Variable Star Network: World Center for Transient Object Astronomy and Variable Stars

Katô, Takeo; Uemura, Makoto; Ishioka, Ryoko; Nogami, Daisaku; Kunjaya, Chatief; Baba, Hajime; Yamaoka, H.

doi:10.1093/pasj/56.sp1.s1

Cited by 136 publications

(96 citation statements)

References 547 publications

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“…This epoch coincided with the second-stage progress of CCD photometry in CV research: using small telescope(s) and CCD to detect short-term variations during outburst, which was first systematically conducted by the author (e.g. Kato et al 2004c). …”

Section: Early Superhumpsmentioning

confidence: 91%

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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Section: Early Superhumpsmentioning

confidence: 91%

WZ Sge-type dwarf novae

Katô

2015

Publications of the Astronomical Society of Japan

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161

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“…Time-resolved CCD photometry was carried out by the Variable Star Network (VSNET) collaboration team (Kato et al 2004) at 17 sites (Table S1) in the 2015 December outburst in V404 Cyg. Table S2 shows the log of our photometric observations in the V, R C and I C bands and with a clear filter.…”

Section: Optical Observationsmentioning

confidence: 99%

Rapid optical variations correlated with X-rays in the 2015 second outburst of V404 Cygni (GS 2023+338)

Kimura

Katô

Isogai

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present optical multi-colour photometry of V404 Cyg during the outburst from December, 2015 to January, 2016 together with the simultaneous X-ray data. This outburst occurred less than 6 months after the previous outburst in June-July, 2015. These two outbursts in 2015 were of a slow rise and rapid decay-type and showed large-amplitude (∼2 mag) and short-term (∼10 min-3 hours) optical variations even at low luminosity (0.01-0.1L Edd ). We found correlated optical and X-ray variations in two ∼1 hour time intervals and obtained a Bayesian estimate of an X-ray delay against the optical emission, which is ∼30-50 s, during those two intervals. In addition, the relationship between the optical and X-ray luminosity was L opt ∝ L 0.25−0.29 X at that time. These features cannot be easily explained by the conventional picture of transient black-hole binaries, such as canonical disc reprocessing and synchrotron emission related to a jet. We suggest that the disc was truncated during those intervals and that the X-ray delays represent the required time for propagation of mass accretion flow to the inner optically-thin region with a speed comparable to the free-fall velocity.

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“…Our time-resolved photometric campaigns were carried out in 2014-2015 for ASASSN-14ei and in 2014 April-May for CR Boo by the VSNET Collaborations [11]. The data were mainly acquired with 30 cm-class telescopes.…”

Section: Observations and Analysismentioning

confidence: 99%

Research on AM CVn stars: ASASSN-14ei and CR Boo

Isogai¹,

Katô²,

Nogami³

et al. 2017

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

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We report on time-resolved photometries of 2014-2015 superoutbursts of AM CVn-type objects, ASASSN-14ei and CR Boo. ASASSN-14ei is the first object which showed WZ Sge-like multiple rebrightening phase with a super long duration (at least 6 months). The superhump period had gradually decreased throughout the rebrightening phase. We suppose that the decreasing period reflects a shrinking disk. During the 2014 April superoutburst of CR Boo, we detected growing superhumps (stage A superhumps) whose period was 0.017669(24) d. By using the superhump period, the mass ratio was estimated to be 0.101(4), which is consistent with that expected by the theoretical evolutionary model. The Golden Age

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Variable Star Network: World Center for Transient Object Astronomy and Variable Stars

Cited by 136 publications

References 547 publications

WZ Sge-type dwarf novae

WZ Sge-type dwarf novae

Rapid optical variations correlated with X-rays in the 2015 second outburst of V404 Cygni (GS 2023+338)

Research on AM CVn stars: ASASSN-14ei and CR Boo

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