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MPIfR Optical & Infrared Interferometry Group

T. Blöcker and T. Driebe:

Stellar evolution with rotation: Through the AGB towards the stage of white dwarfs

Astronomische Gesellschaft Abstract Series (AGM 18, P98)
Five Days of Creation: Astronomy with Large Telescopes from Ground and Space
Annual Scientific Meeting of the Astronomische Gesellschaft at the Joint European and National Meeting JENAM 2001 of the European Astronomical Society and the Astronomische Gesellschaft, Sep 10-15, 2001, Munich, Germany

Abstract. We present evolutionary calculations in consideration of rotation and overshoot for a 2 Msol star from the pre main-sequence through the Asymptotic Giant Branch towards the stage of white dwarfs. Rotation was considered by a centrifugal term in the hydrostatic equation. Angular momentum transport was treated with a diffusion equation. Five rotationally induced mixing processes were taken into account with diffusion coefficients adopted from Heger et al. (2000). Convective overshoot was applied according to the hydrodynamical simulations of Freytag et al. (1996). Mixing efficiencies were calibrated by the observed width of the main sequence and the 12C/13C ratio on the Red Giant Branch, the initial angular momentum by achieving vrot=200 km/s on the zero-age main sequence.
Entering the AGB, the stellar surface rotates only with vrot<1 km/s due to continuous expansion. In contrast to the slow and rigid rotation of the convective envelope the stellar core rotates differentially with velocities vrot of up to a few 100 km/s. Convective overshoot turned out to remain essentiell for the occurence of the third dredge-up. In the presence of dredge-up angular momentum is transferred from the core into the envelope of the star during the thermal pulses leading to a spin-down of the core. The further evolution into a white dwarf is discussed.

bloecker@mpifr-bonn.mpg.de.
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