TY - JOUR
T1 - 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.
AU - Gull, Maude
AU - Weisz, Daniel R.
AU - Senchyna, Peter
AU - Sandford, Nathan R.
AU - Choi, Yumi
AU - McLeod, Anna F.
AU - El-Badry, Kareem
AU - Götberg, Ylva
AU - Gilbert, Karoline M.
AU - Boyer, Martha
AU - Dalcanton, Julianne J.
AU - GuhaThakurta, Puragra
AU - Goldman, Steven
AU - Marigo, Paola
AU - McQuinn, Kristen B.W.
AU - Pastorelli, Giada
AU - Stark, Daniel P.
AU - Skillman, Evan
AU - Ting, Yuan Sen
AU - Williams, Benjamin F.
N1 - Publisher Copyright: © 2022. The Author(s). Published by the American Astronomical Society.
PY - 2022/12/1
Y1 - 2022/12/1
N2 - 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.
AB - 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.
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U2 - 10.3847/1538-4357/aca295
DO - 10.3847/1538-4357/aca295
M3 - Article
SN - 0004-637X
VL - 941
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 206
ER -