Searching for the sub-stellar companions in the LkCa15 proto-planetary disk

¹ INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
e-mail: mariangela.bonavita@oapd.inaf.it
² Dipartimento di Astronomia, Universitá degli Studi di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
³ Laboratoire d’Astrophysique, Observatoire de Grenoble, UJF, CNRS, rue de la piscine, 38400 Saint-Martin d’Hères, France
⁴ LESIA, Observatoire de Paris Meudon, 5 pl. J. Janssen, 92195 Meudon, France
⁵ Institut de Radio-Astronomie Millimétrique, 300 rue de la Piscine, Domaine Universitaire, 38406 Saint-Martin d’Hères, France
⁶ Lab. H. Fizeau, CNRS UMR 6525, Univ. de Nice-Sophia Antipolis, Observatoire de la Côte d’Azur, 06108 Nice Cedex 2, France
⁷ Laboratoire d’Astrophysique de Bordeaux (LAB), Université Bordeaux 1, Bordeaux, France ; CNRS/INSU-UMR 5804, BP 89, 33270 Floirac, France

Received: 14 September 2009
Accepted: 20 April 2010

Abstract

Context. Recent sub-millimetric observations at the Plateau de Bure interferometer showed a cavity of  ~46 AU 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 (≥5 M_Jup) planetary companion, a brown dwarf or a low-mass star companion at about 30 AU from the star.

Aims. 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.

Methods. 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'').

Results. Although we do not report any positive detection of a faint companion that would be responsible for the observed gap in LkCa15’s disk (25−30 AU), 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 ≥ 6 M_Jup and orbiting at a ≥ 100 AU with a significant level of confidence. For closer orbits, brown dwarf companions can be rejected with a detection probability of 90% down to 80 AU (at 80% down to 60 AU). 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 30 AU). Only, further and higher contrast observations should unveil the existence of this putative companion inside the LkCa15 disk.