1995A&A...300..163H

We present high-resolution Hα and Fe II spectroscopic data on the emission line behaviour of five selected Be stars (HR 3237, δ Cen, 48 Lib, α Ara, 66 Oph), four of them showing cyclic V/R line profile variability in the period 1982-1993. With the exception of the shell star 48 Lib, these stars temporarily also show a characteristic asymmetric (steeple-type) profile shape in their Fe II λ5317 emission line (which we have chosen as characteristical optically thin emission line). These profiles are very similar in all three stars. In contrast, the star α Ara has been selected because it exhibits symmetric double-peak profiles for the whole investigated period. Steeple-type profiles are cyclically variable in the sense that they show asymmetric line profiles for almost half a cycle, then asymmetry inversion in the second half-cycle, and re-appear with the same shape after a full cycle which lasts about 8-10 years. In one star, 66 Oph, we report the detection of V/R variability onset in the course of 1988, i.e. a sudden transition from a non-varying, symmetric to a variable, asymmetric line profile shape. We demonstrate that this characteristic steeple-type profile shape and the long-term V/R variability pattern known since long are two manifestations of the same physical phenomenon. We provide arguments in favour of the global disk oscillation scenario as causing a large-scale perturbation of the quasi-Keplerian circumstellar disk which precesses under the influence of the non-spherical gravitational potential of the central star. We finally speculate that the onset of such distortion, as observed in 66 Oph, might be related to some viscous instability in the circumstellar disk.