THE TEMPORAL EVOLUTION OF THE 1-5-MICRON SPECTRUM OF V1974-CYGNI (NOVA-CYGNI 1992)

We present 1-5 mu m moderate- and high-resolution infrared spectra of the ONeMg nova V1974 (Nova Cygni 1992) obtained at multiple epochs during an approximate to 500 day period after outburst. During the first 80 days, the spectra exhibited continuum emission from thermal bremsstrahlung (free-free radiation) with prominent recombination line emission from hydrogen, helium, nitrogen, and oxygen. The measured FWHM of these recombination lines suggests that the initial velocity of the ejecta was approximate to 2400-3400 km s(-1). We estimate from the hydrogen recombination line ratios that the density of the ionized shell at this epoch was approximate to 10(9) cm(-3), with an effective electron temperature of approximate to 5 x 10(3) K. As the temporal evolution of the ejecta progressed, the hydrogen and helium lines diminished in intensity, and coronal lines of aluminum, calcium, magnesium, neon, and sulfur appeared by approximate to day 80. The coronal line emission phase persisted for over 400 days. During this epoch, no significant dust formation occurred. We find that the ejecta of V1974 Cyg were overabundant in aluminum with respect to silicon by a factor of approximate to 5 and in magnesium with respect to silicon by a factor of greater than or equal to 3 relative to the solar photosphere. Comparison of our observed overabundances with recent model predictions of elemental synthesis in ONeMg outbursts suggests that the accreted envelope on V1974 Cyg was close to solar composition and that the precursor ONeMg white dwarf had a mass of approximate to 1 M..