2003MNRAS.339.1006M

We present the results of optical photometry of the recurrent nova CI Aql in a later phase of the outburst which occurred in 2000. Our observation revealed that the object reached the quiescent level between 2001 December and 2002 April, and therefore that CI Aql is a unique recurrent nova characterized by an extremely long (1.4-1.7 yr) plateau phase. The light curve obtained in the outburst suggests that the object is the first example of an intermediate between classical and recurrent novae. In comparison with the estimation given in published theoretical calculations, the long duration of the plateau phase supports a higher hydrogen content of the white dwarf envelope, whereas such an abundance of hydrogen requires a later cessation of the wind, which is in disagreement with the sudden fading observed in late November of 2000. The light curve obtained in the later phase of the outburst indicates that the object was fainter and the gradual decline was steeper than predicted. These discrepancies between the observation and the theoretical prediction demand a drastic modification of the present model of CI Aql.