First detection of the growing humps at the rapidly rising stage of dwarf novae AL Com and WZ Sge

Free access article

Issue		A&A Volume 381, Number 3, January III 2002


Page(s)		L41 - L44
Section		Letters
DOI		10.1051/0004-6361:20011644

A&A 381, L41-L44 (2002)
DOI: 10.1051/0004-6361:20011644

Letter

First detection of the growing humps at the rapidly rising stage of dwarf novae AL Com and WZ Sge

R. Ishioka¹, M. Uemura¹, K. Matsumoto^{1, 2}, H. Ohashi¹, T. Kato¹, G. Masi³, R. Novak³, J. Pietz³, B. Martin³, D. Starkey³, S. Kiyota³, A. Oksanen³, M. Moilanen³, L. Cook³, L. Kral³, T. Hynek³, M. Kolasa³, T. Vanmunster³, M. Richmond³, J. Kern³, S. Davis³, D. Crabtree³, K. Beaulieu³, T. Davis³, M. Aggleton³, K. Gazeas³, P. Niarchos³, A. Yushchenko³, F. Mallia³, M. Fiaschi³, G. A. Good³, D. Boyd³, Y. Sano³, K. Morikawa³, M. Moriyama³, R. Mennickent³, J. Arenas³, T. Ohshima³ and T. Watanabe³

¹ Department of Astronomy, Faculty of Science, Kyoto University, Kyoto 606-8502, Japan
² Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan
³ VSNET Collaboration Team

(Received 29 October 2001 / Accepted 20 November 2001)

Abstract
We report on time-series photometric observations in the earliest stages of superoutbursts of the extreme dwarf novae, AL Com and WZ Sge, which started on 2001 May after the 6 years quiescence and on 2001 July after the 23 years quiescence, respectively. We detected the growth of "early superhumps" during the each rising stage. Our observations reject the mass transfer instability for the trigger of the superoutburst of WZ Sge stars, and show the existence of some relations between the "early superhumps" and the spiral structure, which gives a hint of the origin of the "early superhumps."

Key words: stars: cataclysmic variables -- stars: dwarf novae -- stars: individual (WZ Sge)

Offprint request: R. Ishioka, ishioka@kusastro.kyoto-u.ac.jp

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