Among other spectroscopic variations of Be stars, the V/R variation is notable.
When Be stars show double-peaked emission lines, the relative height of violet
(V) and red (R) components often exhibits a time variation, known as V/R variation.
Figure 7.23 illustrates an example of V/R variation observed in γ Cassiopeiae (γ
Cas).
The V/R variations had thus far been spectroscopically interpreted by two
models: a symmetric rotating-pulsating model and an elliptical disk or ring model
(Ballereau and Chauville 1989). Neither model had any realistic physical reasoning.
Instead, from a dynamical point of view, Kato Shoji of Kyoto University first
pointed out that one-armed low-frequency waves could exist stably in Keplerian
disks. He suggested the applicability of this oscillation to Be stars, and Okazaki
Atsuo of Hokkai-Gakuen University developed this theory as the dynamic
Fig. 7.22 Variations in disk
parameters β (β1, β2) and τ
(Hα) of Pleione in its early
shell phase (Hirata and
Kogure 1984)
Fig. 7.23 V/R variation in Hβ line of γ Cas (Horaguchi et al. 1994)
7.5 Stellar Physics
203