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Shock waves and microturbulence in RRLyrae

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-$\epsilon$ 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

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