Rapid Evolution of the Innermost Dust Disk of Protoplanetary Disks Surrounding Intermediate-mass Stars

摘要

We derived the intermediate-mass (~=1.5--7 M_sun) disk fraction (IMDF) in thenear-infrared JHK photometric bands as well as in the mid-infrared (MIR) bandsfor young clusters in the age range of 0 to ~10 Myr. From the JHK IMDF, thelifetime of the innermost dust disk (~0.3 AU; hereafter the K disk) isestimated to be ~3 Myr, suggesting a stellar mass (M*) dependence of K-disklifetime proportional to M*^-0.7. However, from the MIR IMDF, the lifetime ofthe inner disk (~5 AU; hereafter the MIR disk) is estimated to be ~6.5 Myr,suggesting a very weak stellar mass dependence (proportional to M*^-0.2). Themuch shorter K-disk lifetime compared to the MIR-disk lifetime forintermediate-mass (IM) stars suggests that IM stars with transition disks,which have only MIR excess emission but no K-band excess emission, are morecommon than classical Herbig Ae/Be stars, which exhibit both. We suggest thatthis prominent early disappearance of the K disk for IM stars is due to dustsettling/growth in the protoplanetary disk, and it could be one of the majorreasons for the paucity of close-in planets around IM stars.