Sazuna/UAT_keywords huggingface dataset:
Peeking inside the Black Box: Interpreting Deep-learning Models for Exoplanet Atmospheric Retrievals. Deep-learning algorithms are growing in popularity in the field of exoplanetary science due to their ability to model highly nonlinear relations and solve interesting problems in a data-driven manner. Several works have attempted to perform fast retrievals of atmospheric parameters with the use of machine-learning algorithms like deep neural networks (DNNs). Yet, despite their high predictive power, DNNs are also infamous for being "black boxes." It is their apparent lack of explainability that makes the astrophysics community reluctant to adopt them. What are their predictions based on? How confident should we be in them? When are they wrong, and how wrong can they be? In this work, we present a number of general evaluation methodologies that can be applied to any trained model and answer questions like these. In particular, we train three different popular DNN architectures to retrieve atmospheric parameters from exoplanet spectra and show that all three achieve good predictive performance. We then present an extensive analysis of the predictions of DNNs, which can inform us-among other things-of the credibility limits for atmospheric parameters for a given instrument and model. Finally, we perform a perturbation-based sensitivity analysis to identify to which features of the spectrum the outcome of the retrieval is most sensitive. We conclude that, for different molecules, the wavelength ranges to which the DNNs predictions are most sensitive do indeed coincide with their characteristic absorption regions. The methodologies presented in this work help to improve the evaluation of DNNs and to grant interpretability to their predictions.

Keywords: Exoplanet atmospheric composition , Transit instruments, Neural networks, Convolutional neural networks, Astronomical instrumentation
Triggering a Climate Change Dominated "Anthropocene": Is It Common among Exocivilizations?. We seek to model the coupled evolution of a civilization and its host planet through the era when energy harvesting by the civilization drives the planet into new and adverse climate states. In this way, we ask if triggering "Anthropocenes" of the kind humanity is experiencing might be a generic feature of planet-civilization evolution. This question has direct consequences for both the study of astrobiology and the sustainability of human civilization. Furthermore, if Anthropocenes prove fatal for some civilizations then they can be considered as one form of a "Great Filter" and are therefore relevant to discussions of the Fermi Paradox. In this study, we focus on the effects of energy harvesting via combustion and vary the planet's initial chemistry and orbital radius. We find that in this context, the most influential parameter dictating a civilization's fate is their host planet's climate sensitivity, which quantifies how global temperatures change as CO2 is added to the atmosphere. Furthermore, this is in itself a function of the planet's atmospheric CO2 level, so planets with low levels of CO2 will have high climate sensitivities and high probabilities of triggering climate change. Using simulations of the coupled nonlinear model combined with semi-analytic treatments, we find that most planets in our initial parameter space experience diminished growth due to climate effects, an event we call a "climate-dominated Anthropocene."

Keywords: Astrobiology, Planetary climates, Exoplanets
Rotation and Lithium Confirmation of a 500 pc Halo for the Open Cluster NGC 2516. Recent analyses of the Gaia data have identified diffuse stellar populations surrounding nearby open clusters. It is important to verify that these "halos," "tails," and "strings" are of similar ages and compositions as stars in the denser part of the cluster. We present an analysis of NGC 2516 (≍150 Myr), which has a classical tidal radius of 10 pc and an apparent halo of stars spanning 500 pc (20° on-sky). Combining photometry from Gaia, rotation periods from TESS, and lithium measurements from Gaia-ESO and GALAH, we find that the halo of NGC 2516 is the same age as the cluster's core. Two-thirds of kinematically selected halo members out to 250 pc from the cluster center have rotation periods consistent with a gyrochronological age of 150 Myr. A comparison sample of field stars shows no such trend. The lithium abundances of stars in the halo are higher than in the field and correlated with the stellar rotation rate and binarity fraction, as has been noted in other young open clusters. Broadly speaking, this work supports a new paradigm wherein the halos of open clusters are often more populous than their cores. We highlight implications for spectroscopic survey targeting, open cluster dispersal, and planet searches around young stars. * This is Paper III of the Cluster Difference Imaging Photometric Survey.

