1. Appenzeller, I., Fricke, K.J.: 1972, Astron. Astrophys.
18, 10
2. Arnett, W.D.: 1978, Astrophys. J.
219, 1008
3. Arnett, W.D.: 1990, in Chemical and dynamical evolution of galaxies, ed. F. Ferrini et al., (Giardini:Pisa), in press
4. Barbuy, B., Grenon, M.: 1990, in Bulges of Galaxies, ESO/CTIO workshop, in press
5. Bertola, F.: 1964, Ann. Astrophys.
27, 319