2010A&A...510A..72F

We present the initial result of a large spectroscopic survey aimed at measuring the timescale of mass accretion in young, pre-main-sequence stars in the spectral type range K0-M5. Using multi-object spectroscopy with VIMOS at the VLT we identified the fraction of accreting stars in a number of young stellar clusters and associations of the ages of between 1-30Myr. The fraction of accreting stars decreases from ∼60% at 1.5-2Myr to ∼2% at 10Myr. No accreting stars are found after 10Myr at a sensitivity limit of 10^–11M_☉/yr. We compared the fraction of stars showing ongoing accretion (f_acc) to the fraction of stars with near-to-mid infrared excess (f_IRAC). In most cases we find f_acc<f_IRAC, i.e., mass accretion appears to cease (or drop below detectable level) earlier than the dust is dissipated in the inner disk. At 5Myr, 95% of the stellar population has stopped accreting material at a rate of >10^–11M_☉/yr, while ∼20% of the stars show near-infrared excess emission. Assuming an exponential decay, we measure a mass accretion timescale (τ_acc) of 2.3Myr, compared to a near-to-mid infrared excess timescale (τ_IRAC) of 3Myr. Planet formation and/or migration, in the inner disk might be a viable mechanism to halt further accretion onto the central star on such a short timescale.