Program: GS-2015B-Q-37

We propose to use the new capabilities offered by GPI to conduct a survey for the lowest mass stellar companions to late-B-type stars in young nearby open clusters. The immediate objective of the project is to determine the frequency of "extreme" mass ratio systems (q<0.1) among close visual binaries. Such systems are remarkably rare for solar-type stars (~1%), as indicated by the existence of the so-called brown dwarf desert. This phenomenon reveals a fundamental limit of the (multiple) star formation process which has two main possible interpretations: 1) an absolute companion mass limit that happens to roughly coincide with the substellar limit, or 2) a mass ratio limit, whereby accretion during the early stages of star formation and/or the initial distribution of specific angular momentum preclude the existence of such asymmetric, close systems. The goal of this project is to test the mass-dependency associated with the angular momentum scenario, which predicts that no such low-mass companions will be found. By focusing on stars in the 3-5 Msun range, we can unambiguously disentangle between the two possibilities mentioned above, thus shedding crucial new light on the limits of (multiple) star formation.