Massive Stellar Content of Giant HII Regions in M 33 and M 101

Far-ultraviolet (900-1200A) spectral synthesis of nine giant extragalactic HII regions in M 33 and M 101 is performed to study their massive stellar content. Several parameters are quantified, predicted, and compared to the literature: age, stellar mass, IMF slope, number of O-type and Wolf-Rayet stars, Halpha and 5500A continuum fluxes. The results of this particular technique are consistent with other methods and observations. This work shows that a total stellar mass of a few 10^3 Msun is needed to populate the IMF bins well enough at high masses to obtain accurate results from the spectral synthesis technique in the far-ultraviolet. A flat IMF slope seems to characterize better the stellar line profiles of these objects, which is likely the first sign of a small number statistic effect on the IMF. Finally, the HII region NGC 5461 is identified as a good candidate for hosting a second generation of stars, not yet seen at far-ultraviolet wavelengths.