X-Shooting ULLYSES: Massive stars at low metallicity.
VII. Stellar and wind properties of B supergiants in the Small
Magellanic Cloud
Bernini-Peron, M.; Sander, A. A. C.; Ramachandran, V.; Oskinova, L. M.; Vink, J. S.; Verhamme, O.; Najarro, F.; Josiek, J.; Brands, S. A.; Crowther, P. A.; Gómez-González, V. M. A.; Gormaz-Matamala, A. C.; Hawcroft, C.; Kuiper, R.; Mahy, L.; Marcolino, W. L. F.; Martins, L. P.; Mehner, A.; Parsons, T. N.; Pauli, D.; Shenar, T.; Schootemeijer, A.; Todt, H.; van Loon, J. Th.
Context. B supergiants (BSGs) represent an important connection between
the main sequence and more extreme evolutionary stages of massive stars.
Additionally, lying toward the cool end of the hot star regime,
determining their wind properties is crucial to constrain the evolution
and feedback of massive stars as, for instance, they might manifest the
bi-stability jump phenomenon.
Aims. We undertake a detailed analysis of a representative sample of 18
Small Magellanic Cloud (SMC) BSGs within the ULLYSES and XShootU
datasets. Our UV and optical analysis spans BSGs from B0 to B8 -
covering the bi-stability jump region. We aim to evaluate their
evolutionary status and verify what their wind properties say about the
bi-stability jump in a low-metallicity environment.
Methods. We used the CMFGEN to model the spectra and photometry (from UV
to infrared) of our sample. We compare our results with different
evolutionary models, with previous determinations in the literature of
OB stars, and with diverging mass-loss recipes at the bi-stability jump.
Additionally, we provide the first BSG models in the SMC including
X-rays.
Results. (i) Within a single-stellar evolution framework, the
evolutionary status of early BSGs seem less clear than that of late
BSGs, which agree with H-shell burning models. (ii) UV analysis shows
evidence that BSGs contain X-rays in their atmospheres, for which we
provide constraints. In general, we find higher X-ray luminosity (close
to the standard log(L_X/L) ~ -7) for early BSGs. For cooler BSGs, lower
values are preferred, log(L_X/L) ~ -8.5. (iii) The obtained mass-loss
rates suggest neither a jump nor a monotonic decrease with temperature.
Instead, a rather constant trend is observed, which is at odds with the
increase found for Galactic BSGs. (iv) The wind velocity behavior with
temperature shows a sharp drop at ~19 kK, similar to what is observed
for Galactic BSGs.
This paper in ADS