Visual amplitude of the observed ACEPs as a function of the [Na/Fe] abundance. The solid line shows a linear regression to the data that does not include the three stars with low values of the [Si/Fe], [Ti/Fe] and [Sc/Fe] abundances (green symbols, see labels). In the labels, TW and Lit. indicate the nine stars that were studied spectroscopically in this paper and the three with spectroscopy from the literature, respectively.