Apsidal motion and non-radial pulsations in ψ² Ori^*

¹ Isaac Newton Group of Telescopes, NWO, Apartado 321, 38700 Santa Cruz de La Palma, Spain
² Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Spain
³ Division of Physical Sciences, University of Hertfordshire, Hatfield, Hertfordshire AL10 9AB, UK
⁴ Department of Physics and Astronomy, University College London, Gower St., London WC1E 6BT, UK e-mail: jba@star.ucl.ac.uk
⁵ Astronomical Institute Anton Pannekoek, University of Amsterdam, and Center for High Energy Astrophysics, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
⁶ Space Department, TNO TPD, Stieltjesweg 1, 2600 AD Delft, The Netherlands e-mail: schrijvers@tpd.tno.nl

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

Received: 21 March 2001
Accepted: 9 July 2001

Abstract

We present a time series of high-resolution echelle spectra of the double-lined close binary ψ² Ori. The spectra sample the wavelength region of 3800-6800 Å. In the absorption lines of the early-B type primary we find clear evidence for non-radial pulsations with intermediate values of the modal degree . Using a cross-correlation technique we derive the radial velocity of both components. We compare our orbital solution with those reported in the literature to derive the apsidal motion period in this system: year. We analyse the absorption line profiles of the primary using Fourier techniques to derive apparent pulsation periods and values of two detected modes with apparent frequencies c/d and c/d. We discuss whether the non-radial pulsations in this star are internally excited or due to tidal forcing. Comparing the pulsation frequencies with those expected for tidal forcing and for internally excited modes, we tentatively conclude that these modes are probably due to internally excited β Cephei pulsations.