SUB-STELLAR COMPANIONS AND STELLAR MULTIPLICITY IN THE TAURUS STAR-FORMING REGION

We present results from a large, high- spatial- resolution near- infrared imaging search for stellar and sub- stellar companions in the Taurus- Auriga star- forming region. The sample covers 64 stars with masses between those of the most massive Taurus members at 3 M-circle dot and low-mass stars at 0.2 M-circle dot. We detected 74 companion candidates, 34 of these reported for the first time. Twenty- five companions are likely physically bound, partly confirmed by follow- up observations. Four candidate companions are likely unrelated field stars. Assuming physical association with their host star, estimated companion masses are as low as 2M(Jup.) The inferred multiplicity frequency within our sensitivity limits between 10-1500 AU is 26.3(-4.9)(+ 6.6)% - 4.9%. Applying a completeness correction, 62% 14% of all Taurus stars between 0.7 and 1.4 M appear to be multiple. Higher order multiples were found in 1.8+ 4.2 - 1.5 % of the cases, in agreement with previous observations of the field. We estimate a sub- stellar companion frequency of 3.5%- 8.8% within our sensitivity limits from the discovery of two likely bound and three other tentative very low- mass companions. This frequency appears to be in agreement with what is expected from the tail of the stellar companion mass ratio distribution, suggesting that stellar and brown dwarf companions share the same dominant formation mechanism. Further, we find evidence for possible evolution of binary parameters between two identified sub- populations in Taurus with ages of 2 Myr and 20 Myr, respectively.