Impact of the initial disk mass function on the disk fraction

TL;DR

This paper explores how the initial distribution of disk masses influences the observed decline of disk fractions in young star clusters, highlighting the importance of considering the disk mass function when estimating disk lifetimes.

Contribution

It demonstrates that the disk mass function significantly affects the evolution of disk fraction and clarifies the relationship between individual disk dissipation and observed disk fraction decay.

Findings

Disk fraction decreases more slowly than individual disk mass.

Exponential disk mass decrease can imply a short mass dissipation timescale (~1 Myr).

Disk fraction decay timescale (~2.5 Myr) is useful but must be interpreted carefully.

Abstract

The disk fraction, the percentage of stars with disks 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 an individual disk, 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 $1\,{\rm Myr}$ even when the disk fraction decreases with the time constant of ${\sim}2.5\,{\rm Myr}$. The decay timescale of the disk fraction can be an useful parameter to investigate the disk lifetime, but the difference between the mass dissipation of an individual disk and the decrease in the disk fraction should be properly appreciated to estimate the timescale of the disk mass dissipation.