Characterization of candidate stellar merger progenitors

Abstract

Stellar mergers have traditionally been detected because of their outbursts. A study by Addison et al.(2022) proposed a method to select them based on their position in the Hertzsprung Gap and an increase in luminosity, although without extinction values, resulting in 21 progenitor candidates for Luminous Red Novae. We present their characterization study based on new photometric and spectroscopic data. Initially identified as yellow stars, all candidates were found to be B-type stars, most of them Be stars, which makes them unlikely to be genuine LRNe progenitors. These results underscore the need to incorporate extinction corrections to avoid mischaracterization due to reddening effects. We also compute variation in radial velocities in order to decide if they may be binary systems and rotation velocities for the sources without emission lines, since Be stars are usually fast rotators. As expected, their rotational velocity to critical velocity ratio is 0.47−0.64.