Catalog of four-color photometry of stars, galaxies, and QSOs using SDSS filters

We present a catalog containing the measurements of 2262 sources, including 334 extended sources, 1915 point sources, and 13 known QSOs, in five SDSS passbands. Of these objects, over 1600 are measured in 15 fields covering 0 .5 deg(2), with a limiting magnitude of r* < 19.5, similar to the photometr ic limit of the SDSS spectroscopic survey. Color plots of the data show tha t stars, galaxies, and quasars are fairly well separated by color alone. Th e stellar locus populates a ribbon-like subset of color-color-color space. It is shown that stars, galaxies, and QSOs tend toward the same fundamental plane in three-dimensional color space. The stars are compared with synthe tic photometry from Kurucz models; the agreement is consistent with the err ors in the data. The stellar locus moves in color space by about a tenth of a magnitude from r* = 14 to r* = 19.5. The shift is consistent with a shif t in the metallicity from about [Me/H] = -1 to [Me/H] = -2. We compare this with previously measured metallicity gradients as a function of distance f rom the galactic plane.