A spectrum observed by M. Fujii can be seen at:
A spectrum observed by G. Cole can be seen at: http://www.starphysics.com/CIAQL/ciaql.htm (vsnet-alert 4730).
W. Liller's spectroscopic results: vsnet-alert 4731.
S. Kiyota's spectra and CCD image: http://member.nifty.ne.jp/meineko/ccd/aqlcispe.jpg http://www.age.ne.jp/x/meineko/ccd/aqlci.jpg
With a CCD image taken by S. Kiyota and at Bisei by K. Ayani and K. Shirakami, H. Yamaoka performed astrometry and the calculated accurate position of the nova strongly indicated that it is identical with the eclipsing binary with strange spectrum (IBVS 4232, 4338), which is thought to be a quiescent counterpart of Nova Aql 1917 = CI Aql (vsnet-alert 4717, vsnet-alert 4712, vsnet-alert 4725). The quiescent identification with a 0.6-day eclipsing binary with HeII and CIII/NIII emission lines would then be interpreted as a system closely related to supersoft X-ray source (SSXS) which repeatedly undergo nova explosions. The eclipse light curve and the orbital period strongly resembles those of known SSXS and V Sge stars. The presence of high excitation emission lines are common among them, and CV-type recurrent novae like U Sco (vsnet-alert 4714).
The analysis of combined data by S. Kiyota (Tsukuba, Japan) and the Kyoto team on Jun. 15 has yielded a detection of the primary eclipse minimum. The eclipse was 0.3mag deep. A preliminary analysis yielded a mid-eclipse time of 15.597 UT, while the prediction (based on the epehemeris in IBVS 4232, Mennickent and Honeycutt) was 15.586 UT (vsnet-campaign 220). On June 20, T. Kato reported that the fading of CI Aql has become slower and short-term light variations have become less prominent. This may resemble a "plateau" stage observed in the later stage of recurrent nova outbursts (vsnet-campaign 237). Interrupting the plateau stage, the slightly rising was confirmed through the data on June 30 from Kyoto observations (vsnet-campaign-nova 15). The observation on July 1 at Kyoto has again caught the fading of CI Aql (vsnet-campaign-nova 16). The observation on July 3 by S. Kiyota confirmed the secure appearance of primary eclipses (vsnet-campaign-nova 33). L. Kral caught the whole primary eclipse on July 5/6 and reported the eclipse depth of about 0.2mag and the duration of about 2.3 hours (vsnet-campaign 314). The Kyoto observation on July 9 succeeded in very clearly record the predicted primary eclipse. The eclipse is V-shaped around the minimum, and the eclipse center was determined as July 9.713 UT, giving an O-C of +0.012 to the ephemeris (vsnet-campaign-nova 39). The fading trend stopped since the early August at the magnitude of about 13.6mag (vsnet-campaign-nova 79). As reported in IAUC 7528 (K. Matsumoto and T. Kato), the object has apparently entered the final rapid-decline stage (vsnet-campaign-nova 93).