ABSTRACT
Spectroscopic observations of the post-maximum phase of Nova Cygni 1978 are reported. Emission lines of Fe II and forbidden O I revealed three component emission structures. The radial velocities of the three components of the Fe II emissions showed similar velocity developments, as did the three components of the forbidden O I emissions. Formation of dust within the nova ejecta shell was indicated by the simultaneous appearance of a thermal infrared excess, a gradual acceleration of the forbidden O I emission-line radial velocities at -3 plus or minus 1 cm/sq sec, and a decrease in the strength of the redward peak of the forbidden O I 6300 emission relative to the blueward peak. Variations in these features were found to be directly correlated with changes in the visual light curve, which was similar to those of fast novae.