COMMISSION 27 OF THE I. A. U.
       INFORMATION BULLETIN ON VARIABLE STARS
                   Number 1569

                              Konkoly Observatory
                              Budapest
                              1979 March 16




           IMPROVED EPHEMERIS, V502 OPHIUCHI


   V502 Ophiuchi (BD+0d3562) is a contact binary system which undergoes 
partial eclipses. From his period study of the system, Kwee
(B.A.N. 14, 131, 1958) noted a variability in the period and calculated
the following light elements: JD Hel. Min. I = 2435257.4459 +
0.45339630d E. A more recent study by Binnendijk (A.J. 74, 218, 1969),
indicated a decrease had occured in the period after 1958. Binnendijk
gave the ephemeris JD Hel. Min. I = 2439639.9431 + 0.45339304d E.
   The present observations were made during the interval 4-12 June
1978 with the 0.5 meter 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 used to calibrate the chart. BD+0d3566
was used as the comparison star, and BD+0d3569 and BD+0d3574 were used
as check stars.
   The measurements yielded 587 observations with the B filter and 625
with the V filter, with each observation being the average of two 
consecutive ten-second integrations. Differential extinction corrections
were not made to the observations. Epochs of minimum light were determined 
from the observations defining one primary and three secondary
eclipse curves. The method of bisecting the chords connecting points of
equal magnitude on the opposing branches of an eclipse curve was used to
find the temporal mean. The epochs of minimum light are listed in Table I.
The O-C's were determined from the ephemeris given by Binnendijk, shown
above.



           Table I
------------------------------
Hel.JD       Min.        O-C
2443600+
------------------------------
  65.8463    II        -0.0003d
  66.7545    II        +0.0011
  68.7951    I         +0.0015
  71.7469    II        +0.0062
------------------------------

   A least squares straight line fit to the observations between
JD 2437000 and JD 24413671 yielded the ephemeris:
      JD Hel. Min. I = 2439639.9474 + 0.45339293d E.
This period differs only slightly from that determined by Binnendijk.



                   WILLIAM C. MADDOX
                   BEVERLY B. BOOKMYER
                   Dept. of Physics and Astronomy
                   Clemson University
                   Clemson, SC 29631 USA