Radial velocity variations of the R Coronae Borealis star RY Sgr.

Observations of the shock wave event in the R Coronae Borealis (RCB) star RY Sgr are reported. The shock wave gives rise to a velocity discontinuity at about the time that the star is near minimum radius on its pulsation cycle, and it is observed as a doubling or splitting of the absorption line spectrum. Observations obtained over several pulsation cycles during 1988 are reported. These spectra were of a higher signal-to-noise and were obtained at a higher time resolution than were available for earlier studies of this event. The event may be visible for as much as 0.4-0.5 of a cycle, which corresponds to 15-20 d. The pulsations of RY Sgr are discussed with respect to known characteristics of other RCB stars and recent attempts to model the pulsations of such objects.