adsabs/SciX_UAT_keywords huggingface dataset:
Alert Classification for the ALeRCE Broker System: The Light Curve Classifier

We present the first version of the Automatic Learning for the Rapid Classification of Events (ALeRCE) broker light curve classifier. ALeRCE is currently processing the Zwicky Transient Facility (ZTF) alert stream, in preparation for the Vera C. Rubin Observatory. The ALeRCE light curve classifier uses variability features computed from the ZTF alert stream and colors obtained from AllWISE and ZTF photometry. We apply a balanced random forest algorithm with a two-level scheme where the top level classifies each source as periodic, stochastic, or transient, and the bottom level further resolves each of these hierarchical classes among 15 total classes. This classifier corresponds to the first attempt to classify multiple classes of stochastic variables (including core- and host-dominated active galactic nuclei, blazars, young stellar objects, and cataclysmic variables) in addition to different classes of periodic and transient sources, using real data. We created a labeled set using various public catalogs (such as the Catalina Surveys and Gaia DR2 variable stars catalogs, and the Million Quasars catalog), and we classify all objects with ≥6 g-band or ≥6 r-band detections in ZTF (868,371 sources as of 2020 June 9), providing updated classifications for sources with new alerts every day. For the top level we obtain macro-averaged precision and recall scores of 0.96 and 0.99, respectively, and for the bottom level we obtain macro-averaged precision and recall scores of 0.57 and 0.76, respectively. Updated classifications from the light curve classifier can be found at the ALeRCE Explorer website (http://alerce.online).

Keywords: active galaxies; astronomy data analysis; variable stars; supernovae; surveys
Two Lensed Star Candidates at z ≃ 4.8 behind the Galaxy Cluster MACS J0647.7+7015

We report the discovery of two extremely magnified lensed star candidates behind the galaxy cluster MACS J0647.7+015 using recent multiband James Webb Space Telescope (JWST) NIRCam observations. The star candidates are seen in a previously known, z phot ≃ 4.8 dropout giant arc that straddles the critical curve. The candidates lie near the expected critical curve position, but lack clear counter-images on the other side of it, suggesting these are possibly stars undergoing caustic crossings. We present revised lensing models for the cluster, including multiply imaged galaxies newly identified in the JWST data, and use them to estimate background macro-magnifications of at least ≳90 and ≳50 at the positions of the two candidates, respectively. With these values, we expect effective, caustic-crossing magnifications of ~[103-105] for the two star candidates. The spectral energy distributions of the two candidates match well the spectra of B-type stars with best-fit surface temperatures of ~10,000 K, and ~12,000 K, respectively, and we show that such stars with masses ≳20 M ⊙ and ≳50 M ⊙, respectively, can become sufficiently magnified to be observable. We briefly discuss other alternative explanations and conclude that these objects are likely lensed stars, but also acknowledge that the less-magnified candidate may alternatively reside in a star cluster. These star candidates constitute the second highest-redshift examples to date after Earendel at z phot ≃ 6.2, establishing further the potential of studying extremely magnified stars at high redshifts with JWST. Planned future observations, including with NIRSpec, will enable a more detailed view of these candidates in the near future.

Keywords: strong gravitational lensing; gravitational microlensing; massive stars
Prediction and Understanding of Soft-proton Contamination in XMM-Newton: A Machine Learning Approach

One of the major and unfortunately unforeseen sources of background for the current generation of X-ray telescopes are few tens to hundreds of keV (soft) protons concentrated by the mirrors. One such telescope is the European Space Agency's (ESA) X-ray Multi-Mirror Mission (XMM-Newton). Its observing time lost due to background contamination is about 40%. This loss of observing time affects all the major broad science goals of this observatory, ranging from cosmology to astrophysics of neutron stars and black holes. The soft-proton background could dramatically impact future large X-ray missions such as the ESA planned Athena mission (http://www.the-athena-x-ray-observatory.eu/). Physical processes that trigger this background are still poorly understood. We use a machine learning (ML) approach to delineate related important parameters and to develop a model to predict the background contamination using 12 yr of XMM-Newton observations. As predictors we use the location of the satellite and solar and geomagnetic activity parameters. We revealed that the contamination is most strongly related to the distance in the southern direction, Z (XMM-Newton observations were in the southern hemisphere), the solar wind radial velocity, and the location on the magnetospheric magnetic field lines. We derived simple empirical models for the first two individual predictors and an ML model that utilizes an ensemble of the predictors (Extra-Trees Regressor) and gives better performance. Based on our analysis, future missions should minimize observations during times associated with high solar wind speed and avoid closed magnetic field lines, especially at the dusk flank region in the southern hemisphere.

