Program: GN-2015A-Q-86

We have recently identified a dozen massive white dwarfs (WDs) from the SDSS Data Release 7 with log g > 8.5 and T_eff = 11,000-13,000 K. These are within the empirical boundaries of the ZZ Ceti instability strip. We confirmed pulsations in one of the brighter white dwarfs (J2038 with T_eff = 12,270K and log g = 8.44) at the McDonald 2.1m telescope. Here we propose follow-up Gemini/GMOS observations of six spring targets to search for pulsations in these objects. If confirmed, asteroseismology of these pulsators would provide an unprecedented opportunity to study the crystallized interiors of these massive WDs. With photometric observations of these WDs, the characteristics of their interiors, including the thickness of their hydrogen layers and the degree of crystallization, can be examined. At log g > 8.5, these WDs could have >90% crystallized cores. Further observations of WD pulsators through photometric analysis could provide an upper limit to the mass of CO core WDs, which would place constraints on SNIa progenitor systems.