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 and Gillet, 1996). 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
Cephei (Fokin, Gillet and Breitfellner 1996).
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.