Late Superhumps in WZ Sge-Type Dwarf Novae

Katô, Takeo; Maehara, Hiroyuki; Monard, B.

doi:10.1093/pasj/60.4.l23

Cited by 40 publications

(66 citation statements)

References 36 publications

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“…This is in general agreement with the previous observations of other WZ Sge-type objects (see Patterson et al 1998;Kato et al 2008;Kato 2015, and references therein), although in SSS J122222 these late superhumps were seen for significantly longer time than in any other WZ Sge-type system. Moreover, the stable modulations still persisted even about 420 d after the superoutburst, but their period has further increased by about 2 per cent.…”

Section: Late Superhumpssupporting

confidence: 93%

“…Thus, our observations showed that long after the superoutburst SSS J122222 was still exhibiting very stable superhumps, with a period longer than that of the stage B superhumps. Post-superoutburst superhumps, also called 'late superhumps' (Vogt 1983), were observed in several other WZ Sge-type objects (see Kato, Maehara & Monard 2008;Kato 2015, and references therein). In SSS J122222, however, they were detectable for significantly longer time than in any other system.…”

Section: Post-superoutburst Modulationsmentioning

confidence: 99%

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The remarkable outburst of the highly-evolved post period-minimum dwarf nova SSS J122221.7−311525

Neustroev

Marsh

Zharikov

et al. 2017

Mon. Not. R. Astron. Soc.

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We report extensive 3-yr multiwavelength observations of the WZ Sge-type dwarf nova SSS J122221.7−311525 during its unusual double superoutburst, the following decline and in quiescence. The second segment of the superoutburst had a long duration of 33 d and a very gentle decline with a rate of 0.02 mag d −1 , and it displayed an extended post-outburst decline lasting at least 500 d. Simultaneously with the start of the rapid fading from the superoutburst plateau, the system showed the appearance of a strong near-infrared excess resulting in very red colours, which reached extreme values (B − I ≃ 1.4) about 20 d later. The colours then became bluer again, but it took at least 250 d to acquire a stable level. Superhumps were clearly visible in the light curve from our very first time-resolved observations until at least 420 d after the rapid fading from the superoutburst. The spectroscopic and photometric data revealed an orbital period of 109.80 min and a fractional superhump period excess 0.8 per cent, indicating a very low mass ratio q 0.045. With such a small mass ratio the donor mass should be below the hydrogen-burning minimum mass limit. The observed infrared flux in quiescence is indeed much lower than is expected from a cataclysmic variable with a nearmain-sequence donor star. This strongly suggests a brown-dwarf-like nature for the donor and that SSS J122221.7−311525 has already evolved away from the period minimum towards longer periods, with the donor now extremely dim.

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Section: Late Superhumpssupporting

confidence: 93%

Section: Post-superoutburst Modulationsmentioning

confidence: 99%

The remarkable outburst of the highly-evolved post period-minimum dwarf nova SSS J122221.7−311525

Neustroev

Marsh

Zharikov

et al. 2017

Mon. Not. R. Astron. Soc.

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“…WZ Sge: Patterson et al 2002EG Cnc: Patterson et al 1998, GW Lib and V455 And: Kato et al 2008). Probably the best established case is GW Lib in 2007 and figure 33 in Kato et al 2009a), which showed persistent superhumps for at least 930 cycles (50 d) after the termination of the superoutburst.…”

Section: Late-stage Superhumpsmentioning

confidence: 95%

“…Although Kato et al (2008) interpreted that this increase of the period reflects the expansion of the disk after the outburst, this interpretation was probably incorrect since the pressure effect was not properly treated when comparing superhump periods. As introduced in subsection 6.2, the pressure effect shortens the superhumps period and this effect is strongest in the initial part of stage B .…”

