Publications
of the
MPIfR
Optical & Infrared
Interferometry Group
J.M. Winters, T. Le Berte, K.S. Jeong,
C. Helling, and E Sedlmayr:
A systematic investigation of the mass-loss
mechanism in dust forming
long-period variable stars
Astronomy and Astrophysics 361, 641-659 (2000)
Abstract.
In order to investigate the relations between the mass loss from
pulsating red
giants and quantities which can be obtained from observations, we have
explored the behavior of theoretical models which treat the
time-dependent hydrodynamics of circumstellar outflows, including a
detailed treatment of the dust formation process. This approach, while
ignoring effects such as a possible nonsphericity of the stellar
atmospheres which are difficult to assess, accounts correctly for
factors such as the grain formation and destruction which are crucial
to
the mass-loss mechanism.
We built a grid of ~150 models covering a wide range of physical
situations. This grid allows us to characterize the effects of
different
parameters, such as the stellar luminosity and temperature, the period
and the amplitude of the pulsation, and the C/O element abundance
ratio, on the behavior of AGB winds and on the rates of mass loss.
We find two regimes for the stellar outflows. The first one (A) is
characterized by stable winds with a layered structure of the
circumstellar dust shell, outflow velocities in excess of 5 kms-1,
and a large rate of mass loss. These outflows are dominated by
radiation pressure on dust.
For these
models we find good correlations between near-infrared colors and the
mass
loss rates. In the second regime (B), the winds are slow and do not
present a layered structure.
The outflows displaying the second behavior come, e.g., from red giants
with low luminosity, high temperature, or short period.
For them there is no correlation between color and mass loss rate. The
mass loss rates are low and never exceed 3 10-7 Moyr-1
Radiation pressure on dust plays only a minor role in this regime.
We have explored the effect of different parameters on the behavior of
the stellar winds. We find that, in general, all other parameters been
kept identical, there is a narrow range of values for each
parameter within which the models abruptly change from B to A, and that
once a model is stabilized in the A mode the changes in the values of
each parameter have only a smooth effect on the wind characteristics.
You can get this publication ...