adsabs/SciX_UAT_keywords huggingface dataset:
Interpolation and Synthesis of Sparse Samples in Exoplanet Atmospheric Modeling

This paper highlights methods from geostatistics that are relevant to the interpretation, intercomparison, and synthesis of atmospheric model data, with a specific application to exoplanet atmospheric modeling. Climate models are increasingly used to study theoretical and observational properties of exoplanets, which include a hierarchy of models ranging from fast and idealized models to those that are slower but more comprehensive. Exploring large parameter spaces with computationally expensive models can be accomplished with sparse sampling techniques, but analyzing such sparse samples can pose challenges for conventional interpolation functions. Ordinary kriging is a statistical method for describing the spatial distribution of a data set in terms of the variogram function, which can be used to interpolate sparse samples across any number of dimensions. Variograms themselves may also be useful diagnostic tools for describing the spatial distribution of model data in exoplanet atmospheric model intercomparison projects. Universal kriging is another method that can synthesize data calculated by models of different complexity, which can be used to combine sparse samples of data from slow models with larger samples of data from fast models. Ordinary and universal kriging can also provide a way to synthesize model predictions with sparse samples of exoplanet observations and may have other applications in exoplanet science.

Keywords: exoplanet astronomy; importance sampling; planetary climates
Rotationally Inelastic Collisions of CN- with He: Computing Cross Sections and Rates in the Interstellar Medium

A newly calculated ab initio potential energy surface is used to compute collision-driven state-changing cross sections and rate coefficients over a range from 5 to 100 K for CN-(1Σ), the smallest anion detected in the interstellar medium, interacting with He, an abundant species in this environment. We compare our presently computed rate coefficients with those previously published for the similar and important systems CN-He, CN-H2, and CN--H2 to illustrate the broader network of inelastic, state-changing processes for these four systems. We also discuss the size-scaling effects that occur when changing partners from He to H2. We further analyze the differences in size between collision-driven rate coefficients when going from neutral CN to its anion. All the present results are discussed in detail, to provide accurate and realistic data for chemical networks that wish to include the CN- anion in their modeling of astrochemical environments.

Keywords: molecular physics; molecular clouds; radiative processes; diffuse molecular clouds; de-excitation rates; excitation rates
The Role of Active Galactic Nucleus Winds in Galaxy Formation: Connecting AGN Outflows at Low Redshifts to the Formation/Evolution of Their Host Galaxies

Using Sloan Digital Sky Survey (SDSS) spectra, we applied an automatic method to search for outflows (OFs) in three large samples of narrow-line active galactic nuclei (AGN) at low redshifts (z < 0.4), separated into three spectral activity classes: radio-loud galaxies (RGs), 15,793; radio-quiet Seyfert 2 AGN (Sy2), 18,585; and LINERs, 25,656. In general, the probability of detecting an OF decreases along the sequence Sy1→Sy2→LINER/RG and independently of the AGN class, the wind velocity, traced by W80, increases with the AGN luminosity. Moreover W80 is systematically higher in RGs or any of the other AGN classes when detected in radio. These results support the idea that there are two main modes of production of OF, the radiative mode dominant in radio-quiet AGN and the jet mode dominant in RGs, although both modes could also happen simultaneously at different levels. From the spectra and SDSS photometry, the characteristics of the AGN host galaxies and their supermassive black holes (SMBHs) were also retrieved using the stellar population synthesis code STARLIGHT. This revealed that, independently of the AGN spectral class, (1) galaxy hosts with OFs have systematically later morphological types and higher star formation rates (SFRs) than their counterparts without OF, (2) the AGN occupy different positions in the specific diagnostic diagram (specific black hole accretion rate (sBHAR) versus specific SFR), which suggests they follow different evolutionary paths congruent with the morphology of their galaxy hosts, and (3) they show no evidence of AGN quenching or triggering of star formation. These results are consistent with a scenario explaining the different AGN classes as consequences of different formation processes of galaxies: early-type galaxies (LINERs and RGs) formed bigger bulges and more massive SMBHs, exhausting their reservoir of gas more rapidly than late-type galaxies (Sy2 and Sy1), and thereby quenching their star formation and starving their SMBHs.

