A companion candidate in the gap of the T Chamaeleontis transitional disk

Abstract

Context: T Cha is a young star surrounded by a cold disk. The presence of a gap within its disk, inferred from fitting to the spectral energy distribution, has suggested on-going planetary formation. Aims. The aim of this work is to look for very low-mass companions within the disk gap of T Cha. Methods. We observed T Cha in L′ and Ks with NAOS-CONICA, the adaptive optics system at the VLT, using sparse aperture masking. Results. We detected a source in the L′ data at a separation of 62 ± 7 mas, position angle of ∼78 ± 1 degrees, and a contrast of ΔL′ = 5.1 ± 0.2 mag. The object is not detected in the Ks band data, which show a 3-σ contrast limit of 5.2 mag at the position of the detected L′ source. For a distance of 108 pc, the detected companion candidate is located at 6.7 AU from the primary, well within the disk gap. If T Cha and the companion candidate are bound, the comparison of the L′ and Ks photometry with evolutionary tracks shows that the photometry is inconsistent with any unextincted photosphere at the age and distance of T Cha. The detected object shows a very red Ks - L′ color, for which a possible explanation would be a significant amount of dust around it. This would imply that the companion candidate is young, which would strengthen the case for a physical companion, and moreover that the object would be in the substellar regime, according to the Ks upper limit. Another exciting possibility would be that this companion is a recently formed planet within the disk. Additional observations are mandatory to confirm that the object is bound and to properly characterize it.