On the radial distribution of horizontal branch stars in ngc2808
  We present accurate new ultraviolet and optical BVI photometry for the
Galactic globular cluster ngc2808, based on both ground-based and archival HST
imagery. From this we have selected a sample of ~2,000 HB stars; given the
extensive wavelength range considered and the combination of both
high-angular-resolution and wide-field photometric coverage, our sample should
be minimally biased. We divide the HB stars into three radial bins and find
that the relative fractions of cool, hot and extreme HB stars do not change
radically when moving from the center to the outskirts of the cluster: the
difference is typically smaller than ~2sigma. These results argue against the
presence of strong radial differentiation among any stellar subpopulations
having distinctly different helium abundances. The ratio between HB and RG
stars brighter than the ZAHB steadly increases when moving from the innermost
to the outermost cluster regions. The difference is larger than ~4sigma and
indicates a deficiency of bright RGs in the outskirts of the cluster.
