INFRARED-SPECTROSCOPY OF NOVA-CASSIOPEIAE-1993 .2. EVOLUTION OF THE DUST

We present infrared spectroscopy of the nova V705 Cas (1993), obtained following the dust formation episode. There is 'UIR' emission at 3.3, 3.4, 8.2, 8.7 and 11.4 mu m, and silicate emission at 9.7 mu m. The U IR features are unlike those seen in most other objects displaying UIR emission, but are broadly similar to those present in the infrared sp ectra of the nova V842 Cen and some post-AGE stars. The 3.4/3.3 flux r atio is large compared with that usually seen in the spectra of object s displaying the UIR features, and the '7.7' feature appears at 8.2 mu m. We determine the beta-index for nova dust for the first time; the beta-index changed over the period 1994 August 22 (day 251; beta simil ar or equal to 0.8) to 1994 October/November (day 300/341; beta = 0.3) , suggesting that grain growth continued to occur. The grains attained dimensions greater than or similar to 0.5 mu m. We estimate that abou t 10(-8) M. of carbon dust condensed in the ejecta. The profile of the 9.7-mu m silicate emission feature was somewhat narrower than in othe r novae displaying this feature, suggesting that the silicate in V705 Cas may have been amorphous.