Origin of Circumstellar Dust Clouds and Formation of Planetary Systems

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I have investigated the formation of planetary systems around stars of various masses and obtained the following results.1. By extending the Kyoto theory on planet formation I have shown that Neptune forms within the age of the Solar System, which the previous theories could not derive.2. By applying this theory to stars other than the Sun I investigated what kind of stars can have planets. Because the time needed to form a planet is an increasing function of the distance from the star, there is an outer boundary to the region where planets form within the stellar lifetime. The outer boundary for a more massive star is closer to the star because of the shorter life. Because the temperature is high and solid material cannot exist near the star, there is an inner boundary to the region where planets form. The inner boundary is farther for a massive star because of the higher luminosity. Therefore the region where planets may form is smaller for more massive stars) and it disappears for stars more massive than about 10M<]SY.sun.[).3. There have been two conflicting assertions on the density distribution in the beta Pictoris dust disk, n(gamma) alpha gamma^<-3> and n(gamma) alpha gamma^<-1>, where gamma is the distance from the star and the size of dust has been assumed the same everywhere. The observed surface brightness distribution along the midplane of the disk, which is approximated by a power law I(*) alpha *^<mu> with the index mu = 3.6-4.3, can be reproduced by the distribution of the scattering cross section per unit volume nsigma nsigma alpha gamma^<-1> only if the dust is much more strongly forward-scattering than the interplanetary dust which is responsible for the zodiacal light. Otherwise the distribution nsigma nsigma alpha gamma^<1-mu> can reproduce the observed surface brightness and is an appropriate distribution.