A new semi-empirical mass-loss relation for all cool winds not driven by dust
Klaus-Peter Schroeder (Astronomy Centre, University of Sussex,
Falmer, Brighton BN19QH, UK)
We present a new semi-empirical model for the mass-loss
from cool winds not driven by dust, so far have been
described by the Reimers relation. The wind is treated as
a spill-over of the extended and very turbulent giant
chromospheres. Consequently, the mechanical power input
should be proportional to the (basal) chromospheric
emission line luminosity LChr, and the potential
energy input required to lift the wind material is counted
from a characteristic chromospheric height RChr.
For the latter, we use the sonic point of the
average velocity field (known for the well studied K
supergiant ζ Aur), assuming its height to vary
with g*-1. Since observations also suggest
basal chromospheric flux FChr,bsl ∝
Teff7.5, we find M = η ⋅
L* R*/M* ⋅ (Teff/4000K)3.5 ⋅
(1+gˆ/4300 ⋅ g*).
The new relation makes a significant difference for the
luminous AGB (and post-AGB) stars. Here, RChr
boosts the mass-loss, in good agreement with observation.