Pre-main-sequence stars older than 8 Myr in the Eagle nebula

Attention is given to a population of 110 stars in the NGC 6611 cluster of the Eagle nebula that have prominent near-infrared excess and optical colours typical of pre-main-sequence (PMS) stars older than 8Myr. At least half of those for which spectroscopy exists have a Ha emission line profile revealing active accretion. In principle, the V - I colours of all these stars would be consistent with those of young PMS objects (<1Myr) whose radiation is heavily obscured by a circumstellar disc seen at high inclination and in small part scattered towards the observer by the back side of the disc. However, using theoretical models it is shown here that objects of this type can only account for a fewper cent of this population. In fact, the spatial distribution of these objects, their X-ray luminosities, their optical brightness, their positions in the colour- magnitude diagram and the weak Li absorption lines of the stars studied spectroscopically suggest that most of them are at least eight...