Line-profile variations of the double-lined spectroscopic binary kappa Scorpii

We present a total time series of high signal-to-noise, high-resolution spe ctra of the SiIII lambda 4552.6, lambda 4567.8 and lambda 4574.8 Angstrom l ines of the fast-rotating, spectroscopic binary and beta Cephei star kappa Scorpii. Among this data set is a sample of 422 spectra of intensive monito ring during eight subsequent nights in July 1997. We find variability of th e line profiles on two time-scales: a variation of several months as a resu lt of the orbital motion and rapid variations of a few hours, which are exp lained in terms of non-radial pulsation modes. From the total dataset, cove ring a time span of 9 years, we derive for the first time the orbital param eters of kappa Scorpii and find an orbital period of 195 days. The complex patterns on the grayscale representations of the residual SiIII lambda 4552 .6 Angstrom profiles with respect to the average profile point towards more than one (non-axisymmetric) pulsation mode. A frequency analysis of the th ree normalised velocity moments confirms the main period of 4.80 hours and the second period of 4.93 hours, which were previously derived from photome tric data. We attempt an identification of the pulsation modes by means of the moment method and line-profile fitting and find that kappa Scorpii puls ates in a main prograde sectoral mode of degree 1 or 2 and in an additional tesseral mode for which l = 5, m = 1 are the most likely wavenumbers. In t he variations of the line profiles we find indications for the presence of additional pulsation modes.