Survey of period variations of superhumps in SU UMa-type dwarf novae. V. The fifth year (2012–2013)
Authors: Kato Taichi , Hambsch Franz-Josef , Maehara Hiroyuki , Masi Gianluca , Nocentini Francesca , Dubovsky Pavol A. , Kudzej Igor , Imamura Kazuyoshi , Ogi Minako , Tanabe Kenji , Akazawa Hidehiko , Krajci Thomas , Miller Ian , de Miguel Enrique , Henden Arne , Noguchi Ryo , Ishibashi Takehiro , Ono Rikako , Kawabata Miho , Kobayashi Hiroshi , Sakai Daisuke , Nishino Hirochika , Furukawa Hisami , Masumoto Kazunari , Matsumoto Katsura , Littlefield Colin , Ohshima Tomohito , Nakata Chikako , Honda Satoshi , Kinugasa Kenzo , Hashimoto Osamu , Stein William , Pickard Roger D. , Kiyota Seiichiro , Pavlenko Elena P. , Antonyuk Oksana I. , Baklanov Aleksei V. , Antonyuk Kirill , Samsonov Denis , Pit Nikolaj , Sosnovskij Aleksei , Oksanen Arto , Harlingten Caisey , Tyyskä Jenni , Monard Berto , Shugarov Sergey Yu. , Chochol Drahomir , Kasai Kiyoshi , Maeda Yutaka , Hirosawa Kenji , Itoh Hiroshi , Sabo Richard , Ulowetz Joseph , Morelle Etienne , Michel Raúl , Suárez Genaro , James Nick , Dvorak Shawn , Voloshina Irina B. , Richmond Michael , Staels Bart , Boyd David , Andreev Maksim V. , Parakhin Nikolai , Katysheva Natalia , Miyashita Atsushi , Nakajima Kazuhiro , Bolt Greg , Padovan Stefano , Nelson Peter , Starkey Donn R. , Buczynski Denis , Starr Peter , Goff William N. , Denisenko Denis , Kochanek Christopher S. , Shappee Benjamin , Stanek Krzysztof Z. , Prieto José L. , Itagaki Koh-ichi , Kaneko Shizuo , Stubbings Rod , Muyllaert Eddy , Shears Jeremy , Schmeer Patrick , Poyner Gary , Rodríguez-Marco Miguel 
Published: May 2014

Continuing the project described in Kato et al. (2009, PASJ, 61, S395), we collected times of superhump maxima for SU UMa-type dwarf novae mainly observed during the 2012–2013 season. We found three objects (V444 Peg, CSS J203937, and MASTER J212624) having strongly positive period derivatives despite the long orbital period (Porb). By using the period of growing stage (stage A) superhumps, we obtained mass ratios for six objects. We characterized nine new WZ Sge-type dwarf novae. We made a pilot survey of the decline rate in the slowly fading parts of SU UMa-type and WZ Sge-type outbursts. The decline time scale was found to generally follow an expected $P_{\rm orb}^{1/4}$ dependence, and WZ Sge-type outbursts also generally follow this trend. There are some objects which show slower decline rates, and we consider these objects good candidates for period bouncers. We also studied unusual behavior in some objects, including BK Lyn which made a transition from an ER UMa-type state to a novalike (standstill) state in 2013, and unusually frequent occurrences of superoutbursts in NY Ser and CR Boo. We applied the least absolute shrinkage and selection operator (Lasso) power spectral analysis, which has been proven to be very effective in analyzing the Kepler data, to the ground-based photometry of BK Lyn, and detected a dramatic disappearance of the signal of negative superhumps in 2013. We suggested that the mass-transfer rates did not strongly vary between the ER UMa-type state and novalike state in BK Lyn, and this transition was less likely caused by a systematic variation of the mass-transfer rate.