Multiple Periodicities in Cataclysmic Variable and White Dwarf Stars
The normal dwarf nova (DN) outburst is characterized by a rapid rise, a brief stay near maximum and a slower decline to minimum light; the whole sequence lasts in general for 4 to 6 days, but can take as long as 10 or 12 days in some stars. While not strictly periodic, the DN outbursts are quasi-periodic in the sense that the mean periods derived from intervals sufficient to contain at least 50 outbursts (i,e. a few years for the shortest period systems, up to 30 years for longer period systems) remain sensibly constant. It should be added, however, that in the case of U Gem there is evidence for an increase in its recurrence period which may indicate some evolutionary change: for the first 50 years of observation of U Gem the mean period was 96. 5 days and for the second 50 years it was 107.6 days (Mayall, 1957); during the past four years the mean interval has been 291 days (with only one outburst in 1974).
KeywordsLight Curve White Dwarf Monthly Notice Rapid Oscillation Variable White
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