The following document lists the file abstract/TONAKA_TIMVAR_1.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
Mass loss of AGB stars is an important process for the evolution
of matter in the Galaxy. However, there are a number of unknowns
involved in the mass loss process. The largest uncertainties
reside in the formation process and optical properties of the dust
grains. Model analysis of infrared observations often suggests
a low temperature of silicate dust formation compared to
theoretical predictions, indicating a reconsideration of dust
formation and mass loss process. On the other hand,
interpretation of observations requires the photon absorption
efficiency of silicate dust to be much higher than that of any
known silicate existing on the earth ("dirty silicate model").
The amount of increase of the absorptivity is often arbitrarily
assumed. Both problems interrelate with each other and are
difficult to be investigated separately by analyses solely based
on an IR spectrum of the dust shell. We propose to elucidate
these problems by observing optically thin dust shell around
oxygen-rich long-period variables periodically by ISO. Periodic
observations from near to far infrared will provide the
information of the reaction of dust shell to different incident
radiations from the photosphere. We can determine the change of
the dust temperature and the amount of dust grains separately
owing to the simple nature of optically thin dust shell from
the observations at different epochs. From these results and
the energy balance consideration we can derive the absorptivity
of silicate dust quantitatively and identify the dust forming
region. ISO will provide a unique opportunity to make such
periodic observations of the wide IR region with stable accuracy,
which are essential for this kind of study. The results will
lead to a better understanding of the late stellar evolution and
the circulation of the matter in the Galaxy.