The stellar population and the evolutionary state of HII regions and starburst galaxies

RI-Ills and starbursts are both powered by massive stars. They are the main contributors to the heating of the ISM via radiative and mechanical energy. Techniques to derive the stellar content and the evolutionary state of RH its and starbursts from their ultraviolet and optical integrated light are reviewed. A prototypical RH II (NGC 604) and nuclear starburst (NGC 7714) are discussed in more detail. The results reveal the necessity of multiwavelength analyses of these objects to estimate their stellar content and their evolutionary state in a consistent way. (C) 2000 Elsevier Science B.V. All rights reserved.