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 popu- lation in the nearby (d ¼ 140 pc) � 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 ofOph are tabulated. We define a restricted binary fraction, Fb;r, and a restricted companion fraction, Fc;r, as counting only those systems most detectable in the present and previous high-resolution near-infrared imaging surveys having separations between 0> 1a nd� 1>1 and K-band magnitude differences DK < 3. Analysis of all the available multiplicity data results in updated values of Fb;r ¼ 24% � 11% and Fc;r ¼ 24% � 11% for the Ophiuchus pre-main-sequence population. These values are consistent with the values in the Taurus star- forming region, and Fc;r is in excess by a factor of 2 relative to the main sequence at the 1 � level. Subject headings: binaries: close — infrared: stars — stars: pre-main-sequence — techniques: high angular resolution