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Alert Notice 360: Request to Monitor U Gem and SS Cyg for Radio Observations

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November 5, 2007: Dr. Elmar Koerding, University of Southampton, England, and his collaborators have requested our assistance in a continuing project to monitor two dwarf novae -- U Geminorum (0749+22) and SS Cygni (2138+43) -- in support of radio observations with the MERLIN and VLA telescopes. This new campaign is a continuation of the project described in AAVSO Alert Notice 345.  Koerding and collaborators are attempting to detect and characterize radio emission from dwarf novae during outbursts. Rapid optical detection of an outburst onset will be used to trigger target-of-opportunity (TOO) observations with the MERLIN Array at Jodrell Bank, UK and 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 will be submitted for publication in late 2007. 

Continuous optical monitoring and rapid reporting of observations of U Gem and SS Cyg is requested beginning 2007 November 5 (JD 2454410). This campaign will continue for at least several months, until a total of four outbursts are detected in either of these systems and TOO observations are obtained with the VLA and MERLIN.

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 any and 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 U Gem and SS 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)
0749+22 U GEM   07:55:05.2      +22:00:04       8.8-15.3        13.5 V
2138+43 SS CYG  21:42:42.8      +43:35:10       8.2-12.4        11.0 V

AAVSO Charts for these objects may be generated at:

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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