A WISE-based search for debris discs amongst M-dwarfs in nearby, young, moving groups

Abstract

We present a search for debris discs amongst M-dwarf members of nearby, young (5–150 Myr) moving groups (MGs) using infrared (IR) photometry, primarily from the Wide Infrared Survey Explorer (WISE). A catalogue of 100 MG M dwarfs that have suitable WISE data is compiled, and 19 of these are found to have significant IR excess emission at 22 µm. Our search is likely to be complete for discs where the ratio of flux from the disc to flux from the star fd/f* > 10-3. The spectral energy distributions are supplemented with Two-Micron All-Sky Survey (2MASS) photometry and data at longer wavelengths, and fitted with simple disc models to characterize the IR excesses. There is a bimodal distribution – 12 targets have W1 - W4 > 3, corresponding to fd/f* > 0.02, and are likely to be gas-rich, primordial discs. The remaining seven targets have W1 - W4 < 1 (fd/f* ? 10-3) and include three objects with previously known or suspected debris discs and four new debris disc candidates that are all members of the Beta Pic MG. All of the IR excesses are identified in stars that are likely members of MGs with age <30 Myr. The detected debris disc frequency falls from 13 ± 5 per cent to <7 per cent (at 95 per cent confidence) for objects younger or older than 30 Myr, respectively. This provides evidence for the evolution of debris discs on this time-scale and does not support models where the maximum of debris disc emission occurs much later in lower mass stars.