An XMM-Newton view of the M 17 nebula

We present the analysis of an XMM-Newton observation of the M 17 nebula. The X-ray point source population consists of massive O-type stars and a population of probable low-mass pre-main sequence stars. CEN 1a,b and OI 352, the X-ray brightest O-type stars in M 17, display hard spectra (kT of 3.8 and 2.6 keV) consistent with a colliding wind origin in binary/multiple systems. We show that the strong interstellar reddening towards the O-type stars of M 17 yields huge uncertainties on their L[SUB]X[/SUB]/L[SUB]bol[/SUB] values. The low-mass pre-main sequence stars exhibit hard spectra resulting from a combination of high plasma temperatures and very large interstellar absorption. We find evidence for considerable long term (months to years) variability of these sources. M 17 is one of the few star formation complexes in our Galaxy producing diffuse X-ray emission. We analyze the spectrum of this emission and compare it with previous studies. Finally, we discuss the Optical Monitor UV data obtained simultaneously with the X-ray images. We find very little correspondence between the UV and X-ray sources, indicating that the majority of the UV sources are foreground stars, whilst the bulk of the X-ray sources are deeply embedded in the M 17 complex.