Models of AM CVn star outbursts
TLDR
In this article, the role of helium in the accretion disc instability mechanism was investigated in the case of AM CVn stars, and it was shown that the enhanced mass-transfer rate, due presumably to variable irradiation of the secondary, must not only be taken into account but is a determining factor that shapes AMCVn star outbursts.Abstract:
Outbursting AM CVn stars exhibit outbursts similar to those observed in different types of dwarf novae. Their light-curves combine the characteristic features of SU UMa, ER UMa, Z Cam, and WZ Sge-type systems but also show a variety of properties never observed in dwarf novae. The compactness of AM CVn orbits and their unusual chemical composition make these systems valuable testbeds for outburst models. We aim for a better understanding of the role of helium in the accretion disc instability mechanism, testing the model for dwarf novae outbursts in the case of AM CVn stars, and aim to explain the outburst light-curves of these ultra-compact binaries. We calculated the properties of the hydrogen-free AM CVn stars using our previously developed numerical code adapted to the different chemical composition of these systems and supplemented with formulae accounting for mass transfer rate variations, additional sources of the disc heating, and the primary's magnetic field. We discovered how helium-dominated discs react to the thermal-viscous instability and were able to reproduce various features of the outburst cycles in the light-curves of AM CVn stars. The AM CVn outbursts can be explained by the suitably adapted dwarf-nova disc instability model but, as in the case of its application to hydrogen-dominated cataclysmic variables, one has to resort to additional mechanisms to account for the observed superoutbursts, dips, cycling states, and standstills. We show that the enhanced mass-transfer rate, due presumably to variable irradiation of the secondary, must not only be taken into account but is a determining factor that shapes AM CVn star outbursts. The cause of the variable secondary's irradiation has yet to be understood; the best candidate is the precession of a tilted/warped disc.read more
Citations
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Journal ArticleDOI
Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae. IV. The Fourth Year (2011-2012)
Taichi Kato,Franz-Josef Hambsch,Hiroyuki Maehara,Gianluca Masi,Ian Miller,Ryo Noguchi,Chihiro Aakasaka,Tomoya Aoki,Hiroshi Kobayashi,Katsura Matsumoto,Shinichi Nakagawa,Takuma Nakazato,Takashi Nomoto,Kazuyuki Ogura,Rikako Ono,Keisuke Taniuchi,William Stein,A. A. Henden,Enrique de Miguel,Seiichiro Kiyota,Pavol A. Dubovsky,Igor Kudzej,Kazuyoshi Imamura,Hidehiko Akazawa,Ryosuke Takagi,Yuya Wakabayashi,Minako Ogi,Kenji Tanabe,Joseph Ulowetz,Etienne Morelle,Roger D. Pickard,Tomohito Ohshima,Kiyoshi Kasai,Elena P. Pavlenko,Oksana I. Antonyuk,Aleksei V. Baklanov,Kirill A. Antonyuk,Denis Samsonov,Nikolaj V. Pit,Aleksei A. Sosnovskij,Colin Littlefield,Richard Sabo,Javier Ruiz,Thomas Krajci,Shawn Dvorak,Arto Oksanen,Kenji Hirosawa,William N. Goff,Berto Monard,Jeremy Shears,David Boyd,Irina Voloshina,Sergey Yu. Shugarov,Sergey Yu. Shugarov,Drahomir Chochol,Atsushi Miyashita,Jochen Pietz,Natalia Katysheva,Hiroshi Itoh,Greg Bolt,Maksim V. Andreev,Nikolai Parakhin,Viktor Malanushenko,Fabio Martinelli,Denis Denisenko,Christopher Stockdale,Peter Starr,Mike Simonsen,Paul J. Tristram,Akihiko Fukui,Tamás Tordai,Robert Fidrich,Kevin B. Paxson,Koh-ichi Itagaki,Youichirou Nakashima,Seiichi Yoshida,Hideo Nishimura,Timur V. Kryachko,Andrey V. Samokhvalov,S. A. Korotkiy,Boris L. Satovski,Rod Stubbings,Gary Poyner,Eddy Muyllaert,Vladimir Gerke,Walter MacDonald Ii,Michael Linnolt,Yutaka Maeda,Hubert Hautecler +88 more
TL;DR: In this article, the authors collected times of superhumpmaxima for 86 SUUMa-type dwarf novae, mainly observed during the 2011-2012 season, and confirmed general trends recorded in previous studies, such as the relation between period derivatives and orbital periods.
Journal ArticleDOI
The viscosity parameter alpha and the properties of accretion disc outbursts in close binaries
Iwona Kotko,Jean-Pierre Lasota +1 more
TL;DR: In this article, it has been found that the values of the stress-to-pressure ratio (the alpha "viscosity" parameter) deduced from observations of outbursting discs are an order of magnitude higher than those obtained in numerical simulations.
Journal ArticleDOI
A search for the hidden population of AM CVn binaries in the Sloan Digital Sky Survey
Philip J. Carter,T. R. Marsh,Danny Steeghs,Paul J. Groot,Gijs Nelemans,Gijs Nelemans,David Levitan,Arne Rau,Chris M. Copperwheat,Thomas Kupfer,Gijs H. A. Roelofs +10 more
TL;DR: In this paper, the authors presented the results from a spectroscopic survey designed to uncover the hidden population of AM Canum Venaticorum (AM CVn) binaries in the photometric data base of the Sloan Digital Sky Survey (SDSS).
Journal ArticleDOI
The viscosity parameter α and the properties of accretion disc outbursts in close binaries
TL;DR: In this paper, the authors analyzed a set of observations of dwarf-nova and AM CVn star outbursts and from the measured decay times determined the hot-disc viscosity parameter αh.
Journal ArticleDOI
A review of the disc instability model for dwarf novae, soft X-ray transients and related objects
TL;DR: In this article, the disc instability model (DIM) for dwarf novae and soft X-ray transients is reviewed and its most recent developments, as well as the current limitations of the model, focusing on the dwarf nova case.
References
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Journal ArticleDOI
Global Simulations of Accretion Disks I: Convergence and Comparisons with Local Models
TL;DR: In this paper, a set of global grid-based magnetohydrodynamic (MHD) simulations was performed for the study of astrophysical accretion disks, and the authors showed that the saturation of the MHD turbulence via parasitic modes of the magnetorotational instability is related to the instantaneous correlations between local flux and stress found in global simulations.
Posted Content
Superhumps and post-outburst rebrightening episodes in the AM CVn star SDSS J012940.05+384210.4
TL;DR: In this paper, the first confirmed outburst of the AM CVn system SDSS J012940.05+384210.4 during 2009 December was reported, with a peak-to-peak amplitude of 0.06 mag and Psh = 37.9(2) min.
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