The outburst properties of AM CVn stars

Kotko, Iwona; Lasota, Jean–Pierre; Dubus, G.

doi:10.1002/asna.200911333

Cited by 4 publications

(7 citation statements)

References 13 publications

(10 reference statements)

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“…Outbursts from hydrogen‐accreting cataclysmic variables (CVs) show amplitudes of at least 1 mag (e.g. Koto, Lasota & Dubus 2010). We therefore define an AM CVn system in outburst as that which shows light‐curve variations greater than 1 mag.…”

Section: Resultsmentioning

confidence: 99%

“…On the theoretical side, progress has been more limited compared to the work on hydrogen‐accreting systems. However, the work of Smak (1983), who described a thermal instability model, Whitehurst (1988) and Tsugawa & Osaki (1997), who develop tidal instability models, and Lasota, Dubus & Kruk (2008) and Kotko, Lasota & Dubus (2010), who take into account irradiation effects, are some notable advances in modelling hydrogen‐deficient accreting binaries.…”

Section: Introductionmentioning

confidence: 99%

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The long-term optical behaviour of helium-accreting AM CVn binaries

Ramsay

Barclay

Steeghs

et al. 2011

Monthly Notices of the Royal Astronomical Society

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We present the results of a two and a half year optical photometric monitoring programme covering 16 AM CVn binaries using the Liverpool Telescope on La Palma. We detected outbursts in seven systems, one of which (SDSS J0129) was seen in outburst for the first time. Our study coupled with existing data shows that ∼1/3 of these helium-rich accreting compact binaries show outbursts. The orbital period of the outbursting systems lies in the range 24-44 min and is remarkably consistent with disc-instability predictions. The characteristics of the outbursts seem to be broadly correlated with their orbital period (and hence mass transfer rate). Systems which have short periods (<30 min) tend to exhibit outbursts lasting 1-2 weeks and often show a distinct 'dip' in flux shortly after the onset of the burst. We explore the nature of these dips which are also seen in the near-ultraviolet. The longer period bursters show higher amplitude events (5 mag) that can last several months. We have made simulations to estimate how many outbursts we are likely to have missed.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The long-term optical behaviour of helium-accreting AM CVn binaries

Ramsay

Barclay

Steeghs

et al. 2011

Monthly Notices of the Royal Astronomical Society

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“…These facts as well as the desire to apply our version of the DIM for helium-rich accretion discs (Lasota et al 2008;Kotko et al 2010) to AM CVn outbursts has been the main motivation for writing the present article. In Sect.…”

Section: Introductionmentioning

confidence: 99%

Models of AM Canum Venaticorum star outbursts

Kotko

Lasota

Dubus

et al. 2012

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Context. 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. Aims. 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. Methods. 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. Results. 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. Conclusions. 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.

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“…Although the physics of helium‐dominated accretion is poorly understood, outbursts are thought to be due to instabilities in the accretion disc (e.g. Smak 1983; Tsugawa & Osaki 1997; Kotko, Lasota & Dubus 2010).…”

Section: Introductionmentioning

confidence: 99%

Multiwavelength observations of the helium dwarf nova KL Dra through its outburst cycle

Ramsay

Kotko

Barclay

et al. 2010

Monthly Notices of the Royal Astronomical Society

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We present multiwavelength observations of the helium-dominated accreting binary KL Dra which has an orbital period of 25 min. Our ground-based optical monitoring programme using the Liverpool Telescope has revealed KL Dra to show frequent outbursts. Although our coverage is not uniform, our observations are consistent with the outbursts recurring on a time-scale of ∼60 d. Observations made using Swift show that the outbursts occur with a similar amplitude and duration (2 weeks) at both UV and optical energies. Although KL Dra is a weak X-ray source, we find no significant evidence that the X-ray flux varies over the course of an outburst cycle. We can reproduce the main features of the 60-d outburst cycle using the disc instability model and a helium-dominated accretion flow. Although the outbursts of KL Dra are very similar to those of the hydrogen-accreting dwarf novae, we cannot exclude the fact that they are the AM CVn equivalent of WZ Sge-type outbursts. With outbursts occurring every ∼ 2 months, KL Dra is an excellent target to study helium-dominated accretion flows in general.

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The outburst properties of AM CVn stars

Cited by 4 publications

References 13 publications

The long-term optical behaviour of helium-accreting AM CVn binaries

The long-term optical behaviour of helium-accreting AM CVn binaries

Models of AM Canum Venaticorum star outbursts

Multiwavelength observations of the helium dwarf nova KL Dra through its outburst cycle

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