  High resolution X-ray spectra of very young massive stars opened a new
chapter in the diagnostics and understanding of the properties of stellar wind
plasmas. Observations of several very young early type stars in the Orion
Trapezium demonstrated that the conventional model of shock heated plasmas in
stellar winds is not sufficient to explain the observed X-ray spectra. Detailed
X-ray line diagnostics revealed extreme temperatures in some of the candidates
as well as evidence for high plasma densities. It is also evident from high
resolution spectra of more conventional early type stars, that not all show
such extreme characteristics. However, the fact that some of the stars show hot
and dense components and some do not requires more understanding of the
physical processes involved in stellar wind emissions. The Orion Trapezium
stars distinguish themselves from all the others by their extreme youth. By
comparing the diverse spectral properties of theta Ori A and theta Ori E with
those of theta Ori C, we further demonstrate that X-ray spectral properties of
very young massive stars are far from understood.

Astrophysics