Pre-main sequence candidates in the very young open cluster NGC 6611 D. de Winter, C. Koulis, P. S. Thé, M. E. van den Ancker, M. R. Pérez and E. A. Bibo Astron. Astrophys. Suppl. Ser., 121 2 (1997) 223-242 Published online: 15 February 1997 DOI: 10.1051/aas:1997284