A New Abundance Analysis of the ONeMg Nova QU Vulpeculae

Abstract

This paper presents a new determination of the ejecta elemental abundances of the moderately fast ONeMg nova QU Vul 1984 using published ultraviolet, optical, infrared, and radio observations. The technique uses an optimization code in combination with CLOUDY photoionization models to fit the emission-line spectra obtained at multiple epochs during the nebular phase of the outburst. The best-fit model parameters from four epochs of multiwavelength spectra are compatible with a hot white dwarf source with a roughly constant luminosity of 3 × 1037 ergs s-1. We find the following abundances (by number) with respect to solar: He/H = 1.16 ± 0.08, C/H = 0.2, N/H = 12 ± 0.6, O/H = 2.5, Ne/H = 21.7 ± 1.7, Mg/H = 10, Al/H = 53.3 ± 14.7, Si/H = 2.0, Ar/H = 0.28 ± 0.02, and Fe/H = 0.53 ± 0.03. Previous studies of QU Vul yielded considerable differences in the derived elemental abundances. This analysis, which uses a better physical model, efficient optimization technique, and more multiwavelength data than the previous studies, generally finds the lowest abundance enhancements. The ejected mass could not be determined, because of the large range in distance from the different distance estimate methods. However, even the closest distance of 1.9 kpc gives a lower limit to the ejected mass of ~3.5 × 10-4 M☉, which presents a challenge for hydrodynamical models to reproduce. These results, coupled with the long light curve decay time and nuclear burning timescale, relative to other ONeMg novae, imply that the outburst occurred on a low-mass ONeMg white dwarf. The extreme mass and enhanced abundances imply that a QU Vul-like event might play an important role in the nucleosynthesis of the local interstellar medium.