FUNDAMENTAL PARAMETERS OF CEPHEIDS .3. TURBULENCE VARIATIONS

Observations of the line broadening during the cycle of pulsation are analysed for 41 Cepheids. The main components of this line broadening are the stellar atmospheric turbulence and the velocity fields due to pulsation and to axial rotation. The variation of the broadening due t o pulsation is calculated for each star by using the observed radial v elocity curve. The residual broadening at maximum radius allows to sho w that the value of the equatorial rotational velocity is smaller than similar to 10 km s(-1) for the large majority of classical Cepheids. It will be shown that turbulence is the major effect that can explain the variation of the lines widths during the cycle of pulsation. We sh ow that the behaviours of classical and s-Cepheids are different with respect to turbulence and a new method is proposed to separate these c lasses. This leads to the discovery of a few new s-Cepheids. The secon d overtone Cepheid V473 Lyr does not follow the sequence of s-Cepheids , that are highly suspected to be overtone pulsators. It is also shown that the turbulence is in phase with the acceleration and, particular ly, that the maximum turbulence is attained near minimum radius, where the acceleration is also at its maximum.