A Search for Binary Hot Subdwarfs. II. Infrared Photometry of Palomar-Green Survey sdO Stars

Eight sdO binary candidates have been identified through IR photometry of 25 type O hot subdwarfs. Five of the eight binary candidates are identified for the first time. These new binary candidates complement a list of nine optically identified sdO binary candidates discovered in an earlier portion of this project. The new candidates are identified on the basis of IR color excesses in two-color plots of extinction-corrected data. We estimate that at least 64% of the Palomar-Green Survey sdOC hot subdwarfs are binary.