A.B. Fokin1, D. Gillet2 and M. Chadid3
1 Institute for Astronomy of the Russia Academy of Sciences,
48 Pjatnitskaja, 109017 Moscow, Russia, fokin@inasan.rssi.ru
2 Observatoire de Haute-Provence - CNRS,
F-04870 Saint-Michel l'Observatoire, France, gillet@obs-hp.fr
3 GRAAL, CNRS, CC72, Université MontpellierII,
F-34095, Montpellier cedex 05, France, chadid@graal.univ-montp2.fr
Received ..... 1998; accepted .....
A time variation of the microturbulence velocity
vturb in the atmosphere of RR Lyrae is estimated from a
comparison of the observed and theoretical FWHM curves of the FeII4923.921Å line.
The theoretical line profiles were obtained using a hydrodynamical RR Lyrae model,
discussed in Fokin & Gillet (1997). The estimated value of the
vturb vary from 2 to 7km/s, with a maximum
at the phase 0.7. The increase of the vturb
seems to be caused by strong shocks, propagating through the
line formation region and producing the compression of the
turbulent gas. Indeed, according to the current
k-
or RDT theories, the mean density increase, such as revealed by the model,
should lead to a certain turbulence enhancement. Yet, the detailed mechanism of
such an amplification is to be clarified.
Turbulence - Shock waves - Stars: pulsation - Stars: variables: RR Lyrae - Stars: individual: RR Lyr
Cephei