2010A&A...520L...2A

We search for low-mass companions in the innermost region (<300mas, i.e., 6AU) of the β Pic planetary system. We obtained interferometric closure phase measurements in the K-band with the VLTI/AMBER instrument used in its medium spectral resolution mode. Fringe stabilization was provided by the FINITO fringe tracker. In a search region of between 2 and 60mas in radius, our observations exclude at 3σ significance the presence of companions with K-band contrasts greater than 5x10^–3 for 90% of the possible positions in the search zone (i.e., 90% completeness). The median 1σ error bar in the contrast of potential companions within our search region is 1.2x10^–3. The best fit to our data set using a binary model is found for a faint companion located at about 14.4mas from β Pic, which has a contrast of 1.8x10^–3±1.1x10^–3 (a result consistent with the absence of companions). For angular separations larger than 60mas, both time smearing and field-of-view limitations reduce the sensitivity. We can exclude the presence of brown dwarfs with masses higher than 29M_Jup (resp. 47M_Jup) at a 50% (resp. 90%) completeness level within the first few AUs around β Pic. Interferometric closure phases offer a promising way to directly image low-mass companions in the close environment of nearby young stars.