The low-mass diskless population of Corona Australis

TL;DR

This study identifies new low-mass, diskless and transitional disk candidates in Corona Australis, revealing a high ratio of transitional to primordial disks among very low-mass objects, and suggesting faster disk evolution in such stars.

Contribution

It reports the discovery of the lowest-mass objects with transitional disks and analyzes disk fractions and evolution in the Corona Australis region.

Findings

Five new low-mass candidate members identified.

Approximately 50% of the population has disks, with a high ratio of transitional disks.

Disk evolution appears faster in very low-mass objects compared to solar-type stars.

Abstract

We combine published optical and near-infrared photometry to identify new low-mass candidate members in an area of about 0.64 deg^2 in Corona Australis, using the S-parameter method. Five new candidate members of the region are selected, with estimated ages between 3 and 15 Myr, and masses between 0.05 and 0.15 M_Sun. Using Spitzer photometry, we confirm that these objects are not surrounded by optically thick disks. However, one of them is found to display excess at 24 micron, thus suggesting it harbours a disk with an inner hole. With an estimated mass of 0.07 M_Sun according to the SED fitting, this is one of the lowest-mass objects reported to possess a transitional disk. Including these new members, the fraction of disks is about 50% among the total Corona Australis population selected by the same criteria, lower than the 70% fraction reported earlier for this region. Even so, we find a ratio of transitional to primordial disks (45%) very similar to the value derived by other authors. This ratio is higher than for solar-type stars (5-10%), suggesting that disk evolution is faster in the latter, and/or that the "transitional disk" stage is not such a short-lived step in the case of very low-mass objects. However, this impression needs to be confirmed with better statistics.