... Synthetic spectra of H Balmer and HeI absorption lines . ... The models, which are optimized for galaxies with active star formation, synthesize the profiles of the hydrogen Balmer series (H b , H g , H d , H 8 , H 9 , H 10 , H 11 , H 12 and H 13 ) and the neutral helium absorption lines (HeI 4922, HeI 4471, HeI 4388, HeI 4144, HeI 4121, HeI 4026, HeI 4009 and HeI 3819) for a burst with an age ranging from 1 Myr to 10 Gyr, and different assumptions about the stellar initial mass function (IMF). ...