We report analysis of our data from GO-8769, a 123 orbit exposure with HST/WFPC2 in F606W (wide V) and F814W (I) of a field in the globular cluster M4. Our photometry reaches to V ~ 30 and I ~ 28.5, and we are able to combine our data with imagery obtained 6 years earlier to produce a proper-motion selected sample. The reduced proper motion diagram shows two clumps: a very tight clump corresponding to members of M4, and a separate well-defined clump of stars with a much larger proper motion dispersion, which we attribute to the inner halo. M4 has l,b=(351,16) and the sight line therefore intersects in the inner halo roughly 2.5 kpc from the nucleus. Using the grouping in the reduced proper motion diagram, we are able to isolate those stars with membership in the inner halo (bulge?) population. We find a well defined main sequence extending to V≈ 29, or MV ~ +14 and this also will give one of the deepest luminosity functions ever constructed for the spheroid. The main sequence is substantially wider than that of the cluster, which we attribute both the dispersion in spatial location and metallicity. Our estimate of the proper motion dispersion gives 0.25 arcsec/century, or ≈ 100 km/sec at a distance of 8 kpc --- consistent with that found in other bulge fields. RMR acknowledges support from grant GO-8769 through the Space Telescope Science Institute.
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 2001