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Akademie věd České republiky, v. v. i. |
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Akademie věd České republiky, v. v. i. |
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Pravidelný seminář 5. 3. 2007
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Pozvánka na pravidelný seminář AsÚ AV ČR který se koná v pondělí 5. března 2007 v nové seminární mistnosti AsÚ v Ondřejově PROGRAM: 13:00 Odborná část 14:00 Přestávka/káva 14:20 Informace z vedení ústavu V odborné části vyslechneme informace z oddělení Galaxie a planetární systémy: 1. Novinky z oddělení (Jan Palouš) 2. Přednáška Planet
formation in layered disks
Richard Wünsch It is generally believed that planets form in so called protoplanetary disks made of gas and dust which have been observed around many pre-main-sequence stars. Observations suggest that they are the accretion disks, i.e. the viscous forces cause that the material is transported inwards while the angular momentum is transported outwards. The most promissing source of the viscosity is the magneto-hydrodynamic turbulence driven by the so called magneto-rotational instability (MRI). However, the protoplanetary disks are weakly ionized and the ionization degree in some parts of the disk may be so low that the gas decouples from the magnetic field and the MHD turbulence decays there. Since the important sources of the ionization are the cosmic rays and the X-rays emitted by the central star which ionize just the disk surface, the so called layered accretion model was suggested: the accretion occurs in the surface layers, but not the mid-plane region which is called the dead zone. In this work we use the radiation-hydrodynamic simulations to show that the layered disk suffers from the dynamical instability which causes the dead zone to split into rings. These rings work as traps for a dust which always tends to concentrate in places of pressure maxima. Such mechanism may lead to a substantial increase of the local dust density which is necessary for the formation of planetisimals and rocky planet cores. Moreover, the rings may be a subject of Rossby wave instability which leads to their decomposition into vortices and further dust density enhancement. Srdečně zve Vladimír Karas vedoucí semináře |