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

TL;DR

This 32-year study of the symbiotic binary PU Vul reveals an illumination effect, an eccentric orbit, and an increase in the hot component's temperature, alongside a decrease in luminosity.

Contribution

The paper provides the first long-term optical spectroscopic analysis of PU Vul, revealing an eccentric orbit and detailed evolution of the hot component's temperature and luminosity.

Findings

Eccentric orbit with e ≈ 0.16 identified.

Increase in hot component temperature from 10^5 K to 2×10^5 K.

Hot component luminosity decreased by a factor of 4-6.

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}$.