Keywords: active galaxies; agn host galaxies; active galactic nuclei
The LSST AGN Data Challenge: Selection Methods

Development of the Rubin Observatory Legacy Survey of Space and Time (LSST) includes a series of Data Challenges (DCs) arranged by various LSST Scientific Collaborations that are taking place during the project's preoperational phase. The AGN Science Collaboration Data Challenge (AGNSC-DC) is a partial prototype of the expected LSST data on active galactic nuclei (AGNs), aimed at validating machine learning approaches for AGN selection and characterization in large surveys like LSST. The AGNSC-DC took place in 2021, focusing on accuracy, robustness, and scalability. The training and the blinded data sets were constructed to mimic the future LSST release catalogs using the data from the Sloan Digital Sky Survey Stripe 82 region and the XMM-Newton Large Scale Structure Survey region. Data features were divided into astrometry, photometry, color, morphology, redshift, and class label with the addition of variability features and images. We present the results of four submitted solutions to DCs using both classical and machine learning methods. We systematically test the performance of supervised models (support vector machine, random forest, extreme gradient boosting, artificial neural network, convolutional neural network) and unsupervised ones (deep embedding clustering) when applied to the problem of classifying/clustering sources as stars, galaxies, or AGNs. We obtained classification accuracy of 97.5% for supervised models and clustering accuracy of 96.0% for unsupervised ones and 95.0% with a classic approach for a blinded data set. We find that variability features significantly improve the accuracy of the trained models, and correlation analysis among different bands enables a fast and inexpensive first-order selection of quasar candidates.

Keywords: active galactic nuclei; quasars; active galaxies; neural networks; classification; random forests; support vector machine; catalogs; convolutional neural networks; clustering; sky surveys
Fast Derivation of Contact Binary Parameters for Large Photometric Surveys

Thanks to an enormous release of light curves of contact binaries, it is a challenge to derive the parameters of contact binaries using the Phoebe program and the Wilson-Devinney program with the Markov chain Monte Carlo (MCMC) algorithm. In this paper, we use neural network (NN) and MCMC algorithm to derive the parameters of contact binaries. The fitting of models is still done with the MCMC algorithm, but that the neural network is used to establish the mapping relationship between the parameters and the light curves generated beforehand by Phoebe. The NN model is trained with a set of Phoebe-generated light curves with known input parameters, and then combined with the MCMC algorithm to quickly obtain the posterior distribution of the parameters. Two NN models without and with the influence of third light are established, which can generate light curves with 100 points faster than Phoebe by about four orders of magnitude under the same running condition. In addition, the two models can generate the light curves with an error of less than a millimagnitude. The feasibility of NN and MCMC algorithm is also verified by the synthetic light curves generated by Phoebe and the light curves from Kepler survey data. NN and MCMC algorithms can quickly derive the parameters and the corresponding parameter errors of contact binaries from sky survey. These parameters can also be used as more precise initial input values for the objectives of individual detailed studies.

Keywords: binary stars; eclipsing binary stars; contact binary stars
The X-Ray Binary Population in the Galactic Center Revealed through Multi-decade Observations

We present an investigation of the quiescent and transient X-ray binaries (XRBs) of the Galactic Center (GC). We extended our Chandra analysis of the non-thermal X-ray sources, located in the central parsec, from Hailey et al. (2018), using an additional 4.6 Msec of ACIS-S data obtained in 2012-2018. The individual Chandra spectra of the 12 sources fit to an absorbed power-law model with a mean photon index Γ ≈ 2 and show no Fe emission lines. Long-term variability was detected from nine of them, confirming that a majority are quiescent XRBs. Frequent X-ray monitoring of the GC revealed that the 12 non-thermal X-ray sources, as well as four X-ray transients have shown at most a single outburst over the last two decades. They are distinct from the six known neutron star LMXBs in the GC, which have all undergone multiple outbursts with ≲ 5 year recurrence time on average. Based on the outburst history data of the broader population of X-ray transients, we conclude that the 16 sources represent a population of ~240-630 tightly bound BH-LMXBs with ~4-12 hr orbital periods, consistent with the stellar/binary dynamics modeling in the vicinity of Sgr A*. The distribution of the 16 BH-LMXB candidates is disk-like (at 87% CL) and aligned with the nuclear star cluster. Our results have implications for XRB formation and the rate of gravitational wave events in other galactic nuclei.

