Sazuna/UAT_keywords huggingface dataset:
Machine-learning Inferences of the Interior Structure of Rocky Exoplanets from Bulk Observational Constraints. Characterizing the interiors of rocky exoplanets is important to understand planetary populations and further investigate planetary habitability. New observable constraints and inference techniques have been explored for this purpose. In this work, we design and train mixture density networks (MDNs) to predict the interior properties of rocky exoplanets with large compositional diversity. In addition to measurements of mass and radius, bulk refractory elemental abundance ratios and the static Love number k 2 are used to constrain the interior of rocky exoplanets. It is found that the MDNs are able to infer the interior properties of rocky exoplanets from the available measurements of exoplanets. Compared with powerful inversion methods based on Bayesian inference, the trained MDNs provide a more rapid characterization of planetary interiors for each individual planet. The MDN model offers a convenient and practical tool for probabilistic inferences of planetary interiors.

Keywords: Extrasolar rocky planets, Computational methods, Planetary interior, Neural networks
Statistical Analysis of Long GRBs' Prompt Emission and X-Ray Flares: Multivariate Clustering and Correlations. The extensive observations done by the X-ray Telescope on board Neil Gehrels Swift Observatory have revealed the presence of late-time flares concurrent with the decaying afterglow emission. However, the origins of these flares are elusive. In this work, we make use of the large database of Swift observations (2005-2020) of long gamma-ray bursts (GRBs) to conduct a systematic statistical study between the prompt gamma-ray emission and X-ray flares by characterizing their temporal and spectral properties of duration, quiescent period, peak flux, fluence, minimum variability timescale, and spectral power-law index. The multidimensional database of parameters thereby generated was investigated by principal component analysis, which revealed there is no evident correlation between the different parameters of the prompt emission and X-ray flares. Furthermore, the correlation studies revealed that while there is a trend of positive correlation between the minimum variability timescale of the flare and its duration, and of strong negative correlation with its peak flux, there are no such correlations observed in the prompt emission. Similarly, we find a positive correlation between the quiescent period and the flare duration, and a negative correlation with the flare peak flux, while no such correlations are observed for the prompt emission of the GRBs. Finally, among the X-ray flares, we find two dominant classes, whose variations are driven by the minimum variability timescale, peak flux, and fluence of the flares. A catalog of these different parameters characterizing the prompt and flare emissions is presented.

Keywords: Catalogs, Multivariate analysis, Gamma-ray bursts, Astrostatistics
Siena Galaxy Atlas 2020. We present the 2020 version of the Siena Galaxy Atlas (SGA-2020), a multiwavelength optical and infrared imaging atlas of 383,620 nearby galaxies. The SGA-2020 uses optical grz imaging over ≈20,000 deg2 from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9 and infrared imaging in four bands (spanning 3.4-22 μm) from the 6 year unWISE coadds; it is more than 95% complete for galaxies larger than R(26) ≈ 25″ and r &lt; 18 measured at the 26 mag arcsec-2 isophote in the r band. The atlas delivers precise coordinates, multiwavelength mosaics, azimuthally averaged optical surface-brightness profiles, model images and photometry, and additional ancillary metadata for the full sample. Coupled with existing and forthcoming optical spectroscopy from the DESI, the SGA-2020 will facilitate new detailed studies of the star formation and mass assembly histories of nearby galaxies; enable precise measurements of the local velocity field via the Tully-Fisher and fundamental plane relations; serve as a reference sample of lasting legacy value for time-domain and multimessenger astronomical events; and more.

