5. Concluding remarks
We have obtained and analysed a set of 30 spectra of the early B-type main sequence star Sco. We found the absorption lines of the SiIII triplet to be variable with a dominant periodicity of 15.0 cycles/day. The line-profile variations can be modelled by non-radial pulsations, with a dominant mode of . We estimate the surface velocity amplitude of this mode to be at least 10 km/s, provided that the surface temperature variations are small . The observed frequency of the mode with is consistent with that of a p-mode if the inclination of the star is larger than .
Traditionally, a variable early-B type star can only be labelled a Cephei star, if pulsational brightness variations have been detected photometrically. Now that spectroscopic detections of non-radial modes have become feasible, we find stars of the same spectral type with pulsations that are excited by the same mechanism, but for which brightness variations cannot (yet) be detected because the pulsational degree is too high. Although photometric variability is not detected in the case of Sco, we can certainly label the star a Cephei star on theoretical grounds (see Dziembowski & Pamyatnykh 1993). This raises the question whether we should relax the traditional definition of Cephei stars to allow spectroscopic detection as well as photometric detection.
We are currently gathering more spectroscopic data of Sco, which will be presented in a future paper. A more extensive dataset is needed in order to derive more conclusive constraints on the m value of the dominant pulsation mode, and might reveal other modes as well. This will also enable to determine the contribution of the surface temperature variations to the line-profile variations in Sco.
© European Southern Observatory (ESO) 1998
Online publication: September 30, 1998