The effects of a bulgelike component on the global stability of flat stellar disks are investigated against linear two-armed modes. The global modes are obtained by integrating numerically the linearized collisionless Boltzmann equation as an initial value problem. Modal calculations have been made for a series of disks with bulges of different length scales but of the same mass, half that of the disks. The results show that a very compact bulge can reduce disk instabilities remarkably. It is suggested that the hotness of the central part of a disk and inner Lindblad resonances play an important role in stabilization of a disk.

Key words: Disk-bulge systems; Global instabilities; Linear modal calculations; Stellar dynamics.