Oxygen and Carbon abundances in blue straggler stars

Oxygen abundance as a function of Carbon abundance (both with respect to Iron and in a logarithmic scale) for the Blue straggler stars observed in the globular cluster 47 Tuc. Normal Blue straggler stars are marked with empty circles, while the 6 Carbon and Oxygen-deplete Blue Straggler stars are marked with red squares. Their names are also indicated. The yellow region correspond to the location of other stars in 47 Tuc previously studied