THE ASTRONOMICAL JOURNAL       VOLUME 105, NUMBER 1, PAGE 226      JANUARY 1993

               STELLAR KINEMATIC GROUPS. I. THE URSA MAJOR GROUP

                              DAVID R. SODERBLOM

     Space Telescope Science Institute, 3700 San Martin Drive, Baltimore,
                                Maryland 21218

                                 MICHEL MAYOR

             Observatoire de Geneve, CH-1290 Sauverny, Switzerland

                                   ABSTRACT

    The Ursa Major Group (UMaG) is studied as a test case for the
    authenticity of Stellar Kinematic Groups, using Coravel radial
    velocities, recent compilations of astrometric data and new
    spectroscopic observations.  Spectroscopic age indicators, particularly
    indices of the strength of chromospheric emission, are applied to
    solar-type candidate members of UMaG, and it is shown that stars that
    meet the spectroscopic criteria also have kinematics that agree better
    with the space motions of the nucleus of UMaG than does the starting
    sample as a whole.  The primary limitation on the precision of
    kinematics is now parallaxes instead of radial velocities.  These more
    restrictive kinematic criteria are then applied to other UMaG
    candidates and a list summarizing membership is presented.  UMaG is
    also examined as a cluster, confirming its traditional age of 0.3 Gyr
    and a mean [Fe/H] of -0.08 +/- 0.09 for those stars most likely to be
    bona fide members.