Cool Stars 14 - Submitted Abstract # 365
This version created on 05 October 2006

Planets around low-mass stars - theory


Shigeru Ida, Tokyo Inst. of Tech.
D. N. C. Lin, UCO/Lick observatory

Based of the sequential core accretion model for planet formation
developed by Ida & Lin (2004, ApJ 604, 388), planetary systems around
low-mass stars are discussed.  Relatively low surface density of
protoplanetary disks around low-mass stars tends to inhibit formation
of massive cores and their low disk temperature tends to truncate gas
accretion onto the planets at small masses.  Both lead to significant
depletion of Jupiter-size gas giant planets compared with solar-type
stars, while Neptune-size icy planets can be brought to the proximity
of host stars by type-II migration (Ida & Lin 2005, ApJ 626, 1045).
Here, we also discuss the effects of type I migration of cores without
opening up gaps in the disks.  Even 10  times slower migration than
predicted by the linear theory almost completely shuts down formation
of gas giants around low-mass stars.  As a result, mass distribution
of close-in planets is very sensitive to type-I migration speed.
Since our theoretical model predicts mass and period distribution of
planets, it is directly compared with observation.  We discuss
observational tests for efficiency of type-I migration as well as that
of gas accretion onto cores.  We also discuss prediction of abundance
of habitable planets by a combination of our theoretical model with
radial-velocity observation from ground and future Kepler and SIM
observations.  

----------------------------------