INFRARED-SPECTROSCOPY OF NOVA-CASSIOPEIAE-1993 .1. THE PRE-DUST PHASE

We present infrared spectroscopy of Nova Cassiopeiae 1993 (V705 Gas) i n the period before dust formation. We find strong emission in the fir st-overtone CO bands before the nova reached maximum light - the earli est detection of a molecule in a nova. Our observations suggest the pr esence of a relatively cool (less than or similar to 4500 K), neutral zone in the ejecta, as required by chemical modelling of nova winds. C O formation is likely to have been dominated by the H-2 route rather t han by direct radiative association of C and O. We suggest that radiat ive cooling of the ejected material by CO could play a major role in t he grain formation process.