1995A&A...301..781A

We analyse the pulsational behaviour of the large-amplitude βCephei star BW Vulpeculae from high-resolution spectra. Our observations show very clear line-doublings at the time of maximum outward acceleration. These line-doublings appear and disappear on a time scale of about 30 minutes and lead to discontinuities in the radial-velocity curve. From our observations and photometric data we identify the pulsation mode of BW Vulpeculae by applying respectively the moment method (see e.g. Aerts et al. 1992) and the method of photometric amplitudes (see e.g. Heynderickx et al. 1994). Although a strong non-linear behaviour involving shock waves is suspected in the case of BW Vulpeculae (Crowe & Gillet 1989), both mode-identification techniques, which are developed for linear motions only, point towards a radial pulsation. Combining our result with the one recently found by Moskalik & Buchler (1994) then leads to the conclusion that BW Vulpeculae pulsates in the fundamental radial mode.