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Astronomy & Astrophysics

An XMM-Newton observation of the Lagoon Nebula
and the very young open cluster NGC6530+

G. Rauw1,*, Y. Nazé1,**, E. Gosset1,*, I.R. Stevens2, R. Blomme3, M.F. Corcoran4, J.M. Pittard5 and M.C. Runacres3

1 Institut d'Astrophysique et de Géophysique - Université de Liège, Allée du 6 Août, Bât B5c, B-4000 Liège (Sart Tilman), Belgium
2 School of Physics & Astronomy, University of Birmingham, Edgbaston Birmingham B15 2TT, United Kingdom
3 Royal Observatory of Belgium, Avenue Circulaire 3, B-1180 Brussels, Belgium
3 Emergent Technology Services, Space Sciences Sector, 1801 McCormick Drive, Suite 170, Largo, MD 20774, USA
4 USRA/HEASARC Goddard Space Flight Center, Greenbelt, MD 20771, USA
5 Department of Physics & Astronomy, University of Leeds, Leeds LS2 9JT, United Kingdom

* Research Associate FNRS, Belgium
** Research Fellow FNRS, Belgium

+ Based on observations with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member states and the USA (NASA).


     We report the results of an XMM-Newton observation of the Lagoon Nebula (M8). Our EPIC images of this region reveal a cluster of point sources, most of which have optical counterparts inside the very young open cluster NGC6530. The bulk of these X-ray sources are probably associated with low and intermediate mass pre-main sequence stars. One of the sources experienced a flare-like increase of its X-ray flux making it the second brightest source in M8 after the O4 star 9 Sgr. The X-ray spectra of most of the brightest sources can be fitted with thermal plasma models with temperatures of kT ~ a few keV. Only a few of the X-ray selected PMS candidates are known to display H emission and were previously classified as classical T Tauri stars. This suggests that most of the X-ray emitting PMS stars in NGC6530 are weak-line T Tauri stars. In addition to 9 Sgr, our EPIC field of view contains also a few early-type stars. The X-ray emission from HD164816 is found to be typical for an O9.5 III-IV star. At least one of the known Herbig Be stars in NGC6530 (LkH 115) exhibits a relatively strong X-ray emission, while most of the main sequence stars of spectral type B1 and later are not detected. We also detect (probably) diffuse X-ray emission from the Hourglass Region that might reveal a hot bubble blown by the stellar wind of Herschel 36, the ionizing star of the Hourglass Region.

Key Words
ISM: individual objects: M8 -- open clusters and associations: individual: NGC6530 -- Stars: early-type -- Stars: pre-main sequence -- X-rays: stars

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