Program: GS-2009A-Q-37

About10% of white dwarfs in magnitude-limited samples have too low a mass to have formed from post-AGB evolution, suggesting that they have lost their envelopes while on the RGB. Many of these white dwarfs are components of close binaries, showing that their envelopes were lost through binary interaction. However, a similar fraction are single, suggesting that single stars may somehow be able to lose their envelopes while on the RGB. We expect the two routes to leave differing hydrogen layer masses on the white dwarfs which will be measurable with asteroseismology, if suitable targets can be found. We have managed to find two pulsators in a sample of seven low mass white dwarfs from the SDSS. We apply for Gemini spectroscopy to determine precisely the gravities and temperatures of our sample to establish that they are indeed helium-core white dwarfs. (We are submitting the proposal for both Gemini-N & S.)