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 $\pm$ 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 twice solar Fe. Previous studies (Saizar et al. 1991 and Andreä et al. 1991, 1994) of PW Vul have yielded considerable differences in their derived elemental abundances for the ejecta. Our abundances fall in between the previous studies. To explain the discrepant abundances, we analyze in detail the data and methods used to obtain the previous results. The abundances of Saizar et al. (1991) are significantly smaller then our values because of the lower electron temperature used by Saizar et al. in deriving elemental abundances from ion abundances. Andreä et al. (1991) used an ionization correction method to obtain their abundances and verified their results with a photoionization model (Andreä et al. 1994). Our analysis of their data shows that the absolute fluxes of the optical emission lines used by Andreä are underestimated by 15% leading to a factor of 2 increase in their derived abundances. We also find the photoionization model used by Andreä et al. (1994) predicts 2 times more carbon than the photoionization code we used even when fitting the same data with similar model parameters.