First spectroscopic observations of the sub-stellar companion of the young debris disk star PZ Telescopii

Abstract

In 2010 a sub-stellar companion to the solar analog pre-main sequence star PZ Tel and member of the about 12 Myr old Beta 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 primary and companion. We use 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 H+K band and process the data using the spectral deconvolution technique. The resulting spectrum of the companion is 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 chi^2 minimization analysis. We find a best fitting spectral type of G6.5 for PZ Tel A. The extracted spectrum of the sub-stellar companion, at a spatial position compatible with earlier orbit estimates, yields a temperature Teff= 2500 +138-115 K, a visual extinction A_V= 0.53 +0.84-0.53 mag, a surface gravity of log g= 3.50 +0.51-0.30 dex, and a metallicity at the edge of the grid of [M/H]= 0.30 -0.30 dex. We derive a luminosity of log(Lbol/Lsun)= -2.66 +0.06-0.08, a radius of R= 2.42 +0.28-0.34 R_Jup and a mass of M= 7.5 +16.9-4.3 M_Jup for the PZ Tel companion, being 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 +4-2 Myr. Hence, the PZ Tel companion is most likely a wide brown dwarf companion in the 12 +8-4 Myr old Beta Pic moving group.

7 pages, 6 figures, accepted for publication in A&A

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Cited by in corpus (9)

• MIRACLES: atmospheric characterization of directly imaged planets and substellar companions at 4-5 $\mu$m. I. Photometric analysis of $\beta$ Pic b, HIP 65426 b, PZ Tel B and HD 206893 B
• Astrometric follow-up observations of directly imaged sub-stellar companions to young stars and brown dwarfs
• A medium-resolution spectrum of the exoplanet HIP 65426 b
• Indications of stellar prominence oscillations on fast rotating stars: the cases of HK Aqr and PZ Tel
• Dynamical Mass of the Young Brown Dwarf Companion PZ Tel B
• Detection of H$\alpha$ emission from PZ Tel B using SPHERE/ZIMPOL
• A direct imaging search for close stellar and sub-stellar companions to young nearby stars
• A High-Resolution Spectroscopic Survey of Directly Imaged Companion Hosts: II. Diversity in C/O Ratios among Host Stars
• New constraints on the presence of debris disks around G 196-3 B and VHS J125601.92-125723.9 b