EXPANDING RINGS IN THE WR-NEBULA NGC-2359

Halpha line profiles at both high spectral and angular resolutions wer e obtained at three 2.'6 slit length positions over central and northe rn regions of the NGC 2359 system of nebulae around the WR star HD 569 25. The main outer ring (4.'2 in diameter) expands radially at a veloc ity approximately 26 km s-1. We show that this system results from the effects of the stellar wind and radiation field from a star with an i nitial main sequence mass of about 25 M. as it evolves to its present WR phase. The present dynamics can be reconciled with this evolution o nly if the stellar wind bubbles blown in the fast wind stages are mome ntum rather than energy driven. This implies very clumpy circumstellar material where enhanced radiative losses at interfaces between clumps and shocked stellar winds radiate away most of the wind kinetic energ y. A high velocity component observed at one point may result from loc al dynamical effects associated with enhanced cooling.