2010A&A...522A...2B

Recent sub-millimetric observations at the Plateau de Bure interferometer showed a cavity of ∼46AU in radius in the proto-planetary disk of the T Tauri star LkCa15 (V1079 Tau), located in the Taurus molecular cloud. Additional Spitzer observations have corroborated this result which can possibly be explained by a massive (≥5M_Jup) planetary companion, a brown dwarf or a low-mass star companion at about 30AU from the star. We used the most recent developments of high angular resolution and high-contrast imaging to directly search for this putative companion, and to bring new constraints on its physical and orbital properties. The NACO adaptive optics instrument at the VLT was used to observe LkCa15 with a four-quadrant phase-mask coronagraph to access small angular separations at relatively high contrast. A reference star at the same parallactic angle was carefully observed to optimize the quasi-static speckles subtraction (limiting our sensitivity by less than 1.0''). Although we do not report any positive detection of a faint companion that would be responsible for the observed gap in LkCa15's disk (25-30AU), our detection limits start constraining its probable mass, semi-major axis and eccentricity. Using evolutionary model predictions, the Monte Carlo simulations exclude the presence of low eccentric companions with masses M≥6M_Jup and orbiting at a≥100AU with a significant level of confidence. For closer orbits, brown dwarf companions can be rejected with a detection probability of 90% down to 80AU (at 80% down to 60AU). Our detection limits do not permit us to access the star environment close enough to fully exclude the presence of a brown dwarf or a massive planet within the disk's inner activity (i.e. at less than 30AU). Only, further and higher contrast observations should unveil the existence of this putative companion inside the LkCa15 disk.