Stars in Sculptor dwarf spheroidal galaxy

The proper-motion cleaned color-magnitude diagram retained a broad giant branch, further supporting an intrinsic spread in metallicity. We determined an absolute proper motion for Sculptor, relative to background galaxies, of mu_alpha=+0.036+/-0.022arcsec/century and mu_delta=0.043+/-0.025arcsec/century after correcting for the LSR and peculiar solar motions.

Our proper-motion uncertainty is similar to or smaller than those obtained by different groups for other distant satellites of the Galaxy. When combined with Sculptor's distance and radial velocity, this measurement shows the dwarf spheroidal to have a space velocity of roughly 220+/-125km/s. Although our measurement is less than twice its uncertainty, the direction of Sculptor's motion is significant because it rules out motion along the Magellanic Stream.