An - observation of the Lagoon Nebula and the very young open cluster NGC 6530^*

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

Corresponding author: G. Rauw, rauw@astro.ulg.ac.be

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 a few keV. Only a few of the X-ray selected PMS candidates are known to display Hα 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 (LkHα 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.