Timescale of mass accretion in pre-main-sequence stars

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 1-30 Myr. The fraction of accreting stars decreases from similar to 60% at 1.5-2 Myr to similar to 2% at 10 Myr. No accreting stars are found after 10 Myr at a sensitivity limit of 10(-11) M-circle dot yr(-1). 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 5 Myr, 95% of the stellar population has stopped accreting material at a rate of greater than or similar to 10(-11) M-circle dot yr(-1), while similar to 20% of the stars show near-infrared excess emission. Assuming an exponential decay, we measure a mass accretion timescale (tau(acc)) of 2.3 Myr, compared to a near-to-mid infrared excess timescale (tau(IRAC)) of 3 Myr. 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.