Hertzsprung gap stars as stellar merger progenitors

Abstract

Most close binary stars likely end their evolution in a merger, visible as a bright outburst named Luminous Red Nova (LRN). In this work, we investigated a sample of stars in the Milky Way aiming to find possible LRN progenitor binary systems based on their location in the HR diagram, their variability, their hydrogen emission, and their mid-infrared (mid-IR) excess. For a sample of 449017 stars with a luminosity and a color consistent with known LRN progenitors, we found that 3.7% (16731) are variable, 22% (97972) show emission on Hα or Hβ, and ∼0.5% (∼2250) have mid-IR excess detected by the NEOWISE infrared space telescope. The lightcurves for a small set of ∼100 sources with variability, emission, and mid-IR excess suggest that new unstudied causes for their variability are present, which deserves further study