Sazuna/UAT_keywords huggingface dataset:
The High-energy Radiation Environment around a 10 Gyr M Dwarf: Habitable at Last?. Recent work has demonstrated that high levels of X-ray and UV activity on young M dwarfs may drive rapid atmospheric escape on temperate, terrestrial planets orbiting within the habitable zone. However, secondary atmospheres on planets orbiting older, less active M dwarfs may be stable and present more promising candidates for biomarker searches. In order to evaluate the potential habitability of Earth-like planets around old, inactive M dwarfs, we present new Hubble Space Telescope and Chandra X-ray Observatory observations of Barnard&amp;'s Star (GJ 699), a 10 Gyr old M3.5 dwarf, acquired as part of the Mega-MUSCLES program. Despite the old age and long rotation period of Barnard&amp;'s Star, we observe two FUV (δ130 ≈ 5000 s; E130 ≈ 1029.5 erg each) and one X-ray (EX ≈ 1029.2 erg) flares, and we estimate a high-energy flare duty cycle (defined here as the fraction of the time the star is in a flare state) of ∼25%. A publicly available 5 Å to 10 μm spectral energy distribution of GJ 699 is created and used to evaluate the atmospheric stability of a hypothetical, unmagnetized terrestrial planet in the habitable zone (rHZ ∼ 0.1 au). Both thermal and nonthermal escape modeling indicate (1) the quiescent stellar XUV flux does not lead to strong atmospheric escape: atmospheric heating rates are comparable to periods of high solar activity on modern Earth, and (2) the flare environment could drive the atmosphere into a hydrodynamic loss regime at the observed flare duty cycle: sustained exposure to the flare environment of GJ 699 results in the loss of ≈87 Earth atmospheres Gyr-1 through thermal processes and ≈3 Earth atmospheres Gyr-1 through ion loss processes. These results suggest that if rocky planet atmospheres can survive the initial ∼5 Gyr of high stellar activity, or if a second-generation atmosphere can be formed or acquired, the flare duty cycle may be the controlling stellar parameter for the stability of Earth-like atmospheres around old M stars.

Keywords: Solar extreme ultraviolet emission, Hubble Space Telescope, Stellar activity, Stellar flares, Habitable zone, Exoplanet atmospheres
Reflected Light Observations of the Galilean Satellites from Cassini: A Test Bed for Cold Terrestrial Exoplanets. For terrestrial exoplanets with thin or no atmospheres, the surface contributes light to the reflected light signal of the planet. Measurement of the variety of disk-integrated brightnesses of bodies in the solar system and the variation with illumination and wavelength is essential for both planning imaging observations of directly imaged exoplanets and interpreting the eventual data sets. Here we measure the change in brightness of the Galilean satellites as a function of planetocentric longitude, illumination phase angle, and wavelength. The data span a range of wavelengths from 400 to 950 nm and predominantly phase angles from 0° to 25°, with some constraining observations near 60°-140°. Despite the similarity in size and density between the moons, surface inhomogeneities result in significant changes in the disk-integrated reflectivity with planetocentric longitude and phase angle. We find that these changes are sufficient to determine the rotational periods of the moon. We also find that at low phase angles, the surface can produce reflectivity variations of 8%-36%, and the limited high phase angle observations suggest variations will have proportionally larger amplitudes at higher phase angles. Additionally, all of the Galilean satellites are darker than predicted by an idealized Lambertian model at the phases most likely to be observed by direct imaging missions. If Earth-sized exoplanets have surfaces similar to that of the Galilean moons, we find that future direct imaging missions will need to achieve precisions of less than 0.1 ppb. Should the necessary precision be achieved, future exoplanet observations could exploit similar observation schemes to deduce surface variations, determine rotation periods, and potentially infer surface composition.

