COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                        NUMBER  842

	                                Konkoly Observatory
        	                        Budapest
                	                1973 October 26


 PHOTOELECTRIC OBSERVATIONS OF THE ECLIPSING BINARY V502 OPHIUCHI


Observations of the eclipsing variable star V502 Ophiuchi (HD 150484,
G0) were made at the Stefanion Astronomical Station (lambda = 1h31m19s, 
phi = +37d 45' 09") with the 40 cm Van Straten telescope of the Astronomical 
Institute at Utrecht, equipped with a photoelectric photometer.
Three filters u, b, v were used which closely matched the U, B, V
system. The observations were carried out on J.D. 244 1833, 44, 58,
59 and 60. The comparison stars were HD 150732 (G0) = BD+0d3569 and
HD 149933 (G5)= BD +0d3555.
The magnitudes of the variable and the comparison stars were corrected
for atmospheric extinction using different extinction coefficients for
each night, whereafter both the differences between the magnitude of
the variable and the magnitudes of the comparison stars were calculated 
in each point. The light curves were obtained by taking the mean of
these differences without transforming them to  the U, B, V system.
Individual observations are shown in the figure. The phase was calculated 
with the period as given in the GCVS, 3rd edition, 1st supplement, 
viz. 0.45339304d, hence
       Phase = 2.205592^d-1 (heliocentric Julian Date -244 0000)
The epochs of the minima were found to be
       minimum I = J.D. 244 	1833.462
                       		1844.344:
                       		1858.400
       minimum II = J.D.244	1860.440
The estimated mean error of a single epoch is about +/-0.003 days; the
estimated mean error of a single observation is about +/-0.04 mag. for
U, +/-0.02 for B, and +/-0.02 for V.

New accurate observations are needed to obtain a good idea on the 
behavior of the period; see L. Binnendijk, 1969, A.J. 74, 218.

Kapteyn Astronomical Institute
Groningen, The Netherlands
8 October 1973

                              PATRICIA VADER
                              N.A. VAN DER WAL


                           [FIGURE 1]