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

Recurrent nova CI Aquilae entered the final decline phase a bit before 2001 May, 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 turnoff time of the CI Aql 2000 outburst to be in late 2001 March, after a luminous supersoft X-ray source phase lasting ∼150 days (from 2000 November until 2001 March). We have also found, by fitting our theoretical light curves with the 1917 and 2000 outbursts, the white dwarf (WD) mass to be M_WD = 1.2 ± 0.05 M_⊙; 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 ΔM_max ∼ 8.0 × 10^-6 M_⊙, and the average mass accretion rate is M_acc ∼ 1.0 × 10^-7 M_⊙ yr^-1 for 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 the two outbursts. We have also discussed the possibility of whether CI Aql will explode as a Type la supernova in the future.