Program: GN-2023A-Q-329

A significant fraction of massive white dwarfs (M > 0.9 Msol) are predicted to form through binary mergers. Merger populations can reveal themselves through their kinematics, magnetism, or rapid rotation rates. A recent study of a subsample of M > 1.3 Msol white dwarfs in the Montreal White Dwarfs Database 100 pc sample showed that 56% of these objects are likely merger products. This is significantly higher than expected from the binary population synthesis models. However, it is just a single data point. Here we propose to initiate a survey of all M > 0.9 Msol with temperature above 11,000 K, where the atmospheric composition can be easily constrained based on low-resolution spectroscopy, within the 100 pc sample to constrain the merger fraction as a function of mass. We identify 109 objects that need follow-up spectroscopy. We propose to observe 30 of the faintest targets and/or southern targets in this sample at Gemini. The rest of the sample is currently observed at 2-4 m class telescopes in the northern hemisphere. The proposed Gemini observations are essential for completing this survey, which will, for the first time, provide a precise merger rate of massive white dwarfs.