Circumstellar discs around solar-mass stars in NGC 6611

Abstract

We have performed IZJHKL' observations in NGC 6611, the young cluster that ionises the Eagle Nebula. We have discovered a rich pre-main sequence concentrated around the O-stars in the cluster. As measured by their L'-band excesses, at least 58% +/- 5% of the pre-main sequence objects (0.45 Msun < M < 2 Msun) have circumstellar discs. By comparing this disc frequency with frequencies determined for regions where the pre-main sequence stars are subject to less ionising radiation, we find no evidence that the harsher environment of NGC 6611 (approximately an order of magnitude more ionising Lyman continuum radiation than the Trapezium cluster) significantly hastens the dissipation of circumstellar discs around solar-mass stars.