Observational study of double superoutbursts in long-orbital-period AM CVn stars

Abstract We present an observational study of superoutbursts in six AM CVn systems with orbital periods longer than 35 min. We focused on this range because such systems are expected to have very low mass ratios, making them particularly likely to exhibit double superoutbursts and fading-tail profiles. Using time-resolved photometry from the Variable Star Network and the American Association of Variable Star Observers campaigns, complemented by survey data from the Zwicky Transient Facility, the All-Sky Automated Survey for Supernovae, the Asteroid Terrestrial-impact Last Alert System, Gaia, and the Transiting Exoplanet Survey Satellite, we analyzed nine superoutbursts observed between 2014 and 2021. Among them, four events exhibited clear double superoutburst profiles, analogous to those seen in hydrogen-rich WZ Sge-type dwarf novae. We characterized the fading tail following the second superoutburst and found that it can be divided into three distinct phases (tails A, B, and C) with different power-law fading indices. The effective superoutburst durations were typically 7–13 d, while the dip duration is significantly different among systems. Notably, the effective durations of the second superoutbursts in the double superoutburst were consistently around 5 d. These results highlight the importance of thermal–tidal instabilities in explaining the outbursts of long-orbital-period AM CVn stars. They also suggested that the three-phase fading-tail structure may be a universal feature of the systems and further imply that in systems with short supercycles the effective viscosity during quiescence could be higher than expected from a true quiescent state.

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Journal
Publications of the Astronomical Society of Japan
Published
2025-11-19
DOI
https://doi.org/10.1093/pasj/psaf133
Primary Topic
Astrophysical Phenomena and Observations
Type
article
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article

Observational study of double superoutbursts in long-orbital-period AM CVn stars

Domenico Licchelli, Lewis M. Cook, Tomáš Medulka, Oksana I. Antonyuk et al.
Publications of the Astronomical Society of Japan
Astrophysical Phenomena and Observations
article

Observational study of double superoutbursts in long-orbital-period AM CVn stars

Domenico Licchelli, Lewis M. Cook, Tomáš Medulka, Oksana I. Antonyuk, Ryuhei Ohnishi, Е. П. Павленко, Daiti Fujii, Sho Sumiya, Р. Новак, Katsuaki Kubotera, Miho Kawabata, William Stein, Tomohito Ohshima, K. A. Antonyuk, D. Nogami, Tonny Vanmunster, Rod Stubbings, John Rock, Kazunari MASUMOTO, Hanami Matsumoto, Naoto Kojiguchi, Kengo Nikai, Yoshitomo Maeda, Sjoerd Dufoer, David J. Lane, Hiroshi Itoh, Keisuke Isogai, Yusuke Tampo, Kenneth Menzies, Eddy Muyllaert, Julia V. Babina, D. Chochol, Shawn Dvorak, Tamás Tordai, Yuki Sugiura, S. Yu. Shugarov, G. Stone, R. Matsumura, Kazuki Maeda, Katsura Matsumoto, F. D. Romanov, Risa Matsuda, Pavol A. Dubovský, Yasuyuki Wakamatsu, Stephen M. Brincat, Junpei Ito, Daisuke Sakai, Berto Monard, M. Shibata, Graeme Coates, A. A. Sosnovskij, Peter Starr, Taichi Kato, Mariko Kimura, Gianluca Masi, Raúl Michel, Yuki Zenko, Michael J Cook, Nikolaj Pit, Alex Baklanov, Enrique De Miguel, Daiki Ito, Marlin Costello, Franz-Josef Hambsch, Megumi Takenaka, Stephen Hovell, Taiti Kato, Joseph H Ulowetz, Daiki Fukushima
article en

Abstract

Abstract We present an observational study of superoutbursts in six AM CVn systems with orbital periods longer than 35 min. We focused on this range because such systems are expected to have very low mass ratios, making them particularly likely to exhibit double superoutbursts and fading-tail profiles. Using time-resolved photometry from the Variable Star Network and the American Association of Variable Star Observers campaigns, complemented by survey data from the Zwicky Transient Facility, the All-Sky Automated Survey for Supernovae, the Asteroid Terrestrial-impact Last Alert System, Gaia, and the Transiting Exoplanet Survey Satellite, we analyzed nine superoutbursts observed between 2014 and 2021. Among them, four events exhibited clear double superoutburst profiles, analogous to those seen in hydrogen-rich WZ Sge-type dwarf novae. We characterized the fading tail following the second superoutburst and found that it can be divided into three distinct phases (tails A, B, and C) with different power-law fading indices. The effective superoutburst durations were typically 7–13 d, while the dip duration is significantly different among systems. Notably, the effective durations of the second superoutbursts in the double superoutburst were consistently around 5 d. These results highlight the importance of thermal–tidal instabilities in explaining the outbursts of long-orbital-period AM CVn stars. They also suggested that the three-phase fading-tail structure may be a universal feature of the systems and further imply that in systems with short supercycles the effective viscosity during quiescence could be higher than expected from a true quiescent state.

Publications of the Astronomical Society of JapanVol. 78(1)
New Mexico State University (US), Kanazawa University (JP), Project HOPE (US), University of Nagasaki (JP), WiLAN (Canada) (CA), Pioneer (United States) (US), Osaka Kyoiku University (JP), University of Cape Town (ZA), Okayama University (JP), American Association of Variable Star Observers (US), British Astronomical Association (GB), Slovak Academy of Sciences (SK), Kyoto University (JP), Czech Academy of Sciences, Astronomical Institute (CZ), Point University (US), Government of Extremadura (ES), Concord Consortium (US), Fresno City College (US), Ensenada Institute of Technology (MX), Fresno Unified School District (US), National Solar Observatory (US), Rolling Hills Observatory (US), University of Timor (ID), TÜBİTAK National Observatory (TR), Bundesdeutsche Arbeitsgemeinschaft für Veränderliche Sterne (DE), Vihorlat Observatory (SK), Scope Group (United States) (US), RIKEN (JP), Kanagawa Odawara Nursing School (JP), Tetoora Road Observatory (AU), Queen Astrid Military Hospital (BE), Astrobiology Center (JP), South African Radio Astronomy Observatory (ZA), Hungarian Astronomical Association (HU), Astronomical Institute of the Slovak Academy of Sciences (SK), Abbey Ridge Observatory (CA), Astronomical Observatory (RS), Crimean Astrophysical Observatory (UA), Bronberg Observatory (ZA), Stichting tot Steun VCVGZ (NL), Framingham State University (US), Saint Mary's University (CA), California State University, Fresno (US), The University of Tokyo (JP), Universidad de Huelva (ES), Hyogo University (JP)
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Astrophysical Phenomena and Observations
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