Keywords: Celestial objects catalogs, Galaxy photometry
Quasar Factor Analysis-An Unsupervised and Probabilistic Quasar Continuum Prediction Algorithm with Latent Factor Analysis. Since their first discovery, quasars have been essential probes of the distant Universe. However, due to our limited knowledge of its nature, predicting the intrinsic quasar continua has bottlenecked their usage. Existing methods of quasar continuum recovery often rely on a limited number of high-quality quasar spectra, which might not capture the full diversity of the quasar population. In this study, we propose an unsupervised probabilistic model, quasar factor analysis (QFA), which combines factor analysis with physical priors of the intergalactic medium to overcome these limitations. QFA captures the posterior distribution of quasar continua through generatively modeling quasar spectra. We demonstrate that QFA can achieve the state-of-the-art performance, ~2% relative error, for continuum prediction in the Lyα forest region compared to previous methods. We further fit 90,678 2 &lt; z &lt; 3.5, signal-to-noise ratio &gt;2 quasar spectra from Sloan Digital Sky Survey Data Release 16 and found that for ~30% quasar spectra where the continua were ill-determined with previous methods, QFA yields visually more plausible continua. QFA also attains ≲1% error in the 1D Lyα power spectrum measurements at z ~ 3 and ~4% in z ~ 2.4. In addition, QFA determines latent factors representing more physical motivation than principal component analysis. We investigate the evolution of the latent factors and report no significant redshift or luminosity dependency except for the Baldwin effect. The generative nature of QFA also enables outlier detection robustly; we showed that QFA is effective in selecting outlying quasar spectra, including damped Lyα systems and potential Type II quasar spectra.

Keywords: Supermassive black holes, Bayesian statistics, Quasars, Posterior distribution, Lyman alpha forest, Active galactic nuclei, Intergalactic medium
Transiting Exoplanet Yields for the Roman Galactic Bulge Time Domain Survey Predicted from Pixel-level Simulations. The Nancy Grace Roman Space Telescope (Roman) is NASA's next astrophysics flagship mission, expected to launch in late 2026. As one of Roman's core community science surveys, the Galactic Bulge Time Domain Survey (GBTDS) will collect photometric and astrometric data for over 100 million stars in the Galactic bulge in order to search for microlensing planets. To assess the potential with which Roman can detect exoplanets via transit, we developed and conducted pixel-level simulations of transiting planets in the GBTDS. From these simulations, we predict that Roman will find between ~60,000 and ~200,000 transiting planets-over an order of magnitude more planets than are currently known. While the majority of these planets will be giants (R  p  &gt; 4R ⊕) on close-in orbits (a &lt; 0.3 au), the yield also includes between ~7000 and ~12,000 small planets (R  p  &lt; 4R ⊕). The yield for small planets depends sensitively on the observing cadence and season duration, with variations on the order of ~10%-20% for modest changes in either parameter, but is generally insensitive to the trade between surveyed area and cadence given constant slew/settle times. These predictions depend sensitively on the Milky Way's metallicity distribution function, highlighting an opportunity to significantly advance our understanding of exoplanet demographics, in particular across stellar populations and Galactic environments.

Keywords: Transits, Exoplanets, Planet hosting stars
An R <SUB>V</SUB> Map of the Milky Way Revealed by LAMOST. The total-to-selective extinction ratio, R V, is a key parameter for tracing the properties of interstellar dust, as it directly determines the variation of the extinction curve with wavelength. By utilizing accurate color excess measurements from the optical to the mid-infrared range, we have derived R V values for approximately three million stars from LAMOST data release 7 using a forward-modeling technique. This extensive data set enables us to construct a comprehensive 2D R V map of the Milky Way within the LAMOST footprint at a spatial resolution of ~27.'5. Based on reliable sight lines of E(B - V) &gt; 0.1, we find that R V exhibits a Gaussian distribution centered around 3.25 with a standard deviation of 0.25. The spatial variability of R V in the Galactic disk exhibits a wide range, spanning from small scales within individual molecular clouds to large scales up to kiloparsecs. A striking correlation is observed between the distribution of R V and molecular clouds. Notably, we observe lower R V values within the regions of nearby molecular clouds compared to their surrounding areas. Furthermore, we have investigated the relationships between R V and various parameters, including dust temperature, dust emissivity spectral index, column densities and ratios of atomic and molecular hydrogen, as well as the gas-to-dust ratio. We find that these relationships vary with the level of extinction. These analyses provide new insights into the properties and evolution of dust grains in diverse interstellar environments and also hold significant importance for achieving accurate extinction corrections.

