Winds and Dust Formation by Wolf-Rayet Stars

scientific abstract observations of population i wolfrayet stars with the isosws in the grating mode are proposed in order to determine wind chemical abundances, wind velocities, freefree radiation by winds, mass loss rates, and, of late wc types, continuous and episodic dust formation rates and dust abundances. the selected priority1 targets are the irbrightest dustfree objects among the known galactic wr stars, justifying maximum use of the sws gratingmode capacities. this proposal has been coordinated with lws and phot. abundances: current wr star abundance ratio determinations, based on model atmospheres and mainly for he, n and c, are severely model dependent. determinations of the abundances of nucleosynthesis products o, ne, mg, s and ar, which have forbidden transitions in the sws wavelength range, will provide a direct test of evolutionary studies and of interior model abundance predictions by, e.g., maeder and by langer. presently the (groundbased and iras) observed ne abundance in the wc star gamma velorum (wr11) is in conflict with interior models. isosws observations of wr stars will be crucial to solve this problem. winds and mass loss: different observational methods yield different terminal wind velocity values per star, due to the stratification of these velocities. measurements in the constant velocity regime are essential. ir forbidden lines, formed in the constant wind velocity regime, have to date been measured for one wr star only: wr11. sws will change that. mass loss rates: current mass loss rate determinations for wr stars, based on groundbased ir and radio freefree radiation measurents (for density) and uv pcygni profiles (for velocity), range from 5x10^6 to 10^4 m_sun/yr, with accuracies of at best a factor of 2. yet, even the lower estimates of wr mass loss rates indicate a wind momentum problem: the average wr star radiation field is not strong enough to drive the observed truncated!, P [truncated!, Please see actual data for full text]