THEORETICAL MODELING OF GHRS OBSERVATIONS OF THE OF WN-TYPE STAR-R136A5/

We present a theoretical analysis of the HST GHRS spectrum of R136a5, an O3f/WN star in the R136a cluster in 30 Doradus. Using non-LTE exten ded and expanding model atmospheres, we find a surprisingly high mass- loss rate M = 1.8 +/- 0.5 x 10(-5) M. yr-1 and an effective temperatur e T(eff) = 42.5 +/- 2.5 kK. With the observed visual magnitude, this i mplies a radius R 17 +/- 2 R. and a luminosity L = 8.5 +/- 1 x 10(5) L.. We discuss possible sources of the uncertainties in the derived st ellar parameters and conclude that the effective temperature may be un derestimated; however, if so, the value of the mass-loss rate would no t be affected.