Context. Hot massive stars lose mass through radiation-driven winds, producing significant chemical, radiative, and mechanical feedback in the surrounding environment. The properties of these winds play a crucial role in determining the star’s evolutionary path. Considering the physics of radiation-driven winds, the wind properties should depend on the metal content of the stellar atmosphere. Therefore, studying the wind properties of massive stars in different metallicities (Z) provides a sanity check on prescriptions that are widely used in evolutionary calculations.
Aims. We first aim to obtain the stellar and wind properties of a sample of late-O and B supergiants in the Small Magellanic Cloud (SMC). Using these properties, we aim to quantify the dependence of wind properties on metallicity by comparing them with those of a Large Magellanic Cloud (LMC) counterpart study, which has a similar sample and data, and employed the same modelling techniques used in this study.
Methods. Spectroscopic modelling of UV and optical data from ULLYSES and XShootU was performed using the radiative transfer code CMFGEN. We also employed an updated Bayesian inference method similar to BONNSAI to explore the evolutionary history of our sample.
Results. We derived the stellar and wind properties of 20 late-O and B supergiants. We derived the following metallicity-dependent recipe for wind momentum: logDmom = (1.64 − 0.75logZ/Z⊙)log(Lbol/106L⊙) + 1.38logZ/Z⊙ + 29.17, which is applicable for 5.4 ≤ logLbol/L⊙ ≤ 6.1 and 14 ≤ Teff/kK ≤ 32.
Conclusions. We find a significant dependence of the wind momentum on the metallicity, which is largely due to the mass-loss rates. We do not find any evidence of a discontinuity in either the mass-loss rate or the ratio of the terminal wind velocity to the escape velocity, ∞/ esc, between 25 and 21 kK, which could be attributed to the bi-stability jump, although when taking into account the effect of luminosity in the transformed mass-loss rate, the behaviour appears to be different. Stellar parameters are consistent across different methods and radiative transfer codes, whereas mass-loss rates differ significantly with our values being generally lower. We f ind a discrepancy between the evolutionary and spectroscopic masses in 40% of our sample, with the evolutionary mass usually being systematically higher. The mass-loss rates of blue supergiants are far too low to strip the stellar envelope and the subsequent formation of classical Wolf-Rayet (WR) stars, leading to the conclusion that luminous blue variable eruptions or binary interactions are necessary to explain characteristics of the WR population in the SMC.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)