The Infrared Spectrum of the Optically Thin Dust Shell of V705 Cassiopeiae (Nova Cassiopeiae 1993)

We report 1.25 to 18 μm infrared photometry spectroscopy of the optically thin dust shell of V705 Cassiopeiae (Nova Cas 1993) between 330 and 418 days after the outburst. The measurements show that the dust shell, which had been optically thick until at least day ≈ 131, now shows the spectral signatures of optically thin astrophysical silicate grains at 10 and 20 μm and hydrocarbons at 3.2-3.4 and 11.3 μm. The 1-8 μm continuum which is due to carbon dust is still present, although it no longer has a blackbody spectral energy distribution. We estimate mass of silicate grains required to produce the observed visual extinction and conclude that the condensible elements in the silicate grains may be overabundant with respect to hydrogen.