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[vsnet-nl 121] TT Ari: Asymmetric Superhumps still positive
TT Ari: Asymmetric Superhumps still positive
TT Ari was observed at the 40cm telescope of the Athens University
during 5 nights on August 30, September 8, 10, 11 and 12, 2001
using the CCD camera ST-8. Alltogether 537 points using the
Bessel filters V (HJD 2452151.428-65.488)
and 539 points in R (HJD 2452151.429-65.489) were obtained.
The periodogram analysis using the sine fit showed series of
daily biased peaks with a definitely highest maximum at the
Period=0.148461(20) days and semi-amplitude=0.0794(23) mag (V)
0.148452(22) 0.0730(23) (R)
The numbers in brackets indicate error estimates in the units of
the last digit. This is close to the value P=0.14926 days which
was published by Skillman et al (1998, ApJ 503, L67) after their
discovery of the switch of the superhumps from usually negative
(P~0.1329d) state (see e.g. the campaigns in
1988, Tremko et al., 1996, As.Ap. 312, 121 and
1994, Andronov et al., A.J. 1999, 117, 574).
The magnitude difference Mag=Var-Comp was computed in respect
to the comparison star GSC 1207:1562
The phase curves show high asymmetry, thus we have adopted the
trigonometric polynomial fit (program described by Andronov,
1994, Odessa Astron. Publ., 7, 49, available at
http://il_a.hotbox.ru/wj/oap7_049.ps
(see http://oap14.pochtamt.ru/ for other OAP papers).
According to the Fischer's criterion, for both filters
the statistically significant degree of the trigonometric
polynomial is 2. The mathematical model is
Mag(t)= Mean - R_1*cos(2*pi*((t-BJD_Max)/Period-Phase_1))
- R_2*cos(4*pi*((t-BJD_Max)/Period-Phase_2))
The non-linear best fits are listed in the following table:
Filter V R
Mean -.1483(15) .4999(16)
Period .148513(18) .148509(19)
Asymmetry M-m .378(9) .368(8)
Delta_mag .173(3) .163(3)
Mag_max -.245(3) .411(3)
Mag_min -.072(3) .574(3)
BJD_Max 52160.5967(8) 52160.5955(8)
BJD_Min 52160.5405(12) 52160.5409(11)
R_1 .0789(22) .0723(22)
Phase_1 .0362(45) .0456(49)
R_2 .0217(22) .0221(22)
Phase_2 -.0671(159) -.0763(158)
One may note that the curves are very similar in two bands,
with the corresponding parameters remarkably coinciding within
their error estimates, except only the "Mean", which indicates
large color difference between the comparison star and TT Ari.
The color excess of the superhump variability in respect to the
mean flux may be estimated as
Delta(V-R)=-2.5lg(Delta_mag_V/Delta_mag_R)=-0.06(3),
i.e. close to zero and to the estimate Delta(V-R)=-0.03 by
Tremko et al. (1996) for these colors for the "negative superhump" state.
The wavelet analysis of the residuals of the observations from the
2-nd order trigonometric polynomial was carried out using the method
described by Andronov I.L.(Wavelet analysis of the irregularly spaced
time series.- in: "Self-Similar Systems", eds. V.B. Priezzhev,
V.P. Spiridonov, Dubna, JINR, 1999, 57-70, http://il_a.hotbox.ru).
At the mean wavelet periodogram for the V data, the peaks at the test
function S(P) occur at the values P_w=0.0668d=0.45P, 0.021d=0.14P and
0.010d=0.07P. At the dependence of the effective wavelet (semi-)amplitude
on the period, one may estimate the corresponding values in a range
0.015-0.017 mag, ~5 times smaller than for the main wave.
This value is underestimated, because the variations are not coherent
and thus the fast QPOs vary not only in the amplitude, but in the
period as well. The range of characteristic times 14-30 minutes is
nearly the same, as in the "negative superhump" state (Tremko et al.,
1996, Andronov et al., 1999).
I.L. Andronov
Department of Astronomy, Odessa National University, Odessa, Ukraine,
il-a@mail.ru, http://il_a.hotbox.ru
K.D. Gazeas, V.N. Manimanis, P.G. Niarchos
Department of Astrophysics, Astronomy and Mechanics,
National and Kapodistrian University of Athens,
Athens, Greece,
kgaze@skiathos.physics.auth.gr, pniarcho@cc.uoa.gr
vsnet-adm@kusastro.kyoto-u.ac.jp
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