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APOGEE Net: Improving the Derived Spectral Parameters for Young Stars through Deep Learning
Stassun, Keivan G.; Kounkel, Marina; Covey, K. R. +6 more
Machine learning allows for efficient extraction of physical properties from stellar spectra that have been obtained by large surveys. The viability of machine-learning approaches has been demonstrated for spectra covering a variety of wavelengths and spectral resolutions, but most often for main-sequence (MS) or evolved stars, where reliable synt…
From hydrogen to helium: the spectral evolution of white dwarfs as evidence for convective mixing
Hollands, Mark; Gentile Fusillo, Nicola Pietro; Tremblay, Pier-Emmanuel +2 more
We present a study of the hypothesis that white dwarfs undergo a spectral change from hydrogen- to helium-dominated atmospheres using a volume-limited photometric sample drawn from the Gaia-DR2 catalogue, the Sloan Digital Sky Survey (SDSS), and the Galaxy Evolution Explorer (GALEX). We exploit the strength of the Balmer jump in hydrogen-atmospher…
A New Class of Roche Lobe-filling Hot Subdwarf Binaries
Duev, Dmitry A.; Szkody, Paula; Littlefair, S. P. +30 more
We present the discovery of the second binary with a Roche lobe-filling hot subdwarf transferring mass to a white dwarf (WD) companion. This 56 minute binary was discovered using data from the Zwicky Transient Facility. Spectroscopic observations reveal an He-sdOB star with an effective temperature of Teff = 33,700 ± 1000 K and a surfac…
HAZMAT VI: The Evolution of Extreme Ultraviolet Radiation Emitted from Early M Stars
Loyd, R. O. Parke; Peacock, Sarah; Barman, Travis +4 more
Quantifying the evolution of stellar extreme ultraviolet (EUV, 100-1000 Å) emission is critical for assessing the evolution of planetary atmospheres and the habitability of M dwarf systems. Previous studies from the HAbitable Zones and M dwarf Activity across Time (HAZMAT) program showed the far- and near-UV (FUV, NUV) emission from M stars at var…
SCExAO/CHARIS Direct Imaging Discovery of a 20 au Separation, Low-mass Ratio Brown Dwarf Companion to an Accelerating Sun-like Star
Currie, Thayne; Kwon, Jungmi; Tamura, Motohide +27 more
We present the direct imaging discovery of a substellar companion to the nearby Sun-like star, HD 33632 Aa, at a projected separation of ∼20 au, obtained with SCExAO/CHARIS integral field spectroscopy complemented by Keck/NIRC2 thermal infrared imaging. The companion, HD 33632 Ab, induces a 10.5σ astrometric acceleration on the star as detected wi…
How stellar rotation shapes the colour-magnitude diagram of the massive intermediate-age star cluster NGC 1846
Martocchia, S.; Salaris, M.; Cabrera-Ziri, I. +19 more
We present a detailed study of stellar rotation in the massive 1.5 Gyr old cluster NGC 1846 in the Large Magellanic Cloud. Similar to other clusters at this age, NGC 1846 shows an extended main-sequence turn-off (eMSTO), and previous photometric studies have suggested it could be bimodal. In this study, we use MUSE integral-field spectroscopy to m…
Gaia search for stellar companions of TESS Objects of Interest
Mugrauer, Markus; Michel, Kai-Uwe
The first results of a new survey, which explores the second data release of the ESA Gaia mission, are reported in order to search for stellar companions of (Community) TESS Objects of Interest and to characterize their properties. In total, 193 binary and 15 hierarchical triple star systems are presented, detected among 1,391 target stars, which …
Plateau de Bure High-z Blue Sequence Survey 2 (PHIBSS2): Search for Secondary Sources, CO Luminosity Functions in the Field, and the Evolution of Molecular Gas Density through Cosmic Time
Lenkić, Laura; Bolatto, Alberto D.; Neri, Roberto +8 more
We report on the results of a search for serendipitous sources in CO emission in 110 cubes targeting CO(2 - 1), CO(3 - 2), and CO(6 - 5) at z ∼ 1-2 from the second Plateau de Bure High-z Blue Sequence Survey (PHIBSS2). The PHIBSS2 observations were part of a 4 yr legacy program at the IRAM Plateau de Bure Interferometer aimed at studying early gal…
Aurora in the Polar Cap: A Review
Frey, Harald U.; Kullen, Anita; Maggiolo, Romain +5 more
This paper reviews our current understanding of auroral features that appear poleward of the main auroral oval within the polar cap, especially those that are known as Sun-aligned arcs, transpolar arcs, or theta auroras. They tend to appear predominantly during periods of quiet geomagnetic activity or northwards directed interplanetary magnetic fi…
A Relationship between Stellar Age and Spot Coverage
Morris, Brett M.
We investigate starspot distributions consistent with space-based photometry of F, G, and K stars in six stellar associations ranging in age from 10 Myr to 4 Gyr. We show that a simple light-curve statistic called the "smoothed amplitude" is proportional to stellar age as t-1/2, following a Skumanich-like spin-down relation. We marginal…