Keywords: Stellar ages, Stellar kinematics, Open star clusters, Stellar rotation, Stellar associations
Angular Diameters and Fundamental Parameters of Forty-four Stars from the Navy Precision Optical Interferometer. We measured the angular diameters of 44 stars with the Navy Precision Optical Interferometer, obtaining uncertainties on the limb-darkened diameter of 2% or less for all but four stars. We then used our diameters with Gaia or Hipparcos parallaxes to calculate each star's physical radius. We gathered information from the literature to determine bolometric flux and luminosity, and combined that with our diameters to produce an effective temperature. Our sample consists of mostly giant stars, and spans a wide range of spectral classes from B to M.

Keywords: Fundamental parameters of stars, Optical interferometry, High angular resolution
Far-ultraviolet Variables in M31: Concentration in Spiral Arms and Association with Young Stars. The Andromeda galaxy (M31) is an object of ongoing study with the Ultraviolet Imaging Telescope (UVIT) on AstroSat. Field 2, which is 6.4 kpc in diameter at the distance of M31, includes a substantial part of the NE spiral arms of the galaxy. We have obtained a second observation of Field 2 with the far-ultraviolet (FUV) F148W (148 nm) filter, separated from the first observation by 1465 days. Both observations are analyzed to detect sources that are variable at a &gt;3σ confidence level. For sources with less than ~2″ separation, we apply multi-Gaussian fits, to obtain reliable magnitudes in the presence of source crowding. The variable sources are found to be concentrated in the spiral arms, with fraction of variable to nonvariable sources ~2 times higher than for interarm regions, indicating an association of FUV variables with young stellar populations. UVIT FUV-NUV color-magnitude diagrams confirm the association of FUV variables with young massive/hot stars. Using existing catalogs, we obtain counterparts for 64 of the 82 most variable sources (&gt;5σ). The counterparts include 13 star clusters, three ionized hydrogen (H II) regions, three novae, one S Doradus star, eight eclipsing binaries, 20 foreground sources, two regular variables, and 14 unspecified variables.

Keywords: Ultraviolet astronomy, Early-type variable stars, Andromeda Galaxy, Ultraviolet surveys
Reflected Spectroscopy of Small Exoplanets I: Determining the Atmospheric Composition of Sub-Neptunes Planets. Direct imaging of widely separated exoplanets from space will obtain their reflected light spectra and measure their atmospheric properties, and small and temperate planets will be the focus for the next generation of telescopes. In this work, we used our Bayesian retrieval algorithm ${{\rm\small{EXOREL}}}^{{\mathfrak{R}}}$ to determine the constraints on the atmospheric properties of sub-Neptune planets from observations taken with a HabEx-like telescope. Small and temperate planets may have a non-H2-dominated atmosphere, and therefore we introduced the compositional analysis technique in our framework to explore the bulk atmospheric chemistry composition without any prior knowledge about it. We have developed a novel set of prior functions for the compositional analysis free parameters. We compared the performances of the framework with the flat prior and the novel prior and we reported a better performance when using the novel priors set. We found that the retrieval algorithm cannot only identify the dominant gas of the atmosphere but also to constrain other less abundant gases with high statistical confidence without any prior information on the composition. The results presented here demonstrates that reflected light spectroscopy can characterize small exoplanets with diverse atmospheric composition. The Bayesian framework should be applied to design the instrument and the observation plan of exoplanet direct-imaging experiments in the future.

