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Color-magnitude diagrams from deep, wide-field CCD photometry of the Sculptordwarf spheroidal galaxy reveal that the red horizonal branch (RHB) stars arestrongly concentrated towards the center of the galaxy relative to the dominantold population in Sculptor, confirming an earlier claim of such a gradient (DaCosta et al. 1996). Since we find no radial gradients of the age or metallicitydistribution within Sculptor, neither age nor metallicity can individuallyaccount for the internal `second parameter' problem observed within the galaxy.We have also identified an unusual `spur' of stars that extends from the mainsequence turnoff region and located between the canonical blue straggler regionand the subgiant branch. These stars are also more centrally concentrated thanthe oldest stars in Sculptor, although not as extremely as the RHB stars.Unable to convincingly interpret the spur either as an unusual young populationor as a foreground population of stars, we conclude that binary stars offer themost reasonable explanation for the origin of the spur that is also consistentwith other features in the CMD of Sculptor. We infer that 30-60% of allapparently single stars in the inner region of Sculptor may be binaries. Wespeculate that the possible radial gradient in the binary-star population maybe related to the variation of the HB morphology in Sculptor.Comment: 12 pages, 2 figures; Accepted for publication in ApJ Letter

A New Culprit in the Second-Parameter Problem in the Sculptor Dwarf Spheroidal Galaxy?