Publications
of the
MPIfR
Optical & Infrared
Interferometry Group
J.M. Winters and T. Blöcker:
On the fading of mass-loss beyond the AGB
Astronomische Gesellschaft Abstract Series (AGM 18, P97)
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.
Stellar evolution on the upper Asymptotic Giant Branch is dominated by
continuously increasing stellar winds which effectively erode the stellar
surfaces.
Finally, mass-loss rates of up to ~10-4Msol/yr are reached and the
AGB evolution is terminated when the envelope mass dropped below a few 1/100
Msol. Then the star moves off the AGB and evolves towards the regime of
central stars of planetary nebulae. Observations indicate that mass-loss should
decrease by order of magnitudes during this transition phase. However, up to
now it is only poorly known how and at which temperature this strong decrease
of the mass-loss rates takes place.
We calculated wind models for the very end of the AGB evolution and the
following transition phase in order to study the fading of the strong
AGB mass-loss.
These hydrodynamic wind models treat explicitly the problem of dust formation
(Fleischer et al. 1995) and were calculated along existing evolutionary tracks
(Blöcker 1995). Since dust formation is more and more hampered with
increasing temperature, mass-loss rates of winds driven by radiation pressure
on dust drop by orders of magnitudes during the heating of the star beyond the
AGB. Due to a strongly temperature dependent Eddington-limit this takes place
only in a narrow transition region in the Hertzsprung-Russell diagram.
Blöcker T., 1995, A&A 299, 755
Fleischer A.J., Gauger A., Sedlmayr E., 1995, A&A 297, 543