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M. Ikoma, H. Emori, K. Nakazawa (T.I.Tech)
Recent detection of extrasolar planets as well as the still remaining problems related to the formation of giant planets demand our comprehensive study on their formation processes. In the nucleated instability model in which rapid gas accretion is triggered by the core with a critical mass, behavior of the gas accretion is governed, essentially, by the core accretion rate and the grain opacity in the outermost envelope.
The current planetary accretion theory points out that protoplanets would be isolated from planetesimals and, as a result, the core accretion would almost stop in their later formation stage before their mass reached the critical core mass. In the present study, we have simulated the evolution of the envelope of protoplanets numerically and investigated the characteristic growth times of the envelope mass after the beginning of the gas accretion for various core accretion rates and grain opacities taking into account a halt of the core accretion. Our main results are (1) the growth time depends strongly on the core mass, moderately on the grain opacity, and weakly on the past core accretion process and (2) the growth time, \tau\rm g, is given approximately by \tau\rm g \propto M\rm core-2.5 \kappa\rm gr where M\rm core is the core mass and \kappa\rm gr is the grain opacity. Our results will give a useful knowledge on the various problems concerning the formation of giant planets.
The author(s) of this abstract have provided an email address for comments about the abstract: mikoma@geo.titech.ac.jp