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.
Instrument
LWS02 , PHT03 , SWS01
Temporal Coverage
1996-06-23T21:52:07Z/1997-09-07T07:12:56Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, T. Onaka, 1999, 'TIME VARIATION OF CIRCUMSTELLAR ENVELOPES PART 1 OF 6.', 1.0, European Space Agency, https://doi.org/10.5270/esa-agzlskf
