Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003phdt........15l&link_type=abstract
PhD. Thesis (2003), Laboratoire d'astrophysique de Grenoble
Astronomy and Astrophysics
Astrophysics
1
Radiative Transfer, Formation Of Stars, Pre-Main-Squence Stars, Late Stars, Optical Interferometry
Scientific paper
It is nowadays widely accepted that low mass star formation initiated from a molecular cloud undergoes a phase where the central object is surrounded by a disc, in which planets may form later. The study of such a disc mainly aims at the understanding of the evolutionary sequence of star formation and of planet formation. Radiative transfer in this disc is of high importance, for it is heated by viscous dissipation or stellar irradiation for instance. The production and transportation of thermal energy in this disc therefore conditions its chemical and physical properties inside. It has countless consequences in terms of structure.
I shall present a study of the discs based on a deep analytical description of the radiative transfer and a delay of the numerical implementation. This method allows a better grasp on processes and physical conditions in these objects. I shall constrain model parameters and establish a new diagnosis combining the spectral energy distribution and the visibilities obtained with optical long-baseline interferometers. The former observable is a well known technique, and the latter new and promising: it provides information at the scale of one astronomical unit for the closest star forming regions.
I shall start a generalisation of the analytical studies of the radiative transfer in stellar atmospheres, with two striking discrepancies: viscous heating occurs everywhere in the disc and the surface is illuminated by the star. I apply this formalism in a numerical simulation of a disc heated by viscosity alone. I then develop a simplified version of this transfer in a two-layer disc: the surface is heated by the interior and by the star, and the interior by viscosity and by the surface. This simplification allow to derive a simplified analytical description of the physical conditions in a disc heated by the two processes mentioned above.
I shall tackle the interpretation of observations in the end. I shall of the possibilities brought by interferometry concerning marginally resolved objects, as most young star will be. I then shall present best fits of the two-layer models for low mass young stars already observed by interferometers.
The LaTeX and PDF files of the manuscript (in French with English appendices) are made available by the National Centre for Scientific Reasearch (CNRS) archive site (http://tel.ccsd.cnrs.fr/documents/archives0/00/00/64/74).
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