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Outburst parameters and the long-term activity of the dwarf nova CH Ursae Majoris *
Received 21 June 1999 / Accepted 2 November 1999
An analysis of the historical light curve of the dwarf nova CH UMa, spanning 25 years, is presented. The statistical distribution of the maximum brightness is bimodal and the outbursts can be divided into two classes: "bright" and "faint", the division magnitude being and separation almost . The maximum brightness of the bright outbursts tends to decrease in the course of the covered interval. The bright outbursts fall into two subtypes according to their decay branches (fast and slow). The typical recurrence time of the outbursts 300-370 days is one of the longest among CVs above the period gap. Variations of the cycle-length of the bright outbursts are very prominent and display a strong secular trend of the period decrease. The long-term activity and the outburst parameters, discussed in the framework of the thermal instability, put constraints on the model.
Key words: stars: activity stars: binaries: close stars: binaries: general stars: circumstellar matter stars: novae, cataclysmic variables stars: individual: CH UMa