Detection of two-armed spiral shocks on the accretion disk of the   eclipsing fast nova V1494 Aquilae
  We have modeled the unusual orbital light curve of V1494 Aquilae (Nova Aquilae 1999 No.2) and found that such an unusual orbital light curve can be reproduced when there exist two-armed, spiral shocks on the accretion disk. V1494 Aql is a fast classical nova and found to be an eclipsing system with the orbital period of 0.1346138 days in the late phase of the nova outburst. Its orbital light curve shows a small bump at orbital phase 0.2, a small dip at 0.3, sometimes a small bump at 0.4, and a large bump at 0.6-0.7 outside eclipse. Such a double- or triple-wave pattern outside eclipse has never been observed even though overall patterns look like some supersoft X-ray sources or eclipsing polars. We have calculated orbital light curves including the irradiation effects of the accretion disk and the companion by the hot white dwarf. These unusual patterns can be reproduced when we assume two-armed spiral shocks on the accretion disk. Especially, triple-wave patterns are naturally obtained. This result strongly suggests the existence of two-armed spiral shocks on the accretion disk in the late phase of the nova outburst. 
Izumi Hachisu (Univ. of Tokyo), Mariko Kato (Keio Univ.), Taichi Kato   (Kyoto Univ.)