Program: GN-2011B-Q-83

Despite the fact that many radial velocity and direct imaging studies suggest a deficit of brown dwarf companions to (solar-type) stars at a range of orbital separations, recent higher-contrast observations hint at a population of substellar companions, with mass ratios as low as ~0.01, particularly around >1 Msun stars. These objects (some of which have masses near and below 15Mjup) may represent the bottom end of the stellar companion mass function or the top end of the planet population, though both scenarios pose challenges to conventional formation models. Here we propose to conduct ALTAIR/NIRI observations of 70 members of the Taurus star-forming region, spanning a wide range of masses, to resolve new stellar and substellar companions. Such young and very low-mass companions will provide useful benchmarks for the theoretical models. Finally, the comparison of these observations with those of USco targets (obtained in 2008-10) and the Sco-Cen region (being conducted in 2011A), will allow us to test the dependence of the frequency of companions on the primary mass and its evolution with age.