Abstract

Most stars in our Universe live in binaries. Unstable mass transfer from one star to another can lead to the formation of a common envelope: a shared gaseous shell where both stars orbit. The end of this phase is marked by the quick spiral-in of the secondary star towards its companion, leading to violent interactions between the components. The whole, or part of the binary’s common envelope may get ejected, and the binary may even completely merge. This last phase has been observed as astrophysical transients called luminous red novae (LRNe), allowing us to study the progenitor stars, the energetics of the outburst and the properties of the ejected material. In my talk I In my talk, I will provide an overview of LRNe progenitor systems and their main formation scenarios, as explored by recent theoretical models. In particular, I will present the results of our photometric and spectroscopic follow-up campaign for one well studied LRN in M31 , where several mass loss episodes can be clearly identified.