V1974 Cygni: Optical and Ultraviolet Evolution and Analysis

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Session 61 -- Novae and Stellar Accretion
Oral presentation, Tuesday, 10, 1995, 10:00am - 11:30am

[61.02D] V1974 Cygni: Optical and Ultraviolet Evolution and Analysis

S.J. Austin (Arizona State University)

We have obtained optical and ultraviolet spectra of V1974 Cygni from day 4 to 540 after visual maximum which covers the spectral evolution from the post-maximum Fe II permitted line phase through the forbidden emission line phase. The strengths of the [Ne III]$\lambda$3869 and [Ne V]$\lambda$3425 lines during the nebular phase place V1974 Cygni within the spectral class of neon nova. The spectra of the nova during the nebular phase show exceptionally high ionization coronal lines from transitions of [Fe VII], [Fe X], [Ar X], and [Fe XIV]. We determine the interstellar reddening to be E(B-V)=0.33$\pm$0.04 and conclude from published reports that the distance is 2.8$\pm$0.7 kpc. High resolution line profiles obtained during the nebular phase exhibit a multi-component symmetric saw tooth shape which we model with equatorial and tropical rings at high inclination angles. Spatial projections of these models reproduce the major features of published HST FOC images. Line diagnostics show that the electron density during the nebular phase was above the critical densities for many of the observed nebular transitions. We used the photoionization code CLOUDY (Ferland 1993) to model the emission line flux ratios by mapping the parameter space with a Monte Carlo technique. The inhomogeneity of the ejected material was simulated by assuming large variations in the filling and covering factors, as well as letting the density vary as a function of radius. We determine the elemental abundances, at best, to within factors of two to five. Enhancements above solar are found for He, N, O, and Ne with abundances by number relative to solar 1$<$He/H$<$13, 90$<$N/H$<$380, 40$<$O/H$<$160, 100$<$Ne/H$<$400, and 5$<$Fe/H$<$40. The amount by which O and Ne have been enriched in the ejecta are sufficently high that the underlying white dwarf must must have an ONeMg composition.

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