Long-period SU UMa dwarf nova V1006 Cygni outburst activity and variability at different brightness states in 2015-2017

Abstract

CCD photometric observations of the dwarf nova V1006 Cyg were carried out in 2015 -2017 with 11 telescopes located at 7 observatories. They covered the 2015 superoutburst with rebrightening, five normal outbursts of ∼ 4-day duration and one wide outburst that lasted at least seven days. The interval between normal outbursts was 16 and 22 days, and between superoutbursts is expected to be longer than 124 days. The positive superhumps with the mean period of 0 d .10544(10) and 0 d .10406(17) were detected during the 2015 superoutburst and during the short-term quiescence between rebrightening and the start of the first normal outburst, respectively. During a wide 2017 outburst the orbital period 0 d .09832(15) was found. The amplitude of this signal was ∼ 2.5 times larger at the outburst decline than at its end. During the quiescence stage between the first and the second normal outbursts in 2015 we possibly detected the negative superhumps with the period of 0 d .09714(7).

V1006 Cyg: SU UMa-type dwarf nova in the period gap that wobbles between subclasses

“…Our observations are shown in Fig 1 . They start from JD 2460076 capturing the decline of outburst superposed on the quiescent state at mean brightness about R C ∼ 16 m .4 that turned out to be 1 m − 1 m .5 magnitudes brighter compared to known previous observations in 2015-2017 (Pavlenko et al, 2018). This "bright" quiescence which lasted ∼ three weeks, was terminated by the next long outburst with a duration of 10 d and amplitude of ∼ 2 m .5.…”

“…These QPOs were coherent on a scale of at least about an hour (see Fig 4, b). As during 2016 quiescence, no evidence of an orbital period was found in 2023 quiescence (Pavlenko et al, 2018).…”

“…Note that during the 2015-2017 quiescence there was a brief episode of increased brightness around normal outburst No 3 (see Fig. 1 in Pavlenko et al (2018)).…”

“…In selected nights of outburst and quiescence, V1006 Cyg was observed in the Johnson-Cousins U BV R C I C colour bands (see Tab.1). We used the U BV R C I C values of comparison star No 140 as in the paper by Pavlenko et al (2018) and U = 15 m .58 for this star obtained relatively to the stars with known magnitudes in the vicinity of CH Cyg (Henden & Munari, 2006). Standard data reduction included flat-fielding, bias and dark signal removal.…”

“…Finally, V1006 Cyg was identified as the SU UMa-type dwarf nova in the period gap based on the results of studies during the 2015 superoutburst (Kato et al, 2016). V1006 Cyg got attention not only by its localization in the period gap but also by detection in 2007, 2009 and 2017 of long outbursts without superhumps but with orbital-related brightness variations (Pavlenko et al, 2014(Pavlenko et al, , 2018. It was also found that this star showed three types of outbursts -normal, long normal and superoutbursts (Kato et al, 2016).…”