7. Some remarks on Vt variation and projected rotational velocity
Gillet et al. (1998) used 288 high-resolution spectroscopic profiles of the unblended 5576.09 Å absorption line to determine the turbulence variation in Cep atmosphere. Earlier, Breitfellner & Gillet (1993) presented their results for the entire pulsation cycle with particular emphasis on the interpretation of the behaviour of line width. Fokin et al., (1996) have discussed these results. All these works give the following picture of variation: it is relatively constant during with a slow increase towards =0.7. The maximum takes place between , i.e., at the minimum of the radius and maximum . The lack of the spectra exposed at these phases in our disposal prevents the evaluation of the full amplitude of the parameter variation, but the general tendency of the increase of microturbulence towards the light maximum is seen.
Van Paradijs (1971) performed a curve-of-growth analysis of Cep covering the pulsation cycle and also found the variation of the microturbulent velocity. For the phases close to those of Van Paradijs, our values are about 1 km s-1 lower than those obtained by Van Paradijs. This discrepancy can be interpreted by the different resolving power of the spectroscopic instruments and differences of the methods used.
Using unblended lines we have also estimated the projected rotational velocity for Cep as 9.0 km s-1. This value agrees well with that determined by Fokin et al. (1996), who give 7.5 km s-1.
© European Southern Observatory (ESO) 1999
Online publication: November 3, 1999