1994A&A...288..558T

We discuss the implications of the observations of the Be star β¹ Mon, as presented by Cowley & Gugula (1973), for the theory of one-armed density perturbations in the equatorial discs of Be stars. This theory aims to describe the nature of the long-term (cycles of a few to several years) V/R variations of the Balmer and other emission lines of these stars (Okazaki 1991 and Papaloizou et al. 1992). From the observations of β¹ Mon we infer that a one-armed density structure revolved around the star in the same direction as the nearly Keplerian orbits of the disc material. We conclude that these observations are consistent with a model which predicts prograde precession of a one-armed density perturbation.