Publ. Astron. Soc. Japan, 41, 841-851 (1989)

One-Armed Instabilities of Flat Stellar Disks with a Different Amount of Retrograde Stars

Shunsuke HOZUMI
Department of Astronomy, Faculty of Science, University of Kyoto, Kitashirakawa, Sakyo-ku, Kyoto 606
Kyoto City University of Arts, Oekutsukakecho, Nishikyo-ku, Kyoto 610-11
(Received 1987 August 10; accepted 1989 January 28)


The effects of retrograde stars on the stability of flat stellar disks are examined. The models used are the isochrones with various fractions of retrograde stars. The most unstable global modes are obtained by numerically integrating the linearized collisionless Boltzmann equation. The results show that the growth rate of the one-armed mode becomes higher as the number of retrograde stars increases. On the contrary, the growth rates of the two- and three-armed modes are lowered by retrograde stars. Thus, the one-armed mode grows faster than the two- and three-armed modes when the disk contains a large number of retrograde stars. The behavior of the one-armed mode can be explained in terms of the inner Lindblad resonance of the wave with retrograde stars.

Key words: Global instabilities; Linear modal calculations; Retrograde stars; Stellar Dynamics.