2014A&A...562A.111B

We previously reported the direct detection of a low-mass companion at a projected separation of 55±2 AU around the B9-type star κ Andromedae. The properties of the system (mass ratio, separation) make it a benchmark for understanding the formation and evolution of gas giant planets and brown dwarfs on wide orbits. We present new angular differential imaging (ADI) images of the system at 2.146 (K_s), 3.776 (L'), 4.052 (NB_4.05), and 4.78µm (M') obtained with Keck/NIRC2 and LBTI/LMIRCam, as well as more accurate near-infrared photometry of the star with the MIMIR instrument. We aim to determine the near-infrared spectral energy distribution of the companion and use it to characterize the object. We used analysis methods adapted to ADI to extract the companion flux. We compared the photometry of the object to reference young, and old objects and to a set of seven PHOENIX-based atmospheric models of cool objects accounting for the formation of dust. We used evolutionary models to derive mass estimates considering a wide range of plausible initial conditions. Finally, we used dedicated formation models to discuss the possible origin of the companion. We derive a more accurate J=15.86±0.21, H=14.95±0.13, K_s=14.32±0.09mag for κ And b. We detect the companion in all our high-contrast observations. We confirm previous contrasts obtained at K_s and L' band. We derive NB_4.05=13.0 ±0.2, and b mostly falls in the brown-dwarf regime, owing to remaining uncertainties in age and in mass-luminosity models. According to the formation models, disk instability in a primordial disk may account for the position and a wide range of plausible masses of κ And b.