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Personal information

Georges Michaud

Département de physique
Université de Montréal
C.P. 6128, Succursale Centre-Ville
Montréal, QC
Canada   H3C 3J7
Phone : 514-343-6672
Fax : 514-343-2071
Email: michaudg@astro.umontreal.ca
Office : B-439

Research field : Origin of chemical elements, transport processes in stars

Description of the research project:
We have introduced atomic diffusion into a stellar evolution code and obtain stellar models where particle transport is treated in the radiative zones. Radiative accelerations are calculated self consistently using the atomic data originally used by OPAL to obtain their opacity tables.

In Pop I stars, by increasing the mass of the convective core, atomic diffusion modifies the morphology of the turnoff and the assumption of core overshoot in solar metallicity clusters such as M67 becomes unnecessary. Mass loss rates of around 5 10^-14 solar mass per year have been shown to be a competing process which leads to abundance anomalies as observed on AmFm stars and compatible with their appearance on the pre-main sequence. Sirius A can be reproduced in detail. We plan to investigate the effect of the suggested change of solar metallicity on cluster morphology.

In Pop II stars, the evolution has been carried out successfully from the zero age main sequence to the middle of the horizontal branch, for metallicities ranging from 1/200 solar to solar. It has been shown that the assumption of core overshoot is unnecessary since atomic diffusion of Carbon from the core is sufficient to insure convective neutrality at the helium burning core. It has furthermore been shown that the overabundance of, for instance, iron by a factor of ~100 observed in the hot horizontal branch stars of clusters is explained by atomic diffusion driven by radiative accelerations; this has been shown to be true for all cluster metallicities. These calculations were also extended to observations of field sdB stars where similar anomalies are observed. Most abundance anomalies (some 16 species) are explained as observed in some 100 stars.

We plan to extend the calculations to the end of the Horizontal Branch and to continue on to White Dwarfs. A complete grid of models will also be generated for Pop II stars and they will be used to interpret the implications of WMAP for the Li abundance, taking into account the latest developments.

List of graduate students :

Recipient of the following awards:

    2006-01: Prix Carlyle S. Beals

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