Application of a New Method of Stellar Seismology to a Pulsating Pre-White Dwarf Star

We present preliminary results from several hours of time-resolved spectrophotometry of the pulsating pre-white dwarf star PG0122+200,obtained with the Low Resolution Imaging Spectrometer on the 10-m Keck II telescope. Theory suggests that modes of different spherical degree will show differences in the run of amplitude versus wavelength, and we test this hypothesis for pre-white dwarfs. These data can also provide information on the temperature structure of the stellar atmosphere. Finally, we attempt to directly detect, for the first time in such stars, the transverse surface motion caused by the pulsation. By comparing amplitude ratios and phase differences between velocity and light, constraints can be placed on the driving zone below the photosphere.