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 has entered the final decline phase a bit beforeMay of 2001, about 300 days after the optical maximum, showing the slowestevolution among recurrent novae. Based on the optically thick wind mass-losstheory of the thermonuclear runaway model, we have estimated the turn-off timeof the CI Aql 2000 outburst. It is in late March of 2001 after a luminoussupersoft X-ray source phase lasts 150 days (from November of 2000 until Marchof 2001). We have also obtained, by fitting our theoretical light curves withthe 1917 and 2000 outbursts, the white dwarf (WD) mass to be M_{WD}= 1.2 \pm0.05 M_\sun, the helium enrichment of the envelope is He/H = 0.5 by number, themass of the hydrogen-rich envelope on the WD at the optical maximum is \DeltaM_{max} = 8.0 x 10^{-6} M_\sun, and the average mass accretion rate is \dotM_{acc}= 1.0 x 10^{-7} M_\sun/yr during the quiescent phase between the 1917and 2000 outbursts. Using these obtained values, we have consistentlyreproduced the light curve in quiescence as well as of the two outbursts. Wehave also discussed the possibility whether or not CI Aql will explode as aType Ia supernova in a future.Comment: 16 pages including 9 figures, to appear in the Astrophysical Journa