X-ray properties of the young open clusters HM1 and IC 2944/2948^{⋆,⋆⋆,⋆⋆⋆}

¹ GAPHE, Département AGO, Université de Liège, Allée du 6 Août 17, Bat. B5C, 4000 Liège, Belgium
e-mail: naze@astro.ulg.ac.be
² Astronomical Institute Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH Amsterdam, The Netherlands
³ CRESST/NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771; Univ. Space Res. Ass., Columbia, MD, USA

Received: 14 January 2013
Accepted: 15 May 2013

Abstract

Using XMM-Newton data, we study for the first time the X-ray emission of HM1 and IC  2944/2948. Low-mass, pre-main-sequence objects with an age of a few Myr are detected, as well as a few background or foreground objects. Most massive stars in both clusters display the usual high-energy properties of that type of objects, though with log     [L_X/L_BOL]  apparently lower in HM1 than in IC 2944/2948. Compared with studies of other clusters, it seems that a low signal-to-noise ratio at soft energies, due to the high extinction, may be the main cause of this difference. In HM1, the two Wolf-Rayet stars show contrasting behaviors: WR89 is extremely bright, but much softer than WR87. It remains to be seen whether wind-wind collisions or magnetically confined winds can explain these emissions. In IC 2944/2948, the X-ray sources concentrate around HD 101205; a group of massive stars to the north of this object is isolated, suggesting that there exist two subclusters in the field-of-view.