Mid-infrared spectroscopy of galactic novae

Abstract

We present 8 – 1 3 μm spectroscopy of 10 galactic novae. In 6 of these 10 novae, dust has formed in the ejecta. Each of these 6 cases shows evidence for silicate dust as well as carbon/graphitic dust. Despite limited statistics, it seems clear that the formation of silicate dust as well as carbon dust is a common occurrence in nova ejecta, despite the nova progenitor being generally carbon rich. For carbon and silicate grains to co-exist, the nova ejecta must be chemically and/or spatially inhomogeneous. In the case of Nova Her 91 there is evidence to suggest that the silicate emission may arise from a light echo from silicate grains deposited in a previous nova eruption. In Nova Sco 92 we have identified an extra emission component in the 8–9.5 μm region of the spectrum which is possibly due to emission from SiO molecules in the ejecta.