Far-infrared signatures and inner hole sizes of protoplanetary discs undergoing inside-out dust dispersal

TL;DR

This study uses radiative transfer simulations to analyze how the far-infrared colors of protoplanetary discs change during inside-out dust dispersal, explaining recent observations and proposing diagnostic methods for identifying transition discs.

Contribution

The paper demonstrates that far-infrared brightening is a natural outcome of inner disc removal and suggests that the 70μm band is a powerful diagnostic for transition discs with large inner holes.

Findings

Far-infrared brightening correlates with inner disc dispersal.

70μm band effectively identifies transition discs with large inner holes.

Photometry comparisons can estimate inner hole sizes under certain conditions.

Abstract

By means of radiative transfer simulation we study the evolution of the far-infrared colours of protoplanetary discs undergoing inside-out dispersal, often referred to as transition discs. We show that a brightening of the mid and far-infrared emission from these objects is a natural consequence of the removal of the inner disc. Our results can fully explain recent observations of transition discs in the Chamaleon and Lupus star forming regions from the Herschel Gould Belt Survey, which show a higher median for the 70?um (Herschel PACS 1) band of known transition objects compared with primordial discs. Our theoretical results hence support the suggestion that the 70?um band may be a powerful diagnostic for the identification of transition discs from photometry data, provided that the inner hole is larger than tens of AU, depending on spectral type. Furthermore we show that a comparison of photometry in the K , 12?um and 7u0?m bands to model tracks can provide a rough, but quick estimate of the inner hole size of these objects, provided their inclination is below ?85 degrees and the inner hole size is again larger than tens of AU.