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Astron. Astrophys. 339, 525-530 (1998)

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On the origin of shock waves in the [FORMULA] Cephei star BW Vulpeculae *

P. Mathias 1, D. Gillet 2, A.B. Fokin 2, 3 and T. Cambon 1

1 Observatoire de la Côte d'Azur, Département Fresnel, UMR 6528, BP 4229, F-06304 Nice Cedex 04, France
2 Observatoire de Haute-Provence, F-04870 St Michel l'Observatoire, France
3 Institute for Astronomy of the Russia Academy of Sciences, 48 Pjatnitskaja, 109017 Moscow, Russia

Received 3 July 1998 / Accepted 12 August 1998

Abstract

New high temporal and spectral resolution observations of BW Vul are presented. The line doubling phases, occurring twice per pulsation cycle during the velocity discontinuities, are interpreted in terms of shock waves. The first and largest doubling is seemingly due to the formation of a shock wave during the supersonic infalling motion of the atmosphere. The famous observed stillstand would be only the last phase of the ballistic motion which seems marked by a small bounce of the atmospheric layers on the photosphere. Then, a new shock wave, probably initiated by the iron [FORMULA]-mechanism, sweeps the layers upward. There is some indications that the amplitude of the motion of atmospheric layers changes from one pulsation cycle to another one.

Key words: line: profiles – shock waves – stars: individual: BW Vulpeculae – stars: oscillations

* Based on observations obtained at the Observatoire de Haute Provence (France)

Send offprint requests to: P. Mathias

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© European Southern Observatory (ESO) 1998

Online publication: October 21, 1998
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