Elemental Abundance Analysis of Nova Cygni 1992

摘要

We present the initial results of our analysis of V1974 Nova Cygni 1992 (Cyg 92). Cyg 92 was discovered on 1992 February 19.1. It was a fast ONeMg nova, with t_2 ～ 15 days and t_3 ～45 days. Austin et al. [1] determined the reddening for the nova to be E(B-V) = 0.36 ± 0.04 and the distance to be 2.8 ± 0.7 kpc. We have spectroscopic observations of Cyg 92 in both the visible and ultraviolet. Optical observations were taken from 4 to 540 days after outburst. The UV observations, made by IUE, cover 1 to 500 days after outburst. We have combined the photoionization code CLOUDY 94 and the minimization routine MINUIT to determine physical parameters and elemental abundances for the nova ejecta, as we have done for several other ONeMg novae in the past [2] [3] [4] [5]. Our results for Cyg92 show enhanced abundances, relative to solar material, for helium, nitrogen, oxygen, neon, magnesium, aluminum, silicon, and sulfur. The carbon abundance is approximately solar and iron is slightly below solar. These results are based on independent fits to three different sets of optical + UV observations taken at 300, 400, and 500 days after outburst. Comparing our results with those of previous analyses of Austin et al. [1] and Moro-Martin et al. [6], we find that our abundances are significantly lower than the others. The analysis by Austin et al. [1] suffered from an error in the dereddening of the UV spectra, resulting in inaccurate line flux ratios. Unfortunately, Moro-Martin used Austin's abundances as a starting point for their analysis. While many of the abundances obtained by Moro-Martin are lower than those of Austin's they are still generally much larger than our values, particularly for oxygen and neon. We believe an artificially high helium abundance, resulting from starting with Austin's values, lead to their higher abundances.