The Long-term Activity of the Postnovae Q Cygni and BK Lyncis

Abstract

We show the postnova activity of Q Cyg (Nova Cyg 1876) and BK Lyn (probable Nova Lyn 101). We use both CCD and photographic photometric observations. We show that both systems lie close to the upper limit of the luminosity in which dwarf nova (DN) outbursts occur. Q Cyg shows a novalike high-state activity. Random fluctuations (typically 0.6 mag) from a well-defined curve of the moving averages of brightness often occur on the timescale of weeks. The random fluctuations were suppressed during one fainter interval lasting several months but increased during another. In the author’s interpretation, clumps in the disk wind are likely to play a role in these fluctuations, especially when the luminosity of Q Cyg is near the upper limit of the range in which DN outbursts occur. BK Lyn was observed to spend about 100 yr in a very long state of a high luminosity on the upper limit of the region of DN outbursts before undergoing a time segment in which DN outbursts were present. We find that the individual DN outbursts in BK Lyn all show similar decay rates and fade more gradually than those of DNe that do not also show classical nova eruptions. We attribute it, along with the low amplitude of DN outbursts and the high quiescent luminosity, to the role of extra light. These outburst peaks, higher than the surrounding segments of the flat light curve, speak in favor of the ER UMa-type with superoutburst cycles and standstills rather than the high state in a novalike variable.

Keywords

• Cataclysmic variable stars
• Dwarf novae
• Nova-like variable stars
• Novae