31st Annual Meeting of the DPS, October 1999
Session 2. Extra-solar Planets: Dwarfs and Disks
Contributed Oral Parallel Session, Monday, October 11, 1999, 9:00-10:00am, Sala Kursaal

## [2.05] Dust Rings in Gas Disks. A model for HR 4796A

H.H. Klahr, D.N.C. Lin, P. Bodenheimer (UCO/Lick Observatory)

Circumstellar dust rings like the one observed around HR4796A are not a fail-proof indicator for the formation of massive planets. This paper presents a kinematical model for such a dusty circumstellar ring. A relatively small perturbation (10%) in the surface density distribution of a gas disk produces via secondary effects a dust ring with sharp edges. A distribution of surface density that locally increases outward can be the effect of a small planet (at R < 70 AU), but also could result from photo-evaporation, from an inhomogeneous initial distribution of mass after infall, or from inhomogeneities in the radial viscous transport of material. Given an assumed gas surface density distribution, the dust distribution is calculated including the effects of sub- and hyper-Keplerian disk rotation due to the radial pressure gradients, the Poynting-Robertson effect, direct radiation pressure and turbulent stirring. We find that dust particles have to be larger than 100 \mu m in radius in order to be gravitationally bound to the system. The observed dust distribution can be explained with a gas density perturbation at 70 AU with an amplitude of 10%.