Evolution of the Symbiotic Nova PU Vul -- Outbursting White Dwarf, Nebulae, and Pulsating Red Giant Companion

TL;DR

This study models the long-term evolution of the symbiotic nova PU Vul, analyzing its light curves, eclipses, and nebular emissions over 32 years to understand the white dwarf's activity and system geometry.

Contribution

It provides a comprehensive composite light-curve model incorporating multiple emission components and confirms the ongoing hydrogen burning on the white dwarf through eclipse analysis.

Findings

White dwarf photosphere decreased by two orders of magnitude between 1980 and 1994

Eclipses confirmed total occultation of the WD by the M-giant

Distance to PU Vul estimated at approximately 4.7 kpc

Abstract

We present a composite light-curve model of the symbiotic nova PU Vul (Nova Vulpeculae 1979) that shows a long-lasted flat optical peak followed by a slow decline. Our model light-curve consists of three components of emission, i.e., an outbursting white dwarf (WD), its M-giant companion, and nebulae. The WD component dominates in the flat peak while the nebulae dominate after the photospheric temperature of the WD rises to log T (K) >~ 4.5, suggesting its WD origin. We analyze the 1980 and 1994 eclipses to be total eclipses of the WD occulted by the pulsating M-giant companion with two sources of the nebular emission; one is an unocculted nebula of the M-giant's cool-wind origin and the other is a partially occulted nebula associated to the WD. We confirmed our theoretical outburst model of PU Vul by new observational estimates, that spanned 32 yr, of the temperature and radius. Also our eclipse analysis confirmed that the WD photosphere decreased by two orders of magnitude between the 1980 and 1994 eclipses. We obtain the reddening E(B-V) ~ 0.3 and distance to PU Vul d ~ 4.7 kpc. We interpret the recent recovery of brightness in terms of eclipse of the hot nebula surrounding the WD, suggesting that hydrogen burning is still going on. To detect supersoft X-rays, we recommend X-ray observations around June 2014 when absorption by neutral hydrogen is minimum.