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

TL;DR

This study searches for debris discs around M-dwarfs in nearby young moving groups using WISE infrared data, finding a bimodal distribution of disc types and evidence of disc evolution within the first 30 million years.

Contribution

First systematic WISE-based survey of debris discs around M-dwarfs in young moving groups, revealing bimodal disc populations and their evolution over time.

Findings

19 out of 100 M-dwarfs show IR excess indicative of discs.

Debris disc frequency decreases from 13% to less than 7% after 30 Myr.

Detected discs are predominantly in stars younger than 30 Myr.

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$\mu$m. Our search is likely to be complete for discs where the ratio of flux from the disc to flux from the star $f_{\rm d}/f_{*} > 10^{-3}$. The spectral energy distributions are supplemented with 2MASS photometry and data at longer wavelengths and fitted with simple disc models to characterise the IR excesses. There is a bimodal distribution -- twelve targets have $W1-W4 > 3$, corresponding to $f_{\rm d}/f_{*} > 0.02$ and are likely to be gas-rich, primordial discs. The remaining seven targets have $W1-W4 < 1$ ($f_{\rm d}/f_{*} \lesssim 10^{-3}$) 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 to 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 timescale and does not support models where the maximum of debris disc emission occurs much later in lower-mass stars.