V2487 Ophiuchi: A strong candidate for a recurrent nova and a progenitor of Type Ia supernova

The light curve of the 1998 outburst of V2487 Ophiuchi (Nova Oph 1998) shows a very rapid decline (t_3 ~ 9 day) and a mid-plateau phase from 10 to 30 days after the optical maximum, which are characteristics common to the U Sco subclass of the recurrent novae. We have numerically reproduced light curves of the 1998 outburst based on a thermonuclear runaway model with optically thick winds. The results show that the mass of the white dwarf (WD) is as massive as 1.35 \pm 0.01 M_\sun; the envelope mass of the WD at the optical maximum is ~ 6 x 10^{-6} M_\sun; the hydrogen content of the WD envelope is as low as X ~ 0.1 by mass weight. The mass transfer rate in quiescence is roughly estimated to be \~ 1.5 x 10^{-7} M_\sun yr^{-1} and, therefore, that the recurrence period of nova outbursts is about 40 yr. Since the WD mass may be now growing at a rate of ~ 2 x 10^{-8} M_\sun yr^{-1}, V2487 Oph is a strong candidate for a progenitor of a Type Ia supernova.