Fumio Takahara

Collective Instabilities of Self-Gravitating Systems. III Disk-Halo System

The instability modes of the infinitesimally thin self-gravitating disk, which is composed of rotating and non-rotating parts, are investigated. By solving the dispersion relation numerically under various physical situations, two growing modes are found. They are the modified Jeans mode of rotating component or non-rotating one and the Landau mode by wave-particle (non-rotating component) interactions. Possible relevances to spiral arms are discussed briefly.

Monte Carlo Simulation of the Unsaturated Comptonization in a Semi-Relativistic Plasma

The unsaturated Comptonization in a semi·relativistic plasma layer which is receiving a strong flux of external soft photons is investigated by the Monte Carlo method. We calculate the steady·state spectrum of Comptonized emission and the Compton cooling rate per unit area for various values of the electron temperature, the optical thickness to Thomson scattering and the soft photon tempefature. We have found higher efficiency of Comptonization than expected on the basis of the Kompaneets equation. The emission spectrum turns out to be a power law form for y=4(kTe/mec 2 )Max(rTh, rfh) ~3. Application to CygX·1 is also discussed briefly.