A search for close binaries in the ρ Ophiuchi 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 Oph 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, F-b; r, and a restricted companion fraction, F-c; r, as counting only those systems most detectable in the present and previous high-resolution near-infrared imaging surveys having separations between 0.1 and similar to1.1 and K-band magnitude differences DeltaK < 3. Analysis of all the available multiplicity data results in updated values of F-b; r = 24% +/- 11% and F-c; r = 24% +/- 11% for the Ophiuchus pre-main-sequence population. These values are consistent with the values in the Taurus star-forming region, and F-c; r is in excess by a factor of 2 relative to the main sequence at the 1 σ level.