1996A&A...315..475C

For the first time, the observation of three peaks within the FWHM curve of metallic absorption lines of a RR Lyrae pulsating star (RR Lyr) is clearly reported. A resolving power of 42,000 and a time resolution close to 1% of the pulsating period were necessary. We interpret the main peak (phase 0.926) mainly as a direct consequence of the line doubling phenomenon (Chadid & Gillet, 1996A&A...308..481C). At this phase, the occurrence of a turbulence increase needs to be quantified with a nonlinear, nonadiabatic pulsational model taking into account the propagation of strong shock waves. A second peak appears just after the luminosity maximum (phase 0.03) and is essentialy due to the rotation and pulsation without large turbulence contribution as for δCephei (Fokin et al. 1996A&A...307..503F). The third peak occurs during the secondary acceleration (phase 0.70) and seems caused by the infalling shock ("early shock"). It induces a local overcompression during the atmospheric infalling ballistic motion and can certainly provoke a turbulence increase. Nevertheless, it is again necessary to compare our observations with a relevant theoretical model, to know if a shock turbulence amplification mechanism can give a significative contribution or if this amplification is only due to the global overcompression.