Superoutburst photometry of AL Comae Berenices

Photometric observations obtained during the 1995 April - May superoutburst of the dwarf nova AL Comae Berenices are presented. This star shows rare, large-amplitude outbursts, the last definitely seen in 1975. During the 1995 outburst, as with that of 1961, there was a sharp, two-magnitude temporary minimum in the outburst light curve at about 28 days after maximum light. We offer an explanation for such temporary minima involving the migration of a cooling wave within the accretion disk. V and I band CCD time-series photometry taken throughout the two-month-long event, reveal a complex period structure with two dominant periods, one near 82 min and one near 41 min. Early in the outburst, photometric modulations of 81 and 86 min were seen and are likely to be related to superorbital modulations seen in other large outburst amplitude dwarf novae. Superhumps developed after similar to 10 days and show a quasi-stable, nonphase coherent period of 82.5 min. A low-amplitude 41 min period was present throughout, also appearing not to be phase coherent. We conclude that the two dominant periods seen are of related origin and we list several possible mechanisms for their cause. Previous quiescence observations of AL Com have shown periods near 87 and 41 min. (C) 1996 American Astronomical Society.