Conclusions

On the base of reconstruction of the FeII4923.921Å line profiles for different phases of a pulsating nonlinear RR Lyrae model we estimated the temporal variation of the v_turb in this line formation region. We found that v_turb significantly varies from 2 to 7km/s. The peak of v_turb at $\varphi \approx 0.7$ is mainly provoked by a shock, noted as s3' by Fokin & Gillet (1997). It is not very strong ($\Delta\,v\approx$20-30km/s), though its effect on the density enhancement in the LFR is considerable. The same shock amplification in $\delta$ Cephei seems less important due to systematically weaker shocks.

The work of ABF has been done in part under the auspices of the CNRS (grant 97479) during a two-month stay at the Observatoire de Haute-Provence (OHP) thanks to the determining help of Dr. C. Bertout. ABF also aknowledges the support of the Russian Foundation for Fundamental Researches (grant 95-02-06359)