Prediction 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 is still bright 300 days after the optical maximu m, showing the slowest evolution among recurrent novae. We predict the turn off time of the CI Aql 2000 outburst coming in 2001 August after a supersof t X-ray source (SSS) phase lasts 250 days. We also predict helium enrichmen t of ejecta, He/H similar to 0.25 by number. Observational confirmations ar e urgently required. Based on the optically thick wind mass-loss 0.25 theor y of the thermonuclear runaway model, we have also estimated the white dwar f (WD) mass to be M-WD = 1.2 +/- 0.05 M-circle dot by fitting our theoretic al light curves with the 1917 and 2000 outbursts. The mass of the hydrogen- rich envelope on the WD is also estimated to be DeltaM similar to 6 x 10(-6 ) M-circle dot at the optical maximum, indicating an average mass accretion rate of (M)over dot(acc) similar to0.7 x 10(-7) M-circle dot yr(-1) during the quiescent phase between the 1917 and 2000 outbursts. Using these obtai ned values, we have consistently reproduced the light curve in quiescence a s well as the two outburst phases. Thus, we predict the turnoff time to be in 2001 August for the 2000 outburst. We strongly recommend soft X-ray obse rvations to detect the SSS until 2001 August because the massive wind phase already ended in 2000 December and was followed by an SSS phase that very likely will last until 2001 August.