Shock-powered light curves of luminous red novae as signatures of pre-dynamical mass loss in stellar mergers

Understand

Luminous red novae (LRN) are a class of optical transients believed to originate from the mergers of binary stars, or "common envelope" events.

• Their light curves often show secondary maxima, which cannot be explained in the previous models of thermal energy diffusion or hydrogen recombination without invoking multiple independent shell ejections.
• We propose that double-peaked light curves are a natural consequence of a collision between dynamically-ejected fast shell and pre-existing equatorially-focused material, which was shed from the binary over many orbits preceding the dynamical event.
• The fast shell expands freely in the polar directions, powering the initial optical peak through cooling envelope emission.