Abstract
| - Context. In 2010 a substellar companion to the solar analog pre-main sequence star PZ Tel and member of the approximately 12 Myr old β Pic moving group was found by high-contrast direct imaging independently by two teams. Aims. 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. Methods. 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 D rift-P hoenix 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. Results. 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 Teff = 2500 −115+138 K, a visual extinction A V = 0.53 −0.53+0.84 mag, a surface gravity of log g = 3.50 −0.30+0.51 dex, and a metallicity at the edge of the grid of [M/H] = 0.30 −0.30 dex. Conclusions. We derive a luminosity of log( Lbol/ L⊙) = −2.66 −0.08+0.06, a radius of R = 2.42 −0.34+0.28RJup, and a mass of M = 7.5 −4.3+16.9MJup 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 −2+4 Myr. Hence, the PZ Tel companion is most likely a wide brown dwarf companion in the 12 −4+8 Myr old β Pic moving group.
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