A Search for Close Binaries in the Rho Ophiuchus Star-Forming Region

We have carried out a new, near-infrared speckle imaging survey of 19 members of the young stellar population in the nearby (d=140 pc), Rho Ophiuchi cloud core. Results for four binary and one newly discovered triple system are reported. Data for all known multiple systems among the pre-main-sequence population of Rho Oph are tabulated. We define a "restricted binary fraction", Fbr, and a "restricted companion fraction", Fcr, as counting only those systems most detectable in the present and previous high-resolution near-infrared imaging surveys, having separations between 0.1-1.1 arcsec and K-band magnitude differences, Delta K < 3. Analysis of all the available multiplicity data results in updated values of Fbr=Fcr=24%+/-11% for the Ophiuchus pre-main-sequence population. These values are consistent with the values in the Taurus star-forming region, and Fcr is in excess by a factor of 2 relative to the Main Sequence at the 1-sigma level.