Global density waves in self gravitating flat disks.

The problem of global stability and structure of a class of disk models, both cold and ''warm'' against axisymmetric and nonaxisymmetric perturbations has been reconsidered in the form of an eigenvalue problem involving a triply infinite matrix. Some large wavelength (or open), nonaxisymmetric modes are found to stabilize in centrally concentrated disks. Unstable ''leading'' modes of cold disks become, gradually, ''trailing'' as the thermal energy of the disk is increased. The growth rates of short wavelength modes are lowered significantly by pressure effects in warm disks.