DUST EVOLUTION IN NOVA CASSIOPEIA 1993

We present UKIRT spectroscopy of Nova Cassiopeia 1993 (= V705 Gas) in KLNQ bands, taken in 1994 and 1995. Fitting the continuum indicates a dust temperature T similar to 740 - 750 K in the latter part of 1994; this is similar to earlier measurements, and consistent with the ''iso thermal'' behaviour observed in novae with optically thick dust shells . The beta-index drops from 0.8 to 0.4 over the same period. This sugg ests grain growth; grain diameter increases from < 0.54 mu m around da y 256, to > 0.57 mu m by day 342. The UIR features differ from those i n other Galactic sources, and are similar to those in V842 Cen. This s uggests fundamental differences between the UIR carriers, or environme nts, in novae and other Galactic sources. The silicate feature is cons istent with an amorphous structure, in contrast to previous novae. We believe that grains in V705 Gas form two populations: silicates, and h ydrocarbons.