X-ray emission of extreme He stars

Radiationdriven winds are a common feature of hot stars, not only for massivestars but also for lowmass stars, which display weak winds. Massive stars arewell known Xray sources, in which the observed Xray emission is attributed toturbulence and shocks in the strong winds. Although the winds of lowmass starsare significantly weaker, turbulence and shocks could be present also in thiscase and produce Xray emission. Recently this was confirmed for two lowmassextreme He stars, BD+37 442 and BD+37 1977: in both cases the spectralproperties are similar to those observed in massive stars. Now we propose toobserve with XMM also other extreme He stars, which, although are characterizedby rather different physical properties, have radiationdriven winds comparable to that of the previous sdO stars. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]