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\centerline{\ft ECLIPSE CURVES OF UX UMa IN 1992}
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UX UMa is considered as an example of relative orbital stability 
for an interacting binary although the shape of its light curve is
quite variable. Besides eclipses and flickering Mandel (1965) proposed
that the orbital period itself of this eclipsing binary 
varies with a period of 10600 days.

     The presented photoelectric data of UX UMa were obtained during 
8 nights at the end of December 1992 and at the beginning of January
1993. The observations were carried out with a 0.6 m telescope of
Mt. Suhora Observatory (Poland), equipped with a double beam photometer
and an autoguider (Kreiner et al., 1992). In order to satisfy
the requirement of the two-channel photometer (that the distance 
between a variable and a comparison star to be between 10 and 20
arcmin), we used the star marked ``B'' in Figure 1 as a comparison and
BD+52\degr 1720 (marked ``N'') and BD+52\degr 1722 (marked ``C'') as check stars.
Figure 2 shows that the star ``B'' is constant.

    The data were phased according to the ephemeris of Mandel (1965)

\hspace*{35mm}MIN = J.D.(Hel)2427341.22392 + 0.196671299$\times$E \hfill(1)

    Some of our eclipse curves are presented in Figure 3. On the
right side on every curve is the cycle number introduced in Table 1
(down). The magnitude difference in the sense comparison$-$variable on
the vertical axis is relative to the central curve in every colour.
The other curves are moved up or down to get a good visibility. (The
U curves are omitted from Figure 3 because their quality is too poor.)
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\centerline{2}
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\centerline{Figure 3}
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Table 1 includes the observed times of minima with the errors of
their determination and respective O$-$C values according to the ephemeris (1).
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\centerline{Table 1}
\begin{center}
\begin{tabular}{clcc}
\hline
      Cycle &  &          Minima& \\
     number E& Filter&       J.D.(Hel.)& O$-$C\\
     110000 +&       &         2448900.+& \\
\hline
\\
7 &no&76.63824$\pm$0.00015&$-$0.00194\\
22&no&79.58831$\pm$0.00002&$-$0.00194\\
27&no&80.57149$\pm$0.00002&$-$0.00212\\
31&no&81.35816$\pm$0.00003&$-$0.00213\\
32&no&81.55583$\pm$0.00010&$-$0.00114\\
37&U &82.53816$\pm$0.00033&$-$0.00206\\
37&B &82.53831$\pm$0.00042&$-$0.00191\\
37&V &82.53844$\pm$0.00060&$-$0.00181\\
42&B &83.52089$\pm$0.00025&$-$0.00279\\
42&V &83.52137$\pm$0.00022&$-$0.00231\\
43&B &83.71715$\pm$0.00054&$-$0.00320\\
43&V &83.71796$\pm$0.00038&$-$0.00139\\
52&B &85.48882$\pm$0.00014&$-$0.00157\\
52&V &85.48858$\pm$0.00010&$-$0.00181\\
53&U &85.68473$\pm$0.00079&$-$0.00233\\
53&B &85.68531$\pm$0.00030&$-$0.00175\\
53&V &85.68539$\pm$0.00035&$-$0.00167\\
78&B &90.60191$\pm$0.00005&$-$0.00194\\
\hline
\end{tabular}
\end{center}
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 Analysis of our eclipse curves allows us to draw the following 
conclusions:

     (1)\ The times of minima in different colours in the same cycle
coincide within the errors of their determination. The small differences
between the times of the minima in different colors, when 
observed simultaneously, show that the minima occur in a sequence
U, B and V (except for cycle 52). 

     (2)\ The mean phase of our observations relative to the Mandel's
29.02 yr cycle (Nather \& Robinson, 1974) is 
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\hspace*{40mm}$\psi$ = (J.D.Hel.$-$2435000)$\times$0.0000934 = 0.32 \hfill(2)
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\noindent Then it turns out that our mean O$-$C residual value $-$0\fd 00199 
(marked as a diamond in Figure 4) falls just on the periodic curve
adapted from Quigley \& Africano (1978), i.e. our observational data
support 29.02 yr cycle of UX UMa.

     (3)\ In this observational season we obtain the mean orbital 
period  of 0\fd 1966714. This value is very near to that of Mandel (1965)
and Kukarkin (1977). 

(4) The shape of the eclipse curves in the same colours changes 
from cycle to cycle. Usually the bottom of the eclipse is almost
symmetric with respect to the light minimum, but in some cases its
rising branch is deformed. Similar peculiarities were seen by 
Warner \& Nather (1972);

     (5) The mean duration of the whole minima in different colours 
is about 42 minutes and the mean duration of the stillstand\ on the 
ascending branch of the eclipse is about 17 minutes;

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\centerline{4}
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\centerline{Figure 4. O$-$C residuals according to Mandel's 29.02 yr cycle}

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     (6) The mean depth of minima in different colours is respectively
$\Delta$V=1\fmm; $\Delta$B=1\fm 25; $\Delta$U=1\fm 5.

     (7) A small stillstand is visible on the descending branch of
the eclipse nearly symmetrically to the one on the ascending branch.
It is most apparent in the cycles 22 and 42. This feature is more
clearly visible in B than in V.

Acknowledgements. This work was partially supported by a grant $\phi$-104
from Bulgarian National Science Foundation. The authors are grateful
to the Krakow Pedagogical University for the telescope time and to
Dr. G. Pajdosz for the useful discussion. 
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% Call for macros \authors - \authorsrightcol - \endauthors
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Diana P. KJURKCHIEVA
Dragomir V. MARCHEV
Shoumen University,
9700 Shoumen,
Bulgaria
\endauthors

% Call for macro \references
\references

Kreiner, J. et al., 1993, {\it IAU Coll.}, No.\,136 -- {\it Poster Papers on Stellar
 Photometry}, ed. I. Elliott and C. Butler, Dublin Institute for
 Advanced Studies, p.\,80

Kukarkin, B., 1977, {\it MNRAS}, {\bf 180}, 5P

Mandel, O., 1965, {\it Perem.Zvezdy}, {\bf 15}, 474

Nather, E., Robinson, E., 1974, {\it ApJ}, {\bf 190}, 637

Quigley, R., Africano, J., 1978, {\it PASP}, {\bf 90}, 445

Warner, B., Nather, R., 1972, {\it MNRAS}, {\bf 159}, 429


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