Keywords: galactic center; low-mass x-ray binary stars; stellar mass black holes; x-ray transient sources
Assessment of SDSS-derived Galaxy Morphologies Using HST Imaging

The Sloan Digital Sky Survey (SDSS) was foundational to the study of galaxy evolution, having revealed the bimodality of galaxies and the relationship between their structure and star-forming activity. However, ground-based optical surveys like SDSS are limited in resolution and depth, which may lead to biases or poor quality in the derived morphological properties, potentially impacting our understanding of how and why galaxies cease their star formation (quench). We use archival Hubble Space Telescope (HST) imaging of ∼2000 SDSS objects to assess the reliability of SDSS-derived morphologies, taking advantage of both SDSS statistical samples and HST's superior resolution and sensitivity. Single Sérsic fitting and bulge-disk decomposition is performed on HST images for direct comparison with SDSS results. Of the three catalogs of SDSS-derived morphologies considered, none is significantly more accurate or precise than the others. For disk-dominated galaxies (n < 2.5), global Sérsic indices (n) from Meert et al. (hereafter, M15) are preferred. For bulge-dominated galaxies (n > 2.5), Simard et al. (hereafter, S11) and M15 overestimate n by ∼20%, and derived global n from Blanton et al. are preferred. We provide an empirical relation to correct S11 global Sérsic indices. Global R eff from S11 overestimates R eff for the largest galaxies by 0.1 dex. Despite these moderate biases, SDSS-derived single-component parameters are generally significantly more robust than SDSS-derived two-component parameters. The bulge Sérsic index (n bulge) cannot be reliably constrained from SDSS imaging at all, whereas the bulge-to-total (B/T) ratio can be inferred from SDSS (provided that n bulge = 4 is enforced) but has a large random error of ∼0.2.

Keywords: galaxies; galaxy bulges; galaxy structure; galaxy quenching; galaxy evolution; disk galaxies; early-type galaxies; late-type galaxies; galaxy classification systems; quenched galaxies; galactic and extragalactic astronomy; hubble space telescope
Prospects for the In Situ detection of Comet C/2019 Y4 ATLAS by Solar Orbiter

The European Space Agency's Solar Orbiter spacecraft will pass approximately downstream of the position of comet C/2019 Y4 (ATLAS) in late May and early June 2020. We predict that the spacecraft may encounter the comet's ion tail around 2020 May 31—June 1, and that the comet's dust tail may be crossed on 2020 June 6. We outline the solar wind features and dust grain collisions that the spacecraft's instruments may detect when crossing the comet's two tails. Solar Orbiter will also pass close to the orbital path of C/2020 F8 (SWAN) on 2020 May 22, but we believe that it is unlikely to detect any material associated with that comet.

Keywords: comet tails; space probes; solar wind; interplanetary dust; ionized coma gases; coma dust
LIGHTS. Survey Overview and a Search for Low Surface Brightness Satellite Galaxies

We present an overview of the LBT Imaging of Galactic Halos and Tidal Structures survey, which currently includes 25 nearby galaxies that are on average ∼1 mag fainter than the Milky Way, and a catalog of 54 low central surface brightness (24 < μ 0,g /mag arcsec‑2 < 28) satellite galaxy candidates, most of which were previously uncatalogued. The depth of the imaging exceeds the full 10 yr depth of the Rubin Observatory's Legacy Survey of Space and Time. We find, after applying completeness corrections, rising numbers of candidate satellites as we approach the limiting luminosity (M r ∼ ‑8 mag) and central surface brightness (μ 0,g ∼ 28 mag arcsec‑2). Over the parameter range we explore, each host galaxy (excluding those that are in overdense regions, apparently groups) has nearly four such candidate satellites to a projected radius of ∼100 kpc. These objects are mostly just at or beyond the reach of spectroscopy unless they are H I rich or have ongoing star formation. We identify three, possibly four, ultra-diffuse satellite galaxies (effective radius >1.5 kpc). This incidence rate falls within expectations of the extrapolation of the published relationship between the number of ultra-diffuse satellite galaxies and host halo mass. Last, we visually identify 12 candidate satellites that host a nuclear star cluster (NSC). The NSC occupation fraction for the sample (12/54) matches that published for satellites of early-type galaxies, suggesting that the parent's morphological type plays at most a limited role in determining the NSC occupation fraction.