Keywords: Interstellar dust, Interstellar dust extinction
The Chandra Cygnus OB2 Legacy Survey: Design and X-Ray Point-source Catalog. The Cygnus OB2 association is the largest concentration of young and massive stars within 2 kpc of the Sun, including an estimated ~65 O-type stars and hundreds of OB stars. The Chandra Cygnus OB2 Legacy Survey is a large imaging program undertaken with the Advanced CCD Imaging Spectrometer on board the Chandra X-ray Observatory. The survey has imaged the central 0.5 deg2 of the Cyg OB2 association with an effective exposure of ~120 ks and an outer 0.35 deg2 area with an exposure of ~60 ks. Here we describe the survey design and observations, discuss the data reduction and source detection, and present a catalog of ~8000 X-ray point sources. The survey design employs a grid of 36 heavily (~50%) overlapping pointings, a method that overcomes Chandra's low off-axis sensitivity and produces a highly uniform exposure over the inner 0.5 deg2. The full X-ray catalog is described here and is made available online.

Keywords: Massive stars, Pre-main sequence stars, X-ray stars
Simulating the Sensitivity to Stellar Point Sources of Chandra X-Ray Observations. The Chandra Cygnus OB2 Legacy Survey is a wide and deep X-ray survey of the nearby and massive Cygnus OB2 association. The survey has detected ~8000 X-ray sources, the majority of which are pre-main-sequence X-ray-emitting young stars in the association itself. To facilitate quantitative scientific studies of these sources, as well as the underlying OB association, it is important to understand the sensitivity of the observations and the level of completeness the observations have obtained. Here we describe the use of a hierarchical Monte Carlo simulation to achieve this goal by combining the empirical properties of the observations, analytic estimates of the source verification process, and an extensive set of source detection simulations. We find that our survey reaches a 90% completeness level for a pre-main-sequence population at the distance of Cyg OB2 at an X-ray luminosity of 4 × 1030 erg s-1 and a stellar mass of 1.3 M ⊙ for a randomly distributed population. For a spatially clustered population such as Cyg OB2 the 90% completeness level is reached at 1.1 M ⊙ instead, as the sources are more concentrated in areas of our survey with a high exposure. These simulations can easily be adapted for use with other X-ray observations and surveys, and we provide X-ray detection efficiency curves for a very wide array of source and background properties to allow these simulations to be easily exploited by other users.

Keywords: Pre-main sequence stars, X-ray stars
Optical and Infrared Counterparts of the X-Ray Sources Detected in the Chandra Cygnus OB2 Legacy Survey. The young massive OB association Cygnus OB2, in the Cygnus X complex, is the closest (~1400 pc) star-forming region to the Sun hosting thousands of young low-mass stars and up to 1000 OB stars, among which are some of the most massive stars known in our Galaxy. This region holds great importance for several fields of modern astrophysics, such as the study of the physical properties of massive and young low-mass stars and the feedback provided by massive stars on star and planet formation processes. Cyg OB2 has been recently observed with Chandra/ACIS-I as part of the 1.08 Ms Chandra Cygnus OB2 Legacy Project. This survey detected 7924 X-ray sources in a square degree area centered on Cyg OB2. Since a proper classification and study of the observed X-ray sources also requires the analysis of their optical and infrared counterparts, we combined a large and deep set of optical and infrared catalogs available for this region with our new X-ray catalog. In this paper we describe the matching procedure and present the combined catalog containing 5703 sources. We also briefly discuss the nature of the X-ray sources with optical and infrared counterparts using their position in the color-magnitude and color-color diagrams.

Keywords: Astronomy databases, Catalogs
Classification of Chandra X-Ray Sources in Cygnus OB2. We have devised a predominantly Naive Bayes-based method to classify X-ray sources detected by Chandra in the Cygnus OB2 association into members, foreground objects, and background objects. We employ a variety of X-ray, optical, and infrared characteristics to construct likelihoods using training sets defined by well-measured sources. Combinations of optical photometry from the Sloan Digital Sky Survey (riz) and Isaac Newton Telescope Photometric Hα Survey (r  I  i  I Hα), infrared magnitudes from United Kingdom Infrared Telescope Deep Sky Survey and Two-Micron All Sky Survey (JHK), X-ray quantiles and hardness ratios, and estimates of extinction A v are used to compute the relative probabilities that a given source belongs to one of the classes. Principal component analysis is used to isolate the best axes for separating the classes for the photometric data, and Gaussian component separation is used for X-ray hardness and extinction. Errors in the measurements are accounted for by modeling as Gaussians and integrating over likelihoods approximated as quartic polynomials. We evaluate the accuracy of the classification by inspection and reclassify a number of sources based on infrared magnitudes, the presence of disks, and spectral hardness induced by flaring. We also consider systematic errors due to extinction. Of the 7924 X-ray detections, 5501 have a total of 5597 optical/infrared matches, including 78 with multiple counterparts. We find that ≈6100 objects are likely association members, ≈1400 are background objects, and ≈500 are foreground objects, with an accuracy of 96%, 93%, and 80%, respectively, with an overall classification accuracy of approximately 95%.

