Solar prominences with Na and Mg emissions and centrally reversed Balmer line

We study spectral lines in exceptionally bright solar limb prominences with pronounced sodium and magnesium emission. We find that most prominences with significant NaD2 and Mgb2 emission show centrally reversed profiles of H-alpha and occasionally even of H-beta, which are are well reproduced by semi-infinite models. The maximum H-alpha source function corresponds to an excitation temperature of 3950 K, for pronounced central reversions 4000 K; the related optical thickness exceeds 10.0. The narrow widths of the NaD2 and Mgb2 profiles yield a non-thermal broadening of 5 km/s.