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\centerline{\ft PHOTOELECTRIC PHOTOMETRY OF OO Aql}
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OO Aquilae  (BD+8\degr 4224, HD\,187183, SAO\,125084) is a ninth-magnitude 
binary with a W Ursae Maioris-type light curve and relatively deep minima. 
Photoelectric light curves have been published by Binnendjik (1968) and Lafta 
and Grainger (1985). Binnendijk found over several seasons that the shape of
the light curves varied with time. Demircan and G\"ud\"ur (1981) have published
B and V observations, and have also gathered a large number of times
minimum light as a part of a period study. In addition, a number of other observers
have  published occasional times of minimum light.

A spectral type of G5 has been assigned to the system by Roman (1956), and K0
by Hill et al. (1975) based upon classification spectra.

Photoelectric UBV observations of the W UMa type eclipsing binary OO Aql were
carried out in the years 1991, 1992 and 1993 at Ankara University Observatory.
During a program of photoelectric observations of eclipsing binaries the system
was observed in 1991 in two colours (B and V) and in 1992 and 1993 in three colours
(U, B and V). The observations were made with a 30-cm Maksutov telescope 
equipped with an SSP5-A photometer head which is used with an Hamamatsu R1414 
photomultiplier tube. Before 29 September 1991 the observations were made by using
an EMI\,9789QB photomultiplier attached to the Maksutov telescope. The filters 
used are in close accordance with the standard UBV bands.

The same comparison star BD+8\degr 4220 was chosen as by Demircan and G\"ud\"ur
(1981), and Lafta and Grainger (1985) for nearness in position and brightness
to OO Aql. All differential observations were reduced outside the atmosphere
using the extinction coefficients calculated in the usual way, and heliocentric 
correction was made for all the observations. The phases were calculated with 
the new light elements as:
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\centerline{T$_0$=2448853.38634+0\fd 50678848$\times$E}
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The observations are shown in Figures 1, 2 and 3 for the years 1991, 1992 and
1993 respectively together with the (B$-$V) and (U$-$B) colour curves. 1991 
observations in Figure 1 were made with both photomultipliers cited above.

Total of six primary and six secondary times of minima were calculated using
Kwee and van Woerden's (1956) method and listed in Table 1 with their mean errors.
The columns in Table 1 are minima type, heliocentric Julian Date, mean error (I)
which found by Kwee and van Woerden's (1956) method and filters used respectively.
The last two columns are the averaged minima times (mean) and mean errors (II)
calculated using the function given as follows:
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\[t_{min(mean)}= \frac {\sum_{i} (t_{i}/\sigma^{2}_{i})}{\sum_{i} (1/\sigma^{2}_{i})} \]
\[{\rm and}\ \sigma^{2}_{mean}=\frac{1}{\sum_{i} (1/\sigma^{2}_{i})}\ \  {\rm (Mean\ err.\,II)} \]
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\centerline{Figure 1}
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\centerline{Figure 2}
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\centerline{Figure 3}
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\centerline{Table I}
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\hbox to 13cm {
\begin{tabular}{clcclc}
\hline
Min.&HJD min.&Mean&Filters&HJD min.&Mean\\
Type&+2400000&err.& &(mean)&err.\\
 & &(I)& & &(II)\\
\hline
I&48475.3217&$\pm$0.00093&B&48475.3217&$\pm$0.00093\\
\hline
I&48477.34759&$\pm$0.00047&V&48477.34765&$\pm$0.00042\\
I&48477.34794&$\pm$0.00101&B& & \\
\hline
II&48530.30831&$\pm$0.00036&B&48530.30876&$\pm$0.00030\\
II&48530.30987&$\pm$0.00056&V& & \\
\hline
II&48531.32242&$\pm$0.00029&B&48531.32242&$\pm$0.00029\\
\hline
II&48532.3357&$\pm$0.00036&V&48532.33591&$\pm$0.00022\\
II&48532.33604&$\pm$0.00028&B& & \\
\hline
II&48838.43569&$\pm$0.00046&U&48838.43601&$\pm$0.00017\\
II&48838.436&$\pm$0.00019&B& & \\
II&48838.43679&$\pm$0.00068&V& & \\
\hline
I&48853.3862&$\pm$0.00029&U&48853.38634&$\pm$0.00014\\
I&48853.38632&$\pm$0.00019&B& & \\
I&48853.38651&$\pm$0.00028&V& & \\
\hline
I&48854.39871&$\pm$0.00041&U&48854.39936&$\pm$0.00016\\
I&48854.39935&$\pm$0.00026&B& & \\
I&48854.39957&$\pm$0.00023&V& & \\
\hline
II&49179.5057&$\pm$0.00026&B&49179.50586&$\pm$0.00021\\
II&49179.50602&$\pm$0.00039&V& & \\
II&49179.50681&$\pm$0.00088&U& & \\
\hline
I&49186.34666&$\pm$0.00063&U&49186.34731&$\pm$0.00017\\
I&49186.3471&$\pm$0.00028&V& & \\
I&49186.34752&$\pm$0.00022&B& & \\
\hline
I&49193.44171&$\pm$0.00033&V&49193.44196&$\pm$0.00019\\
I&49193.4419&$\pm$0.00031&U& & \\
I&49193.44227&$\pm$0.00033&B& & \\
\hline
II&49238.29217&$\pm$0.00025&U&49238.29249&$\pm$0.00016\\
II&49248.29257&$\pm$0.00025&V& & \\
II&49238.29301&$\pm$0.00038&B& & \\
\hline
\end{tabular}}

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Birol G\"UROL
Ankara University Observatory
06100 Tando\v{g}an-Ankara
T\"urkiye\endauthors

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\references

Binnendijk, L., 1968, {\it A.J.}, {\bf 73}, 32

Demircan, O., G\"ud\"ur, N., 1981, in Photometric and Spectroscopic Binary Systems,
ed. E. B. Carling and Z. Kopal, D. Reidel Publ., p. 413 \BIBCODE{1981psbs.conf..413D}

Hill, G., Hilditch, R. W., Younger, F., and Fischer, W. A., 1975, {\it Mem. RAS},
{\bf 79}, 131

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

Lafta, S. J., Grainger, J. F., 1985, {\it Ap. Space Sci.}, {\bf 114}, 23

Roman, N. G., 1956, {\it Ap. J.}, {\bf 123}, 247

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