Comparison with $\delta$Cephei

A comparison of the v_turb curbes predicted for RR Lyrae in the present paper, and for $\delta$ Cephei, obtained by Gillet et al. (1998a), reveals the same peak at phase 0.6-0.7, but in $\delta$ Cephei it is much weaker (2.8km/s), which can be explained by generally fainter shocks in Cepheids.

On the other hand, the peak at $\varphi=0.85$ in the Cepheid, originated from the main global compression, is very prominent (about 10 km/s). As mentionned above, at present we cannot say whether the peak expected in RR Lyrae due to the main compression maximum at $\varphi\approx 0.92$is as strong as in $\delta$ Cephei due to the Doppler splitting in the shock. It is clear, however, that the major difference between those types of stars is that in $\delta$ Cephei the most important mechanism of amplification seems to relat to the global compression of the atmosphere, while in RR Lyrae the shock amplification is very important. In this context it would be interesting to apply the theoretic analysis of turbulence amplification to RR Lyrae, as it was done for $\delta$ Cephei in Gillet et al. (1998b).