Keywords: Galilean satellites, Exoplanet surface characteristics, Exoplanet atmospheres
Cluster Difference Imaging Photometric Survey. II. TOI 837: A Young Validated Planet in IC 2602. We report the discovery of TOI 837b and its validation as a transiting planet. We characterize the system using data from the NASA Transiting Exoplanet Survey Satellite mission, the ESA Gaia mission, ground-based photometry from El Sauce and ASTEP400, and spectroscopy from CHIRON, FEROS, and Veloce. We find that TOI 837 is a T = 9.9 mag G0/F9 dwarf in the southern open cluster IC 2602. The star and planet are therefore ${35}_{-5}^{+11}$ million years old. Combining the transit photometry with a prior on the stellar parameters derived from the cluster color-magnitude diagram, we find that the planet has an orbital period of $8.3\,\mathrm{days}$ and is slightly smaller than Jupiter ( ${R}_{{\rm{p}}}={0.77}_{-0.07}^{+0.09}\,{R}_{\mathrm{Jup}}$ ). From radial velocity monitoring, we limit ${M}_{{\rm{p}}}\sin i$ to less than 1.20 MJup (3σ). The transits either graze or nearly graze the stellar limb. Grazing transits are a cause for concern, as they are often indicative of astrophysical false-positive scenarios. Our follow-up data show that such scenarios are unlikely. Our combined multicolor photometry, high-resolution imaging, and radial velocities rule out hierarchical eclipsing binary scenarios. Background eclipsing binary scenarios, though limited by speckle imaging, remain a 0.2% possibility. TOI 837b is therefore a validated adolescent exoplanet. The planetary nature of the system can be confirmed or refuted through observations of the stellar obliquity and the planetary mass. Such observations may also improve our understanding of how the physical and orbital properties of exoplanets change in time.

Keywords: Transits, Stellar ages, Exoplanets, Young star clusters, Exoplanet evolution
A Fast, Two-dimensional Gaussian Process Method Based on Celerite: Applications to Transiting Exoplanet Discovery and Characterization. Gaussian processes (GPs) are commonly used as a model of stochastic variability in astrophysical time series. In particular, GPs are frequently employed to account for correlated stellar variability in planetary transit light curves. The efficient application of GPs to light curves containing thousands to tens of thousands of data points has been made possible by recent advances in GP methods, including the celerite method. Here we present an extension of the celerite method to two input dimensions where, typically, the second dimension is small. This method scales linearly with the total number of data points when the noise in each large dimension is proportional to the same celerite kernel and only the amplitude of the correlated noise varies in the second dimension. We demonstrate the application of this method to the problem of measuring precise transit parameters from multiwavelength light curves and show that it has the potential to improve transit parameters measurements by orders of magnitude. Applications of this method include transit spectroscopy and exomoon detection, as well a broader set of astronomical problems.

Keywords: Natural satellites (Extrasolar), Transits, Bayesian statistics, Exoplanets, Astrostatistics, Transmission spectroscopy, Gaussian Processes regression
Spectroscopic Analysis of the Bulge Globular Cluster ESO 456-SC38. It has been suggested that the oldest stellar populations in the Milky Way are tightly bound and confined to the central regions of the Galaxy. This is one of the reasons why a handful of globular clusters located in the bulge region are thought to be remnants of the primeval formation stages of the Milky Way. The globular cluster, ESO 456-SC38 (Djorgovski 2), is one such cluster; it has a blue horizontal branch, is projected very close to the center of the Galaxy, and has an orbit confining it to the bulge/bar region. The first α abundances of seven stars in this heavily reddened cluster are presented using Apache Point Observatory Galaxy Evolution Experiment Data Release 16. A significant spread in the abundances of N, C, Na, and Al indicates the presence of multiple stellar populations in this cluster. Using Gaia DR2 proper motions and radial velocities from the Bulge Radial Velocity Assay for RR Lyrae stars, we confirm that RR Lyrae stars belong to this globular cluster. * Based on observations taken by APOGEE.

Keywords: Globular star clusters, Stellar populations, Stellar abundances, Milky Way dynamics, Galactic bulge, Chemical abundances, Stellar astronomy
The Hα Dots Survey. II. A Second List of Faint Emission-line Objects. We present the second catalog of serendipitously discovered compact extragalactic emission-line sources—Hα Dots. These objects have been discovered in searches of moderately deep narrow-band images acquired for the ALFALFA Hα project. In addition to cataloging 119 new Hα Dots, we also present follow-up spectral data for the full sample. These spectra allow us to confirm the nature of these objects as true extragalactic emission-line objects, to classify them in terms of activity type (star-forming or AGN), and to identify the emission line via which they were discovered. We tabulate photometric and spectroscopic data for the all objects, and we present an overview of the properties of the full Hα Dot sample. The Hα Dots represent a broad range of star-forming and active galaxies detected via several different emission lines over a wide range of redshifts. The sample includes Hα-detected blue compact dwarf galaxies at low redshift, [O III]-detected Seyfert 2 and Green Pea-like galaxies at intermediate redshifts, and QSOs detected via one of several UV emission lines, including Lyα. Despite the heterogeneous appearance of the resulting catalog of objects, we show that our selection method leads to well-defined samples of specific classes of emission-line objects with properties that allow for statistical studies of each class.

