Program: GS-2023A-Q-227

A recent analysis of the 100 pc white dwarf (WD) sample within the SDSS footprint showed for the first time that the DA WD mass distribution has an extremely narrow peak at 0.59 Msol, with a shoulder from relatively massive WDs with M = 0.7-0.9 Msol. In addition, the mass distribution of cool DAs shows a near absence of M > 1 Msol WDs. These are consistent with the effects of core crystallization. However, the current evolutionary models are unable to match the significance of the pile-up of 0.8 Msol and the sudden disappearance of the more massive stars. Our objective is to extend the 100 pc sample to WDs with temperatures between 5000-6000 K. Several important physical processes occur in this narrow temperature range: the majority of WDs (with 0.6 Msol) crystallize, coupling between the degenerate interior and the convective layers significantly changes the cooling rate, and many non-DA WDs also seem to change their spectral type. A spectroscopically complete volume-limited WD sample in this temperature range will enable us to study these physical effects, and provide invaluable constraints on the temperature and spectral evolution of WDs. A 2022B Gemini South program is observing 49 fall targets in the 5000-6000 K range. Here we propose to complete our survey by observing 50 spring targets visible from Gemini South in the 2023A semester. The proposed Gemini observations are essential for completing our survey.