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arXiv · 2211.14349

A Panchromatic Study of Massive Stars in the Extremely Metal-Poor Local Group Dwarf Galaxy Leo A

Maude Gull·Daniel R. Weisz·Peter Senchyna·Nathan R. Sandford·Yumi Choi·Anna F. McLeod·Kareem El-Badry·Ylva Götberg·Karoline M. Gilbert·Martha Boyer·Julianne J. Dalcanton·Puragra GuhaThakurta·Steven Goldman·Paola Marigo·Kristen B. W. McQuinn·Giada Pastorelli·Daniel P. Stark·Evan Skillman·Yuan-sen Ting·Benjamin F. Williams
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Abstract

We characterize massive stars (M>8 M_sun) in the nearby (D~0.8 Mpc) extremely metal-poor (Z~5% Z_sun) galaxy Leo A using Hubble Space Telescope ultra-violet (UV), optical, and near-infrared (NIR) imaging along with Keck/LRIS and MMT/Binospec optical spectroscopy for 18 main sequence OB stars. We find that: (a) 12 of our 18 stars show emission lines, despite not being associated with an H II region, suggestive of stellar activity (e.g., mass loss, accretion, binary star interaction), which is consistent with previous predictions of enhanced activity at low metallicity; (b) 6 are Be stars, which are the first to be spectroscopically studied at such low metallicity -- these Be stars have unusual panchromatic SEDs; (c) for stars well-fit by the TLUSTY non-local thermodynamic equilibrium (non-LTE) models, the photometric and spectroscopic values of T_eff and log(g) agree to within ~0.01 dex and ~0.18 dex, respectively, indicating that NUV/optical/NIR imaging can be used to reliably characterize massive (M ~ 8-30 M_sun) main sequence star properties relative to optical spectroscopy; (d) the properties of the most massive stars in H II regions are consistent with constraints from previous nebular emission line studies; and (e) 13 stars with M>8 M_sun are >40 pc from a known star cluster or H II region. Our sample comprises ~50% of all known massive stars at Z < 10% Z_sun with derived stellar parameters, high-quality optical spectra, and panchromatic photometry.

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Maude Gull, Daniel R. Weisz, Peter Senchyna, Nathan R. Sandford, Yumi Choi, Anna F. McLeod, Kareem El-Badry, Ylva Götberg, Karoline M. Gilbert, Martha Boyer, Julianne J. Dalcanton, Puragra GuhaThakurta, Steven Goldman, Paola Marigo, Kristen B. W. McQuinn, Giada Pastorelli, Daniel P. Stark, Evan Skillman, Yuan-sen Ting, Benjamin F. Williams. 2022-11-25. A Panchromatic Study of Massive Stars in the Extremely Metal-Poor Local Group Dwarf Galaxy Leo A. https://doi.org/10.3847/1538-4357%2Faca295

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