SIMBAD references

An improved proper-motion catalog is presented, combining the USNO-B and Sloan Digital Sky Survey (SDSS) catalogs in the area of sky covered by SDSS Data Release 1 (DR1; 2099 deg²). USNO-B positions are recalibrated using SDSS galaxies, and proper motions are recomputed including both the USNO-B and SDSS positions. Statistical errors in the USNO-B proper motions are decreased by roughly 20%-30%, systematic errors are greatly reduced, and the proper motions are placed on an absolute reference frame. Requiring a match to an SDSS object removes the large number of false high proper motion objects in USNO-B. The resultant catalog is 90% complete to g<19.7, with statistical errors in the component proper motions of roughly 3-3.5 mas/yr, substantially smaller systematic errors, and a contamination rate of less than 0.5%. A number of studies are currently underway using proper motions from this catalog. The catalog is available via ftp.