Keywords: Exoplanet atmospheric composition , Bayesian statistics, Ocean planets, Posterior distribution, Bayes' Theorem, Prior distribution, Exoplanet atmospheres
Toward Precise Galaxy Evolution: A Comparison between Spectral Indices of z  1 Galaxies in the IllustrisTNG Simulation and the LEGA-C Survey. We present the first comparison of observed stellar continuum spectra of high-redshift galaxies and mock galaxy spectra generated from hydrodynamical simulations. The mock spectra are produced from the IllustrisTNG TNG100 simulation combined with stellar population models and take into account dust attenuation and realistic observational effects (aperture effects and noise). We compare the simulated Dn4000 and EW(Hδ) of galaxies with $10.5\leqslant \mathrm{log}({M}_{* }/{M}_{\odot })\leqslant 11.5$ at 0.6 ≤ z ≤ 1.0 to the observed distributions from the LEGA-C survey. TNG100 globally reproduces the observed distributions of spectral indices, implying that the age distribution of galaxies in TNG100 is generally realistic. Yet there are small but significant differences. For old galaxies, TNG100 shows small Dn4000 when compared to LEGA-C, while LEGA-C galaxies have larger EW(Hδ) at fixed Dn4000 . There are several possible explanations: (1) LEGA-C galaxies have overall older ages combined with small contributions (a few percent in mass) from younger (&lt;1 Gyr) stars, while TNG100 galaxies may not have such young subpopulations; (2) the spectral mismatch could be due to systematic uncertainties in the stellar population models used to convert stellar ages and metallicities to observables. In conclusion, the latest cosmological galaxy-formation simulations broadly reproduce the global age distribution of galaxies at z ~ 1 and, at the same time, the high quality of the latest observed and simulated data sets help constrain stellar population synthesis models as well as the physical models underlying the simulations.

Keywords: Surveys, Galaxy ages, Galaxy evolution, Spectral index, Galaxy spectroscopy, Galaxies, Magnetohydrodynamical simulations
The Baryonic Tully-Fisher Relation in the Local Group and the Equivalent Circular Velocity of Pressure-supported Dwarfs. We explore the baryonic Tully-Fisher relation in the Local Group. Rotationally-supported Local Group galaxies adhere precisely to the relation defined by more distant galaxies. For pressure-supported dwarf galaxies, we determine the scaling factor βc that relates their observed velocity dispersion to the equivalent circular velocity of rotationally-supported galaxies of the same mass such that Vo = βcσ*. For a typical mass-to-light ratio Υ* = 2 M⊙/L⊙ in the V band, we find that βc = 2. More generally, $\mathrm{log}{\beta }_{c}=0.25\mathrm{log}{{\rm{\Upsilon }}}_{* }+0.226$ . This provides a common kinematic scale relating pressure and rotationally-supported dwarf galaxies.

Keywords: Local Group, Orbital motion, Galaxies, Scaling relations
OGLE-2019-BLG-0304: Competing Interpretations between a Planet-binary Model and a Binary-source + Binary-lens Model. We analyze the microlensing event OGLE-2019-BLG-0304, whose light curve exhibits two distinctive features: a deviation in the peak region and a second bump appearing ~61 days after the main peak. Although a binary-lens model can explain the overall features, it leaves subtle but noticeable residuals in the peak region. We find that the residuals can be explained by the presence of either a planetary companion located close to the primary of the binary lens (3L1S model) or an additional close companion to the source (2L2S model). Although the 3L1S model is favored over the 2L2S model, with Δχ2 ~ 8, securely resolving the degeneracy between the two models is difficult with the currently available photometric data. According to the 3L1S interpretation, the lens is a planetary system, in which a planet with a mass ${0.51}_{-0.23}^{+0.51}\,{M}_{{\rm{J}}}$ is in an S-type orbit around a binary composed of stars with masses ${0.27}_{-0.12}^{+0.27}\,{M}_{\odot }$ and ${0.10}_{-0.04}^{+0.10}\,{M}_{\odot }$ . According to the 2L2S interpretation, however, the source is composed of G- and K-type giant stars and the lens is composed of a low-mass M dwarf and a brown dwarf with masses ${0.12}_{-0.05}^{+0.12}\,{M}_{\odot }$ and ${0.045}_{-.019}^{+0.045}\,{M}_{\odot }$ , respectively. The event illustrates the need for thorough model testing in the interpretation of lensing events with complex features in light curves.

