EDP Sciences
Free access
Issue
A&A
Volume 395, Number 2, November IV 2002
Page(s) 499 - 513
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20021230


A&A 395, 499-513 (2002)
DOI: 10.1051/0004-6361:20021230

An $\vec{XMM}$- $\vec{Newton}$ observation of the Lagoon Nebula and the very young open cluster NGC 6530

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, Université de Liège, Allée du 6 Août, Bât. B5c, 4000 Liège (Sart Tilman), Belgium
2  School of Physics & Astronomy, University of Birmingham, Edgbaston Birmingham B15 2TT, UK
3  Royal Observatory of Belgium, Avenue Circulaire 3, 1180 Brussels, Belgium
4  USRA/HEASARC Goddard Space Flight Center, Greenbelt, MD 20771, USA
5  Department of Physics & Astronomy, University of Leeds, Leeds LS2 9JT, UK

(Received 5 June 2002 / Accepted 26 August 2002)

Abstract
We report the results of an XMM-Newton observation of the Lagoon Nebula (M 8). Our EPIC images of this region reveal a cluster of point sources, most of which have optical counterparts inside the very young open cluster NGC 6530. 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 M 8 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 $kT \sim$ a few keV. Only a few of the X-ray selected PMS candidates are known to display H $\alpha$ emission and were previously classified as classical T Tauri stars. This suggests that most of the X-ray emitting PMS stars in NGC 6530 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 HD 164816 is found to be typical for an O9.5 III-IV star. At least one of the known Herbig Be stars in NGC 6530 (LkH $\alpha$ 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: M 8 -- open clusters and associations: individual: NGC 6530 -- stars: early-type -- stars: pre-main sequence -- X-rays: stars

Offprint request: G. Rauw, rauw@astro.ulg.ac.be

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