Abstract
The infrared excess in the SEDs (Spectral Energy Distributions) of protoplanetary disks is observed only around stars younger than 107 yr. This is thought to be because the life time of protoplanetary disks is less than 107 yr. In this study, we perform simulations of dust growth and settling in passive disks and investigate evolution of optical properties of protoplanetary disks due to dust growth. As a result of growth, dust particles has a power-law size distribution with the index of -3. The dust growth decreases the disk optical thickness. We also found that the dust growth can reproduce the decay in luminosity of infrared radiation in 106-7 yr. Our result suggests that the life time of gaseous disks can be longer than 107 yr.
