X-Shooting ULLYSES: Massive stars at low metallicity

Abstract

Massive stars drive the ionization and mechanical feedback within young star-forming regions. The Large Magellanic Cloud (LMC) is an ideal galaxy for studying individual massive stars and quantifying their feedback contribution to the environment. We analyze eight exemplary targets in LMC N11 B from the Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES) program using novel spectra from HST (COS and STIS) in the UV, and from VLT (X-shooter) in the optical. We model the spectra of early to late O-type stars using state-of-the-art PoWR atmosphere models. We determine the stellar and wind parameters (e.g., T_{⋆, log g, L⋆, Ṁ, and v∞) of the analyzed objects, chemical abundances (C, N, and O), ionizing and mechanical feedback (QH, QHeI, QHe II, and Lmec), and X-rays. We report ages of 2–4.5 Myr and masses of 30–60 M⊙ for the analyzed stars in N11 B, which are consistent with a scenario of sequential star formation. We note that the observed wind-momentum–luminosity relation is consistent with theoretical predictions. We detect nitrogen enrichment by up to a factor of seven in most of the stars. However, we do not find a correlation between nitrogen enrichment and projected rotational velocity. Finally, based on their spectral type, we estimate the total ionizing photons injected from the O-type stars in N11 B into its environment. We report log (Σ QH) = 50.5 ph s^{−1, log (Σ QHe I) = 49.6 ph s−1, and log (Σ QHe II)= 44.4 ph s−1, consistent with the total ionizing budget in N11.}}