The Stellar Content of the Young Cluster in M 17

We present preliminary results of a multicolour BVRI and JHK imaging study of the young cluster in M 17. Colour--colour-diagrams of the form V - λ vs. B - V corroborate previous results about an abnormal extinction law in that region. We find a ratio of total--to--selective extinction R ˜ 4.4 . The reddening of the cluster consists of a normal uniform foreground contribution with AV ˜ 1.8 mag and an abnormal portion inside the HII region with AV-values up to 30 mag. A re-investigation of the cluster distance by means of ZAMS fitting in the B,V colour--magnitude diagram yields D = 2.5 ± 0.3 kpc. To a limiting magnitude of K = 16.5 the spectral types extend from O4 to K5. The IMF for more than 2200 cluster members within an area of 5' × 5' has a slope of -1.5, while for the central portion of the cluster -- including about 750 stars within 2' × 2' -- the IMF becomes flatter. There is evidence for mass separation in the sense that a pronounced concentration of several hundred O, B and A stars is present around the major ionizing multiple O star system CEN 1, while outside this region massive stars are less frequent but the density of low mass stars becomes higher. The overall stellar density towards the molecular cloud M 17 SW supports the scenario of sequential star formation. As witnessed by their excess emission, cocoons and/or disks seem to be present around stars of all spectral types. From the (V-K)/(B-V) diagram which includes mainly early type stars we find an overall disk frequency of 17% that increases from 5% for O stars to 50% around G stars.