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Astron. Astrophys. 344, 935-941 (1999)

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Turbulence variation in the atmosphere of [FORMULA] Cephei

D. Gillet 1, A.B. Fokin 2, M.G. Breitfellner 3, S. Mazauric 1 and A. Nicolas 4

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 Ecole Normale Supérieure de Lyon, 46 allée d'Italie, F-69364 Lyon Cedex 07, France

Received 16 July 1998 / Accepted 18 January 1999


Using 288 high resolution spectra obtained over 3 consecutive years (1993-1995), the microturbulence velocity curve of [FORMULA] Cephei is determined with a high temporal resolution. From the observed FWHM variation of the unblended Fe I 5576.0883 Å absorption line, and from nonlinear nonadiabatic pulsating models, it is shown that the global compression/expansion of the atmosphere provokes the variation of the turbulence. The turbulent velocity reaches its maximum, of about 7 km s-1, at minimum radius, and decreases up to 2 km s-1 during the expansion of the star. It is also shown that the compression waves and shocks certainly provoke some rapid turbulence variations during their propagation in the atmosphere. The turbulence amplification due to these waves, being in general smaller than the global compression effect, increases with the wave amplitude.

Key words: line: profiles – shock waves – turbulence – stars: individual: ffi Cep – stars: variables: Cepheids

© European Southern Observatory (ESO) 1999

Online publication: March 29, 1999