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 \geq 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 } .