Description
Young loose nearby associations are unique samples of close (<150pc), young (~5-100Myr) pre-main sequence (PMS) stars. A significant number of members of these associations have been identified in the SACY collaboration. We can use the proximity and youth of these members to investigate key ingredients in star formation processes, such as multiplicity. We present the statistics of identified multiple systems from 113 confirmed SACY members. We derive multiplicity frequencies, mass-ratio, and physical separation distributions in a consistent parameter space, and compare our results to other PMS populations and the field. We have obtained adaptive-optics assisted near-infrared observations with NACO (ESO/VLT) and IRCAL (Lick Observatory) for at least one epoch of all 113 SACY members. We have identified multiple systems using co-moving proper-motion analysis and using contamination estimates. We have explored ranges in projected separation and mass-ratio of a [3-1000AU], and q [0.1-1], respectively. We have identified 31 multiple systems (28 binaries and 3 triples). We derive a multiplicity frequency (MF) of MF_3-1000AU_=28.4^+4.7^_-3.9_% and a triple frequency (TF) of TF_3-1000AU_=2.8^+2.5^_-0.8_% in the separation range of 3-1000AU. We do not find any evidence for an increase in the MF with primary mass. The estimated mass-ratio of our statistical sample (with power-law index {gamma}=-0.04+/-0.14) is consistent with a flat distribution ({gamma}=0).
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