The transition disc frequency in M stars

TL;DR

This study re-evaluates the frequency of transition discs in M stars, suggesting previous high estimates were due to misclassification, and proposes more accurate identification criteria based on spectral energy distribution analysis.

Contribution

It provides a revised estimate of transition disc fraction in M stars and clarifies the criteria for identifying transition discs using spectral energy distributions.

Findings

Transition disc fraction in M stars is about 15% rather than 50%.

Misclassification occurs when discs without inner holes are mistaken for transition discs.

Transition discs in M stars are best identified with emission close to photospheric levels beyond 10um.

Abstract

We re-examine the recent suggestion of a high fraction of transition discs (i.e. those with a cleared inner hole) in M stars, motivated by the fact that we expect that, for M stars, even discs without inner holes should exhibit very weak excess shortward of around 10um. Our analysis of spectral energy distribution models suggest that this indeed means that M stars where a detectable excess begins at around 6um may be mis-classified as transition discs when in fact they have optically thick dust extending in to the dust sublimation radius. Consequently, we estimate that the transition disc fraction among M stars in the Coronet cluster is ~15 +/-10 % (rather than the recently claimed value of 50%). This revised figure would imply that the transition disc fraction is not after all markedly higher in later type stars. We suggest that for M stars, transition discs can only be readily identified if they have emission that is close to photospheric out to > 10um.