We present 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 ages between 1 - 50 Myr. The fraction of accreting
stars decreases from ~60% at 1.5 - 2 Myr to ~2% at 10 Myr. No accreting stars
are found after 10 Myr at a sensitivity limit of 10−11 Msun 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
> 10^{-11} Msun yr-1, while ~20% of the stars show near-infrared excess
emission. Assuming an exponential decay, we measure a mass accretion timescale
(t_acc) of 2.3 Myr, compared to a near-to-mid infrared excess timescale
(t_IRAC) of 2.9 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.Comment: Accepted for publicatio