COMMISSION 27 OF THE I.A.U.
                INFORMATION BULLETIN ON VARIABLE STARS
                            Number 3218

                                                        Konkoly Observatory
                                                        Budapest
                                                        27 July 1988

                                                        HU ISSN 0374 - 0676


                 PHOTOELECTRIC LIGHT CURVE OF V502 Oph

V502 Oph is a W UMa type eclipsing system with components of spectral
types: G2V + F9V (Binnendijk 1969). The system shows variability in the
period and in its light curve shape (Maddox and Bookmyer 1979).
The new observations were made at the Astronomical Station of the
Jagiellonian University in Bieszczady Mountains using a 20 cm refractor
equipped with a one-channel photometer with blue and yellow filters. The
FEU 92 Russian photomultiplier was used. Observations were carried out during
two seasons: 1985 and 1986, using BD +1d3300 as the comparison star. 
Measurements were corrected for atmospheric extinction making use of the mean
coefficients for the station and next, they were reduced to the UBV system
(the reduction procedure was described by Flin et al, 1985). We were able to
determine five moments of minima. The results are presented in Table I.
   Phases in the paper were calculated with the following elements:

        Min. I. (HJD) = 2446555.5244 + 0.45339293d E

   In order to obtain the physical parameters of the system we used the
Wilson-Devinney code: DCMF (Wilson 1979). The following parameters were
adjusted: inclination and mass ratio of the system, temperature of the
second component, luminosity of the primary component and its Roche potential.
Calculations were performed in mode 3 of the code simultaneously in both
filters, assuming that there is no third light in the system. As the starting
mass ratio we adopted its spectroscopic value (Struve and Gratton 1948), for
temperatures of components, the values corresponding to their spectral types
(Allen 1965).


                  Table I
         Times of minima of V502 Oph

  min            time (HJD)          filter

primary      2446530.5866+/-0.0004       V
primary      2446555.5244+/-0.0004       V
primary      2446915.5165+/-0.0003       B
secondary    2446528.5488+/-0.0005       V
secondary    2446529.4572+/-0.0005       V



                       [FIGURE 1]
                       [FIGURE 2]


                         Table II

                  Parameters of V502 Oph

wavelength independent:

    i          T_1      T_2       g     A         Omega           q

 70.2+/-0.2   6140   5750+/-30  0.32   0.50   6.072+/-0.025   2.64+/-0.01


wavelength dependent:

          L_1              L_2         X

  B    4.682 +/- 0.009    7.863      0.78
  V    4.498 +/- 0.008    8.062      0.65

   The limb darkening coefficients were taken from the tables published by Al
Naimiy (1978) for bolometric albedo and gravity darkening we assumed their
theoretical values. The starting value for the inclination was assumed to be
70 deg. The results of light curve synthesis are listed in Table II and 
graphically presented in Figure 1 and Figure 2 (B and V filters respectively),

Acknowledgements.

We thank Dr. M. Winiarski for doing a part of observations in V filter. This
work was partially supported by grant RPBR-I-11/1-05.


                       S. ZOLA
                 Astronomical Observatory
                 Jagellonian University,
                    Cracow, Poland

                     J. KRZESINSKI
                 Astronomical Observatory
                  Pedagogical University
                     Cracow, Poland



References:

Allen, C.W., 1965, Astrophysical Quantities (London, Univ, of London).
Al Naimiy, H.M., 1978, Astr, Sp. Sci, 53, 181. [BIBCODE 1978Ap&SS..53..181A ]
Binnendijk, L., 1969, Astr, J., 74, 222. [BIBCODE 1969AJ.....74..218B ]
Flin, P., Winiarski, M., Zola, S., 1985, IBVS, No. 2678.
Maddox, W.C., Bookmyer, B.B., 1979, IBVS, No. 1569.
Struve, O., Gratton, L., 1948, Ap. J., 108, 497. [BIBCODE 1948ApJ...108..497S ]
Wilson, R.E., 1979, Ap. J., 234, 1054. [BIBCODE 1979ApJ...234.1054W ]