Observations
of the February/March 2004 outburst of BZ UMa
February and March typically
are not very good months for variable star observing in
Belgium, because of the highly unstable weather
during that period. 2004 was no exception to this
rule. We had 2 clear nights
during the February/March 2004 (normal) outburst of BZ
UMa.
February 26/27,
2004
Below, I present my observations, obtained on
Feb 26/27, 2004 using a 0.35-m f/6.3 telescope and
an unfiltered ST-7XME CCD camera. In total, I
collected 491 observations over a period of 7.30h,
under very good sky conditions.
Overall, BZ UMa faded an impressive 0.4 mag over
the duration of the observations (corresponding to
1.3 mag per day). See figure 1 below. Using a Beta
version of the new period analysis software package Peranso,
I first detrended the observations. This clearly
revealed the presence of oscillations with an
amplitude of about 0.04 mag (figure 2). All period
analysis techniques available in Peranso (I used
PDM, a few Fourier methods and a few string methods)
essentially indicated the non-periodicity of the oscillations.
Fig 1 - overall light curve of
BZ UMa, with superimposed trendline (Peranso
screenshot)
Fig 2 - lightcurve after detrending,
revealing oscillations (Peranso screenshot)
February 29/March 01, 2004
The light curve of Feb 29 / Mar 01, 2004
showed a totally different BZ UMa outburst stage.
The object had faded by about 2.85 mag compared to
my previous observation night. I
collected 397 observations over a period of 7.9h,
under mediocre sky conditions (haze, strong
moonlight).
Figure 3 - light curve of
BZ UMa on 2004, Feb 29 / Mar 01 (Peranso
screenshot)
The most dominant feature in the light curve this
time are high-amplitude modulations (average
amplitude about 0.4 mag). See figure 3 above. Using a Beta
version of the period analysis software Peranso,
I combined these observations with the ones I
obtained on Feb 26/27 (yielding a total of 888
observations), and started looking for significant
periods using a number of techniques (PDM,
Lomb-Scargle, Bloomfield). All analyses pointed to a
dominant period at 0.0691 +/- 0.0010 d, which is
pretty close to the orbital period value of 0.06799
d, derived by Jurcevic et al. (Jurcevic, J.S.,
Honeycutt, R.K., Schlegel, E.M., and Webbink, R.F.
1994, PASP, 106, 481).
Figure 4 - Lomb-Scargle period
determination based on all available BZ UMa
observations (Peranso screenshot)
I finally left out the observations
of Feb 26/27, 2004 an again used the Lomb-Scargle
method in Peranso to make a period analysis,
resulting in figure 5 below. Clearly, the same period
is found, but this time without the "noise"
induced by the Feb 26/27 observations.
Figure 5 - Lomb-Scargle period
determination based on Feb 29/Mar 01 observations
(Peranso screenshot)
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