Contents of: VI/111/./abstract/MCREECHE_MCREE129.abs

The following document lists the file abstract/MCREECHE_MCREE129.abs from catalogue VI/111.
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It is clear that dust-driven mass loss from stars affects chemical evo-
lution of the interstellar medium in galaxies. IRAS LRS observations
clearly show that the 10 micron dust feature varies with the optical
light curve. However, because observations were not performed with IRAS
to obtain variability relationships, it is difficult to make accurate
predictions on the phase relationship between stellar surface and
circumstellar shell constituents. It is feasible to observe, with high
signal to noise, certain circumstellar components from the ground for
objects with a few hundred Janskys of flux. However, ISO is capable of
studying objects at the lower flux limit of the IRAS LRS survey for
which ground based observations are noise limited. We wish to test the
hypothesis that the SiO, silicate and iron oxide features vary on the
same time scale as the period of the circumstellar shell. There are
several broad features of particular interest to us due to their mutual
chemical interactions and origins in the stellar atmosphere: silicate
emission features at 10 and 18 microns, molecular SiO absorption at 7.6
microns and iron oxide emission features, specifically magnetite and
hematite, in the 17 to 35 micron range. There is evidence to indicate
that the SiO feature, which is severly limited by atmospheric methane in
ground based observations, plays an important role in the circumstellar
chemistry. Furthermore, the nature of the chemical interactions of Si,
C, O, Mg and Fe may help determine the compositions of the circumstellar
shell and stellar interior. In order to obtain good phase coverage, 20 M
type LPV stars with periods of 300 to 400 days and fluxes of 20 Janskys
(+/-5 Jy)at 8 microns were chosen from a list compiled by Little-Marenin
and Little of 291 M Mira variables observed with IRAS LRS. We request
that a series of four observations of this sample occur at intervals of
45 to 60 days. This sample was chosen to complement the CP and current
ground based surveys. It is vital to ascertain the variability relation-
ship if the process of LPV loss mass is to be understood.

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