Disc Clearing of Young Stellar Objects: Evidence for Fast Inside-out Dispersal

TL;DR

This study uses radiative transfer modelling and infrared colour diagrams to classify young stellar objects' disc evolution, revealing that inside-out dispersal is the dominant and rapid mode of circumstellar disc clearing across various stellar types.

Contribution

The paper introduces new infrared diagnostic diagrams for classifying disc evolution stages and provides statistical evidence that inside-out dispersal is the prevalent and fast dispersal mechanism.

Findings

Approximately 39% of YSOs have primordial discs.

Around 31-32% disperse via inside-out clearing.

Less than 2% are in the homogeneous draining regime.

Abstract

The time-scale over which and the modality by which young stellar objects (YSOs) disperse their circumstellar discs dramatically influences the eventual formation and evolution of planetary systems. By means of extensive radiative transfer (RT) modelling, we have developed a new set of diagnostic diagrams in the infrared colour-colour plane (K-[24] vs. K-[8]), to aid with the classification of the evolutionary stage of YSOs from photometric observations. Our diagrams allow the differentiation of sources with unevolved (primordial) discs from those evolving according to different clearing scenarios (e.g. homologous depletion vs. inside-out dispersal), as well as from sources that have already lost their disc. Classification of over 1500 sources in 15 nearby star-forming regions reveals that approximately 39 % of the sources lie in the primordial disc region, whereas between 31 % and 32 % disperse from the inside-out and up to 22 % of the sources have already lost their disc. Less than 2 % of the objects in our sample lie in the homogeneous draining regime. Time-scales for the transition phase are estimated to be typically a few 10^5 years independent of stellar mass. Therefore, regardless of spectral type, we conclude that currently available infrared photometric surveys point to fast (of order 10 % of the global disc lifetime) inside-out clearing as the preferred mode of disc dispersal.