Keywords: Starburst galaxies, Blue compact dwarf galaxies, Quasars, Dwarf galaxies, Emission line galaxies, Seyfert galaxies, Galaxy abundances, Star formation
Dynamical Mass Estimates of the β Pictoris Planetary System through Gaussian Process Stellar Activity Modeling. Nearly 15 yr of radial velocity (RV) monitoring and direct imaging enabled the detection of two giant planets orbiting the young, nearby star β Pictoris. The δ Scuti pulsations of the star, which overwhelm planetary signals, need to be carefully suppressed. In this work, we independently revisit the analysis of the RV data following a different approach than available in the literature to model the activity of the star. We show that a Gaussian process (GP) with a stochastically driven damped harmonic oscillator kernel can model the δ Scuti pulsations. It provides similar results to parametric models but with a simpler framework, using only three hyperparameters. It also enables us to model poorly sampled RV data that were excluded from previous analyses, hence extending the RV baseline by nearly five years. Altogether, the orbit and mass of both planets can be constrained from RV only, which was not possible with the parametric modeling. To characterize the system more accurately, we also perform a joint fit of all available relative astrometry and RV data. Our orbital solutions for $\beta \ \mathrm{Pic}$ b favor a low eccentricity of ${0.029}_{-0.024}^{+0.061}$ and a relatively short period of ${21.1}_{-0.8}^{+2.0}$ yr. The orbit of $\beta \ \mathrm{Pic}$ c is eccentric with ${0.206}_{-0.063}^{+0.074}$ with a period of 3.36 ± 0.03 yr. We find model-independent masses of 11.7 ± 1.4 and 8.5 ± 0.5 ${M}_{\mathrm{Jup}}$ for $\beta \ \mathrm{Pic}$ b and c, respectively, assuming coplanarity. The mass of $\beta \ \mathrm{Pic}$ b is consistent with the hottest start evolutionary models, at an age of 25 ± 3 Myr. A direct detection of $\beta \ \mathrm{Pic}$ c would provide a second calibration measurement in a coeval system.

Keywords: Delta Scuti variable stars, Exoplanets, Astrometry, Gaussian Processes regression, Radial velocity, Orbit determination
Discovery of Extended Tidal Tails around the Globular Cluster Palomar 13. We use photometry from the DECam Legacy Survey to detect candidate tidal tails extending ∼5° on either side of the Palomar 13 globular cluster. The tails are aligned with the proper motion of Palomar 13 and are consistent with its old, metal-poor stellar population. We identify three RR Lyrae stars (RRLs) that are plausibly associated with the tails, in addition to four previously known in the cluster. From these RRLs, we find that the mean distance to the cluster and tails is 23.6 ± 0.2 kpc and estimate the total (initial) luminosity of the cluster to be ${L}_{V}={5.1}_{-3.4}^{+9.7}\times {10}^{3}\,{L}_{\odot }$ , consistent with previous claims that its initial luminosity was higher than its current luminosity. Combined with previously determined proper motion and radial velocity measurements of the cluster, we find that Palomar 13 is on a highly eccentric orbit (e ∼ 0.8) with a pericenter of ∼9 kpc and an apocenter of ∼69 kpc, and a recent pericentric passage of the cluster ∼75 Myr ago. We note a prominent linear structure in the interstellar dust map that runs parallel to the candidate tidal features, but conclude that reddening due to dust is unlikely to account for the structure that we observe. If confirmed, the Palomar 13 stellar stream would be one of very few streams with a known progenitor system, making it uniquely powerful for studying the disruption of globular clusters, the formation of the stellar halo, and the distribution of matter within our Galaxy.

