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Turbulence variation in the atmosphere of $\delta$Cephei

D. Gillet¹, A.B. Fokin², M.G. Breitfellner³, S. Mazauric⁴ and A. Nicolas⁵

¹ Observatoire de Haute-Provence - CNRS, F-04870 Saint-Michel l'Observatoire, France
² Institute for Astronomy of the Russia Academy of Sciences, 48 Pjatnitskaja, 109017 Moscow, Russia
³ ESA Villafranca Del Castillo, ISO Science Team, Apartado - P.O. Box 50727, E-28080 Madrid, Spain
⁴ von Karman Institute for Fluid Dynamics, 72 Chaussée de Waterloo, B-1640 Rhode-Saint-Genèse, Belgium
⁵ Ecole Normale Supérieure de Lyon, 46 allée d'Italie, F-69364 Lyon cedex 07, France

Received date; accepted date

Abstract:

This paper is devoted to the determination of the turbulence velocity curve of the classical Cepheid $\delta$ Cephei with a high temporal resolution using 288 high resolution spectra obtained over 3 consecutive years (1993-1995). From the FWHM variation of the unblended FeI 5576.0883Å absorption line and non-linear non-adiabatic pulsating models, it is shown that the global compression/expansion of the atmosphere i.e., the star pulsation, induces a variation of the turbulence. It is maximum at the minimum radius and minimum at the maximum expansion of the star. It is also shown that large amplitude compression waves and shock waves provoke some turbulence variations during their propagation in the atmosphere. The minimun turbulence velocity is around 2.2km/s while it reaches a value also high that 7.5km/s at the maximum compression. The wave turbulence amplifications are smaller but lightly increase with the wave amplitude.

stars: variables: Cepheids - line: profiles - turbulence - shock waves - stars: individual: $\delta$ Cephei