"The Changing Nature of WOHG64: Spectral Evolution and Implications for Pre-Supernova Evolution"

Abstract:

Understanding extreme mass loss in the final stages of massive-star evolution is crucial for connecting massive stars to their resulting supernova types. The dust-enshrouded red supergiant WOHG64 in the LMC provides an excellent laboratory to understand this phase. We report the spectral variations of WOHG64 over the past ~20 years using MIKE, MagE, X-Shooter, and UVES data. Previous studies suggest that the star had transitioned into a yellow hypergiant (YHG) star, primarily due to the disappearance of TiO bands. However, our recent findings suggest that it continues to be an RSG with TiO bands reappearing after 2024. We also find a likely composite spectrum showing forbidden emission lines of [O I] and [Ca II], which are signatures of hotter stars (incl. YSG/YHG, B[e]), supporting the growing consensus that WOHG64 is a binary system. We argue that the ejection of a significant fraction of the outer layers, potentially driven by a violent interaction such as a collision or a common envelope phase, is required to explain this transition. I will discuss the implications of these results in the context of pre-supernova evolution and how they may provide insights into events like SN2023ixf, which exhibited extreme mass loss prior to explosion.