Keywords: x-ray telescopes; x-ray detectors; x-ray observatories; space plasmas; astronomy data modeling; astronomy data analysis
On the Interpretation of XSPEC Abundances and Emission Measures

The purpose of this work is to describe the assumptions built into the X-ray spectrum fitting software XSPEC for the calculation of element abundances and emission measure of a plasma and to describe the effects when those assumptions are not accurate. The ratio of electron density to hydrogen density in XSPEC is fixed at a constant. The correct ratio can be calculated from the ionization states of the elements. We show the constant value used in XSPEC is valid to within ≃3.5% for a solar-abundance plasma. For a plasma that deviates from solar abundance, e.g., hydrogen-poor or heavy-element-rich plasmas such as those found in the ejecta of supernova remnants, this ratio can be smaller by factors of 0.1–0.001. The hydrogen emission measure, defined by integral of electron density times hydrogen density over plasma volume, is derived from the norm in XSPEC, but one needs to include the hydrogen abundance factor. For other elements, the emission measures are the XSPEC values multiplied by the element abundance factors. Using the correct electron-to-hydrogen ratio and emission measures, we show the correct electron density is smaller by the square root of the correct electron density ratio divided by the XSPEC value. Element densities and total masses (for given distance and volume) are larger by the abundance factors divided by the above square root. Because hydrogen-poor plasmas occur in the ejecta of Type Ia supernova remnants, previously estimated element masses from X-ray spectra are likely to be significantly underestimated.

Keywords: plasma astrophysics; supernova remnants; chemical abundances; nucleosynthesis; atomic spectroscopy
Dark Off-limb Gap: Manifestation of a Temperature Minimum and the Dynamic Nature of the Chromosphere

We study off-limb emission of the lower solar atmosphere using high-resolution imaging spectroscopy in the Hβ and Ca II 8542 Å lines obtained with the CHROMospheric Imaging Spectrometer (CHROMIS) and the CRisp Imaging SpectroPolarimeter (CRISP) on the Swedish 1 m Solar Telescope. The Hβ line-wing images show the dark intensity gap between the photospheric limb and chromosphere, which is absent in the Ca II images. We calculate synthetic spectra of the off-limb emissions with the RH code in one-dimensional spherical geometry and find good agreement with the observations. The analysis of synthetic line profiles shows that the gap in the Hβ line-wing images maps the temperature minimum region between the photosphere and chromosphere due to the well-known opacity and emissivity gap of Balmer lines in this layer. However, the observed gap is detected farther from the line core in the outer line-wing positions than in the synthetic profiles. We found that an increased microturbulence in the model chromosphere is needed to reproduce the dark gap in the outer line wing, suggesting that the observed Hβ gap is the manifestation of the temperature minimum and the dynamic nature of the solar chromosphere. The temperature minimum produces a small enhancement in synthetic Ca II line-wing intensities. Observed off-limb Ca II line-wing emissions show similar enhancement below the temperature minimum layer near the edge of the photospheric limb.

Keywords: spectroscopy; ground telescopes; solar chromosphere; high resolution spectroscopy; radiative transfer simulations
The Investigation of Seven Kepler Contact Binaries in the Field of NGC 6819

Using the Kepler Eclipsing Binary Catalog, we found seven EW-type eclipsing binaries within the tidal radius of the intermediate-aged open cluster NGC 6819 (about 40'). These seven EW eclipsing binaries are all confirmed to be contact binaries by light curve analysis with the 2015 version Wilson-Devinney program. Using the parameter characteristics of contact binaries, we found that only KIC 4937217 could be a member of NGC 6819. Moreover, KIC 5199489 should be a shallow, unity-mass-ratio contact binary implying an early contact stage or a mass-ratio reverse stage. Nevertheless, KIC 5198934 and KIC 5374883 should be deep, low mass ratio contact binaries (DLMRCBs), which are usually considered as premergers.

