Abundance analysis of the slow nova PW Vulpeculae 1984

Abstract

We determine the elemental abundances for the ejecta of the slow nova PW Vul 1984. Our technique uses a minimization of the emission-line fits of a photoionization model to available ultraviolet, optical and infrared spectra. We find the following abundances (by number) with respect to solar: He/H=1.0+/-0.4, C/H=7.0^+7_-4, N/H=85^+59_-41 and O/H=6^+7_-2. In addition, there is weak evidence for solar Ne and Mg, and for twice solar Fe. Previous studies of PW Vul by Saizar et al. and Andrea et al. yielded considerable differences in their derived elemental abundances for the ejecta. Our abundances fall in between those found in the previous studies. To explain the discrepant abundances, we analyse in detail the data and methods used to obtain the previous results. The abundances found by Saizar et al. are significantly smaller than our values because of the lower electron temperature used by them in deriving elemental abundances from ion abundances. Andrea et al. used an ionization correction method to obtain their abundances and later verified their results with a photoionization model. Our analysis of their data shows that the absolute fluxes of the optical emission lines used by Andrea et al. are underestimated by 15 per cent, leading to a factor of 2 increase in their derived abundances. We also find that the photoionization model used by Andrea et al. predicts twice as much carbon as the photoionization code we used even when fitting the same data with similar model parameters.