Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae. IV. The Fourth Year (2011–2012)
Authors: Kato Taichi , Hambsch Franz-Josef , Maehara Hiroyuki , Masi Gianluca , Miller Ian , Noguchi Ryo , Aakasaka Chihiro , Aoki Tomoya , Kobayashi Hiroshi , Matsumoto Katsura , Nakagawa Shinichi , Nakazato Takuma , Nomoto Takashi , Ogura Kazuyuki , Ono Rikako , Taniuchi Keisuke , Stein William , Henden Arne , De miguel Enrique , Kiyota Seiichiro , Dubovsky Pavol A. , Kudzej Igor , Imamura Kazuyoshi , Akazawa Hidehiko , Takagi Ryosuke , Wakabayashi Yuya , Ogi Minako , Tanabe Kenji , Ulowetz Joseph , Morelle Etienne , Pickard Roger D. , Ohshima Tomohito , Kasai Kiyoshi , Pavlenko Elena P. , Antonyuk Oksana I. , Baklanov Aleksei V. , Antonyuk Kirill , Samsonov Denis , Pit Nikolaj , Sosnovskij Aleksei , Littlefield Colin , Sabo Richard , Ruiz Javier , Krajci Thomas , Dvorak Shawn , Oksanen Arto , Hirosawa Kenji , Goff William N. , Monard Berto , Shears Jeremy , Boyd David , Voloshina Irina B. , Shugarov Sergey Yu. , Chochol Drahomir , Miyashita Atsushi , Pietz Jochen , Katysheva Natalia , Itoh Hiroshi , Bolt Greg , Andreev Maksim V. , Parakhin Nikolai , Malanushenko Viktor , Martinelli Fabio , Denisenko Denis , Stockdale Chris , Starr Peter , Simonsen Mike , Tristram Paul J. , Fukui Akihiko , Tordai Tamas , Fidrich Robert , Paxson Kevin B. , Itagaki Koh-ichi , Nakashima Youichirou , Yoshida Seiichi , Nishimura Hideo , Kryachko Timur V. , Samokhvalov Andrey V. , Korotkiy Stanislav A. , Satovski Boris L. , Stubbings Rod , Poyner Gary , Muyllaert Eddy , Gerke Vladimir , Macdonald Walter , Linnolt Michael , Maeda Yutaka , Hautecler Hubert 
Published: March 2014

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.