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Astron. Astrophys. 345, 172-180 (1999)

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Non-radial pulsations in the O stars [FORMULA] Persei and [FORMULA] Cephei

J.A. de Jong 1, H.F. Henrichs 1, C. Schrijvers 1, D.R. Gies 2, J.H. Telting 3, L. Kaper 1 and G.A.A. Zwarthoed 1

1 Astronomical Institute `Anton Pannekoek', University of Amsterdam, Kruislaan 403, 1098SJ Amsterdam, The Netherlands (jdj; huib; coen; lexk@astro.uva.nl)
2 CHARA, Georgia State University, Atlanta, GA 30303, USA (gies@chara.gsu.edu)
3 Isaac Newton Group of Telescopes, ASTRON/NFRA, Apartado 321, E-38780 Santa Cruz de la Palma, Spain (jht@ing.iac.es)

Received 27 August 1998 / Accepted 8 February 1999

Abstract

A new time-series analysis of profile changes in the photospheric He I [FORMULA]4713 spectral line from data taken during 5 days in 1989 at the Calar Alto and Kitt Peak observatories has provided evidence for the presence of a non-radial prograde p-mode in the O 7.5 giant [FORMULA] Per ([FORMULA] = 3, P = 3.5) and probably two such modes in the O6 supergiant [FORMULA] Cep ([FORMULA] = 3, P = 12.3 h and [FORMULA] = 5, P = 6.6 h). The corotating pulsation periods are in both cases much shorter than the estimated stellar rotation period. Modeling the observed amplitude of the line-profile changes (assuming [FORMULA]) yields a velocity amplitude of approximately 5 km s-1 of the pulsation in [FORMULA] Per and 6 km s-1 in [FORMULA] Cep.

Any such a pulsation by itself is unlikely to be the cause of the well-known cyclical wind variability in these stars because the pulsation period is too short, but the cumulative action of multiple modes could cause such an effect. Weak magnetic fields anchored at the surface remain the strongest candidate for the origin of wind variability.

Key words: stars: early-type – stars: individual: Per – stars: individual: Cep – stars: mass-loss – stars: winds, outflows

Send offprint requests to: J.A. de Jong

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© European Southern Observatory (ESO) 1999

Online publication: April 12, 1999
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