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

Ishioka, Ryoko; Uemura, Makoto; Matsumoto, Katsura; Ohashi, Hiroyuki; Katô, Takeo; Masi, G.; Novák, Rudolf; Pietz, J.; Martin, Brian; Starkey, Donn R.; Kiyota, S.; Oksanen, A.; Moilanen, Marko; Cook, Lewis M.; Král, L.; Hynek, Tomáš; Kolasa, M.; Vanmunster, Tonny; Richmond, M.; Kern, J. R.; Davis, Stacey M.; Crabtree, D.; Beaulieu, Kevin; Davis, Tracy C.; Aggleton, Matt; Gazeas, K.; Niarchos, P. G.; Yushchenko, A. V.; Mallia, F.; Fiaschi, M.; Good, Gerry A.; Boyd, David; Sano, Y.; Morikawa, Koichi; Moriyama, M.; Mennickent, R. E.; Arenas, J.; Ohshima, Tomohito; Watanabe, T.

doi:10.1051/0004-6361:20011644

Cited by 80 publications

(105 citation statements)

References 12 publications

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“…Figure 1(a) represents the overall light curve of the 2015 outburst of AL Com. As can be seen in Figure 1(a), the duration of the plateau stage is ∼10 d. This duration is significantly shorter than those of previous superoutbursts, for which the plateau stages lasted for 20 d or more (Kato et al 1996;Ishioka et al 2002;Uemura et al 2008;Kato et al 2014a). In addition, the maximum magnitude was 14.1 mag, about 2 mag fainter than those of previous superoutbursts.…”

Section: Observations and Resultsmentioning

confidence: 78%

Unexpected superoutburst and rebrightening of AL Comae Berenices in 2015

Kimura¹,

Katô²,

Imada³

et al. 2016

Publications of the Astronomical Society of Japan

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In 2015 March, the notable WZ Sge-type dwarf nova AL Com exhibited an unusual outburst with a recurrence time of ∼1.5 yr, which is the shortest interval of superoutbursts among WZ Sge-type dwarf novae. Early superhumps in the superoutburst light curve were absent, and a precursor was observed at the onset of the superoutburst for the first time in WZ Sge-type dwarf novae. The present superoutburst can be interpreted as a result of the condition that the disk radius barely reached the 3:1 resonance radius, but did not reach the 2:1 resonance one. Ordinary superhumps immediately grew following the precursor. The initial part of the outburst is indistinguishable from those of superoutbursts of ordinary SU UMa-type dwarf novae. This observation supports the interpretation that the 2:1 resonance suppresses a growth of ordinary superhumps. The estimated superhump period and superhump period derivative are P sh = 0.0573185(11) d and P dot = +1.5(3.1) × 10 −5 , respectively. These values indicate that the evolution of ordinary superhumps is the same as that in past superoutbursts with much larger extent. Although the light curve during the plateau stage was typical for an SU UMa-type dwarf nova, this superoutburst showed a rebrightening, together with a regrowth of the superhumps. The overall light curve of the rebrightening was the almost the same as those observed in previous rebrightenings. This implies that the rebrightening type is inherent in the system.

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Section: Observations and Resultsmentioning

confidence: 78%

Unexpected superoutburst and rebrightening of AL Comae Berenices in 2015

Kimura¹,

Katô²,

Imada³

et al. 2016

Publications of the Astronomical Society of Japan

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“…During the rising phase of V455 And (2007), the object did not show any evidence of early superhumps from ∼6 mag to ∼1.5 mag before the maximum then these superhumps started to grow quickly figure 12). In WZ Sge (2001), early superhumps became evident around ∼1.0 mag below maximum (figure 13; Ishioka et al 2002). These two systems are best studied ones during the growing stage of early superhumps.…”

Section: Evolution Of Early Superhumpsmentioning

confidence: 99%

“…In well-observed systems, early superhumps grow as the object rises to the outburst maximum (WZ Sge and AL Com: Ishioka et al 2002). During the rising phase of V455 And (2007), the object did not show any evidence of early superhumps from ∼6 mag to ∼1.5 mag before the maximum then these superhumps started to grow quickly figure 12).…”

Section: Evolution Of Early Superhumpsmentioning

confidence: 99%

WZ Sge-type dwarf novae

Katô

2015

Publications of the Astronomical Society of Japan

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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“…Early superhumps, double-wave modulations with a period almost the same as the orbital one usually appear prior to superhumps during superoutbursts of WZ Sgetype DNe (Kato 2002;Ishioka et al 2002). However, during the first plateau stage of the 2015 outburst of ASASSN-15jd (during BJD 2457155-2457164.4), any humps with an amplitude of >0.02 mag were not observed in the range of 97.5-99.5% of the estimated superhump period in the previous paragraph.…”

Section: Superhumpsmentioning

confidence: 82%

“…There are two important observational properties of them. One is the presence of doublepeaked modulations called early superhumps having a period almost equal to the orbital one in the early stage of the superoutburst (Kato 2002;Ishioka et al 2002). They are considered to be triggered by the 2:1 resonance tidal instability (Osaki, Meyer 2002;Osaki, Meyer 2003).…”

Section: Introductionmentioning

confidence: 99%

ASASSN-15jd: WZ Sge-type star with intermediate superoutburst between single and double ones

Kimura

Isogai

Katô

et al. 2016

Publications of the Astronomical Society of Japan

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We present optical photometry of a WZ Sge-type dwarf nova (DN), ASASSN-15jd. Its light curve showed a small dip in the middle of the superoutburst in 2015 for the first time among WZ Sge-type DNe. The unusual light curve implies a delay in the growth of the 3:1 resonance tidal instability. Also, the light curve is similar to those of other two WZ Sge-type stars, SSS J122221.7−311523 and OT J184228.1+483742, which are believed to be the best candidates for a period bouncer on the basis of their small values of the mass ratio (q ≡ M 2 /M 1 ). Additionally, the small mean superhump amplitude (< 0.1 mag) and the long duration of no ordinary superhumps at the early stage of the superoutburst are common to the best candidates for a period bouncer. The average superhump period was P sh = 0.0649810(78) d and no early superhumps were detected. Although we could not estimate the mass ratio of ASASSN-15jd with high accuracy, this object is expected to be a candidate for a period bouncer, a binary accounting for the missing population of post-period minimum cataclysmic variables, based on the above characteristics.

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

Cited by 80 publications

References 12 publications

Unexpected superoutburst and rebrightening of AL Comae Berenices in 2015

Unexpected superoutburst and rebrightening of AL Comae Berenices in 2015

WZ Sge-type dwarf novae

ASASSN-15jd: WZ Sge-type star with intermediate superoutburst between single and double ones

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