SILICATE FEATURE VARIATION IN LONG-PERIOD VARIABLE-STARS .1. INITIAL OBSERVATIONS

We report new mid-infrared spectra of five bright, long-period variabl e (LPV) stars, as well as related objects, obtained at the Wyoming Inf rared Observatory with Denver University's medium-resolution CAESR ins trument. The data, when combined with low-resolution spectrometer spec tra from IRAS, show variation of the silicate feature with phase of th e LPV. We perform a calculation for impingement time of the shock on t he circumstellar dust shell to demonstrate that this variation could b e the result of a shock-shell interaction.