Color-induced displacement double stars in SDSS

We report the first successful application of the astrometric color-induced displacement technique (CID, the displacement of the photocenter between different bandpasses due to a varying contribution of differently colored components to the total light), originally proposed by Christy et al. (1983) for discovering unresolved binary stars. Using the Sloan Digital Sky Survey (SDSS) Data Release 2 with ∼4.1 × 10⁶ stars brighter than 21 ^m in the u and g bands, we select 346 candidate binary stars with CID greater than 0.5 arcsec. The SDSS colors of the majority of these candidates are consistent with binary systems including a white dwarf and any main sequence star with spectral type later than ∼K7. The astrometric CID method discussed here is complementary to the photometric selection of binary stars in SDSS discussed by Smolčić et al. (2004), but there is considerable overlap (15%) between the two samples of selected candidates. This overlap testifies both to the physical soundness of both methods, as well as to the astrometric and photometric quality of SDSS data.