Contributed Talk - Splinter Stars

Tuesday, 14 September 2021, 10:40   (virtual Stars)

Impact of the uncertain velocity fields on the spectral appearance of Wolf-Rayet stars

Roel Lefever, Tomer Shenar, Luka Poniatowski, Karan Dsilva, Andreas Sander
KU Leuven, Zentrum für Astronomie der Universität Heidelberg

Wolf-Rayet stars serve as strong contributors to galactic energetics, both via their powerful stellar winds and their strong radiation. This radiation effectively pushes away the outer layers of the Wolf-Rayet star, causing the star to be embedded in an optically thick cloud of wind material. The light spectrum that does escape originates from the stellar wind. Consequently, detailed knowledge of the structure and velocity in the stellar wind is required in order to know how the light from the star propagates through the wind and leads to the emergent spectrum. Parameters of Wolf-Rayet stars hence depend strongly on the modelling of their stellar wind. Common approaches use a so-called beta-velocity law. However, we often find discrepancies between the deduced radii and the expectations from stellar evolution modelling, leading to the so-called "Wolf-Rayet radius problem". In our study, we quantified this by computing and analysing Wolf-Rayet star winds where we have adopted several different wind velocity fields for stellar models with representable parameters. We find that the different velocity fields have a significant effect on emergent spectral lines, to the extent that classification of these spectra return entirely different spectral classes for the same stellar model. In this talk, we will present the spectral imprint of different assumptions for Wolf-Rayet velocity fields including a first approach to go beyond current simplifications and potentially solve the Wolf-Rayet radius problem.