COMMISSION 27 OF THE I.A.U.
               INFORMATION BULLETIN ON VARIABLE STARS
                            Number 1457

                                                      Konkoly Observatory
                                                      Budapest
                                                      1978 August 4


       PHOTOELECTRIC EPOCH OF MINIMUM LIGHT, V566 OPHIUCHI

V566 Ophiuchi (BD +5d3547, HD 163611) is a contact binary system
which undergoes complete eclipses. Secondary eclipse is total. Bookmyer
(P.A.S.P. 88, 473, 1976) noted that the period had increased after being
constant for at least 11 years and that there were small variations in
the shape of the light curve.
   The present observations were made on the night of 11-12 June 1978
with the 0.5 m Cassegrain telescope at Palomar Observatory. The photometer
housed standard B,V filters and a 1P21 photomultiplier refrigerated with
dry ice. A digital counter was used for the intensity measurements, and
the time of each observation was obtained from a strip chart tracing.
A WWV receiver was utilized to calibrate the chart. BD +4d3553 was used
as a comparison star, and no corrections were made for differential
extinction.
   The measurements yielded 46 observations with the B filter and 70
with the V filter, with each observation being the average of two 
consecutive ten-second integrations. The primary eclipse curve is wall
defined by the observations. An epoch of minimum light, JD Hel. Min. I
= 2443671.8964, was determined by the method of bisecting chords connecting
points of equal magnitude on the opposing branches to find the temporal
mean. A residual of +0d.0390 was calculated from the ephemeris given by
Bookmyer (A.J. 74, 1197, 1969), JD Hel. Min. I = 2436744.4200 + 0d.40964091 E.
This represents an increase in the O-C values since the studies by Bookmyer
(1976) and Dawson and Narayanaswamy (P.A.S.P. 89, 47, 1977).
   It is important that the period behavior of V566 Oph be followed
and that additional light curves be observed and compared with earlier
observations.


                      WILLIAM C. MADDOX
                      BEVERLY B. BOOKMYER

                      Dept. of Physics and Astronomy
                      Clemson University
                      Clemson, S.C. 29631 USA