[Na/Fe] as a function of [O/Fe]. The bottom panels display all stars in the Na-O plane by using LTE (left) and NLTE Na abundances (right). The top left-hand panel contains only s-poor stars and the top right-hand panel contains only s-rich stars. The dashed lines in the top panels represent a free-hand representation of the mean Na-O trend of only the s-poor stars. Symbols are as in Fig. 6.