Two populations of transition discs?

TL;DR

This study analyzes the distribution of transition discs based on mm flux, revealing that mm bright transition discs may have a distinct physical origin characterized by higher accretion rates and larger inner holes, differing from faint mm transition discs.

Contribution

It identifies a potential separate physical origin for mm bright transition discs, based on their distinct properties compared to faint mm transition discs.

Findings

Transition discs generally have lower mm fluxes than primordial discs.

Mm bright transition discs have higher accretion rates and larger inner holes.

Mm bright transition discs are associated with earlier spectral types.

Abstract

We examine the distribution of transition discs as a function of mm flux. We confirm that as expected in any model in which most primordial discs turn into transition discs and in which mm flux declines with time, transition discs have lower mm fluxes on average than primordial discs. However, we find that the incidence of transition discs does not, as expected, fall monotonically towards large mm fluxes and we investigate the hypothesis that these mm bright transition discs may have a distinct physical origin. We find that mm bright transition discs occupy a separate region of parameter space. Transition discs in the bright mm sub-sample have systematically higher accretion rates and inner hole radii than those in the faint mm sub-sample, along with being systematically weighted to earlier spectral types.