Impact of the initial disk mass function on the disk fraction

Abstract

The disk fraction, the percentage of stars with a disk in a young cluster, is widely used to investigate the lifetime of the protoplanetary disk, which can impose an important constraint on the planet formation mechanism. The relationship between the decay timescale of the disk fraction and the mass dissipation timescale of individual disks, however, remains unclear. Here we investigate the effect of the disk mass function (DMF) on the evolution of the disk fraction. We show that the time variation in the disk fraction depends on the spread of the DMF and the detection threshold of the disk. In general, the disk fraction decreases more slowly than the disk mass if a typical initial DMF and a detection threshold are assumed. We find that, if the disk mass decreases exponentially, the mass dissipation timescale of the disk can be as short as 1 Myr even when the disk fraction decreases with a time constant of ∼2.5 Myr. The decay timescale of the disk fraction can be a useful parameter to investigate the disk lifetime, but the difference between the mass dissipation of individual disks and the decrease in the disk fraction should be properly appreciated to estimate the timescale of the disk mass dissipation.