[vsnet-campaign 1231] V368 Peg, WZ Sge

["Ivan L. Andronov" <il-a@mail.ru>]

I.L.Andronov^1, A.V.Yushchenko^1, P.G.Niarchos^2, K.Gazeas^2
Orbital Variability vs Early Superhumps in WZ Sge,
"the King of Superoutbursts"

^1 Department of Astronomy and Astronomical Observatory,
   Odessa National University, Odessa, Ukraine, http://il-a.pochtamt.ru
^2 Department of Astrophysics, Astronomy and Mechanics,
   National and Kapodistrian University of Athens, Greece

The time series analysis of 6 nights of our CCD data has shown, that
the superhumps have started at the early stage of the superoutburst,
at least two days after the maximum, much earlier than August 5, when 
the light curve became superhump-dominating over the orbital variability.

Having applied the multi-harmonic fit superimposed onto the linear
trend with differential corrections to the period
(Andronov 1994), We have obtained the statistically significant
order of the trigonometric polynomial s=3 with a "false alarm
probability" of the last component of 10^{-3.7} (according to
the Fischer's distribution). The fit corresponds to the
linear ephemeris
T_{max}=BJD 2452118.7483(3) + 0.0566513(22) E
T_{min}=BJD\,52118.7670(2),
full amplitude 0\fm218(4)
and a very high asymmetry M-m=0.670(9),
a secondary minimum 0.38P after the main one.

The object was also observed during 6 nights at the 40cm reflector
of the University of Athens Observatory by using a CCD SBIG ST-8
camera by K.G., A.Y., P.N. in the Bessel R filter. The comparison
star is GSC 1621:1830 (="C") with R=8.663 (Hemden 2001).
Altogether 1109 data points have been obtained from July 24 to
July 31. The time series analysis was made by I.L.A.

The runs obtained on July 24 and 30, 2001
differ from the ones obtained during 4 intermediate nights on July
25--28 either by the amplitude and by the slope of the trend. Thus
we have used an "abbreviated" set of observations (n=653) from
these nights of similar behavior.
The best fit for the residuals of the data from the "orbital+trend" curve:
period P_{sh}=0.057286(16)d
semi-amplitude 0.042(3) mag
initial epoch T_{max,sh}=BJD 2452117.7012(8).

Thus one may conclude that superhumps have occurred at least on July 25,
much before than "there was an interchange of the main maxima from early to
'genuine' superhumps around Aug. 5.8 UT." (Kato et al., 2001).

Other groups of daily aliased peaks correspond to the frequencies
57.87 and 68.80 cycles/day (25 and 21 minutes, respectively) with
nearly the same semi-amplitude of 0\fm014. However, this
variability is seen as transient waves, making the curve very
complicated. To study these instable variations, we plan to make a
scalegram/wavelet analysis after collecting all available
observations, which are still in a progress.

The authors are thankful to F.Meyer and Y.Osaki for helpful
discussions.

References
Andronov, I.L. 1994, Odessa Astron. Publ, 7, 49
(oap14.pochtamt.ru/oap7.htm)
Kato, T. Ohashi, H., Ishioka, R., et al. 2001, IAUC 7680
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This note is an extended abstract of the paper presented at 
the CV Conference in Goettingen
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Internet links to extensive pages on WZ Sge:
www.kusastro.kyoto-u.ac.jp/vsnet/DNe/wzsge01.html VSNET
cba.phys.columbia.edu CBS
www.aavso.org AAVSO
www.eurolink.it/comets/wzsge.htm G.Masi
www.astro.soton.ac.uk/~ds/wzsge.html D.Steeghs

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