Revised analysis of the supersoft X-ray phase, helium enrichment, and turn-off time in the 2000 outburst of recurrent nova CI Aquilae

Abstract

Recurrent nova CI Aquilae has entered the final decline phase a bit before May of 2001, about 300 days after the optical maximum, showing the slowest evolution among recurrent novae. Based on the optically thick wind mass-loss theory of the thermonuclear runaway model, we have estimated the turn-off time of the CI Aql 2000 outburst. It is in late March of 2001 after a luminous supersoft X-ray source phase lasts 150 days (from November of 2000 until March of 2001). We have also obtained, by fitting our theoretical light curves with the 1917 and 2000 outbursts, the white dwarf (WD) mass to be M_{WD}= 1.2 \pm 0.05 M_\sun, the helium enrichment of the envelope is He/H = 0.5 by number, the mass of the hydrogen-rich envelope on the WD at the optical maximum is \Delta M_{max} = 8.0 x 10^{-6} M_\sun, and the average mass accretion rate is \dot M_{acc}= 1.0 x 10^{-7} M_\sun/yr during the quiescent phase between the 1917 and 2000 outbursts. Using these obtained values, we have consistently reproduced the light curve in quiescence as well as of the two outbursts. We have also discussed the possibility whether or not CI Aql will explode as a Type Ia supernova in a future.