Abstract

Contributed Talk - Splinter MassiveStars

Monday, 09 September 2024, 16:55   (S23)

Hydrodynamially consistent models of B hypergiants

Matheus Bernini-Peron, Andreas Sander
ZAH/ARI, Universität Heidelberg

A proper understanding of evolved high-mass stars is fundamental to constraining the evolution and the collective impact of massive stars in their host galaxies. Towards cooler temperatures in the radiative-driven-wind regime, we observe a variety of post-main sequence objects, namely: B supergiants, late Wolf-Rayet stars, luminous blue variables, and B hypergiants (BHGs). The evolutionary connections between each of these classes and others are still quite uncertain. They are also implicated in the discussions about the so-called bi-stability jump phenomenon, where it is still not known whether changes in the ionization at the wind onset at lower temperatures, possibly combined with the proximity to the Eddington limit, could increase the mass-loss rates. Hence, to understand the wind launching mechanism in this crucial regime, we present a detailed pioneering study on the wind driving in the context of BHGs using hydrodynamically-consistent PoWR stellar atmosphere code. We model the spectrum (UV to radio) of the “prototypical” BHG HD152236 (B1.5Ia+) and investigate how different stellar properties can affect the wind parameters and map the importance of different ions for the mass loss and for the wind velocity structure. We find that Fe III is the main wind driver. The resulting velocity profile differs from the classical beta-law, even when considering higher beta values. Additionally, we infer that low clumping is necessary, and would start deep in subsonic layers. The UV spectral appearance demands the inclusion of X-ray emission to reproduce P Cygni profiles from highly ionized ions, which affects the ionization stages and thus the resulting radiative acceleration at upper layers of the wind.