THE ASTRONOMICAL JOURNAL    VOLUME 109, NUMBER 1, PAGE 359         JANUARY 1995

             OBSERVATIONS AND ANALYSIS OF THE CONTACT BINARY H235
                          IN THE OPEN CLUSTER NGC 752

           E. F. MILONE, C. R. STAGG, B. A. SUGARS, AND J. R. McVEAN

    Department of Physics and Astronomy, Rothney Astrophysical Observatory,
              The University of Calgary, 2500 University Dr., NW
                         Calgary, AB, T2N 1N4, Canada
                    Electronic mail: milone@acs.ucalgary.ca

                                S. J. SCHILLER

        Department of Physics, South Dakota State University, Box 2219,
                      Brookings, South Dakota 57007-0395
                   Electronic mail: schilles@mg.sdstate.edu

                                  J. KALLRATH

      BASF-AG, ZXA/ZC, Kaiser Wilhelm Strasse 52, D-67056, Ludwigshafen,
   Federal Republic of Germany, and Astronomische Institute der Universitaet
      Bonn, Auf dem Huegel 71, D-53121 Bonn, Federal Republic of Germany
                    Electronic mail: kallrath@zx.basf-ag.de

                               D. H. BRADSTREET

         Department of Physical Sciences, Eastern College, St. Davids,
                            Pennsylvania 19087-3696
                   Electronic mail: bradstreet@ucis.vill.edu

                                   ABSTRACT

    The short-period variable star Heinemann 235 in the open cluster NGC
    752 has been identified as a contact binary with a variable period of
    about 0.4118 d.  BVRI light curves and radial velocity curves have been
    obtained and analyzed with enhanced versions of the Wilson-Devinney
    light curve program.  We find that the system is best modeled as an
    A-type W UMa system, with a contact parameter of 0.21 +/- 0.11.  The
    masses of the components are found to be 1.18 +/- 0.17 and 0.24 +/-
    0.04 Msun, with bolometric magnitudes of 3.60 +/- 0.10 and 5.21 +/-
    0.13, for the hotter (6500 K, assumed) and cooler (6421 K) components,
    respectively, with Delta T = 79 +/- 25 K.  The distance to the binary
    is established at 381 +/- 17 pc.  H235 becomes one of a relatively
    small number of open-cluster contact systems with detailed light curve
    analysis for which an age may be estimated.  If it is coeval with the
    cluster, and with the detached eclipsing and double-lined spectroscopic
    binary H219 (DS And), H235 is ~1.8 Gyr old, and may provide a fiducial
    point for the evolution of contact systems.  There is, however,
    evidence for dynamical evolution of the cluster and the likelihood of
    weak interactions over the age of the binary precludes the
    determination of its initial state with certainty.