The Binary Fraction of Red Supergiants

The percentage of massive main sequence OB stars in binary systems is thought to be as high as 100%. However, very few Galactic binary red supergiants (RSGs) have been identified, despite the fact that these stars are the evolved descendants of OB stars. As shown in our recent paper, binary RSGs will likely have B-type companions, as dictated by stellar evolution. Such a system will have a very unique photometric signature due to the shape of the spectral energy distribution. After observing candidate RSG+B star binaries in the Local Group Galaxies of M31, M33, and the Magellanic Clouds we discovered over 250 new systems. We are now in the process of determining the binary frequency of RSGs as a function of metallicity.