Establishing Shock Diagnostics in the Pulsating Extreme Helium Star V652 Herculis

V652 Her is an extreme helium star which pulsates with a period of 0.108 d. The pulsations are almost unique in that for 90% of the pulsation cycle the photosphere follows a near-ballistic trajectory. This is punctuated by a short acceleration phase which shows evidence of a high Mach-number shock moving outward through the photosphere. To explore the shock phase in more detail, we have obtained a series of spectra at high time resolution with the high-dispersion spectrograph of the Subaru telescope. We have also developed a theoretical framework for coupling a hydrodynamic model of the pulsating envelope to a radiative transfer model of the photosphere. We present first results of a comparison between theoretical and observed spectra around minimum radius.