Identification of non-radial pulsation modes in the close-binary β Cephei star ν Centauri^*

¹ Astronomical Institute Anton Pannekoek, University of Amsterdam, and Center for High Energy Astrophysics, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
² Space Department, TNO TPD, Stieltjesweg 1, 2600 AD Delft, The Netherlands e-mail: schrijvers@tpd.tno.nl
³ Nordic Optical Telescope, 38700 Santa Cruz de La Palma, Spain e-mail: jht@not.iac.es

Corresponding author: J. Telting, jht@not.iac.es

Received: 2 April 2001
Accepted: 7 August 2002

Abstract

We present time series of high-resolution spectra of the β Cephei star ν Cen, showing multi-periodic variations in the Siiii λ 4552 and λ 4567 line profiles. After correction for the binary motion, we analyse the time series of spectra by Fourier transforms for each position in the line profile. For selected frequencies we perform a direct fit of multiple sinusoids. Four frequencies are needed to describe the pattern of moving bumps in the line profiles. We present the distributions of variational amplitude and phase across the line profile and use these diagnostics to show that most of the variability can be explained by multiple non-radial pulsations. From the phase distributions across the line profiles we derive estimates for the degree of the individual pulsation modes in ν Cen. We find values ranging from 6 to 10. We find no trace of a previously reported low-degree pulsation with a period of 0.17 day. We briefly discuss these observations, and those of the other close-binary β Cephei stars α Vir and Ori, in terms of tidal effects on pulsation-mode stability.