Protostars and Planets VI, Heidelberg, July 15-20, 2013
Poster 2S060
The Lifetime of Protoplanetary Disks Surrounding Intermediate-mass Stars
Yasui, Chikako (University of Tokyo)
Naoto, Kobayashi (University of Tokyo)
Tokunaga, Alan (University of Hawaii)
Saito, Masao (National Astronomical Observatory of Japan)
Abstract:
To quantitatively and comprehensively study the lifetime of protoplanetary disks surrounding intermediate-mass (IM) stars (~=1.5--7 M_sun), we derived the intermediate-mass disk fraction (IMDF) in the near-infrared JHK photometric bands as well as in the mid-infrared (MIR) bands for a large number (~20) of well-established nearby (D <~ 1.5 kpc) young clusters in the age range of 0 to ~10 Myr. The IM stars were selected from each cluster by making use of published spectral types in the literature, and the IMDF was derived assuming a single age per cluster. The derived JHK IMDF, which traces the innermost dust disk (hereafter the K disk), and MIR IMDF, which traces the inner disk at radii larger than the K disk (hereafter the MIR disk), appear to approximately follow an exponential decay with cluster age. The disk lifetime of the K disk for IM stars is estimated to be ~4 Myr, while that for low-mass (LM) stars is estimated to be ~10 Myr from the data in the literature. This suggests a stellar mass (M*) dependence of K-disk lifetime proportional to M*^{-0.5}. However, for the MIR disk, we found that the disk lifetimes for the IM stars (~7 Myr) and the LM stars (~9 Myr) are similar, so that the stellar mass dependence is very weak (proportional to M*^{-0.1}). The much shorter K-disk lifetime compared to the MIR-disk lifetime 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. If this is confirmed, our results set the time-scale of dust settling/growth in the K disk of the IM stars at ~3 Myr. We also discuss the possible implications of our results for the lack of close-in planets and the high frequency of Jupiter-mass planets around IM stars. Our results, the early dispersal of the K disk around IM stars, could be one of the major reasons for the paucity of close-in planets around IM stars.
Click here to view poster PDF