THE ASTRONOMICAL JOURNAL    VOLUME 114, NUMBER 4, PAGE 1488       OCTOBER 1997

   DEEP HST V- AND I-BAND OBSERVATIONS OF TWO GLOBULAR CLUSTERS IN THE HALO
                                    OF M31

           STEPHEN HOLLAND, GREGORY G. FAHLMAN, AND HARVEY B. RICHER

           Department of Physics and Astronomy, #129-2219 Main Mall,
        University of British Columbia, Vancouver, B.C., V6T 1Z4 Canada
                     Electronic mail: holland@astro.ubc.ca


                                   ABSTRACT

     We present deep (V =~ 27) V- and I-band stellar photometry of G302 and
     G312, two globular star clusters in the halo of M31. These data were
     obtained using the Hubble Space Telescope's Wide Field/Planetary
     Camera 2. We find iron abundances of [Fe/H] = -1.85 +/- 0.12 for G302
     and [Fe/H] = -0.56 +/- 0.03 for G312, consistent with spectroscopic
     measurements. The color-magnitude diagrams for each cluster show no
     evidence for an intermediate-aged population of stars, or a second
     parameter effect in the morphology of the horizontal branch. G302
     shows no evidence for a color gradient but the inner regions of G312
     are bluer than the outer regions.  G312 shows no evidence of
     ellipticity or an extended halo of stars. G302 has a projected
     ellipticity of epsilon = 0.195 +/- 0.012 with the projected major axis
     oriented towards the center of M31. G302 also shows evidence of an
     extended asymmetric stellar halo extending to at least twice the
     fitted Michie-King tidal radius. The amount of mass beyond the tidal
     radius of G302 is consistent with the stellar escape rates which have
     been predicted by N-body simulations of globular clusters in the
     Galactic tidal field. (c) 1997 American Astronomical Society.