Keywords: Gravitational microlensing exoplanet detection
A Search for Transits among the Delta Scuti Variables in Kepler. We search for transits around all known pulsating δ Sct variables (6500 K &lt; Teff &lt; 10,000 K) in the long-cadence Kepler data after subtracting the pulsation signal through an automated routine. To achieve this, we devise a simple and computationally inexpensive method for distinguishing between low-frequency pulsations and transits in light curves. We find three new candidate transit events that were previously hidden behind the pulsations, but caution that they are likely to be false positive events. We also examined the Kepler Objects of Interest catalog and identify 13 additional host stars that show δ Sct pulsations. For each star in our sample, we use the nondetection of pulsation timing variations for a planet that is known to be transiting a δ Sct variable to obtain both an upper limit on the mass of the planet and the expected radial velocity semi-amplitude of the host star. Simple injection tests of our pipeline imply 100% recovery for planets of 0.5 RJup or greater. Extrapolating our number of Kepler δ Sct stars, we expect 12 detectable planets above 0.5 RJup in TESS. Our sample contains some of the hottest known transiting planets around evolved stars, and is the first complete sample of transits around δ Sct variables. We make available our code and pulsation-subtracted light curves to facilitate further analysis (https://github.com/danhey/dsct-exoplanet).

Keywords: Exoplanet astronomy, Exoplanet detection methods, Delta Scuti variable stars
TESS and ZTF Observations of an Eclipsing Z Cam-type Dwarf Nova IPHAS J051814.34+294113.2. We present an analysis of both Transiting Exoplanet Survey Satellite (TESS) and Zwicky Transient Facility (ZTF) observations of the eclipsing cataclysmic variable IPHAS J051814.34+294113.2 (IPHAS J0518). The TESS light curve shows numerous eclipses superimposed on two outbursts, and ZTF data show frequently outbursts recurring on average every 20.7 days and 12.9 days for long and short outbursts, respectively. This makes IPHAS J0518 to be identified as a possible Z Cam-type dwarf nova. Its quiescent magnitude is ~16.7 in the g band. The orbital period is determined to be 4.95 hr. By combining the observed orbital period with the semiempirical relations of Knigge et al., we estimate the donor mass as M2 = 0.48M⊙. The eclipse phase measurements are used to constrain the binary parameters. The orbital inclination is limited in the range of 75°3 ≤ i &lt; 81°7, and the mass ratio is derived as 0.33 &lt; q ≤ 0.73. Furthermore, we analysis the accretion disk eclipse and find that the total disk eclipse is possible during quiescence, whereas during outburst the disk would be only partially obscured. This indicates that the disk will become larger as the outburst proceeds. We also study the changes of the eclipse depth against the out-of-eclipse flux in IPHAS J0518. The results show evidence of the expansion in the disk size and the variations in the radial-temperature gradient during outburst.

Keywords: Eclipsing binary stars
Searching for Changing-state AGNs in Massive Data Sets. I. Applying Deep Learning and Anomaly-detection Techniques to Find AGNs with Anomalous Variability Behaviors. The classic classification scheme for active galactic nuclei (AGNs) was recently challenged by the discovery of the so-called changing-state (changing-look) AGNs. The physical mechanism behind this phenomenon is still a matter of open debate and the samples are too small and of serendipitous nature to provide robust answers. In order to tackle this problem, we need to design methods that are able to detect AGNs right in the act of changing state. Here we present an anomaly-detection technique designed to identify AGN light curves with anomalous behaviors in massive data sets. The main aim of this technique is to identify CSAGN at different stages of the transition, but it can also be used for more general purposes, such as cleaning massive data sets for AGN variability analyses. We used light curves from the Zwicky Transient Facility data release 5 (ZTF DR5), containing a sample of 230,451 AGNs of different classes. The ZTF DR5 light curves were modeled with a Variational Recurrent Autoencoder (VRAE) architecture, that allowed us to obtain a set of attributes from the VRAE latent space that describes the general behavior of our sample. These attributes were then used as features for an Isolation Forest (IF) algorithm that is an anomaly detector for a "one class" kind of problem. We used the VRAE reconstruction errors and the IF anomaly score to select a sample of 8809 anomalies. These anomalies are dominated by bogus candidates, but we were able to identify 75 promising CSAGN candidates.

