The Progenitors and Products of Stellar Mergers

A considerable fraction of stars live in binary systems and may exchange mass with each other. One of the outcomes of this mass transfer is a contact phase in which the two stars share a common envelope. If this contact phase is unstable, the binary components will merge and leave behind a merger product. In the first part of this thesis, we evolve several thousand binary systems with varying initial parameters and assumptions regarding the efficiency of mass transfer to trace which binaries evolve into a contact phase and which of these may merge. We identify the mechanisms leading to contact and stellar mergers, assess the influence of our assumptions, and compare our population of contact binaries to observations. In the second part of this thesis, we predict the pulsations of stellar merger products to investigate whether they differ significantly from those of genuine single stars. We find that the peculiar internal structure of these merger products affects their predicted asteroseismic signatures, both for merger products on the main sequence and more evolved merger products. With these predictions, we demonstrate the potential of asteroseismology to distinguish merger products from genuine single stars.