1111.7001 (James S. Jenkins et al.)

Benchmark cool companions: New ages and abundances for the PZ Tel system    [PDF]

James S. Jenkins, Yakiv V. Pavlenko, Oleksiy Ivanyuk, Jose Gallardo, Matias I. Jones, Avril . C. Day-Jones, Hugh R. A. Jones, Maria-Teresa Ruiz, David J. Pinfield, Larissa Yakovina

We present new ages and abundance measurements for the pre-main sequence star PZ Tel. PZ Tel was recently found to host a young and low-mass companion. Using FEROS spectra we have measured atomic abundances (e.g. Fe and Li) and chromospheric activity for PZ Tel and used these to obtain metallicity and age estimates for the companion. We find PZ Tel to be a rapidly rotating (vsini=73\pm5km/s), ~solar metallicity star (logN(Fe)=-4.37\pm0.06dex or [Fe/H]=0.05\pm0.20dex) with a measured mean logR'HK of -4.12. We measure a NLTE lithium abundance of logN(Li)=3.1\pm0.1dex, which from depletion models gives rise to an age of 7+4-2 Myrs for the system. The measured chromospheric activity returns an age of 26\pm2Myrs, as does fitting pre-main sequence evolutionary tracks (Tau_evol=22\pm3Myrs), both of which are in disagreement with the lithium age. We speculate on reasons for this difference and introduce new models for lithium depletion that incorporates both rotation and magnetic field affects. We also synthesize solar, metal-poor and metal-rich substellar evolutionary models to better determine the bulk properties of PZ Tel B, showing that PZ Tel B is probably more massive than previous estimates, meaning the companion is not a giant exoplanet. We show how PZ Tel B compares to other currently known age and metallicity benchmark systems and try to empirically test the effects of dust opacity as a function of metallicity on the near infrared colours of brown dwarfs. Current models suggest that in the near infrared observations are more sensitive to low-mass companions orbiting more metal-rich stars. Finally, an emerging anti-correlation is found between metallicity and the near infrared colours that may point towards dust settling deeper in the atmospheres of metal-rich substellar objects, giving rise to a possible origin for the peculiar blue L dwarfs. [Abridged]

View original: http://arxiv.org/abs/1111.7001