Keywords: Surveys, Interdisciplinary astronomy, Active galactic nuclei, Astronomy data analysis
New Investigations of Dark-floored Pits In the Volatile Ice of Sputnik Planitia on Pluto. Sputnik Planitia, Pluto's gigantic, volatile ice glacier, hosts numerous scientific mysteries, including the presence of thousands of elongated pit structures. We examine various attributes of these pit structures in New Horizons data sets, revealing their length, aspect ratio, and orientation properties; we also study their reflectivities, colors, and compositions, and compare these attributes to some other relevant regions on Pluto. We then comment on origin mechanisms of the pits and also the fate of the missing volatiles represented by the pits on Sputnik Planitia. From a sample of 317 pits, we find typical length/width ratios of 2-4, with their major axis preferentially oriented approximately north-south. We also find that the floors of large pits in our sample have similar single-scattering albedos and colors to dark material on crater rims and floors (i.e., possible subsurface windows) in Burney basin. We also find that the base of the three pits in our sample, large enough to study with LEISA IR spectroscopy, display both CH4 and N2 absorption features, as do the dark regions in crater windows in Burney basin. Evidence for a sublimation erosion origin for the pits is supported over both the explosion/ejecta venting and structural collapse alternatives. Finally, we find that the mass lost by the pits on Sputnik Planitia most likely lies condensed elsewhere, on Pluto's surface, relocated there by volatile transport as opposed to removal by escape to space or photochemical conversion.

Keywords: Atmospheric effects, Surface ices, Surface processes, Pluto
The Instrument of the Imaging X-Ray Polarimetry Explorer. While X-ray spectroscopy, timing, and imaging have improved much since 1962 when the first astronomical nonsolar source was discovered, especially wi the launch of the Newton/X-ray Multi-Mirror Mission, Rossi/X-ray Timing Explorer, and Chandra/Advanced X-ray Astrophysics Facility, the progress of X-ray polarimetry has been meager. This is in part due to the lack of sensitive polarization detectors, which in turn is a result of the fate of approved missions and because celestial X-ray sources appear less polarized than expected. Only one positive measurement has been available until now: the Orbiting Solar Observatory measured the polarization of the Crab Nebula in the 1970s. The advent of microelectronics techniques has allowed for designing a detector based on the photoelectric effect of gas in an energy range where the optics are efficient at focusing in X-rays. Here we describe the instrument, which is the major contribution of the Italian collaboration to the Small Explorer mission called IXPE, the Imaging X-ray Polarimetry Explorer, which will launch in late 2021. The instrument is composed of three detector units based on this technique and a detector service unit. Three mirror modules provided by Marshall Space Flight Center focus X-rays onto the detectors. We show the technological choices, their scientific motivation, and results from the calibration of the instrument. IXPE will perform imaging, timing, and energy-resolved polarimetry in the 2-8 keV energy band opening this window of X-ray astronomy to tens of celestial sources of almost all classes.

Keywords: X-ray astronomy, X-ray detectors, Polarimetry
TESS Data for Asteroseismology (T'DA) Stellar Variability Classification Pipeline: Setup and Application to the Kepler Q9 Data. The NASA Transiting Exoplanet Survey Satellite (TESS) is observing tens of millions of stars with time spans ranging from ~27 days to about 1 yr of continuous observations. This vast amount of data contains a wealth of information for variability, exoplanet, and stellar astrophysics studies but requires a number of processing steps before it can be fully utilized. In order to efficiently process all the TESS data and make it available to the wider scientific community, the TESS Data for Asteroseismology working group, as part of the TESS Asteroseismic Science Consortium, has created an automated open-source processing pipeline to produce light curves corrected for systematics from the short- and long-cadence raw photometry data and to classify these according to stellar variability type. We will process all stars down to a TESS magnitude of 15. This paper is the next in a series detailing how the pipeline works. Here, we present our methodology for the automatic variability classification of TESS photometry using an ensemble of supervised learners that are combined into a metaclassifier. We successfully validate our method using a carefully constructed labeled sample of Kepler Q9 light curves with a 27.4 days time span mimicking single-sector TESS observations, on which we obtain an overall accuracy of 94.9%. We demonstrate that our methodology can successfully classify stars outside of our labeled sample by applying it to all ~167,000 stars observed in Q9 of the Kepler space mission.

Keywords: Asteroseismology