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arXiv · 2602.20239

X-Shooting ULLYSES: Massive stars at low metallicity XIV. Properties of SMC late-O and B supergiants reveal the metallicity dependence of winds in the Magellanic Clouds

T. Alkousa·P. A. Crowther·J. M. Bestenlehner·H. Sana·F. Tramper·J. S. Vink·F. Najarro·A. A. C. Sander·M. Bernini-Peron·L. Oskinova·J. Th. van Loon·R. Kuiper·The XShootU collaboration
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Abstract

Considering the physics of radiation-driven winds of massive stars, the wind properties should depend on the metal content of the stellar atmosphere. Therefore, studying the winds of massive stars in different metallicities provides a sanity check on prescriptions that are widely used in evolutionary calculations. We obtained the stellar and wind properties of a sample of 20 late-O and B supergiants in the Small Magellanic Cloud (SMC) from a quantitative combined UV and optical spectroscopic analysis using CMFGEN. By comparing these properties with those of a Large Magellanic Cloud counterpart study, which has a similar sample and data, and employed the same modelling techniques used in this study, We derived a metallicity-dependent recipe for wind momentum, which is applicable for $5.4 \leq \log{L_{\rm bol}/L_{\odot}} \leq6.1$ and $14 \leq T_{\rm eff}/{\rm kK} \leq 32$. 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 between $25$ and $21$~kK, which could be attributed to the bi-stability jump. Stellar parameters are consistent across different methods and radiative transfer codes, whereas mass-loss rates differ significantly, with our values being generally lower. We find 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 the characteristics of the WR population in the SMC.

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T. Alkousa, P. A. Crowther, J. M. Bestenlehner, H. Sana, F. Tramper, J. S. Vink, F. Najarro, A. A. C. Sander, M. Bernini-Peron, L. Oskinova, J. Th. van Loon, R. Kuiper, The XShootU collaboration. 2026-02-23. X-Shooting ULLYSES: Massive stars at low metallicity XIV. Properties of SMC late-O and B supergiants reveal the metallicity dependence of winds in the Magellanic Clouds. https://doi.org/10.1051/0004-6361/202557856

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