A Panchromatic Study of Massive Stars in the Extremely Metal-poor Local Group Dwarf Galaxy Leo A* * This paper includes data gathered with the 10 m Keck Telescopes located at W. M. Keck Observatory, Hawaii and with the 6.5 m Multiple Mirror Telescope (MMT) located at Mt. Hopkins, Arizona.

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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4 Scopus citations

Abstract

We characterize massive stars (M > 8 M ) in the nearby (D ∼ 0.8 Mpc) extremely metal-poor (Z ∼ 5% Z ) galaxy Leo A using Hubble Space Telescope ultraviolet (UV), optical, and near-infrared (NIR) imaging along with Keck/Low-Resolution Imaging Spectrograph 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) six 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 nonlocal thermodynamic equilibrium models, the photometric and spectroscopic values of log ( T eff ) and log ( g ) agree to within ∼0.01 dex and ∼0.18 dex, respectively, indicating that near-UV/optical/NIR imaging can be used to reliably characterize massive (M ∼ 8-30 M ) 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 > 8M 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 with derived stellar parameters, high-quality optical spectra, and panchromatic photometry.

Original languageEnglish (US)
Article number206
JournalAstrophysical Journal
Volume941
Issue number2
DOIs
StatePublished - Dec 1 2022

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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