Keywords: Observational astronomy - Ultraviolet surveys - Young star clusters

1. INTRODUCTION

2. SAMPLE DESCRIPTION & SELECTION

3. COS DATA REDUCTION

3.1. Grating setup and observing strategy

3.2. Extraction, spectral calibration, final combined spectra

3.3. Effective spectral resolution

3.4. Fit of the Lyα absorption wings

5. SPECTRAL ANALYSIS

5.1. Single and double stellar population

5.2. Multiple populations

6. RESULTS

7. DISCUSSION

8. CONCLUSIONS