1. Spada G., “Proc.of Workshop on Now-thermal and very High Temperature Phenomena in X-Ray Astronomy”, eds.G.C. Perola, M. Salvati - Roma 19–20 December 1983, (1983)
2. Perola G.C. i.b.d.
3. Butler R.C. and Scarsi L., Proc.of IAU Symp. 123, G.S.F.C. 1990. To be published
4. Citterio O. et al. Applied Optics 27, 1470, (1988)
5. Citterio O. et al. Proc.of SPIE, 1343 (1990)