EPoS Contribution
EPoS Contribution
M17 - a test bed for the formation of high-mass stars

Rolf Chini
Astronomisches Institut Bochum, Bochum, Germany
The stellar cluster in M17 has been investigated with unprecedented sensitivity, leading to the detection of more than 40 new exciting stars and several hundred PMS stars seen for the first time; multiplicity for the most massive (O4-O8) stars could be established. There is a bimodal population of stars suggesting at least two episodes of star formation: From both the age and the spatial distribution, the younger group (< 300.000 yrs) seems to be the second generation of stars triggered by the slightly older group. The IMF of this extremely young aggregate is presented. Direct imaging of O and early B stars reveals circumstellar disks and jets associated with types as early as O6. The total IR excess frequency is at least 74%, increasing with decreasing stellar mass. The high excess rate of 62% for stars earlier A4 suggests that the accretion scenario works also in the high-mass regime. Nevertheless, there is evidence for a merger event that has led to the formation of an O-type star. Future observations to clarify the formation of high-mass stars are suggested.