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Description
We derived the intermediate-mass (=~1.5-7M_{sun}_) 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 (=~1.5-7M_{sun}_). 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.
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