THE ASTRONOMICAL JOURNAL    VOLUME 113, NUMBER 3, PAGE 1026     MARCH 1997 

            FABRY-PEROT OBSERVATIONS OF GLOBULAR CLUSTERS. III. M15

                                 KARL GEBHARDT

      Department of Astronomy, Dennison Building, University of Michigan,
                           Ann Arbor, Michigan 48109
                                       
                       CARLTON PRYOR AND T. B. WILLIAMS

   Department of Physics and Astronomy, Rutgers, The State University of New
            Jersey, P.O. Box 849, Piscataway, New Jersey 08855-0849
                                       
                     JAMES E. HESSER AND PETER B. STETSON

    Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics,
       National Research Council of Canada, 5071 W. Saanich Road, R.R.5,
                        Victoria, B.C., V8X 4M6, Canada
                                       
    We have used an Imaging Fabry-Perot Spectrophotometer with the
    Sub-arcsecond Imaging Spectrograph on the Canada-France-Hawaii
    Telescope to measure velocities for 1534 stars in the globular cluster
    M15 (NGC 7078) with uncertainties between 0.5 and 10 km/s.  Combined
    with previous velocity samples, the total number of stars with measured
    velocities in M15 is 1597. An average seeing of 0.8" allowed us to
    obtain velocities for 144 stars within 10" of the center of M15,
    including 12 stars within 2". The velocity dispersion profile for M15
    remains flat at a value of 11 km/s from a radius of 0.4 into our
    innermost reliable point at 0.02 (0.06 pc). Assuming an isotropic
    velocity dispersion tensor, this profile and the previously-published
    surface brightness profile can be equally well represented either by a
    stellar population whose M/L varies with radius from 1.7 in solar units
    at large radii to 3 in the central region, or by a population with a
    constant M/L of 1.7 and a central black hole of 1000 Msun. A
    non-parametric mass model that assumes no black hole, no rotation, and
    isotropy constrains the mass density of M15 to better than 30% at a
    radius of 0.07 parsecs. The mass-density profile of this model is well
    represented by a power law with an exponent of -2.2, the value
    predicted by models of cluster core-collapse. Using the assumption of
    local thermodynamic equilibrium, we estimate the present-day mass
    function and infer a significant number of 0.6-0.7 Msun objects in the
    central few parsecs, 85% of which may be in the form of stellar
    remnants. Not only do we detect rotation; we find that the position
    angle of the projected rotation axis in the central 10" is 100 deg
    different from that of the whole sample. We also detect an increase in
    the amplitude of the rotation at small radii. Although this increase
    needs to be confirmed with better-seeing data, it may be the result of
    a central mass concentration. (Copyright) 1997 American Astronomical
    Society.