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\IBVShead{4126}{16 December 1994}     % Use it with dummy or empty arguments

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\centerline{\ft PHOTOELECTRIC OBSERVATIONS AND MINIMA TIMES OF FOUR}
\centerline{\ft W UMa SYSTEMS: LS Del, SW Lac, V839 Oph AND AQ Psc\footnote{Paper
dedicated to research assistant H. D\"undar who died after ulcer operation
on 25 of September 1994}}
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\begintext


During the Summer School of Young Astronomers held at Ankara University
Observatory, between 22 Aug.-3 Sept. 1994, four W UMa systems: LS Del, SW
Lac, V839 Oph and AQ Psc were observed in B and V filters using a single
channel unrefrigerated SSP-5 photometer attached to the 30 cm Maksutov
telescope. The observations were carried out by the 28 participant
students (six groups in turn) and some colleagues of the Ankara University
Observatory, as part of the Summer School program. The school was
sponsored by The Ankara University Science Faculty, The Ankara University
Graduate School of Natural and Applied Sciences, The Technical and
Research Council and The Turkish Astronomical Society.

The identification and general properties of program stars are listed in
Table 1, where Sp, No, T$_0$ and P stand for the spectral type of the system,
number of observations obtained in each filter, epoch and orbital period
used in phase calculation. Each observation comprises three five second
integrations through B or V filter in sequence
comparison-sky-variable-sky-variable-comparison-sky with occasional
interruptions for background and check star measurements. Typical r.m.s.
error of a single observation is around 0.01 mag. The control of the
photometer head, data acquisition and data reduction for atmospheric
extinction and heliocentric correction were carried out with a software
prepared by M\"uyessero\v{g}lu (1992). The light and color curves of the program
stars by using the light elements from Table 1 are shown in Figures 1, 2
and 3. Part of the scatter in observations (see figures) is due to night
to night light variations. The observations of AQ Psc cover only the
phase interval 0.46-0.86 around secondary minimum.
\vskip 2mm
\centerline{Table 1. Identification and general properties of the program stars.}
\vskip 1mm
\begin{center}
\begin{tabular}{lcccc}
\hline
LS Del&          SW Lac&        V839 Oph&        AQ Psc&               \\
\hline
\\
Var. Star &      BD+19\degr 4574&      BD+37\degr 4717  &    BD+09\degr 3584&  BD+06\degr 0203\\
Comp. Star&      BD+19\degr 4568&      BD+37\degr 4715  &    BD+09\degr 3578&  BD+05\degr 0177\\
Check Star&      BD+19\degr 4576&      BD+37\degr 4711  &    BD+09\degr 3590&  BD+06\degr 0204\\
Sp        &      G5        &      G8V+G8V     &    F8V       &  F8V\\
No        &      132       &      335         &    379       &  133\\
T$_0$        &      47790.42696&     49594.4684  &    49590.3794&  44562.4691\\
P         &      0.363840   &     0.3207209   &    0.40899532&  0.47564\\
Reference &      Demircan   &     Pena et al. &    Niarchos  &  Sarma and\\
          &      et al. 1991&     1993        &    1989      &  Radhakrishnan\\
          &                 &                 &              &  1982\\
\hline
\end{tabular}
\end{center}
\vfill \eject

\centerline{2}
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\centerline{\epsffile{4126-f1.ps}}
\centerline{Figure 1}
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\centerline{\epsffile{4126-f2.ps}}
\centerline{Figure 2}
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\centerline{3}
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\centerline{\epsffile{4126-f3.ps}}
\centerline{Figure 3} 
\vskip 3mm
\centerline{Table 2. Times of minima}
\vskip 1mm
\begin{center}
\begin{tabular}{cccc}
\hline
   LS Del &            SW Lac &          V839 Oph   &       AQ Psc\\
\hline
\\
49588.3451 B II &   49589.4973 B II   & 49590.3780 B I&    49596.4629 B II\\
   $\pm$0.0007      &      $\pm$0.0003        &    $\pm$0.0009    &       $\pm$0.0009\\
49588.3431 V II &   49589.4989 V II   & 49590.3797 V I&    49596.5183 V II\\
   $\pm$0.0008      &      $\pm$0.0003        &    $\pm$0.0004    &       $\pm$0.0006\\
   &49594.4696 B I&     49596.3118 B II&  \\
   &   $\pm$0.0003    &        $\pm$0.0002& \\
   & 49594.4674 V I&     49596.3116 V II& \\
   &   $\pm$0.0003    &        $\pm$0.0003& \\
   & 49597.5156 B II&    49598.3573 B II&  \\
   &    $\pm$0.0003     &       $\pm$0.0003&  \\
   & 49597.5159 V II&    49598.3573 V II& \\
   &    $\pm$0.0003     &       $\pm$0.0003  & \\
\hline
\end{tabular}
\end{center}

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\centerline{4}
\vskip 1mm
From these new observations 16 new times of minimum light were calculated by
using the method of Kwee and Woerden (1956). The times of
minimum light for the asymmetric eclipse curves of SW Lac were checked by
using the well known graphical``chord" method. The resulting new times of
minimum light together with their r.m.s. errors are listed in Table 2 for each
system.

\vskip 1cm
\begin{center}
\begin{tabular}{lllll}
O. Demircan &Z. Aslan  & C. Ibano\v{g}lu& Z. M\"uyessero\v{g}lu& S.O. Selam\\
M. Tanriver &H. Ak     & H. D\"{u}ndar  & B. Albayrak    & K. Y\"{u}ce\\
A. Devlen   &A. G\"{o}k\c{c}e & H. \c{C}al\i \c{s}kan& A. Iskender& Y. Kaya\\
A. Bulut    &E. \c{C}\i nar& H. Varl\i   & N. \c{C}ubukcu & K. Ulu\c{c}\\
A. Savranlar&G. \c{S}en& H. \"{O}zdemir & \"{O}. \c{C}ak\i rl\i   & M. Da\v{g}c\i \\
Y. Y\"{u}ksel &G. Ta\c{s}& Y. Alemdar & R. T. Y\i ld\i r\i m  & Y. Erdal\\
A. A\c{s}\c{c}ilar  & E. A\c{c}\i kg\"{o}z& B. Bekta\c{s}li&F. G\"{o}ksen& N. K\"{o}ker\\
\end{tabular}
\end{center}
\vskip 2mm
\centerline{Ankara University Observatory}
\centerline{Faculty of Science}
\centerline{TR 06100 Tandogan, Ankara}
\centerline{Turkey}

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\references

Demircan, O., Selam, S.O. and Derman,E., 1991, {\it Ap\&SS}, {\bf 186}, 57

Kwee, K.K. and van Woerden, H., 1956, {\it Bull. Astr. Neth.}, {\bf 12}, 327

M\"uyessero\v{g}lu Z., 1992, Ankara Univ. Obs. (unpublished)

Niarchos, P.G., 1989, {\it Ap\&SS}, {\bf 153}, 143

Pena, J.H., Hobart, M.A. and Rodriguez, E., 1993, {\it Rev. Mex. A\&Ap.}, {\bf 25}, 63

Sarma, M.B.K. and Radhakrishnan, K.R., 1982, {\it IBVS}, No.\,2073

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