SUPERHUMPS IN CATACLYSMIC BINARIES .11. V603-AQUILAE REVISITED

After a decade of near stability at P = 0.146 d, the photometric ''suh erhump'' periodicity of the old nova V603 Aquilae experienced a remark able change between 1991 and 1992. Observation in 1992-1994 indicates that the dominant signal was then at a period in the range 0.1338-0.13 45 d, 3% shorter than the orbital period. Like its predecessor, the ne w signal also wanders in period on a timescale of a few months. The fu ll amplitude in 1994 was 0.20 mag, more than twice as great as the sup erhump displayed during 1980-1991. An intensive observing campaign in 1994 revealed that the old superhump at 0.146 d was still present with approximately undiminished amplitude (averaging 0.07 mag). Tn a prece ssion model, the simultaneous presence of superhumps above and below t he orbital period strongly suggests identification with two independen t types of precessional sideband, The observed periods and period chan ges are consistent with a simple hypothesis: that the longer period (' 'positive superhump'') arises from the prograde motion of the line of apsides, and the shorter period (''negative superhump'') arises from t he retrograde motion of the line of nodes. A detailed account of how a fluid disk manages to maintain such well-organized motions is sorely needed.