2014MNRAS.442.2543Y

We derived the intermediate-mass ( ≃ 1.5-7M_☉) disc fraction (IMDF) in the near-infrared JHK photometric bands as well as in the mid-infrared (MIR) bands for young clusters in the age range of 0 to ∼ 10Myr. From the JHK IMDF, the lifetime of the innermost dust disc ( ∼ 0.3au; hereafter the K disc) is estimated to be ∼ 3Myr, suggesting a stellar mass (M*) dependence of K-disc lifetime ( ≃ 1.5-7 M_☉). However, from the MIR IMDF, the lifetime of the inner disc ( ∼ 5au; hereafter the MIR disc) is estimated to be ∼ 6.5Myr, suggesting a very weak stellar mass dependence (M*). The much shorter K-disc lifetime compared to the MIR-disc lifetime for intermediate-mass (IM) stars suggests that IM stars with transition discs, which have only MIR excess emission but no K-band excess emission, are more common than classical Herbig Ae/Be stars, which exhibit both. We suggest that this prominent early disappearance of the K disc for IM stars is due to dust settling/growth in the protoplanetary disc, and it could be one of the major reasons for the paucity of close-in planets around IM stars.