Alert Notice 390: Request to monitor three dwarf novae in support of radio observations

November 13, 2008 : Dr. Elmar Koerding (CEA Saclay & Universite Paris Diderot) and collaborators have requested our assistance to monitor the dwarf novae YZ Cnc, Z Cam, and EM Cyg for outbursts, in support of radio observations with the NRAO Very Large Array telescope.  This new campaign is a continuation of the projects described in AAVSO Alert Notices 345 and 360.  Koerding and collaborators are attempting to detect and characterize radio emission from dwarf novae during outbursts.  Rapid optical detection of the onset of outbursts will be used to trigger target-of-opportunity (TOO) observations with the NRAO Very Large Array (VLA) in New Mexico.  Observations of SS Cygni during the first campaign yielded important new results, and a paper on those observations was published in the journal Science (Koerding et al., 2008, Science 320, 1318).

Optical monitoring of the dwarf novae Z Cam, YZ Cnc, and EM Cyg and rapid reporting of observations is requested beginning immediately (2008 November 13; JD 2454784) and will continue for the next year, or until the maximum number of allocated outburst follow-ups have been made with the Very Large Array.

Rapid reporting of observations is again critical to the success of this campaign.  Observers are requested to report their observations to the AAVSO within one (1) hour using WebObs or EmailObs, especially if an object appears to be in transition to outburst.  Quiescent and full outburst observations are also important as they can be used to constrain when an outburst begins and and ends.  This includes "fainter-than" observations during quiescence, so please submit all observations you make as soon as you are able.

Both visual and CCD observations are requested, but CCD time-series observations should only be performed if the data can be reduced and submitted immediately if an outburst has not yet been reported.  Once an outburst has been detected and acknowledged by the radio observatories, time-series observations will then be very useful, and observers capable of performing filtered time series are encouraged to do so.

The table below lists the (J2000) coordinates, V-band ranges, and V-band outburst thresholds for YZ Cnc, Z Cam, and EM Cyg.  The outburst threshold is the magnitude at which the star is highly likely to go into outburst if it reaches this point.  Please report any observations equal to or brighter than the given threshold to the AAVSO immediately.

Desig.     Name      RA(2000)         Dec(2000)       Range(V)       Thresh.(V)
0804+28 YZ CNC  08:10:56.62     +28:08:33.6    10.4-16.3        13.5 V
0814+73 Z CAM   08:25:13.20     +73:06:39.2    10.2-14.0        11.4 V
1934+30 EM CYG  19:38:40.10     +30:30:28.0    11.8-14.4        13.4 V

AAVSO Charts for these objects may be generated using the AAVSO International Variable Star Plotter (VSP):

Please indicate the chart IDs and comparison stars used when reporting all observations.

For more information on this project, please visit:

Your careful observations and prompt reporting are essential to the success of this important project.  Many thanks from the Principal Investigator and collaborators, and from AAVSO Headquarters for your astronomical contributions!

Clear skies, & good observing,

Matthew Templeton
AAVSO Headquarters



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