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[53.12] Gas Accretion Flows onto Giant Protoplanets: High-Resolution Two-Dimensional Local Simulation

T. Tanigawa, S. Watanabe (Dept. of Earth and Planetary Sciences, Nagoya Univ.)

We investigate the gas accretion flows onto the giant protoplanets from protoplanetary disks in detail in order to clarify the gas capturing process of the giant planets after the onset of a gravitational instability of the proto-atmosphere, using high-resolution two-dimensional numerical simulations with local Cartesian coordinates. We use ZEUS-2D code, which is a kind of finite-difference time-marching methods, and obtain the steady gas-accretion flows depending on normalized sound speed \tilde{c} corresponding to the ratio of disk scale height to Hill radius. Then we find that; (1) Accretion flow patterns: There exist two types of steady shocks; a pair of bow shocks around the planetary gravitational sphere and a pair of spiral shocks in the sphere. And only gases in narrow bands are able to flow into the planetary gravitational sphere. The band location is about 2.5 Hill radius away from the planetary orbit and the width is about 0.1 Hill radius. The band width increases with decreasing \tilde{c} and the band location approaches the planetary orbit with decreasing \tilde{c}. (2) Gas accretion rates onto the giant protoplanets: When the gas temperature is given by the radiative equilibrium with central star and the ratio of specific heats \gamma is chosen to unity (isothermal), we get \dot{M} = 8.0 \times 10^-3 M_{\rm E} (a/{\rm 5.2AU})^-1.5 (M_{\rm p}/10M_{\rm E})^1.3 (f\Sigma₀/\Sigma_{\rm min}) {\rm yr}^-1, where f is the depletion factor of the surface density at the flow-in band caused by the formation of a gap, \Sigma₀ is the original surface density, which has no gap, and \Sigma_{\rm min} is the surface density of minimum mass disk model. The accretion rate decreases with increasing \gamma. (3) Migration of giant planets: The circum-planetary spiral-shock structures may strongly affect the torque about a central star exerted on the planet by the gas.

The author(s) of this abstract have provided an email address for comments about the abstract: tanigawa@eps.nagoya-u.ac.jp