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Astron. Astrophys. 344, 930-934 (1999)

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Shock waves and microturbulence in RR Lyrae

A.B. Fokin 1, D. Gillet 2 and M. Chadid 3

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, CC 72, Université Montpellier II, F-34095 Montpellier cedex 05, France (chadid@graal.univ-montp2.fr)

Received 16 July 1998 / Accepted 21 January 1999


A time variation of the microturbulence velocity [FORMULA] in the atmosphere of RR Lyrae is estimated from a comparison of the observed and theoretical FWHM curves of the Fe II 4923.921 Å absorption line. The theoretical line profiles were obtained using a hydrodynamical RR Lyrae model, discussed in Fokin & Gillet (1997). The estimated value of the [FORMULA] varies from 2 to 7 km/s, with a maximum at the phase 0.7. The dominant increase of the [FORMULA] seems to be caused by a strong shock, propagating through the line formation region and producing compression of the turbulent gas. Indeed, according to the current theories of the shock/turbulence interaction, the mean density increases, 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.

Key words: shock waves – turbulence – stars: individual: RR Lyr – stars: oscillations – stars: variables: RR Lyr

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© European Southern Observatory (ESO) 1999

Online publication: March 29, 1999