Keck time-resolved spectroscopy of G 29-38

We have conducted time-resolved spectroscopy of the ZZ Ceti star G 29-38 using the Keck II Low Resolution Imaging Spectrograph (LRIS). We have used these observations to test a method for identifying the spherical harmonic degree l of pulsation modes. The method relies upon model atmosphere predictions that mode amplitudes should change within spectral lines in an l-dependent manner. Our analysis of the observations shows amplitude changes consistent with model predictions, allowing us to identify the l value of the modes present. In addition, our data reveal the surface velocities associated with ZZ Ceti pulsations for the first time and provide a mean spectrum of extremely high signal-to-noise.