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

We characterize massive stars (M > 8 M (& ODOT;)) in the nearby (D & SIM; 0.8 Mpc) extremely metal-poor (Z & SIM; 5% Z (& ODOT;)) 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(Teff) log(g) & ODOT;) 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 (& ODOT;) are > 40 pc from a known star cluster or H II region. Our sample comprises & SIM;50% of all known massive stars at Z & LSIM; 10% Z (& ODOT;)with derived stellar parameters, high-quality optical spectra, and panchromatic photometry.