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.