Abstract :
Red supergiants (RSGs) are evolved massive stars with initial masses between 8-25 Mּּsun, which are assumed to be progenitors of Type II Supernova (SN). However, the lack of observations of Type II SNe produced by RSGs with an initial mass greater than 18 Mּּsun creates a conflict. The well-known “RSG problem” suggests that massive RSGs either collapse directly into a black hole without an explosion or evolve to warmer stages, where they end their lives in a post-RSG phase. Yellow supergiants with circumstellar dust have already been proposed as post-RSG candidates. Nevertheless, the physical process that induces an RSG to become a warmer supergiant is currently unclear. According to current evolutionary models, the standard RSG winds are not strong enough to make them evolve to a warmer stage. Moreover, other processes might be needed to strip their envelopes, such as episodic mass-loss or binary interactions. In this talk, we present an in-depth study of two of the largest, most massive, and luminous RSGs in the Large Magellanic Cloud (LMC) that show evidence of significant mass loss and interaction with their circumstellar material (CSM). One of the RSGs is surrounded by clumpy shocked material, and its walkaway status places it as the first extragalactic candidate RSG with a bow shock. The 30-year light curve revealed three dimming events similar in amplitude and time scales, with a recurrence of ~12 years. Furthermore, multi-epoch spectroscopy demonstrated recent episodic mass loss during the last event, exhibiting similarities to the Great Dimming of Betelgeuse. Our other RSG has recently changed from a late-M type to show spectral features of regular sgB[e], such as asymmetric P-Cygni profiles and emission in Fe II, hydrogen, and Ca II triplet, plus forbidden emission lines. The loss of periodicity in the light curve and the change in V-I color propose significant changes in the atmosphere, which might be associated with a severe episodic mass-loss event. Studying this new stage would shed light on the origin of sgB[e], the post-RSG evolution, and the connection with the RSG problem.
