CI Aquilae :A recurrent nova with an unusually long plateau phase

Abstract

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.

A New Clue to the Transition Mechanism between Optical High and Low States of the Supersoft X‐Ray Source RX J0513.9−6951, Implied By the Recurrent Nova CI Aquilae 2000 Outburst Model

“…Assuming this efficiency being kept, we can expect that the white dwarf in RX J0513.9−6951 will explode as a Type Ia supernova after about 0.6M ⊙ is transferred even when the WD mass is 1.2 M ⊙ . Matsumoto et al 2001Matsumoto et al , 2002. Small open circles indicate observational Rc-magnitudes.…”

“…Fig.3.-A calculated Rc-light curve are plotted against time (HJD 2,450,000+) together with the observational points of the CI Aql 2000 outburst (taken fromMatsumoto et al 2001Matsumoto et al , 2002. Small open circles indicate observational Rc-magnitudes.…”

On the Possibility of V4444 Sgr as a Recurrent Nova

“…The observed duration of the plateau phase (∼ 50 d) is longer than ∼16 d of the U Sco outburst in 1999 (Matsumoto et al 2003b) and ∼20 d for the suggested recurrent nova V2487 Oph (Hachisu et al 2002), but is shorter than ∼1.4-1.7 yr of the CI Aql outburst in 2000 (Matsumoto et al 2003a). 3 After JD 2451400, the nova started to fade more rapidly, which is consistent with the termination of the plateau phase, rather than a more continuous decrease in the decline rate in most of classical novae (cf.…”

“…Our observational knowledge of recurrent novae has recently made a significant advancement, particularly led by the most recent detections, and prompt announcements through VSNET, of three recurrent nova outbursts: U Sco in 1999 (Schmeer et al 1999;Munari et al 1999;Kahabka et al 1999;Lépine et al 1999;Anupama, Dewangan 2000;Evans et al 2001;Iijima 2002), CI Aql in 2000 (Takamizawa et al 2000;Kiss et al 2001;Matsumoto et al 2001;Matsumoto et al 2003a;Burlak, Esipov 2001), and IM Nor in 2002 (Liller 2002;Kato et al 2002). Theoretical models have been able to reproduce the observed features of the recurrent novae (Hachisu et al 2000a, Hachisu et al 2000b.…”

Time Development of Recurrent Nova CI Aquilae's 2000 Outburst between 0.8 and 2.5 MICRONS

“…Thus, CI Aql is a ''moderately fast'' nova (Payne-Gaposchkin 1957), although the object's subsequent behavior indicated a relatively slow evolution. Based on optical photometry, Matsumoto et al (2003) regard the unusually long plateau phase as indicating that CI Aquilae is intermediate in nature between classical and recurrent novae.…”