Keywords: eclipsing binary stars; binary stars; contact binary stars; open star clusters
Discovery of a 500 au Protobinary in the Massive Prestellar Core G11.92-0.61 MM2

We present high-resolution (≲160 au) Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm observations of the high-mass prestellar core candidate G11.92-0.61 MM2, which reveal that this source is in fact a protobinary system with a projected separation of 505 au. The binary components, MM2E and MM2W, are compact (radii <140 au) sources within the partially optically thick dust emission with α 0.9 cm-1.3 mm = 2.47-2.94. The 1.3 mm brightness temperatures, T b = 68.4/64.6 K for MM2E/MM2W, imply internal heating and minimum luminosities L * > 24.7 L ⊙ for MM2E and L * > 12.6 L ⊙ for MM2W. The compact sources are connected by a "bridge" of lower-surface-brightness dust emission and lie within more extended emission that may correspond to a circumbinary disk. The circumprotostellar gas mass, estimated from ~0.″2 resolution VLA 0.9 cm observations assuming optically thin emission, is 6.8 ± 0.9 M ⊙. No line emission is detected toward MM2E and MM2W in our high-resolution 1.3 mm ALMA observations. The only line detected is 13CO J = 2-1, in absorption against the 1.3 mm continuum, which likely traces a layer of cooler molecular material surrounding the protostars. We also report the discovery of a highly asymmetric bipolar molecular outflow that appears to be driven by MM2E and/or MM2W in new deep, ~0.″5 resolution (1685 au) ALMA 0.82 mm observations. This outflow, traced by low-excitation CH3OH emission, indicates ongoing accretion onto the protobinary system. Overall, the super-Alfvénic models of Mignon-Risse et al. agree well with the observed properties of the MM2E/MM2W protobinary, suggesting that this system may be forming in an environment with a weak magnetic field.

Keywords: star formation; star forming regions; protostars; stellar accretion; binary stars; stellar accretion disks
Heating or Cooling: Study of Advective Heat Transport in the Inflow and the Outflow of Optically Thin Advection-dominated Accretion Flows

Advection is believed to be the dominant cooling mechanism in optically thin advection-dominated accretion flows (ADAFs). When outflow is considered, however, the first impression is that advection should be of opposite sign in the inflow and the outflow, due to the opposite direction of radial motion. Then how is the energy balance achieved simultaneously? We investigate the problem in this paper, analyzing the profiles of different components of advection with self-similar solutions of ADAFs in spherical coordinates (r θ ϕ). We find that for n < 3γ/2 - 1, where n is the density index in ρ ∝ r -n and γ is the heat capacity ratio, the radial advection is a heating mechanism in the inflow and a cooling mechanism in the outflow. It becomes 0 for n = 3γ/2 - 1, and turns to a cooling mechanism in the inflow and a heating mechanism in the outflow for n > 3γ/2 - 1. The energy conservation is only achieved when the latitudinal (θ direction) advection is considered, which takes an appropriate value to maintain energy balance, so that the overall effect of advection, no matter the parameter choices, is always a cooling mechanism that cancels out the viscous heating everywhere. For the extreme case of n = 3/2, latitudinal motion stops, viscous heating is balanced solely by radial advection, and no outflow is developed.