Keywords: companion galaxies; low surface brightness galaxies; dwarf galaxies; galaxy stellar halos
Second-scale Submillimeter Variability of Sagittarius A* during Flaring Activity of 2019: On the Origin of Bright Near-infrared Flares

In 2019, Sgr A*-the supermassive black hole in the Galactic Center-underwent unprecedented flaring activity in the near-infrared (NIR), brightening by up to a factor of 100 compared to quiescent values. Here we report Atacama Large Millimeter/submillimeter Array (ALMA) observations of Sgr A*'s continuum variability at 1.3 mm (230 GHz)-a tracer of the accretion rate-conducted one month after the brightest detected NIR flare and in the middle of the flaring activity of 2019. We develop an innovative light-curve extraction technique which (together with ALMA's excellent sensitivity) allows us to obtain light curves that are simultaneously of high time resolution (2 s) and high signal-to-noise ratio (~500). We construct an accurate intrinsic structure function of the Sgr A* submm variability, improving on previous studies by about two orders of magnitude in timescale and one order of magnitude in sensitivity. We compare the 2019 June variability behavior with that of 2001-2017 and suggest that the most likely cause of the bright NIR flares is magnetic reconnection.

Keywords: galactic center; supermassive black holes; submillimeter astronomy; low-luminosity active galactic nuclei
GRB 211211A: A Neutron Star-White Dwarf Merger?

The gamma-ray burst GRB 211211A and its associated kilonova-like emission were reported recently. A significant difference between this association event and GRB 170817A/AT 2017gfo is that GRB 211211A has a very long duration. In this Letter, we show that this association event may arise from a neutron star-white dwarf (NS-WD) merger if the central engine leaves a magnetar behind. Within the NS-WD merger, the main burst of GRB 211211A could be produced by magnetic bubble eruptions from toroidal magnetic field amplification of the premerger NS. This toroidal field amplification can be induced by the runaway accretion from the WD debris disk if the disk is in low initial entropy and efficient wind, while the extended emission of GRB 211211A is likely involved with magnetic propelling. The observed energetics and duration of the prompt emission of GRB 211211A can be fulfilled in comparison with those of accretion in a hydrodynamical thermonuclear simulation, as long as the WD has a mass ≳1M ⊙. Moreover, if the X-ray plateau in GRB afterglows is due to the magnetar spin-down radiation, GRB optical afterglows and kilonova-like emission can be jointly well modeled combining the standard forward shock with the radioactive decay power of 56Ni adding a rotational power input from the postmerger magnetar.

Keywords: magnetars; gamma-ray bursts; compact binary stars; neutron stars; white dwarf stars
Autonomous Navigation Performance Using Natural Feature Tracking during the OSIRIS-REx Touch-and-Go Sample Collection Event

When the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft collected a sample of surface material from asteroid Bennu in 2020 October, it was the first time that an autonomous optical navigation system relying on natural terrain features had been used to guide a spacecraft to a planetary surface. This system, called Natural Feature Tracking (NFT), works by rendering features from digital terrain models and then correlating them with the terrain in real-time navigation images to estimate the spacecraft's position and velocity with respect to the asteroid. Here we describe how the OSIRIS-REx mission built the catalog of features for NFT and how those features performed during rehearsals for and execution of the Touch-and-Go (TAG) sample collection event. Feature performance (quality and accuracy of match) in the rendering and correlation process is the basis of the NFT measurement. All features scored well above the minimum correlation threshold thanks to the effort invested in selecting and modeling them. Residuals across the TAG trajectory were small, indicating that features in the catalog were defined consistently relative to each other. NFT delivered the spacecraft to within 1 m of the targeted location, with a difference of only 3.5 cm and 1.4 s from the predicted location and time of touch. This exceptional performance was crucial for spacecraft safety given Bennu's rough and hazardous terrain.