Keywords: Bayesian statistics, Star forming regions, Astrostatistics techniques, Standard stars, OB associations, Astrostatistics, X-ray stars, Open star clusters, Catalogs
The Statistical Uncertainties on X-Ray Flux and Spectral Parameters from Chandra ACIS-I Observations of Faint Sources: Application to the Cygnus OB2 Association. We investigate the uncertainties of fitted X-ray model parameters and fluxes for relatively faint Chandra ACIS-I source spectra. Monte Carlo (MC) simulations are employed to construct a large set of 150,000 fake X-ray spectra in the low photon count statistics regime (from 10 to 350 net counts) using the XSPEC spectral model-fitting package. The simulations employed both absorbed thermal (APEC) and nonthermal (power-law) models, in concert with the Chandra ACIS-I instrument response and interstellar absorption. Simulated X-ray spectra were fit assuming a wide set of different input parameters and C-statistic minimization criteria to avoid numerical artifacts in the accepted solutions. Results provide an error estimate for each parameter (absorption, N H, plasma temperature, kT, or power-law slope, Γ, and flux) and for different background contamination levels. The distributions of these errors are studied as a function of the 1σ quantiles, and we show how these correlate with different model parameters, net counts in the spectra, and relative background level. Maps of uncertainty in terms of the 1σ quantiles for parameters and flux are computed as a function of spectrum net counts. We find very good agreement between our estimated X-ray spectral parameter and flux uncertainties and those recovered from spectral fitting for a subset of the X-ray sources detected in the Chandra Cygnus OB2 Legacy Survey diagnosed to be association members and that have between 20 and 350 net counts. Our method can provide uncertainties for spectral parameters whenever formal X-ray spectral fits cannot be well constrained, or are unavailable, and predictions useful for computing Chandra ACIS-I exposure times for observation planning.

Keywords: Computational methods, Astronomical methods, X-ray sources
X-Ray Spectral Characterization of the Young Cygnus OB2 Population. We analyze the X-ray spectra of the ~8000 sources detected in the Cygnus OB2 Chandra Legacy Survey (this focus issue), with the goals of characterizing the coronal plasma of the young low-mass stars in the region and estimating their intrinsic X-ray luminosities. We adopt two different strategies for X-ray sources for which more or less than 20 photons were detected. For the brighter sample we fit the spectra with absorbed isothermal models. In order to limit uncertainties, for most of the fainter Cygnus OB2 members in this sample we constrain the spectral parameters to characteristic ranges defined from the brightest stars. For X-ray sources with &lt;20 net photons we adopt a conversion factor from detected photon flux to intrinsic flux. This was defined, building on the results for the previous sample, as a function of the 20% quantile of the detected photon energy distributions, which we prove to also correlate well with extinction. We then use the X-ray extinction from the spectral fits to constrain the ratio between optical and X-ray extinction toward Cyg OB2, finding it consistent with standard "Galactic" values, when properly accounting for systematics. Finally, we exploit the large number of sources to constrain the average coronal abundances of several elements, through two different ensemble analyses of the X-ray spectra of low-mass Cyg OB2 members. We find the pattern of abundances to be largely consistent with that derived for the young stellar coronae in the Orion Nebula Cluster.

