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

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

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 $\mathrm{log}({T}_{\mathrm{eff}})$ and $\mathrm{log}(g)$ 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.

Citation

Gull, M., Weisz, D. R., Senchyna, P., Sandford, N. R., Choi, Y., McLeod, A. F., …Williams, B. F. (2022). A Panchromatic Study of Massive Stars in the Extremely Metal-poor Local Group Dwarf Galaxy Leo A*. Astrophysical Journal, 941(2), Article 206. https://doi.org/10.3847/1538-4357/aca295

• Journal Article Type: Article
• Acceptance Date: Nov 11, 2022
• Online Publication Date: Dec 27, 2022
• Publication Date: Dec 20, 2022
• Deposit Date: Oct 31, 2023
• Publicly Available Date: Oct 31, 2023
• Journal: The Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 941
• Issue: 2
• Article Number: 206
• DOI: https://doi.org/10.3847/1538-4357/aca295
• Keywords: Space and Planetary Science; Astronomy and Astrophysics
• Public URL: https://durham-repository.worktribe.com/output/1872491