Transit Target Selection Using Reduced Proper Motions

In searches for planetary transits in the field, well over half of the surveystars are typically giants or other stars that are too large to permitstraightforward detection of planets. For all-sky searches of bright V<~11stars, the fraction is ~90%. We show that the great majority of thesecontaminants can be removed from the sample by analyzing their reduced propermotions (RPMs): giants have much lower RPMs than dwarfs of the same color. Weuse Hipparcos data to design a RPM selection function that eliminates mostevolved stars, while rejecting only 9% of viable transit targets. Our methodcan be applied using existing or soon-to-be-released all-sky data to starsV<12.5 in the northern hemisphere and V<12 in the south. The method degrades atfainter magnitudes, but does so gracefully. For example, at V=14 it can stillbe used to eliminate giants redward of V-I~0.95, that is, the blue edge of thered giant clump.Comment: Submitted to ApJ, 17 pages including 6 figure