Apsidal motion and non-radial pulsations inψ2Ori

Abstract

We present a time series of high-resolution echelle spectra of the double-lined close binary ψ 2 Ori. The spectra sample the wavelength region of 3800-6800 A. 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 $\ell$. 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: $47.5 \pm 0.7$ year. We analyse the absorption line profiles of the primary using Fourier techniques to derive apparent pulsation periods and $\ell$ values of two detected modes with apparent frequencies $f_1=10.48$ c/d and $f_2=10.73$ 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.