Stellar mergers: buried in the infrared
|Date||27 May 2020|
Stellar mergers are direct probes of the failed common envelope phase in binary evolution. In this phase, unstable mass transfer from one star to another can lead to the formation of a shared gaseous shell where both stars orbit: the common envelope. 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, leaving a more compact binary, or a coalesced star. This dynamical ejection phase has been serendipitously witnessed 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 will provide an overview of LRNe, their progenitor systems and their main formation scenarios, explored by recent theoretical models. Late-time observations of these common envelope transients show that, while the emission quickly fades in the optical bands, their infrared signatures remain bright, revealing the formation of cold dust shells reprocessing the light of the newly formed star.