  We present BV photometry of the Sculptor dwarf galaxy to V=22. These data
give evidence for a bimodality in Sculptor's metallicity distribution based on
a discontinuity in the luminosities of horizontal branch (HB) stars and by the
presence of two distinct red giant branch (RGB) bumps. A consistent picture of
the evolved stars in Sculptor is given by the presence of (1) a metal-poor
population of [Fe/H] ~ -2.3 with an exclusively blue HB and that corresponds to
the blueward side of the Sculptor RGB and the more luminous RGB bump, and (2) a
less metal-poor population of [Fe/H] ~ -1.5 required to explain the less
luminous red HB, the red side of the RGB, and a second, less luminous RGB bump.
Best fits to the HB populations are obtained with enhanced oxygen abundances,
[O/Fe] ~ +0.5. Variations in the global HB and RGB morphology of Sculptor can
be explained by differences in the radial distribution of these two
populations. The presence of these two populations shows that the Sculptor
dwarf galaxy has an internal second parameter problem.
