Optical observations of five X-ray selected BL Lacertae objects M. Villata, C. M. Raiteri, M. D. Popescu, G. Sobrito, G. De Francesco, L. Lanteri and L. Ostorero Astron. Astrophys. Suppl. Ser., 144 3 (2000) 481-485 Published online: 15 June 2000 DOI: 10.1051/aas:2000222