Infrared spectroscopy of Nova Cassiopeiae 1993 -- II. Evolution of the dust

We present IR 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 microns, and silicate emission at 9.7 microns. The UIR features are unlike those seen in most other objects displaying UIR emission, but are broadly similar to those present in the infrared spectra of the nova V842 Cen and some post-AGB stars. The 3.4/3.3 flux ratio is large compared with that usually seen in the spectra of objects displaying the UIR features, and the '7.7' feature appears at 8.2 microns. 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 = 0.8) to 1994 October/November (day 300/341; beta = 0.3), suggesting that grain growth continued to occur. The grains attained dimensions of at least 0.5 micron. We estimate that about 10 exp -8 solar mass of carbon dust condensed in the ejecta. The profile of the 9.7-micron silicate emission feature was somewhat narrower than in other novae displaying this feature, suggesting that the silicate in V705 Cas may have been amorphous.