Recurrent novae as a progenitor system of Type Ia supernovae. I. RS Ophiuchi subclass: Systems with a red giant companion

Theoretical light curves of four recurrent novae in outburst are modeled to obtain various physical parameters. The four objects studied here are thos e with a red giant companion, i.e., T Coronae Borealis, RS Ophiuchi, V745 S corpii, and V3890 Sagittarii. Our model consists of a very massive white dw arf (WD) with an accretion disk and a red giant companion. Light-curve calc ulation includes reflection effects of the companion star and the accretion disk together with a shadowing effect on the companion by the accretion di sk. We also include a radiation-induced warping instability of the accretio n disk to reproduce the second peak of T CrB outbursts. The early visual li ght curves are well reproduced by applying a thermonuclear runaway model to a very massive white dwarf close to the Chandrasekhar mass limit, i.e., M- WD = 1.37 +/- 0.01 M. for T CrB and 1.35 +/- 0.01 M. for RS Oph with solar metallicity (Z = 0.02), but 1.377 +/- 0.01 M. for RS Oph with low metallici ty (Z = 0.004), 1.35 +/- 0.01 MD for V745 Sco, and 1.35 +/- 0.01 M, for V38 90 Sgr. Optically thick winds, which blow from the WDs during the outbursts , play a key role in determining the nova duration and the speed of decline because the wind quickly reduces the envelope mass on the WD. The envelope mass at each optical maximum is also estimated to be DeltaM similar to 3 x 10(-6) M. (T CrB), 2 x 10(-6) M. (RS Oph), 5 x 10(-6) M. (V745 Sco), 3 x 1 0' MD (V3890 Sgr), indicating average mass accretion rates of M-acc similar to 0.4 x 10(-7) M. yr(-1) (80 yr; T CrB), 1.2 x 10(-7) M. yr(-1) (18 yr; R S Oph), 0.9 x 10(-7) M. yr(-1) (52 yr; V745 Sco), and 1.1 x 10(-7) M. yr(-1 ) (28 yr; V3890 Sgr) during the quiescent phase before the last outburst. A lthough a large part of the envelope mass is blown off in the wind, each WD retains a substantial part of the envelope mass after hydrogen burning end s. Thus, we have obtained net mass-increasing rates of the WDs as (M)over d ot(He) similar to 0.1 x 10(-7) M. yr(-1) (T CrB), 0.12 x 10(-7) M. yr(-1) ( RS Oph), 0.05 x 10(-7) M. yr(-1) (V745 SCO), 0.11 x 10(-7) M. yr(-1) (V3890 Sgr). These results strongly indicate that the WDs in the recurrent novae have now grown to near the Chandrasekhar mass limit and will soon explode a s a Type Ia supernova if the WDs consist of carbon and oxygen. We have also clarified the reason that T CrB shows a secondary maximum but the other th ree systems do not.