2014A&A...566A..85S

In 2010 a substellar companion to the solar analog pre-main sequence star PZ Tel and member of the approximately 12Myr old β Pic moving group was found by high-contrast direct imaging independently by two teams. In order to determine the basic parameters of this companion more precisely and independent of evolutionary models, hence age-independent, we obtained follow-up spectroscopic observations of the primary and companion. We used the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) at the Very Large Telescope Unit 4/Yepun of ESO's Paranal Observatory in the H+K band and processed the data using the spectral deconvolution technique. The resulting spectrum of the companion was then compared to a grid of Drift-Phoenix synthetic model spectra, a combination of a general-purpose model atmosphere code with a non-equilibrium, stationary cloud and dust model, using a χ² minimization analysis. We find a best fitting spectral type of G6.5 for PZ Tel A. The extracted spectrum of the substellar companion, at a spatial position compatible with earlier orbit estimates, yields a temperature T_eff=2500⁺¹³⁸_–115K, a visual extinction A_V=0.53^+0.84_–0.53mag, a surface gravity of logg=3.50^+0.51_–0.30dex, and a metallicity at the edge of the grid of [M/H]=0.30_–0.30dex. We derive a luminosity of log(L_bol/L_☉)=-2.66^+0.06_–0.08, a radius of R =2.42^+0.28_–0.34R_Jup, and a mass of M=7.5^+16.9_–4.3M_Jup for the PZ Tel companion, which is consistent with most earlier estimates using photometry alone. Combining our results with evolutionary models, we find a best-fitting mass of about 21 Jupiter masses at an age corresponding to the recently determined lithium depletion age of 7⁺⁴_–2Myr. Hence, the PZ Tel companion is most likely a wide brown dwarf companion in the 12⁺⁸_–4Myr old β Pic moving group.