Rotation, pulsations and outbursts in the Be star υ Cygni (HD 202904)

¹ RSSD, Estec, ESA, Keplerlaan 1, 2201 AZ Noordwijk ZH, The Netherlands e-mail: coralie@ster.kuleuven.ac.be
² Observatoire de Paris-Meudon, GEPI, UMR 8111 du CNRS, 92195 Meudon Cedex, France
³ Observatoire Royal de Belgique, 1180 Brussels, Belgium
⁴ Department of Astronomy, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
⁵ Okayama Astrophysical Observatory, National Astronomical Observatory, Kamogata, Okayama 719-0232, Japan
⁶ CHARA, Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, USA
⁷ CNES, 18 rue Edouard Belin, 31401 Toulouse, France

Received: 25 August 2004
Accepted: 20 February 2005

Abstract

υ Cyg is a Be star that shows variations at all timescales. We monitored its spectrum for several years from 1998 to 2004 and, in particular, during a spectroscopic multisite campaign in 2000. In this paper we present and analyse the data. We observed several outbursts including an intense one in 2000. Moreover, we found several periods of short-term variations, including two frequencies at 2.95 and 2.6 c d^-1, which are well reproduced by models of non radial pulsations with a retrograde mode with and and a zonal mode with or 4 and , respectively. The stellar rotation is probably also identified at c d^-1, which is coherent with the rotation frequency deduced from our determination of stellar parameters. The peak-to-peak amplitude of variations also seems to vary in time, maybe due to a beating effect between close frequencies, but the resolution in time of our data does not allow us to separate such close frequencies. Finally, a longer timescale variation may be present, with a period around 11 years, which could be associated with a binary companion.