Long-lived disc accretion in the η Chamaeleontis pre-main sequence star cluster

Abstract

High-resolution spectroscopic study of late-type members of the ≈9-L39-old η Chamaeleontis star cluster shows that four stars, RECX 5, 9, 11 and ECHA J0843.3–7905, have broad Hα profiles indicative of ballistic accretion of material from circumstellar discs first identified by virtue of their infrared (IR) excess emission. Quantitative analysis of the profiles finds accretion in η Cha stars at rates comparable to that derived by Muzerolle et al. for members of the similarly aged TW Hydrae Association (TWA); rates 1–3 orders of magnitude lower than in younger classical T Tauri (CTT) stars. Together these studies indicate that the fraction of long-lived inner discs can be significantly higher than that inferred from study of younger pre-main sequence (PMS) populations, which suggest a disc lifetime of <6 Myr. The detection of long-lived discs may have implications for the formation of planetary systems. If slow accretion processes are the dominant formation mechanism for Jovian planets then long-lived discs may be ideal sites to search for evidence for protoplanets.