Section: Late-stage Superhumpsmentioning

confidence: 99%

WZ Sge-type dwarf novae

Katô

2015

Publications of the Astronomical Society of Japan

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161

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We have summarized the current understanding and recently obtained findings about WZ Sge-type dwarf novae. We also reviewed the historical development of the understanding of these objects, provided the modern criteria, and reviewed the past research in relation to superhumps, early superhumps and the outburst mechanism. We regard that the presence of early superhumps (reflecting the 2:1 resonance) and long or multiple rebrightenings are the best distinguishing properties of WZ Sge-type dwarf novae. We provided the updated list of nearly 100 WZ Sge-type dwarf novae mainly based on the data obtained by the VSNET Collaboration up to Kato et al. (2015) and discussed the statistics. We could detect early superhumps with amplitude larger than 0.02 mag in 63% of the studied WZ Sge-type dwarf novae, which makes early superhumps a useful distinguishing feature for WZ Sge-type dwarf novae. Theoretical light curves of early superhumps generally appear to reproduce the existence of many low-amplitude objects, supporting the geometrical origin of early superhumps. Using the recently developed method of measuring mass ratios using developing phase of superhumps (stage A superhumps), we showed that there is a linear relation between the period variation of superhumps and the mass ratio in WZ Sge-type objects. By using this relation, we were able to draw an evolutionary picture of a large number of WZ Sge-type and identified the type of outburst to be an evolutionary sequence: type C → D → A → B → E, with some outliers for type-B objects. The duration of stage A (evolutionary phase) of superhumps is also well correlated with the estimated mass ratios. By using mass ratios from stage A superhumps and durarion of stage A, we have been able to identify best candidates for period bouncers.

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“…The stable pulsation signals reported by van Zyl et al (2000) were immediately swamped by the light from the accretion disc and an orbital superhump near 80 min became the dominant variability in the optical light curve (Kato, Maehara & Monard 2008;Bullock et al 2011). To date, several prominent signals have recurrently shown up (Copperwheat et al 2009;Schwieterman et al 2010;Bullock et al 2011;Vican et al 2011;Szkody et al 2012).…”

Section: Introductionmentioning

confidence: 93%

GW Librae: A Unique laboratory for pulsations in an accreting white dwarf

Castillo¹,

Gaensicke²,

Hermes³

et al. 2017

Proceedings of the Golden Age of Cataclysmic Variables and Related Objects - III — PoS(Golden2015)

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Non-radial pulsations have been identified in a number of accreting white dwarfs in cataclysmic variables. These stars offer insight into the excitation of pulsation modes in atmospheres with mixed compositions of hydrogen, helium, and metals, and the response of these modes to changes in the white dwarf temperature. Among all pulsating cataclysmic variable white dwarfs, GW Librae stands out by having a well-established observational record of three independent pulsation modes that disappeared when the white dwarf temperature rose dramatically following its 2007 accretion outburst. Our analysis of Hubble Space Telescope (HST) ultraviolet spectroscopy taken in 2002, 2010, and 2011, showed that pulsations produce variations in the white dwarf effective temperature as predicted by theory. Additionally in 2013 May, we obtained new HST/Cosmic Origin Spectrograph ultraviolet observations that displayed unexpected behaviour: besides showing variability at 275 s, which is close to the post-outburst pulsations detected with HST in 2010 and 2011, the white dwarf exhibits highamplitude variability on an 4.4 h time-scale. We demonstrate that this variability is produced by an increase of the temperature of a region on white dwarf covering up to 30 per cent of the visible white dwarf surface. We argue against a short-lived accretion episode as the explanation of such heating, and discuss this event in the context of non-radial pulsations on a rapidly rotating star.

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Late Superhumps in WZ Sge-Type Dwarf Novae

Cited by 40 publications

References 36 publications

The remarkable outburst of the highly-evolved post period-minimum dwarf nova SSS J122221.7−311525

The remarkable outburst of the highly-evolved post period-minimum dwarf nova SSS J122221.7−311525

WZ Sge-type dwarf novae

GW Librae: A Unique laboratory for pulsations in an accreting white dwarf

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