EVIDENCE FOR BINARITY AND MULTIPERIODICITY IN THE BETA-CEPHEI STAR BETA-CRUCIS

We present numerous high signal-to-noise spectroscopic data of the bet a Cep star beta Crucis that were gathered during a total time span of 13 years. Although only one pulsation period was up to now known for b eta Crucis, our data clearly point out that the star is multiperiodic. We find evidence for the presence of at least two new frequencies, be sides the one already detected in photometric observations. Different modes are dominant in each of the observing seasons. We attempted an i dentification of the pulsation modes by means of the moment method and find that none of them is radial. The newly detected frequencies belo ng to modes that have l greater than or equal to 3, explaining why the y were not detected photometrically. We also find that the star is see n at a low inclination angle. The average radial velocity varies for d ifferent seasons; its peak-to-peak amplitude amounts to 12 km/s and co nfirms the binary nature of beta Crucis. We have determined the orbita l parameters of the system and find an eccentric orbit (e = 0.38) with a period of 5 years. From spectroscopic B2V companion.