Unveiling Massive Main-Sequence Stars in Sextans A through Panchromatic Photometry
Abstract
We present a study of the metal-poor (~6% Z_sun) massive (>8 M_sun) main-sequence star population in the star-forming dwarf galaxy Sextans A. By modeling near-UV to near-IR photometry of individual stars using the Bayesian Extinction and Stellar Tool (BEAST) we infer stellar parameters such as effective temperature, luminosity, and initial mass. We identify 867 massive main-sequence star candidates (present-day mass >8 M_sun and surface gravity >3.7 dex [cgs]) with a plausible spectral energy distribution (SED) fit, 500 of which show a probable SED fit. Comparisons to spectral types of existing observed spectra are consistent with the BEAST-derived stellar parameters, with most discrepancies explained. We identify 292 OBe star candidates through IR photometric signatures and find lower-limit OBe fractions of 15% for M > 8 M_sun, 23% for M > 15 M_sun, and 17% for M > 20 M_sun. We find 57 OB associations and that 24-28% of massive stars are isolated (distance to nearest massive star >28 pc). We discuss six likely runaway candidates (suggested velocities of ~ 50-340 km/s) not clearly associated with any major star-forming complexes. Lastly, we predict Lyman continuum (LyC) escape fractions of f_esc=0.27-0.76 across the star-forming regions and a global value of 0.35-0.71 by assuming low overall extinction and a range of porous geometries, indicating efficient leakage of ionizing photons. Future spectroscopic follow-up and resolved ISM studies will refine these constraints and solidify Sextans A as a benchmark for studying massive-star evolution and feedback at extremely low metallicity.
Cite
@article{arxiv.2603.11215,
title = {Unveiling Massive Main-Sequence Stars in Sextans A through Panchromatic Photometry},
author = {Maude Gull and Daniel R. Weisz and Yumi Choi and Benjamin F. Williams and Karoline M. Gilbert and Julianne J. Dalcanton and Kareem El-Badry and Puragra Guhathakurta and Steven R. Goldman and Kristen B. W. McQuinn and Alessandro Savino and Evan D. Skillman},
journal= {arXiv preprint arXiv:2603.11215},
year = {2026}
}