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WZ Sge-Type Dwarf Novae


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, arXiv/1507.05610) 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 D->C->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 the period bouncer.


Author: Taichi Kato (Kyoto U.)


Read the full paper on astro-ph






It’s all about the  standstills, those episodes where the star gets stuck at a mid-point between maximum and minimum. If it doesn’t exhibit standstills it isn’t a Z Cam star.





AM Her stars in need of further investigation








Data from Catalina Real Time Survey 
Drake et al. 2009, ApJ, 696, 87

Northern CVs brighter than 17th magnitude here.

Southern CV's brighter than 17th magnitude here.

    
ACTIVITY AT A GLANCE

New outbursts and unusual activity reported in the last 72 hours

Last updated 08:31 UT August 03, 2015

YYYYMMDD

20150803
EM Cyg

20150802
RX And
KT Per
TY Psc


# indicates a noteworthy or unusual outburst
 
'Activity At A Glance' is gleaned from observations reported to AAVSO MyNewsFlash, BAAVSS-Alert, CVnet-Outburst, VSObs-share and VSNET-outburst. We sincerely thank all the observers who contribute timely observations and reports of activity to these email lists.

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