Age determination of the HR8799 planetary system using asteroseismology

Abstract

Discovery of the first planetary system by direct imaging, around HR 8799, has made the age determination of the host star a very important task. This determination is the key to deriving accurate masses of the planets and to studying the dynamical stability of the system. The age of this star has been estimated using different procedures. In this Letter we show that some of these procedures have problems and large uncertainties, and the real age of this star is still unknown, needing more observational constraints. Therefore we have developed a comprehensive modelling of HR 8799 and, taking advantage of its γ Doradus-type pulsations, we have estimated the age of the star using asteroseismology. The accuracy in the age determination depends on the rotation velocity of the star, and therefore an accurate value of the inclination angle is required to solve the problem. Nevertheless, we find that the age estimate for this star previously published in the literature ([30, 160] Myr) is unlikely, and a more accurate value might be around a Gyr. This determination has significant implications for the value of the mass of the objects orbiting HR 8799. An age around ≈1 Gyr implies that these objects would be brown dwarfs. © 2010 The Authors. Journal compilation © 2010 RAS.