The May 2003 outburst of OU Vir
OU
Vir (LBQS 1432-0033) was detected as a cataclysmic
variable (CV) of unknown type by C. Berg during the
course of his QSO (Quasi Stellar Objects)
spectroscopic survey (Berg et al. 1992). During the
June 2000 outburst, T. Vanmunster (CBA Belgium
Observatory), F. Velthuis and J. McCormick (CBA
Pakuranga, NZ) detected superhumps in OU Vir with a
period of 0d.078 ±0d.002 and
also found eclipses yielding an orbital period of 0d.07273
±0d.00001 [IBVS 4955]. These
observations firmly established OU Vir as a genuine
eclipsing SU UMa-type dwarf nova.
The present May 2003
outburst of OU Vir is receiving very good coverage
from CV photometrists all over the world, allowing a
refinement of our findings published in IBVS 4955.
In a VSNET message of May 09, 2003 (vsnet-campaign-dn
3640),
T. Kato announced following intermediate results :
"From the superhump period analysis of all
the data up to now, we
obtained a preliminary period of 0.0750 d, which is
slightly smaller than reported in
Vanmunster et al. (2000) IBVS 4955. Combined
with the eclipse period, the fractional superhump
excess with the new
period is 3.1%, which looks like a more acceptable
value."
Below, I report my own observations of this
intriguing object. I first started monitoring OU Vir
on the night of May 6/7, 2003, during a session that
lasted for 2.6 hours. The equipment used was a
0.35-m f/6.3 SCT telescope and unfiltered SBIG ST7
CCD camera. The resulting light curve is depicted
below. It shows a rather complex modulation, because
of the superposition of superhump maxima and eclipses. An
eclipse was predicted to occur around JD 2766.470 and
is fairly easy to recognize in the light curve. The
subsequent one, on JD 2766.543, is much more
difficult to distinguish.
The night of May 7/8, 2003 was clear again, and
allowed me to monitor OU Vir for about 4.0 hours under
relatively good atmospheric conditions. This time, 3
eclipses were recorded and are much easier to recognize in the overall
light curve, next to the superhumps.
Although the night of
May 10/11, 2003 was not really excellent (cloud fields
passing over), we nevertheless set up an unfiltered
photometry session on OU Vir, the result of which is
shown below. One eclipse was caught towards the
beginning of the session, but the other ones were lost
due to breaks related to cloud fields. The eclipse
depth was about 0.7 mag. The session lasted for 4.5
hours.