Keywords: accretion; hydrodynamics; high energy astrophysics
Unveiling the Population of Wandering Black Holes via Electromagnetic Signatures

While most galaxies appear to host a central supermassive black hole (SMBH), they are expected to also contain a substantial population of off-center "wandering" SMBHs naturally produced by the hierarchical merger-driven process of galaxy assembly. This population has been recently characterized in an analysis of the ROMULUS cosmological simulations, which correct for the dynamical forces on SMBHs without artificially pinning them to halo centers. Here we predict an array of electromagnetic signatures for these wanderers. The predicted wandering population of SMBHs from ROMULUS broadly reproduces the observed spatial offsets of a recent sample of hyperluminous X-ray sources. We predict that the sources with the most extreme offsets are likely to arise from SMBHs within satellite galaxies. These simulations also predict a significant population of secondary active galactic nuclei (AGNs) with luminosities at least 10% that of the central AGN. The majority of galaxies at z = 4 that host a central AGN with bolometric luminosity Lbol > 1042 erg s-1 are predicted to host a companion off-center AGN of comparable brightness. We demonstrate that stacked X-ray observations of similar mass galaxies may reveal a halo of collective emission attributable to these wanderers. Finally, because wanderers dominate the population of SMBHs with masses of ≲107 M⊙ in ROMULUS, they may dominate tidal disruption event (TDE) rates at these masses if they retain a stellar component (e.g., a nuclear star cluster). This could warrant an order of magnitude correction to current theoretically estimated TDE rates at low SMBH masses.

Keywords: supermassive black holes; active galactic nuclei; agn host galaxies; hydrodynamical simulations
The M-dwarf Ultraviolet Spectroscopic Sample. I. Determining Stellar Parameters for Field Stars

Accurate stellar properties are essential for precise stellar astrophysics and exoplanetary science. In the M-dwarf regime, much effort has gone into defining empirical relations that can use readily accessible observables to assess physical stellar properties. Often, these relations for the quantity of interest are cast as a nonlinear function of available data; in Bayesian modeling, however, the reverse is needed. In this article, we introduce a new Bayesian framework to self-consistently and simultaneously apply multiple empirical calibrations to fully characterize the mass, luminosity, radius, and effective temperature of a field age M dwarf. This framework includes a new M-dwarf mass-radius relation with a scatter of 3.1% at fixed mass. We further introduce the M-dwarf Ultraviolet Spectroscopic Sample (MUSS), and apply our methodology to provide consistent stellar parameters for these nearby low-mass stars, selected as having available spectroscopic data in the ultraviolet. These targets are of interest largely as either exoplanet hosts or benchmarks in multiwavelength stellar activity. We use the field MUSS stars to define a low-mass main sequence in the solar neighborhood through Gaussian Process (GP) regression. These results enable us to empirically measure a feature in the GP derivative at ${{ \mathcal M }}_{b}=0.337{\pm }_{0.026}^{0.013}$ M⊙ that indicates where the MUSS transitions from fully to partly convective interiors.

Keywords: m dwarf stars; astrostatistics; fundamental parameters of stars
Resolving Io's Volcanoes from a Mutual Event Observation at the Large Binocular Telescope

Unraveling the geological processes ongoing at Io's numerous sites of active volcanism requires high spatial resolution to, for example, measure the areal coverage of lava flows or identify the presence of multiple emitting regions within a single volcanic center. In de Kleer et al. (2017) we described observations with the Large Binocular Telescope during an occultation of Io by Europa at ~6:17 UT on 2015 March 8 and presented a map of the temperature distribution within Loki Patera derived from these data. Here we present emission maps of three other volcanic centers derived from the same observation: Pillan Patera, Kurdalagon Patera, and the vicinity of Ulgen Patera/PV59/N Lerna Regio. The emission is localized by the light curves and resolved into multiple distinct emitting regions in two of the cases. Both Pillan and Kurdalagon Paterae had undergone eruptions in the months prior to our observations, and the location and intensity of the emission are interpreted in the context of the temporal evolution of these eruptions observed from other facilities. The emission from Kurdalagon Patera is resolved into two distinct emitting regions separated by only a few degrees in latitude that were unresolved by Keck observations from the same month.

