate, whether surface, internal, or radial differential rotation, is weak. Our data support previous assertions that most lithium-rich giants are in the core-helium-burning phase. We also note a tentative correlation between the highest lithium abundances and unusual carbon-to-nitrogen ratios, which is suggestive of binary interactions, though we find no simple correlation between lithium richness and indicators of binarity.

Keywords: Lithium stars, Stellar rotation, Red giant stars
Accurate and Efficient Photoeccentric Transit Modeling. A planet's orbital eccentricity is fundamental to understanding the present dynamical state of a system and is a relic of its formation history. There is high scientific value in measuring the eccentricities of Kepler and Transiting Exoplanet Survey Satellite (TESS) planets given the sheer size of these samples and the diversity of their planetary systems. However, Kepler and TESS light curves typically only permit robust determinations of the planet-to-star radius ratio r, orbital period P, and transit midpoint t 0. Three other orbital properties, including the impact parameter b, eccentricity e, and argument of periastron ω, are more challenging to measure because they are all encoded in the light curve through subtle effects on a single observable-the transit duration T 14. In Gilbert et al., we showed that a five-parameter transit description {P, t 0, r, b, T 14} naturally yields unbiased measurements of r and b. Here, we build upon our previous work and introduce an accurate and efficient prescription to measure e and ω. We validate this approach through a suite of injection-and-recovery experiments. Our method agrees with previous approaches that use a seven-parameter transit description {P, t 0, r, b, ρ ⋆, e, ω}, which explicitly fits the eccentricity vector and mean stellar density. The five-parameter method is simpler than the seven-parameter method and is "future-proof" in that posterior samples can be quickly reweighted (via importance sampling) to accommodate updated priors and updated stellar properties. This method thus circumvents the need for an expensive reanalysis of the raw photometry, offering a streamlined path toward large-scale population analyses of the eccentricity from transit surveys.

Keywords: Astronomy data modeling, Bayesian statistics, Exoplanets, Light curves, Transit photometry, Eccentricity