A multiplicity survey of the ρ Ophiuchi molecular clouds

We present a volume-limited multiplicity survey with magnitude cutoff ( m(K) <= 10.5 mag) of 158 young stellar objects located within or in the vicinity of the p Ophiuchi Dark Cloud. With exception of eleven already well observed objects, all sources have been observed by us in the K-band with 3.5 m telescopes by using speckle techniques. The separation range covered by our survey is 0.13 <= theta <= 6.4, where the lower limit is given by the diffraction limit of the telescopes and the upper limit by confusion with background stars. The multiplicity survey is complete for flux ratios >= 0.1 (Delta m(K) <= 2.5) at the diffraction limit. After taking the background density into account the degree of multiplicity is 29.1% +/- 4.3% and thus only marginally higher than the value 23.5% +/- 4.8% derived for the given separation range for the main-sequence solar-like stars in the solar neighbourhood (Duquennoy & Mayor 1991). We discuss the implications of these findings.