open clusters and associations: individual: HM1; open clusters and associations: individual: IC 2944; stars: early-type; open clusters and associations: individual: IC 2948; X-rays: stars
Abstract :
[en] 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[SUB]X[/SUB]/L[SUB]BOL[/SUB]] 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. Tables 2, 5, and Figs. 5, 9 are available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A>Based on observations collected with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).Tables 1, 3 and 4 are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A83">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A83</A>