Trend of the α elements vs. [Fe/H] for the FLAMES targets (blue circles), compared with literature samples from Monaco et al. (2005), Sbordone et al. (2007), Mucciarelli et al. (2017), and Sestito et al. (2024a). For all the samples, Mg and Ca abundances, propagating their corresponding uncertainties, were averaged and then fitted with two linear functions connected by a smoothing function. The gray shading represents the fit uncertainties, which are also displayed as residuals in the bottom plot. As explained in the text, the data from Sestito et al. (2024a) were excluded from the fitting procedure. The dashed gray line marks our results for the knee position at [Fe/H] = − 1.05, while the dotted black line at [Fe/H] = − 1.3 represents an approximation of the results from Carretta et al. (2010) and de Boer et al. (2014).