Rotation, pulsations and outbursts in the Be star
 Cyg (HD 202904)
C. Neiner,1,2,3
M. Floquet,2
A.-M. Hubert,2
Y. Frémat,4
R. Hirata,5
S. Masuda,6
D. Gies,7
C. Buil,8 and
C. Martayan2
1
RSSD, Estec, ESA, Keplerlaan 1, 2201 AZ Noordwijk ZH, Netherlands
2
Observatoire de Paris-Meudon, GEPI, UMR 8111 du CNRS, 92195 Meudon Cedex, France
3
Current Affiliation: Institute for astronomy, KU Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
4
Observatoire Royal de Belgique, 1180 Brussel, Belgium
5
Department of Astronomy, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
6
Okayama Astrophysical Observatory, National Astronomical Observatory,
Kamogata, Okayama, 719-0232, Japan
7
CHARA, Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, USA
8
CNES, 18 rue Edouard Belin, 31401 Toulouse, France
 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
 =3 and m=3 and a zonal
mode with
=3 or 4 and m=0, respectively. The stellar rotation is
probably also identified at f~1.5 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.
Accepted by A&A
Preprints from
coralie@ster.kuleuven.ac.be
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