N/C vs. N/O abundances (in numbers) in the open cluster NGC 6611 from observations by Hunter et al. (2009). The blue shaded area shows the domain predicted for the Geneva stellar models, between 5 and 60 M_⊙ with solar composition (as given in Fig. 1). The error bars on the observed N/C ratios are indicated. The error bars on the N/O ratios are of the same order of magnitude. The numbers attached to the data points correspond to the identifiers employed within the FLAMES Survey. Normal stars are marked by a filled symbol, binaries (or binaries candidates) or Be stars by an open symbol.