Disk Accretion at 10 Myr: Results from the Tw Hydrae Association

We present an analysis of the accretion properties of the members of the TW Hydrae association. The emission line profile of Hα provides explicit evidence of an active accretion flow in 3 out of the 23 observed members of the association; we use radiative transfer models to derive approximate accretion rates for these 3 objects. The resulting accretion rates for the three 10 Myr-old objects (< 10−9 M⊙ yr −1) are well over an order of magnitude lower than typical values in 1 Myr-old T Tauri stars. The small fraction of TW Hydrae association objects still accreting (13%, compared with ∼ 70% in 1 Myr-old regions like Taurus), along with the very small accretion rates, points to significant disk evolution over 10 Myr, providing an important constraint on the timescales for planet formation.