The oxygen abundance in the bulge

Ratio of Oxygen over Iron abundance as a function of the iron content in stars (both axis are using logarithmic scales). The green circle denotes the stars in the Bulge studied by the present astronomers, while the yellow triangles and blue crosses are previous data obtained for stars in the disc of our Galaxy. The bulge stars are clearly more oxygen-rich than disc stars, highlighting the 'genetic difference' between the bulge and disc stars.