Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae
Authors: Kato Taichi , Imada Akira , Uemura Makoto , Nogami Daisaku , Maehara Hiroyuki , Ishioka Ryoko , Baba Hajime , Matsumoto Katsura , Iwamatsu Hidetoshi , Kubota Kaori , Sugiyasu Kei , Soejima Yuichi , Moritani Yuuki , Ohshima Tomohito , Ohashi Hiroyuki , Tanaka Junpei , Sasada Mahito , Arai Akira , Nakajima Kazuhiro , Kiyota Seiichiro , Tanabe Kenji , Imamura Kazuyoshi , Kunitomi Nanae , Kunihiro Kenji , Taguchi Hiroki , Koizumi Mitsuo , Yamada Norimi , Nishi Yuichi , Kida Mayumi , Tanaka Sawa , Ueoka Rie , Yasui Hideki , Maruoka Koichi , Henden Arne , Oksanen Arto , Moilanen Marko , Tikkanen Petri , Aho Mika , Monard Berto , Itoh Hiroshi , Dubovsky Pavol A. , Kudzej Igor , Dancikova Radka , Vanmunster Tonny , Pietz Jochen , Bolt Greg , Boyd David , Nelson Peter , Krajci Thomas , Cook Lewis M. , Torii Ken’ichi , Starkey Donn R. , Shears Jeremy , Jensen Lasse-Teist , Masi Gianluca , Hynek Tomáš , Novák Rudolf , Kocián Radek , Král Lukáš , Kučáková Hana , Kolasa Marek , Šťastný Petr , Staels Bart , Miller Ian , Sano Yasuo , Ponthière Pierre de , Miyashita Atsushi , Crawford Tim , Brady Steve , Santallo Roland , Richards Tom , Martin Brian , Buczynski Denis , Richmond Michael , Kern Jim , Davis Stacey , Crabtree Dustin , Beaulieu Kevin , Davis Tracy , Aggleton Matt , Morelle Etienne , Pavlenko Elena P. , Andreev Maksim , Baklanov Alexander , Koppelman Michael D. , Billings Gary , Urbančok L’ubomír , Ögmen Yenal , Heathcote Bernard , Gomez Tomas L. , Voloshina Irina , Retter Alon , Mularczyk Krzysztof , Złoczewski Kamil , Olech Arkadiusz , Kedzierski Piotr , Pickard Roger D. , Stockdale Chris , Virtanen Jani , Morikawa Koichi , Hambsch Franz-Josef , Garradd Gordon , Gualdoni Carlo , Geary Keith , Omodaka Toshihiro , Sakai Nobuyuki , Michel Raul , Cárdenas A. A. , Gazeas Kosmas D. , Niarchos Panos G. , Yushchenko Alexander V. , Mallia Franco , Fiaschi Marco , Good Gerry A. , Walker Stan , James Nick , Douzu Ken-ichi , Julian Wm Mack , Butterworth Neil D. , Shugarov Sergey Yu. , Volkov Igor , Chochol Drahomir , Katysheva Natalia , Rosenbush Alexander E. , Khramtsova Maria , Kehusmaa Petri , Reszelski Maciej , Bedient James , Liller William , Pojmański Grzegorz , Simonsen Mike , Stubbings Rod , Schmeer Patrick , Muyllaert Eddy , Kinnunen Timo , Poyner Gary , Ripero Jose , Kriebel Wolfgang 
Published: March 2014

Abstract
We systematically surveyed period variations of superhumps in SU UMa-type dwarf novae based on newly obtained data and past publications. In many systems, the evolution of the superhump period is found to be composed of three distinct stages: an early evolutionary stage with a longer superhump period, a middle stage with systematically varying periods, and a final stage with a shorter, stable superhump period. During the middle stage, many systems with superhump periods of less than 0.08 d show positive period derivatives. We present observational characteristics of these stages and give greatly improved statistics. Contrary to an earlier claim, we found no clear evidence for a variation of period derivatives among different superoutbursts of the same object. We present an interpretation that the lengthening of the superhump period is a result of the outward propagation of an eccentricity wave, which is limited by the radius near the tidal truncation. We interpret that late-stage superhumps are rejuvenated excitation of a 3:1 resonance when superhumps in the outer disk are effectively quenched. The general behavior of the period variation, particularly in systems with short orbital periods, appears to follow a scenario proposed in Kato, Maehara, and Monard (2008, PASJ, 60, L23). We also present an observational summary of WZ Sge-type dwarf novae. Many of them have shown long-enduring superhumps during a post-superoutburst stage having longer periods than those during the main superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to be strongly correlated with the fractional superhump excess, or consequently with the mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with multiple rebrightenings tend to have smaller period derivatives, and are excellent candidates for those systems around or after the period minimum of evolution of cataclysmic variables.