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 in assessing 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 (normalized 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 results obtained using simple models to the results from 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 discless weak‐lined T Tauri stars.

The dispersal of protoplanetary discs

“…We plot in Figure 2, the time-scale ratio between K and M-stars and show that this ratio is consistent with unity. This suggests that there is no significant dependence of the time-scale on stellar mass, as has already been pointed out by [21], who performed a spatial analysis of the distribution of K and M-stars with discs in young star-forming regions and found no significant difference in the distributions.…”

On the theory of disc photoevaporation

“…Calvet et al 2005; Najita, Strom & Muzerolle 2007; Hughes et al 2009) while others do not (Cieza et al 2010; Merín et al 2010); there is also evidence in some systems that the deficit in opacity at NIR wavelengths does not necessarily preclude significant quantities of gas and small amounts of dust in the inner disc (Espaillat et al 2010) although this is not always the case (Calvet et al 2002). The frequency of these ‘transition/pre‐transition’ discs compared to those of primordial discs suggests that approximately 10–20 per cent of discs are in this stage (Strom et al 1989; Skrutskie et al 1990; Luhman et al 2010; Ercolano et al 2011a; Furlan et al 2011). Assuming that these objects are in transition from a primordial to a fully cleared state, this observation provides two important constraints: the transition time from primordial to cleared is approximately 10 per cent of the discs total lifetime, and that the clearing process proceeds from the inside out.…”

An ALMA survey for disks orbiting low-mass stars in the TW Hya Association

“…This high-energy radiation can drive disk dissipation via photoevaporation (e.g., Gorti & Hollenbach 2009). Nevertheless, the limited studies that have been performed to explore the disk lifetimes of substellar objects have found disk dissipation timescales are at least as long as for solar-mass stars (see, e.g., Luhman & Mamajek 2012;Ercolano et al 2011;Williams & Cieza 2011, and references therein). Investigations aimed at establishing the masses of gas and dust around similarly young M stars are key to advancing our understanding of disk evolution timescales and processes.…”