Spectrum comparison of typical metal-rich giant stars observed towards the Galactic bulge with two different α-enhancements. The main atmospheric parameters are T_eff = 4250 K, log(g) = 2.0, and [M/H] = 0.0. Left panel: same as Fig. 3 for normalised spectra computed with only one line specy in the synthesis and assuming [α/Fe] = +0.0 as detected in certain Galactic bulge directions and in the Galactic thin disk. Right panel: line blocking differences between the left panel case ([α/Fe] = +0.0) and a bulge component star having [α/Fe] = +0.4. It can be seen that increasing the abundance of α-elements leads to weaker lines of non α-atoms and molecules since the continuum flux becomes weaker (see Sect. 4 for more details).