Keywords: Stellar abundances, Stellar activity, T Tauri stars, Pre-main sequence stars, Stellar coronae, X-ray stars
Photoevaporation and Close Encounters: How the Environment around Cygnus OB2 Affects the Evolution of Protoplanetary Disks. In our Galaxy, star formation occurs in a variety of environments, with a large fraction of stars formed in clusters hosting massive stars. OB stars have an important feedback on the evolution of protoplanetary disks orbiting around nearby young stars and likely on the process of planet formation occurring in them. The nearby massive association Cyg OB2 is an outstanding laboratory to study this feedback. It is the closest massive association to our Sun and hosts hundreds of massive stars and thousands of low-mass members, both with and without disks. In this paper, we analyze the spatial variation of the disk fraction (i.e., the fraction of cluster members bearing a disk) in Cyg OB2 and study its correlation with the local values of far-ultraviolet (FUV) and extreme-ultraviolet (EUV) radiation fields and the local stellar surface density. We present definitive evidence that disks are more rapidly dissipated in the regions of the association characterized by intense local UV fields and large stellar density. In particular, the FUV radiation dominates disk dissipation timescales in the proximity (i.e., within 0.5 pc) of the O stars. In the rest of the association, EUV photons potentially induce a significant mass loss from the irradiated disks across the entire association, but the efficiency of this process is reduced at increasing distances from the massive stars owing to absorption by the intervening intracluster material. We find that disk dissipation due to close stellar encounters is negligible in Cyg OB2 and likely to have affected 1% or fewer of the stellar population. Disk dissipation is instead dominated by photoevaporation. We also compare our results to what has been found in other young clusters with different massive populations, concluding that massive associations like Cyg OB2 are potentially hostile to protoplanetary disks but that the environments where disks can safely evolve in planetary systems are likely quite common in our Galaxy.

Keywords: Pre-main sequence stars, Star formation
Diffuse X-Ray Emission in the Cygnus OB2 Association. We present a large-scale study of diffuse X-ray emission in the nearby massive stellar association Cygnus OB2 as part of the Chandra Cygnus OB2 Legacy Program. We used 40 Chandra X-ray ACIS-I observations covering ~1.0 deg2. After removing 7924 point sources detected in our survey and applying adaptive smoothing to the background-corrected X-ray emission, the adaptive smoothing reveals large-scale diffuse X-ray emission. Diffuse emission was detected in the subbands soft (0.5-1.2 keV) and medium (1.2-2.5 keV) and marginally in the hard (2.5-7.0 keV) band. From X-ray spectral analysis of stacked spectra we compute a total (0.5-7.0 keV) diffuse X-ray luminosity of ${L}_{{\rm{X}}}^{\mathrm{diff}}\approx $ 4.2 × 1034 erg s-1, characterized by plasma temperature components at kT ≈ 0.11, 0.40, and 1.18 keV, respectively. The H I absorption column density corresponding to these temperatures has a distribution consistent with N H = (0.43, 0.80, 1.39) × 1022 cm-2. The extended medium-band energy emission likely arises from O-type stellar winds thermalized by wind-wind collisions in the most populated regions of the association, while the soft-band emission probably arises from less energetic termination shocks against the surrounding interstellar medium. Supersoft and soft diffuse emission appears more widely dispersed and intense than the medium-band emission. The diffuse X-ray emission is generally spatially coincident with low-extinction regions that we attribute to the ubiquitous influence of powerful stellar winds from massive stars and their interaction with the local interstellar medium. Diffuse X-ray emission is volume filling, rather than edge brightened, oppositely to other star-forming regions. We reveal the first observational evidence of X-ray halos around some evolved massive stars.

Keywords: Massive stars, X-ray stars, Stellar winds
Survey of Bare Active Galactic Nuclei in the Local Universe (z &lt; 0.2). I. On the Origin of Soft Excess. We analyze a sample of 21 "bare" Seyfert 1 active galactic nuclei, a subclass of Seyfert 1 galaxies, with intrinsic absorption N H ~ 1020 cm-2, in the local Universe (z &lt; 0.2) using XMM-Newton and Swift/XRT observations. The luminosities of the primary continuum, the X-ray emission in the 3-10 keV energy range, and the soft excess-the excess emission that appears above the low-energy extrapolation of the power-law fit of 3-10 keV X-ray spectra-are calculated. Our spectral analysis reveals that the long-term intrinsic luminosities of the soft excess and the primary continuum are tightly correlated $({L}_{\mathrm{PC}}\propto {L}_{\mathrm{SE}}^{1.1\pm 0.04})$ . We also found that the luminosities are correlated for each source. This result suggests that both the primary continuum and soft excess emissions exhibit a dependency on the accretion rate in a similar way.

Keywords: Accretion, Black hole physics, Seyfert galaxies, X-ray active galactic nuclei