Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000phdt.........3a&link_type=abstract
PhD Thesis, Laboratoire d'Astrophysique de l'Observatoire de Grenoble (LAOG), France, 2000.
Astronomy and Astrophysics
Astrophysics
Scientific paper
The recently discovered extrasolar planets have formed in gaseous and dusty disks possibily analogous to those observed around stars close to the Main Sequence, such as β Pictoris. This thesis deals with the dust in circumstellar environments around such stars and combines: high angular resolution observations, the modeling of grains' physical and chemical properties to deduce their optical behaviour, the modeling of optically thin disks, and the dynamics of planetesimals that release the dust grains observed. Our images obtained with the Hubble Space Telescope reveal two new circumstellar disks around HD 141569 and HD 100546, two stars sometimes classified as Herbig-like stars. Whereas the two systems have almost the same age (~10 million years), their morphologies differ. These observations highlight the difficulties to ellaborate a single scenario that would describe the all evolution of protoplanetary systems. The dust ring surrounding HR 4796 A, a star with an age similar to the two previous stars, is marginaly resolved from the ground. The full modeling of this disk allows to reproduce all the available observations. These results imply that, whereas the star is still quite young, planetesimals should be present to supply the disk in porous and amorphous dust grains which are afterwards blown away by radiation pressure. A dynamical model for the prototypical disk around β Pictoris is proposed. Assuming realistic optical grain properties, this approach allows to reproduce the main caracteristics of the disk and in particular the fine asymmetries that are observed. This model assumes the presence of a planetary companion which perturbes a disk of planetesimals and takes into account the differential effect of the radiation pressure on the grains. Finally, the disk model I developped during the thesis is used in order to optimize the use of future observationnal instruments.
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