Stellar population models to predict the H Balmer and HeI lines in absorption are presented. Models are computed for burst and continuous star formation. It is found that the Balmer and HeI line profiles are sensitive to the age, except during the first 4 Myr of the evolution, when the equivalent widths of these lines are constant. The comparison of these lines with the corresponding nebular emission lines indicates that Hd and the higher-order terms of the Balmer series and HeI (3819, 4026, 4388 and 4922) in absorption are very good age-indicators of starbursts. Models are applied to date the super-star cluster B in NGC 1569.

Contribution to the workshop "Spectrophotometric Dating of Stars and Galaxies" Annapolis Maryland, 25-29 April 1999