Color-Induced Displacement double stars in SDSS^*

¹ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544-1001, USA e-mail: [ivezic;gk;jeg;rhl]@astro.princeton.edu
² Institut d'Astronomie et d'Astrophysique, Université Libre de Bruxelles, CP 226, Boulevard du Triomphe, 1050 Bruxelles, Belgium e-mail: pourbaix@astro.ulb.ac.be
³ HN Russell Fellow, on leave from the University of Washington

Received: 27 February 2004
Accepted: 8 May 2004

Abstract

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 [CITE] for discovering unresolved binary stars. Using the Sloan Digital Sky Survey (SDSS) Data Release 2 with ~ 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 [CITE], 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.