Our work focuses on the understanding of the origin of CNO-anomalies, which have been detected in several Galactic globular clusters. The novelty and advantage of this study is that it is based on a homogeneous data set of hundreds of medium-resolution spectra of stars in eight Galactic globular clusters (M 15, M 22, M 55, NGC 288, NGC 362, NGC 5286, Palomar 12, and Terzan 7). Two of the clusters (Palomar 12 and Terzan 7) are believed to be former members of the Sagittarius dwarf spheroidal (Sgr dSph) galaxy. The large homogeneous data set allows for a detailed differential study of the line strengths in the stellar spectra of the observed clusters. Our sample comprises stars in different evolutionary states, namely the main-sequence turn-off (MSTO) region, the subgiant branch (SGB) and the base of the red giant branch (RGB). We compare the relative CN and CH line strengths of stars in the same evolutionary states (with similar logg and T_eff_).

Cone search capability for table J/A+A/486/437/tablea1 (List of spectroscopic sample stars, ordered by increasing V magnitude)