10
April 2007 : initial outburst stage of BZ UMa
End of March 2007 and early April so far have
provided excellent nights over Belgium. As a
consequence, I'm currently flooded by CBA and XO CCD
images, coming from the 2 telescopes at CBA Belgium
Observatory, working all night long - but you won't
hear me complain ;-).
Also the night of Apr 10/11, 2007 was clear.
Following the announcement of an outburst of BZ UMa
by German amateur astronomer Wolfgang Kriebel (cvnet-outburst),
I immediately started a time-series CCD observation
session. It lasted for 7.5 hours, covering the
initial stage of the outburst of this cataclysmic
variable.
The resulting light curve is quite spectacular :
it consists of >500 observations, and clearly
shows the rise to maximum light (from mag 14.0 CCDR
to mag 13.3 CCDR), dominated by a number of
small-amplitude hump-like structures (amplitude of
0.02 - 0.06 mag) and 1 or 2 larger-amplitude
"bumps" (amplitude of 0.10 mag). The
origin of these irregular and non-periodic features
is not at all clear to me. Note that even more
spectacular high-amplitude modulations were seen
during the April
2004 outburst of BZ Uma - during my observation
session of Apr 19, 2004, I observed a 0.76 mag
'flare'.
BZ UMa light curve of Apr 10/11, 2007 - CBA Belgium
Observatory
During
previous outbursts of BZ UMa, I have also monitored
this cataclysmic variable, but so far no superhumps
have been seen in this system : Jan
2005, Apr
2004, Feb
2004, Dec
2002.