[vsnet-campaign 1637] TT Ari: "negative superhump" state and standstill and after December 18, 2005

[Ivan L.Andronov]

TT Ari: "negative superhump" state and standstill and after December 18, 2005

Continuation of the table of nightly mean magnitudes of TT Ari in 
VSNET-campaign 1630, 1635, 1636:
<t>-2400000  <m_R>    sigma
53731.02173 10.8290  0.0039
53732.01320 10.6882  0.0045
53734.07165 10.7913  0.0053
53742.05811 10.6814  0.0043
53743.00344 10.6474  0.0042
53743.96000 10.7455  0.0055

The CCD observations have been obtained at the 40-cm telescope of the 
University Observatory,
Chungbuk National University, Cheongju, Korea, during 32 nights from 
25.10.2005 to 08.01.2006.

Contrary to previous outburst after a standstill at lower brightness,
the system shows another stanstill in the middle between the maxima and minima
with a mean level <R>=10.732 and a scatter of 0.107 mag, which is much 
larger than
a r.m.s. error of one measurement of 0.020 mag.
The long-term light curve based on 32 nights of observations
is shown at http://uavso.pochta.ru/TT_Ari32.gif

The "Lambda-scalegram" analysis (Andronov 2003) shows a most prominent peak 
corresponding to
the (quasi-)periodic variations with an effective period of 
0.01439d=20.7min and semi-amplitude
of 0.061mag. The superhump variability is less prominent (semi-amplitude 
0.033mag and period 0.128d).
This is typical for the "negative superhump" state observed before 1997 
(Tremko et al. 1996,
Andronov et al. 1999). Similar periods (0.01486d, 0.1166d) are present at 
the sine-based periodogram
(Andronov 1994), but the corresponding peaks are low enough arguing for a 
quasi-periodic character
of variations, rather than truly periodic.

The continuation of monitoring is needed to check variability at 14-25 min, 
3h, ~3d time scales.

J.N. Yoon (CBNU, Korea), I.L. Andronov (ONU, Ukraine), S.M.Cha (CBNU, Korea),
L.L.Chinarova (ONU, Ukraine), Y. Kim (CBNU, Korea)