Dr John Cannizzo, of NASA's Goddard Space Flight Center (GSFC) in Baltimore,
Maryland, is an expert on models of dwarf nova outbursts. He has a theory
that all the long outbursts of SS Cygni have a short precursor outburst,
which can be seen at the beginning of the long outburst as a period of time
during which the brightness is not quite as high as it later becomes. This
is quite a small effect, and cannot be seen in the visual light curves.
However, there is some evidence of it in CCD data, as seen for example in
the accompanying plot of data from August 2012, taken by colleagues of mine
in Mexico, which shows an initial slight dip followed by a rise on the last
night (unfortunately clouded out before many data points were obtained). Dr
Cannizzo has seen this plot, and is keen to see more evidence. I would
therefore like to ask readers with CCD cameras to consider monitoring the
outbursts of SS Cygni, particularly the long ones (about every second one is
a long one - see the AAVSO charts) and passing the processed data to Dr
Cannizzo at GSFC (John.K.Cannizzo@nasa.gov). If anyone already has such
data, please also pass that on.