Keywords: asteroid surfaces
Post-merger Gravitational-wave Signal from Neutron-star Binaries: A New Look at an Old Problem

The spectral properties of the post-merger gravitational-wave signal from a binary of neutron stars encodes a variety of information about the features of the system and of the equation of state describing matter around and above nuclear saturation density. Characterizing the properties of such a signal is an "old" problem, which first emerged when a number of frequencies were shown to be related to the properties of the binary through "quasi-universal" relations. Here we take a new look at this old problem by computing the properties of the signal in terms of the Weyl scalar ψ 4. In this way, and using a database of more than 100 simulations, we provide the first evidence for a new instantaneous frequency, ${f}_{0}^{{\psi }_{4}}$ , associated with the instant of quasi-time-symmetry in the dynamics, and which also follows a quasi-universal relation. We also derive a new quasi-universal relation for the merger frequency ${f}_{\mathrm{mer}}^{h}$ , which provides a description of the data that is 4 times more accurate than previous expressions while requiring fewer fitting coefficients. Finally, consistent with the findings of numerous studies before ours, and using an enlarged ensemble of binary systems, we point out that the ℓ = 2, m = 1 gravitational-wave mode could become comparable with the traditional ℓ = 2, m = 2 mode on sufficiently long timescales, with strain amplitudes in a ratio ∣h 21∣/∣h 22∣ ~ 0.1-1 under generic orientations of the binary, which could be measured by present detectors for signals with a large signal-to-noise ratio or by third-generation detectors for generic signals should no collapse occur.

Keywords: neutron stars; gravitational waves; compact binary stars
Strong Correlation between Fe II/Mg II Ratio and Eddington Ratio of Type 1 Active Galactic Nuclei

The Fe II/Mg II line flux ratio has been used as an indicator of the Fe/Mg abundance ratio in the broad-line region (BLR) of active galactic nuclei (AGNs). On the basis of archival rest-frame UV spectra obtained via the Hubble Space Telescope and the Sloan Digital Sky Survey, we investigate the Fe II/Mg II ratios of type 1 AGNs at z < 2. Over wide dynamic ranges of AGN properties (i.e., black hole mass, AGN luminosity, and Eddington ratio), we confirm that the Fe II/Mg II ratio strongly correlates with Eddington ratio but not with black hole mass, AGN luminosity, or redshift. Our results suggest that the metallicity in the BLR are physically related to the accretion activity of AGNs, but not to the global properties of galaxies (i.e., galaxy mass and luminosity). With regard to the relation between the BLR metallicity and the accretion rate of AGNs, we discuss that metal cooling may play an important role in enhancing the gas inflow into the central region of host galaxies, resulting in the high accretion rate of AGNs.

Keywords: active galaxies; active galactic nuclei; interstellar medium; interstellar line emission; ultraviolet astronomy
LSST Survey Strategy in the Galactic Plane and Magellanic Clouds

Galactic science encompasses a wide range of subjects in the study of the Milky Way and Magellanic Clouds, from young stellar objects to X-ray binaries. Mapping these populations, and exploring transient phenomena within them, are among the primary science goals of the Vera C. Rubin Observatory's Legacy Survey of Space and Time. While early versions of the survey strategy dedicated relatively few visits to the Galactic Plane region, more recent strategies under consideration envision a higher cadence within selected regions of high scientific interest. The range of galactic science presents a challenge in evaluating which strategies deliver the highest scientific returns. Here we present metrics designed to evaluate Rubin survey strategy simulations, based on the cadence of observations they deliver within regions of interest to different topics in galactic science, using variability categories defined by timescale. We also compare the fractions of exposures obtained in each filter with those recommended for the different science goals. We find that the baseline_v2.x simulations deliver observations of the high-priority regions at sufficiently high cadence to reliably detect variability on timescales >10 days or more. Follow-up observations may be necessary to properly characterize variability, especially transients, on shorter timescales. Combining the regions of interest for all the science cases considered, we identify those areas of the Galactic Plane and Magellanic Clouds of highest priority. We recommend that these refined survey footprints be used in future simulations to explore rolling cadence scenarios, and to optimize the sequence of observations in different bandpasses.

Keywords: galactic and extragalactic astronomy; milky way galaxy; magellanic clouds; galactic bulge; optical astronomy; optical observation; astronomical methods; time domain astronomy