[vsnet-campaign 1630] TT Ari: back from a positive superhump state!

[Ivan L.Andronov]

TT Ari: back from a positive superhump state!
Call for observations.

Based on 531(V) + 534(R) CCD observations obtained on October 14-19, 2005 
in the Observatory of the University of Athens by K.G. and P.N.,
the cataclysmic variable TT Ari was found to be away from its
recent "positive superhump" state, which started in 1997 
(Skillman et al 1998, Andronov et al 1999) and continued till
2004 (period=0.1484d; Andronov, Ostrova and Burwitz, 2004, [vsnet-campaign
1555]).

No positive superhumps with a characteristic asymmetric shape (M-m=0.32) are
present.
The light curve is dominated by ~14-min QPOs with a semi-amplitude of 0.04mag
(practically same in V and R) superimposed onto long-term (negative superhump?)
variations.

The mean magnitude differences "TT Ari - Comp=GSC 1207:1562" are
<Delta V>=0.254(4) mag
<Delta R>=0.836(4) mag
So this comparison is very red as compared with the variable.

We suggest that the system returned to its negative superhump state.
Such switches may be owed to variability of the accretion rate caused 
by a magnetic activity of the red dwarf (Kraicheva et al 1999).

As the "superhump-scale" light curve is different from that observed in
the "true" negative superhump state observed during intensive campaigns in 1987 
(Tremko et al 1996) and 1994 (Andronov et al 1999), we suggest that the
transition
from one state to another had not ended during our observations, and a new
monitoring
is needed to study details of the transition.

Because of a possible superhump-orbital beat of few days, the required
number of runs (>5-8 hour)
is >6-8 nights. Because of the increasing Moon, the dezired filter is R.
We plan few nights at the CrAO 1.25m telescope AZT-11 equipped with the
UBVRI photometer-polarimeter, so no VR CCD data with alternating filters are
not needed, contrary to long dense R series.

Ivan L. Andronov, Department of Astronomy, Odessa National University,
Ukraine, il-a @ mail.ru
Kosmas Gazeas, Panagiotis G. Niarchos, 
Department of Astrophysics, Astronomy and Mechanics, University of Athens,
Greece, pniarcho @ cc.uoa.gr