An illumination effect and an eccentric orbit for the symbiotic binary PU Vul revealed by 32 years of optical spectroscopy

Abstract

We analyze \(\sim\)32 years of optical spectra and photometry for the symbiotic binary PU Vul. Light curves for the He I \(\lambda\)4471, He II \(\lambda\)4686 and H\(\beta\) \(\lambda\)4861 emission lines reveal an illumination effect, where the hot white dwarf ionizes the outflowing wind of the red giant, and evidence for an eccentric orbit with e \(\approx\) 0.16. Along with the gradual appearance of high ionization emission from [Fe VII] and O VI, the relative fluxes of these lines suggest an increase in the effective temperature of the hot component, from roughly \(10^5\) K on JD 2448000 (1990) to roughly \(2\times 10^5\) K on JD 2455000 (2009). During this period, the luminosity of the hot component dropped by a factor of 4\(-\)6 to a current value of roughly 1000 L\(_{\odot}\).