UV-Observations of Young Populous Clusters in the Large Magellanic Cloud

Extract

The young populous star clusters give evidence for the ‘explosive’ star formation in the Magellanic Clouds which took place in the time interval 5·10⁶ yrs to < 10⁸ yrs agoe. They are also key objects for the understanding of the formation of massive stellar clusters, because they are still situated close to their ‘birthplace’ in the parent galaxy and are dynamically not relaxed (Geyer et al. 1979). Their HRD-morphology shows most of the member stars in the upper Main Sequence range with only a few massive yellow and red supergiants. The lower massive stars are still in the pre-main-sequence evolution phase (‘T-Tauri state’), which cannot be observed at the MC's distances. Thus in the uv-spectral range the blue stars with (B-V) < 0.1 on the upper MS contribute to the uv-fluxes. In the optical spectral regions the bright ‘blue’ globular clusters seem not be embedded in remanent interstellar matter, though neighbouring loose stellar aggregates of similar age are in many cases surrounded by dense HII-regions. This rises the questions wether the starformation process in such massive clusters was so efficient that no remanent matter was left over, or was this material blown away by the uv-radiation of the numerous OB-member stars?