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AAVSO 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 at the following URLs:







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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