Volume 566, June 2014
|Number of page(s)||7|
|Section||Planets and planetary systems|
|Published online||20 June 2014|
First spectroscopic observations of the substellar companion of the young debris disk star PZ Telescopii⋆
Astrophysikalisches Institut und Universitäts-Sternwarte, Universität
2 Departamento de Física y Astronomía, Universidad de Valparaíso, Avenida Gran Bretaña 1111, Valparaíso, Chile
3 Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
4 SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS, UK
5 Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Ave., Chicago IL 60637, USA
Accepted: 26 March 2014
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 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.
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 AV = 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+0.28 RJup, and a mass of M = 7.5−4.3+16.9 MJup 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.
Key words: brown dwarfs / stars: pre-main sequence / stars: atmospheres / planetary systems / planets and satellites: formation / stars: individual: PZ Tel
© ESO, 2014
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