<p> Planetary migration has become one of the most important processes in planet formation since the first discovery of an exoplanet around 51Peg. A decade after the discovery, the total number of exoplanets has increased to about three hundred. Theoretical work has shown that the disk configuration in which planets are formed strongly affects the subsequent migration of planets within them. Disks evolve and their shape transits from flared to fiat. This is thought to arise because of dust settling. We take this effect into account in our models of planet migration in protoplanetary disks that are heated by the radiation of their central stars. In particular we solve the radiative transfer equation for disks by means of the Monte Carlo method, and then consider planetary migration. We focus on planets around very low mass stars (VLMSs). </p> <p> Our calculations reproduce the disk configurations of Chiang & Goldreich (1997). As dust settles, the superheated and inner layer declines toward the mid-plane. At the same time, dust settling causes the temperature of the upper layer to increase and that of the inner layer to decrease. In order to calculate the migration time accurately, we include the gravity of planets, which causes the density around them to be compressed. This results in shadowing (in front of the planet) and illumination (behind the planet) regions. We included disk evolution by taking into account the effect of dust settling. We found that dust settling itself (without planetary gravity) can reduce the migration time by a factor of 8. When we included the gravity of planets, the effect of dust settling is somewhat washed out. This is because the effect of dust settling on migration acts in a similar way to that of planetary gravity. Thus, when the migration time without dust settling is compared to the case of dust settling (including planetary gravity), dust settling can reduce the migration time by a factor of 2. </p> <p> We also found that the migration time of massive planets(> 5MEB) in such low mass disks, for both cases, is comparable to the disk life time ( rv 107 years). This suggests that planets around VLMS do not plunge into the star within a disk lifetime. This finding is consistent with the discovery of the super-Earth (rv 5.5MEB) at 2.6 AU around M dwarf (Beaulieu et al., 2006). For lower mass planets, the migration time is about two orders of magnitude longer than the disk life time. Thus, the long planetary migration around VLMS does not cause any serious time mismatch problem as in the case of classical T Tauri star system. </p> / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/21357 |
| Date | January 2008 |
| Creators | Hasegawa, Yasuhiro |
| Contributors | Pudritz, Ralph, Physics and Astronomy |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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