Keywords: occultation; interferometry; galilean satellites; io; volcanism
Particle Clustering in Turbulence: Prediction of Spatial and Statistical Properties with Deep Learning

We investigate the utility of deep learning for modeling the clustering of particles that are aerodynamically coupled to turbulent fluids. Using a Lagrangian particle module within the Athena++ hydrodynamics code, we simulate the dynamics of particles in the Epstein drag regime within a periodic domain of isotropic forced hydrodynamic turbulence. This setup is an idealized model relevant to the collisional growth of micron- to millimeter-sized dust particles in early-stage planet formation. The simulation data are used to train a U-Net deep-learning model to predict gridded three-dimensional representations of the particle density and velocity fields, given as input the corresponding fluid fields. The trained model qualitatively captures the filamentary structure of clustered particles in a highly nonlinear regime. We assess model fidelity by calculating metrics of the density field (the radial distribution function) and of the velocity field (the relative velocity and the relative radial velocity between particles). Although trained only on the spatial fields, the model predicts these statistical quantities with errors that are typically <10%. Our results suggest that, given appropriately expanded training data, deep learning could complement direct numerical simulations in predicting particle clustering within turbulent flows.

Keywords: hydrodynamical simulations; protoplanetary disks; neural networks; planet formation
Orientations of Dark Matter Halos in FIRE-2 Milky Way-mass Galaxies

The shape and orientation of dark matter (DM) halos are sensitive to the microphysics of the DM particles, yet in many mass models, the symmetry axes of the Milky Way's DM halo are often assumed to be aligned with the symmetry axes of the stellar disk. This is well motivated for the inner DM halo, but not for the outer halo. We use zoomed-in cosmological baryonic simulations from the Latte suite of FIRE-2 Milky Way-mass galaxies to explore the evolution of the DM halo's orientation with radius and time, with or without a major merger with a Large Magellanic Cloud analog, and when varying the DM model. In three of the four cold DM halos we examine, the orientation of the halo minor axis diverges from the stellar disk vector by more than 20° beyond about 30 galactocentric kpc, reaching a maximum of 30°-90°, depending on the individual halo's formation history. In identical simulations using a model of self-interacting DM with σ = 1 cm2 g-1, the halo remains aligned with the stellar disk out to ~200-400 kpc. Interactions with massive satellites (M ≳ 4 × 1010 M ⊙ at pericenter; M ≳ 3.3 × 1010 M ⊙ at infall) affect the orientation of the halo significantly, aligning the halo's major axis with the satellite galaxy from the disk to the virial radius. The relative orientation of the halo and disk beyond 30 kpc is a potential diagnostic of self-interacting DM, if the effects of massive satellites can be accounted for.

Keywords: dark matter; galaxies; computational methods; disk galaxies; milky way dark matter halo; galaxy dark matter halos
The GAPS Programme at TNG XXXIX. Multiple Molecular Species in the Atmosphere of the Warm Giant Planet WASP-80 b Unveiled at High Resolution with GIANO-B

Detections of molecules in the atmosphere of gas giant exoplanets allow us to investigate the physico-chemical properties of the atmospheres. Their inferred chemical composition is used as tracer of planet formation and evolution mechanisms. Currently, an increasing number of detections is showing a possible rich chemistry of the hotter gaseous planets, but whether this extends to cooler giants is still unknown. We observed four transits of WASP-80 b, a warm transiting giant planet orbiting a late-K dwarf star with the near-infrared GIANO-B spectrograph installed at the Telescopio Nazionale Galileo and performed high-resolution transmission spectroscopy analysis. We report the detection of several molecular species in its atmosphere. Combining the four nights and comparing our transmission spectrum to planetary atmosphere models containing the signature of individual molecules within the cross-correlation framework, we find the presence of H2O, CH4, NH3, and HCN with high significance, tentative detection of CO2, and inconclusive results for C2H2 and CO. A qualitative interpretation of these results, using physically motivated models, suggests an atmosphere consistent with solar composition and the presence of disequilibrium chemistry and we therefore recommend the inclusion of the latter in future modeling of sub-1000 K planets. ∗ Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated by the Fundación Galileo Galilei (FGG) of the Istituto Nazionale di Astrofisica (INAF) at the Observatorio del Roque de los Muchachos (La Palma, Canary Islands, Spain).

Keywords: exoplanet atmospheres; exoplanet astronomy; exoplanet atmospheric composition; exoplanet detection methods; transit photometry; high resolution spectroscopy; molecular spectroscopy