Ratio of the average of the explosive α elements (Ca and Ti) to the hydrostatic α elements (Mg) as a function of [Mg/Fe]. The color code encodes the metallicity of the Sgr stars (filled circles). The square symbols denote the theoretical models from Nomoto et al. (2013), which incorporate yields from both SNe II and HNe. The dashed-dotted line delineates the region of chemical space where stars could have originated from gas enriched by both CCSNe and HNe.