Study of Negative and Positive Superhumps in ER Ursae Majoris
Abstract
We carried out the photometric observations of the SU UMa-type dwarf nova ER UMa during 2011 and 2012, which showed the existence of persistent negative superhumps even during the superoutburst. We performed two-dimensional period analysis of its light curves by using a method called "least absolute shrinkage and selection operator" (Lasso) and "phase dispersion minimization" (PDM) analysis, and we found that the period of negative superhumps systematically changed between a superoutburst and the next superoutburst. The trend of the period change can beinterpreted as reflecting the change of the disk radius. This change of the disk radius is in good agreement with the predicted change of the disk radius by the thermal-tidal instability (TTI) model. The normal outbursts within a supercycle showed a general trend that the rising rate to maximum becomes slower as the next superoutburst approaches. The change can be interpreted as the consequence of the increased gas-stream flow onto the inner region of the disk as the result of the tilted disk. Some of the superoutbursts were found to be triggered by a precursor normal outburst when the positive superhumps appeared to develop. The positive and negative superhumps co-existed during the superoutburst. The positive superhumps were prominent only during four or five days after the supermaximum, while the signal of the negative superhumps became strong after the middle phase of the superoutburst plateau. A simple combination of the positive and negative superhumps was found to be insufficient in reproducing the complex profile variation. We were able to detect the developing phase of positive superhumps (stage A superhumps) for the first time in ER UMa-type dwarf novae. Using the period of stage A superhumps, we obtained a mass ratio of 0.100(15), which indicates that ER UMa is on the ordinary evolutional track of CVs.
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Cite
@article{arxiv.1402.5747,
title = {Study of Negative and Positive Superhumps in ER Ursae Majoris},
author = {Tomohito Ohshima and Taichi Kato and Elena Pavlenko and Hidehiko Akazawa and Kazuyoshi Imamura and Kenji Tanabe and Enrique de Miguel and William Stein and Hiroshi Itoh and Franz-Josef Hambsch and Pavol A. Dubovsky and Igor Kudzej and Thomas Krajci and Alex Baklanov and Denis Samsonov and Oksana Antonyuk and Viktor Malanushenko and Maksim Andreev and Ryo Noguchi and Kazuyuki Ogura and Takashi Nomoto and Rikako Ono and Shin'ichi Nakagawa and Keisuke Taniuchi and Tomoya Aoki and Miho Kawabata and Hitoshi Kimura and Kazunari Masumoto and Hiroshi Kobayashi and Katsura Matsumoto and Kazuhiko Shiokawa and Sergey Yu. Shugarov and Natalia Katysheva and Irina Voloshina and Polina Zemko and Kiyoshi Kasai and Javier Ruiz and Hiroyuki Maehara and Natalia Virnina and Jani Virtanen and Ian Miller and Boyd Boitnott and Colin Littlefield and Nick James and Tamas Tordai and Fidrich Robaert and Stefono Padovan and Atsushi Miyashita},
journal= {arXiv preprint arXiv:1402.5747},
year = {2015}
}
Comments
PASJ accepted