Long-term Evolution of Photoevaporating Protoplanetary Disks

TL;DR

This study models the long-term evolution of photoevaporating protoplanetary disks, showing that photoevaporation alone can explain observed disk dispersal timescales and linking initial cloud angular momentum to disk clearing.

Contribution

It introduces a detailed one-dimensional, two-zone disk model that demonstrates how photoevaporation and initial angular momentum influence disk evolution and dispersal times.

Findings

Disks have transitional phases lasting less than 20% of their lifetime.

Initial angular momentum distribution favors slowly rotating cores for effective disk clearing.

Reducing photoevaporation rates by a factor of 10 hampers disk dispersal within observed timescales.

Abstract

We perform calculations of our one-dimensional, two-zone disk model to study the long-term evolution of the circumstellar disk. In particular, we adopt published photoevaporation prescriptions and examine whether the photoevaporative loss alone, coupled with a range of initial angular momenta of the protostellar cloud, can explain the observed decline of the frequency of optically-thick dusty disks with increasing age. In the parameter space we explore, disks have accreting and/or non-accreting transitional phases lasting of $\lesssim20 %$ of their lifetime, which is in reasonable agreement with observed statistics. Assuming that photoevaporation controls disk clearing, we find that initial angular momentum distribution of clouds needs to be weighted in favor of slowly rotating protostellar cloud cores. Again, assuming inner disk dispersal by photoevaporation, we conjecture that this skewed angular momentum distribution is a result of fragmentation into binary or multiple stellar systems in rapidly-rotating cores. Accreting and non-accreting transitional disks show different evolutionary paths on the $\dot{M}-R_{\rm wall}$ plane, which possibly explains the different observed properties between the two populations. However, we further find that scaling the photoevaporation rates downward by a factor of 10 makes it difficult to clear the disks on the observed timescales, showing that the precise value of the photoevaporative loss is crucial to setting the clearing times. While our results apply only to pure photoevaporative loss (plus disk accretion), there may be implications for models in which planets clear disks preferentially at radii of order 10 AU.