Multicolor Photometry of Nova Lacertae 1910 = DI Lac in 1962-2002

Abstract

We present an analysis of the behavior of nova DI Lac 52 years after the outburst and over the next 40 years. Similar to a dwarf nova, DI Lac demonstrates flare activity with a characteristic time of 36 days and an amplitude of about 0^m.6. A flare profile is asymmetrical, the rise in brightness lasting about five days and the fading lasting about twenty days. Shorter flares sometimes occur between the main ones. The flares can be divided into three types in accordance with their behavior on magnitude–color diagrams. The ascending and descending branches of flares of the first type practically coincide on the diagrams, the second type describe counterclockwise loops, and the third type describe clockwise loops. The first and second types of flares can be explained within the framework of the theory of thermal instability as arising first in the outer and inner parts of the accretion disk, respectively. The nature of flares of the third type is still unclear.