On the lifetime of discs around late-type stars

Abstract

We address the question of whether protoplanetary discs around low mass stars (e.g. M-dwarfs) may be longer lived than their solar-type counterparts. This question is particularly relevant to assess the planet-making potential of these lower mass discs. Given the uncertainties inherent to age-dating young stars, we propose an alternative approach that is to analyse the spatial distribution of disc-bearing low-mass stars and compare it to that of disc-bearing solar-type stars in the same cluster. A significant age difference between the two populations should be reflected in their average nearest neighbour distance (normalised to the number of sources), where the older population should appear more spread out. To this aim, we perform a Minimum Spanning Tree (MST) analysis on the spatial distribution of disc-bearing young stellar objects (YSOs) in six nearby low mass star forming regions. We find no evidence for significant age differences between the disc-bearing low-mass (later than M2) and 'solar-type' (earlier than M2) stars in these regions. We model our results by constructing and analysing synthetic fractal distributions that we evolve for typical values of the velocity dispersions. A comparison of simple models to our MST analysis suggests that the lifetime of discs around M-stars is similar to that of discs around solar-type stars. Furthermore, a model-independent spatial analysis of the observations robustly shows that any age differences between the two samples must be smaller than the average age difference between disc-bearing classical T-Tauri stars and disc-less Weak-Lined T-Tauri stars.