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Session 114 - Circumstellar Material & Nebulae.
Oral session, Saturday, January 10

[114.02] Silicate Feature Variation in Long-Period Variable Stars

M. J. Creech-Eakman (California Institute of Technology)

The silicate feature of the dust around oxygen-rich stars, caused by the bend or stretch of the Si-O bonds in the SiO_4 tetrahedron, is a hallmark spectral feature in the 10 and 18 micron regions. Long Period Variable (LPV) stars produce copious quantities of silicate dust over this short stage of their stellar evolution. A long-term study of a group of 30 oxygen-rich LPVs was conducted during a sixteen month period with University of Denver Astronomy group's mid-infrared camera, TNTCAM. Service data on a limited subset of these LPVs taken using CGS3, a moderate-resolution mid-infrared spectrometer at UKIRT, will also be presented. It will be shown that the silicate features in the environment of these LPVs can be very different from one source to another and for a given star at different phases in its cycle, perhaps dependent upon the evolutionary state of the star and its circumstellar environment. In particular, it appears that the variable star's phase is an important catalyst in the dust formation process. Based upon these data and statistical analysis of the sample, certain new conclusions have been reached concerning the chemistry and kinematics of the oxygen-rich dust formation processes in LPVs.

Program listing for Saturday