Keywords: Milky Way stellar halo, Stellar structures, Milky Way dynamics, Milky Way Galaxy
Kepler Binary Stars in the NGC 6819 Open Cluster: KIC 5113146 and KIC 5111815. In this study, an investigation of two double-lined binary stars KIC 5113146 and KIC 5111815 in the NGC 6819 open cluster is presented based on both photometric and spectroscopic data. Simultaneous analysis of light and radial velocity curves was made and the absolute parameters of the systems' components were determined for the first time. We find that both systems have F-type main-sequence components. The masses and radii were found to be M1 = 1.29 ± 0.02M⊙, R1 = 1.47 ± 0.03 ${R}_{\odot }$ and M2 = 1.19 ± 0.02 ${M}_{\odot }$ , R2 = 1.13 ± 0.02 ${R}_{\odot }$ for the primary and secondary components of KIC 5113146; and M1 = 1.51 ± 0.08 ${M}_{\odot }$ , R1 = 2.02 ± 0.05 ${R}_{\odot }$ and M2 = 1.19 ± 0.07 ${M}_{\odot }$ , R2 = 1.32 ± 0.04 ${R}_{\odot }$ for the components of KIC 5111815, respectively. The evolutionary status of the components was evaluated based on the MESA evolutionary tracks and isochrones. The ages of KIC 5111815 and KIC 5113146 were derived to be about 2.50 ± 0.35 Gyr and 1.95 ± 0.40 Gyr, respectively. Photometric distances were calculated to be 2850 ± 185 pc for KIC 5113146 and 3120 ± 260 pc for KIC 5111815. The results reveal that both KIC 5113146 and KIC 5111815 systems are the most likely members of NGC 6819.

Keywords: Stellar astronomy, Open star clusters, Binary stars, Detached binary stars
Earth as an Exoplanet. I. Time Variable Thermal Emission Using Spatially Resolved Moderate Imaging Spectroradiometer Data. Among the more than 4000 exoplanets known today, some terrestrial planets have been detected in the so-called habitable zone of their host stars and their number is expected to increase in the near future, energizing a drive to understand and interpret the eagerly awaited wealth of data to identify signs of life beyond our solar system. So far, Earth remains the best and only example of a habitable (and inhabited) world. Although, it seems extremely unlikely that any other exoplanets will be true Earth twins, it is important to explore and understand the full range of spectral signatures and variability of Earth in order to inform the design of future instruments and missions, and understand their diagnostic power as well as potential limitations. In this work we use Earth observation data collected by the MODIS instrument aboard the Aqua satellite. The complete data set comprises 15 years of thermal emission observations in the 3.66-14.40 μm range for five different locations on Earth (Amazon Rainforest, Antarctica, Arctic, Indian Ocean, and the Sahara Desert). We then determine flux levels and variations as a function of wavelength and surface type (i.e., climate zone and surface thermal properties) and investigate whether periodic signals indicating Earth&amp;'s tilted rotation axis can be detected. Our findings suggest that (1) viewing geometry plays an important role when thermal emission data is analyzed as Earth&amp;'s spectrum varies by a factor of three and more depending on the dominant surface type underneath; (2) typically strong absorption bands from CO2 (15 μm) and O3 (9.65 μm) are significantly less pronounced and partially absent in data from the polar regions implying that estimating correct abundance levels for these molecules might be challenging in these cases; and (3) the time-resolved thermal emission spectrum encodes information about seasons/planetary obliquity, but the significance depends on the viewing geometry and spectral band considered.

Keywords: Space vehicle instruments, Infrared sources, Exoplanet atmospheres, Earth atmosphere
Physical Nature of the Eclipsing δ Scuti Star AO Serpentis. We present the absolute properties of the eclipsing binary AO Ser with a pulsating component from our BV photometric and high-resolution spectroscopic observations, which were performed between 2017 April and May. The radial velocities (RVs) for both components were measured, and the effective temperature and projected rotational velocity of the primary star were determined to be Teff,1 = 8,820 ± 62 K and ${v}_{1}\sin {i}_{1}$ = 90 ± 18 km s-1, respectively, by comparing the observed spectrum with the Kurucz models. The accurate fundamental parameters of AO Ser were determined by a simultaneous analysis of the light and RV curves. The masses and radii of the primary and secondary components are M1 = 2.55 ± 0.09 M⊙ and R1 = 1.64 ± 0.02 R⊙ and M2 = 0.49 ± 0.02 M⊙ and R2 = 1.38 ± 0.02 R⊙, respectively. Multiple frequency analyses for the eclipse-subtracted light residuals were conducted. As a result, we detected two frequencies of f1 = 21.852 days-1 and f2 = 23.484 days-1. The evolutionary position on the HR diagram and the pulsational characteristics indicate that the primary star is a δ Sct pulsator with a radial fundamental mode. On the other hand, the relatively evolved secondary is oversized for its own mass.

