X-RAY-EMISSION FROM WIND BLOWN INTERSTELLAR BUBBLES .1. ROSAT OBSERVATIONS OF NGC-6888

The interaction of fast stellar winds with the surrounding interstellar medium produces large amounts of hot X-ray emitting gas. Scarce previous observations indicated substantial differences between simple one-dimensional models and the data. We have obtained ROSAT images of several wind blown interstellar bubbles. In this first paper we present an X-ray map of the prototype ring nebula NGC 6888. Although we confirm previous total flux determinations and the possibility to reconcile these values with theory by introducing ionization non - equilibrium, our map demonstrates that the assumed geometry (a thick shell) is far from reality. The X-ray emission is outlined by the brightest optical parts of the nebula and is concentrated in a few filament type structures which cannot fill much more than about 1 % of the volume of the bubble. The scale lengths of these structures is from 1.5 pc down to our resolution limit less than or similar 0.5 pc. A solution of these discrepancies is not yet at hand. A few point sources in the image including the central Wolf-Rayet star HD 192163 are briefly discussed.