We derived the intermediate-mass ( \simeq 1.5–7 M _ { \odot } ) disk 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 \sim 10 Myr .
From the JHK IMDF , the lifetime of the innermost dust disk ( \sim 0.3 AU ; hereafter the K disk ) is estimated to be \sim 3 Myr , suggesting a stellar mass ( M _ { * } ) dependence of K -disk lifetime \propto M ^ { -0.7 } _ { * } .
However , from the MIR IMDF , the lifetime of the inner disk ( \sim 5 AU ; hereafter the MIR disk ) is estimated to be \sim 6.5 Myr , suggesting a very weak stellar mass dependence ( \propto M ^ { -0.2 } _ { * } ) .
The much shorter K -disk lifetime compared to the MIR-disk lifetime for intermediate-mass ( IM ) stars suggests that IM stars with transition disks , 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 disk for IM stars is due to dust settling/growth in the protoplanetary disk , and it could be one of the major reasons for the paucity of close-in planets around IM stars .