Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae. IV. The Fourth Year (2011–2012)

Abstract

Continuing the project described by Kato et al. (2009, PASJ, 61, S395), we collected times of superhump maxima for 86 SU UMa-type dwarf novae, mainly observed during the 2011–2012 season. We confirmed general trends recorded in our previous studies, such as the relation between period derivatives and orbital periods. There are some systems showing positive period derivatives despite the long orbital period. We observed the 2011 outburst of the WZ Sge-type dwarf nova BW Scl, and recorded an $ O$$-$$ C$ diagram similar to those of previously known WZ Sge-type dwarf novae. The WZ Sge-type dwarf nova OT J184228.1$ +$ 483742 showed an unusual pattern of double outbursts composed of an outburst with early superhumps and one with ordinary superhumps. We propose an interpretation that a very small growth rate of the 3:1 resonance due to an extremely low mass-ratio led to quenching the superoutburst before the ordinary superhump appeared. We systematically studied ER UMa-type dwarf novae, and found that V1159 Ori showed positive superhumps similar to ER UMa in the 1990s. The recently recognized ER UMa-type object BK Lyn dominantly showed negative superhumps, and its behavior was very similar to the present-day state of ER UMa. The pattern of period variations in AM CVn-type objects was very similar to that of short-period hydrogen-rich SU UMa-type dwarf novae, making them a helium analogue of hydrogen-rich SU UMa-type dwarf novae. SBS 1108$ +$ 574, a peculiar hydrogen-rich dwarf nova below the period minimum, showed a very similar pattern of period variations to those of short-period SU UMa-type dwarf novae. The mass-ratio derived from the detected orbital period suggests that this secondary is a somewhat evolved star whose hydrogen envelope was mostly stripped during the mass-exchange. CC Scl, MASTER OT J072948.66$ +$ 593824.4, and OT J173516.9$ +$ 154708 showed only low-amplitude superhumps with complex profiles. These superhumps are likely to be a combination of two closely separated periods.

Cataclysmic Variables Observed During K2 Campaigns 0 and 1

“…The O-C diagram of the superhumps derived by Kato et al (2013) show a downward quadratic curve covering these three superoutbursts with an extremely negative decline rate of −5.34×10 −4 on the basis of the superhump period of 0.0936 day derived from the superoutburst in 2003. Kato & Makoto (2001) estimated that the cycle length of the normal outbursts is ∼13.5 day, but there is not enough data to derive the supercycle length (Otulakowska-Hypka & Olech 2013).…”

The evolutionary status of Cataclysmic Variables: eclipse modelling of 15 systems

“…Given our updating of the superhump-mass ratio relations above, we revisit the analysis of donor star properties in Knigge (2006) and Knigge et al (2011). Firstly, P sh values for all SU UMa-type DNe in the Patterson et al (2005) sample (70 systems) were replaced by P B sh measurements from the SU UMa-type DNe survey of Kato et al (2009Kato et al ( , 2010Kato et al ( , 2012Kato et al ( , 2013Kato et al ( , 2014aKato et al ( ,b, 2015Kato et al ( , 2016Kato et al ( , 2017. For a number of systems, P orb was also updated, either from measurements made by Tables 2 and B1 Patterson et al (2005).…”

The bridge between ER Ursae Majoris-type dwarf nova and nova-like system

“…In RZ LMi, the mass transfer rate is not secularly decreasing as in the scenario given by [19]. BK Lyn also returned to ints original NL state in late 2013 from its temporal ER UMa-type state [20]. The hypothetical cooling sequence from NL objects to SU UMa-type DNe via ER UMa-type DNe after nova eruptions is not very consistent with observational staticsics.…”

“…This object showed an almost complete transition from an ER UMa-type object to a permanent superhuper (Nova-like object). BK Lyn is another object which experienced the transitions between ER UMa-type object and a permanent superhumper ( [19]; [20]).…”