A HOT NEON NOVA - OPTICAL SPECTROPHOTOMETRY AND THE PHYSICS OF NOVA CYGNI 1992

We present the results of low-resolution optical spectrophotometric observations of Nova Cygni 1992 obtained at the Pine Bluff Observatory between 8 and 450 days after outburst. The early emission spectra show the Balmer spectrum of H i, Fe II lines, and some He I lines. As the nova declines, the continuum fades rapidly, and the emission lines become dominant. The decreasing densities in the expanding shell and the hardening of the nova's radiation field lead to the emergence by 1993 April 30, of the nebular lines [O III] lambda4363, [O II] lambda5007, and [Ne III] lambda3869. By August 21 the [Ne III] lambdalambda3869, 3968 and [Ne v] lambdalambda3346, 3426 emission lines have become the main features of the nebular spectrum and establish Nova Cygni as a neon nova. The unusual strength of [O III] lambda4363 is attributed to high densities collisionally deexciting the nebular lines, while the extreme [Ne v] intensity during late phases suggests a very high temperature photosphere for the nova. A wide ionization range also implies high electron densities as compared to normal nebulae.