A theoretical light-curve model for the 1985 outburst of RS ophiuchi

A theoretical light-curve model of the 1985 outburst of RS Ophiuchi based on a thermonuclear runaway model is presented. The system consists of a very massive white dwarf (WD) with an accretion disk and a red giant. The early phase of the V light curve is well reproduced only by the bloated WD photosphere of the thermonuclear runaway model on a 1.35 ± 0.01 M_⊙ WD, while the later phase is dominated both by the irradiated accretion disk and by the irradiated red giant underfilling the inner critical Roche lobe. The UV light curve is also well reproduced by the same model with a distance of 0.6 kpc to RS Oph. The envelope mass at the optical peak is estimated to be 2 x 10^-6 M_⊙, indicating a rather high mass accretion rate of 1.2 × 10^-7 M_⊙ yr^-1 between the 1967 and 1985 outbursts. About 90% of the envelope mass is blown off in the outburst wind, while the residual 10% (2 × 10^-7 M_⊙) has been left and added to the helium layer of the WD. The net increasing rate of the WD mass is 1.2 × 10^-8 M_⊙ yr^-1. Thus, RS Oph is certainly a strong candidate for a Type Ia supernova progenitor.