LIFETIMES AND ACCRETION RATES OF PROTOPLANETARY DISKS

Abstract

ABSTRACT Protoplanetary disks originate in the collapse of molecular cloud cores. The formation and evolution of disks are influenced by the properties of molecular cloud cores. In this paper we investigate the dependence of disk lifetimes and accretion rates on cloud core properties. We find that the lifetime increases as the angular velocities and the mass of cloud cores increase and that the lifetime decreases as the core temperature increases. We have calculated the distribution of disk lifetimes and disk fractions with stellar age. Our calculations show that the lifetime is in the range of 1–15 Myr and that the typical lifetime is 1–3 Myr. There are a few disks with lifetimes greater than 10 Myr and ∼ 30 % ?> of the disks have lifetimes less than 1 Myr. We also fit the disk fraction by an exponential decay curve with characteristic time ∼3.7 Myr. Our results explain the observations of disk lifetimes. We also find that the accretion rate does not change significantly with ω and generally decreases with T cd ?> . At the early evolution of the disks, the M ˙ – M * ?> relation is about M ˙ ∝ M * 1.2 − 2 ?> . Since the effects of the photoevaporation are weak at this stage, this relation is the consequence of the cloud core properties. At the late evolution of the disks, the M ˙ – M * ?> relation is about M ˙ ∝ M * 1.2 − 1.7 ?> . For low accretion rates at this stage, the M ˙ – M * ?> relation results from the effects of X-ray photoevaporation. The calculated M ˙ – M * ?> relations are consistent with the observations.