Program: GS-2022A-Q-303

A significant fraction of ultramassive white dwarfs with (M>1.3 Msol) are predicted to form through binary mergers. Merger populations can reveal themselves through their kinematics, magnetism, or rapid rotation rates. A recent analysis of the ultramassive white dwarfs in the Montreal White Dwarf Database 100 pc sample found that at least 8 of the 25 white dwarfs in that sample are likely merger products. However, this fraction may be much higher. Here we propose to perform a spectroscopic and photometric survey of this population to obtain, for the first time, a precise merger rate for ultramassive white dwarfs. This has important implications for binary population synthesis models and understanding the contribution of double white dwarfs to the Type Ia supernova rate.