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AAVSO Alert Notice 565

December 19, 2016

YZ Cnc Chandra observing campaign

Dr. Christian Knigge (University of Southampton) and colleagues have requested AAVSO coverage of the SU UMa-type dwarf nova YZ Cnc in support of Chandra X-ray observations to be carried out via a Target of Opportunity (TOO) triggering when the system is in a suitable outburst.

YZ Cnc has normal outbursts about every 7-10 days, and superoutbursts about every 100-110 days. The astronomers are planning to use a superoutburst to trigger the TOO observations.

The last well-documented superoutburst occurred in March 2016, and a possible superoutburst was observed in June 2016. No superoutburst was seen in September, but YZ Cnc was just emerging from conjunction so there were very few observations. The next superoutburst of YZ Cnc, expected in late December-early January, may or may not be well placed for Chandra's schedule, so monitoring may need to continue through more than one superoutburst before the TOO observations can be triggered. Once the TOO observations have been triggered, coverage will need to continue through at least one normal outburst after the Chandra observations have been completed.

Good coverage of YZ Cnc from AAVSO observers this season is essential; your observations will be used to decide when to trigger the TOO observations. An AAVSO Special Notice with further instructions will be issued when the Chandra observations are triggered, so please be sure to subscribe to the Special Notices. Subscription to Special Notices (free) is via the Email Settings tab on your My Account page on the AAVSO website.

Please observe YZ Cnc beginning now (one to a few times, widely spaced, per night), continuing until the Chandra observations have been carried out and the end of the campaign is announced. Visual and V or CV band observations are requested; other bands are welcome but are not essential. Please report your observations to
the AAVSO via WebObs as soon after you make them as possible, especially if you see YZ Cnc at visual magnitude 13.8 or brighter. Typical normal outbursts reach visual magnitude ~12.0, and superoutbursts ~11.0-11.3. In recent years at minimum YZ Cnc has been ~14.6-14.8.

Coordinates (2000.0):  R.A. 08 10 56.65   Dec. +28 08 33.2

Charts: Charts with a comparison star sequence for YZ Cnc may be created using the AAVSO Variable Star Plotter (VSP) at

Please submit observations to the AAVSO International Database using the name YZ CNC.

This campaign is being monitored on the AAVSO Observing Campaigns webpage at and is being followed on the Campaigns and Observation Reports Forum at

YZ Cnc. AAVSO IDB 2016-17

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.


New outbursts and unusual activity reported in the last 72 hours

Last updated 09:25 UT January 18, 2017


TT Boo
U Gem
SDSS J162830.89+240259.1

DV UMa (eclipsing)
CSS J020633.5+205707
SDSS J161012.52+222110.8

# indicates a noteworthy or unusual outburst
:  indicates confirmation required
'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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