Keywords: Fundamental parameters of stars, Multi-periodic pulsation, Photometry, Spectroscopy, Eclipsing binary stars, Stellar oscillations, Asteroseismology
An ALMA Survey of λ Orionis Disks: From Supernovae to Planet Formation. Protoplanetary disk surveys by the Atacama Large Millimeter/submillimeter Array (ALMA) are now probing a range of environmental conditions, from low-mass star-forming regions like Lupus to massive OB clusters like σ Orionis. Here we conduct an ALMA survey of protoplanetary disks in λ Orionis, an ∼5 Myr old OB cluster in Orion with dust mass sensitivities comparable to the surveys of nearby regions (∼0.4 M⊕). We assess how massive OB stars impact planet formation, in particular from the supernova that may have occurred ∼1 Myr ago in the core of λ Orionis; studying these effects is important, as most planetary systems, including our solar system, are likely born in cluster environments. We find that the effects of massive stars, in the form of presupernova feedback and/or a supernova itself, do not appear to significantly reduce the available planet-forming material otherwise expected at this evolved age. We also compare a lingering massive "outlier" disk in λ Orionis to similar systems in other evolved regions, hypothesizing that these outliers host companions in their inner disks that suppress disk dispersal to extend the lifetimes of their outer primordial disks. We conclude with numerous avenues for future work that highlight how λ Orionis still has much to teach us about perhaps one of the most common types of planet-forming environments in the Galaxy.

Keywords: Millimeter astronomy, Surveys, OB stars, Protoplanetary disks, Circumstellar disks, Submillimeter astronomy, Exoplanet formation, Supernovae, Planet formation
TESS Observations of the Hot Jupiter Exoplanet XO-6b: No Evidence of Transit Timing Variations. From previous ground-based observations, the hot Jupiter exoplanet XO-6b was reported to exhibit apparently periodic transit timing variations (TTVs), with a semi-amplitude of 14 minutes and a period of about 450 days. These variations were interpreted as being due to a resonant perturbation between XO-6b and a hitherto unknown low-mass planet orbiting the same star. To understand this enigmatic planetary system better, we analyzed three sectors of data, spanning over seven months, from the Transiting Exoplanet Survey Satellite (TESS), which produces high-quality light curves that are well suited to characterizing exoplanets and searching for TTVs. Here we present an updated orbital period of 3.7649893 ± 0.0000037 days and a transit epoch of 2456652.7157 ± 0.0022 BJDTDB. The planetary parameters we report, while consistent with their discovery values, have greatly improved precision. Notably, we find no evidence for TTVs: we can rule out TTVs ≳2.5 minutes at the 3σ level. Therefore, the TESS data have sufficient precision and time baseline to readily reveal the previously reported TTVs of approximately 10 minutes. Our findings highlight the capability of TESS for robust follow-up, and confirm that TTVs are rarely seen in hot Jupiters, unlike is the case with small planets.

Keywords: Exoplanet dynamics, Exoplanets, Hot Jupiters, Transit timing variation method, Photometry
Recoverability of Known Near-Earth Asteroids. This paper analyzes the current population of known near-Earth asteroids (NEAs) and presents statistics on the recoverability of NEAs with both targeted observation campaigns and all-sky surveys. For an asteroid to be observable at a future apparition, given the right geometry, the plane-of-sky uncertainty must be small enough to be covered by a telescope's field of view and the asteroid must be brighter than the detector's limiting magnitude. Since recoverability is a telescope-dependent property, we select two representative instruments that span a wide range of capability and availability: the 1.0 m I52 telescope of the Catalina Sky Survey and the Hyper Suprime-Cam of the 8.2 m Subaru telescope. Based on this choice, we classify asteroids as recoverable, potentially recoverable, and not recoverable depending on whether they could be detected with an I52-class telescope, only with a Subaru-class telescope, or with neither, respectively. Using these definitions, we find that the majority (90%) of NEAs with H &lt; 22 and most (93%) potentially hazardous asteroids are recoverable or potentially recoverable in the next 50 yr. When considering fainter asteroids down to H ≤ 28, about two-thirds of the NEA population and half of the low minimum-orbit intersection distance (MOID) asteroids (MOID ≤ 0.05 au) are either recoverable or potentially recoverable. As of 2019 October 13, the Sentry risk list includes 193 objects with an impact probability greater than 10-6 that are not recoverable. The fraction of NEAs and low-MOID NEAs that are not recoverable can be reduced by up to 47% and 43%, respectively, when incorporating statistical estimates of serendipitous recoveries by all-sky surveys.

Keywords: Near-Earth objects, Sky surveys, Asteroids, Solar system astronomy