High-resolution CCD spectra of stars in globular clusters. IX. The "young" clusters Ruprecht 106 and PAL 12

We have performed a spectroscopic abundance analysis of two stars each in the anomalously young globular clusters Rup 106 and Pal 12. We find [Fe/H] ≃ -1.45 for Rup 106 and -1.0 for Pal 12. The abundance ratios in both clusters are peculiar in comparison to other globulars: The α-elements are not enhanced over the solar ratio. We find that oxygen in Rup 106 is also relatively low, with [O/Fe] ≃ 0.0±0.1. The similarity of the ratio of the alpha-elements to iron to the solar ratio shows that species contributed by supernovae of type Ia have "caught up" with species produced by SN II's. The similar contributions of the α-and Fe-peak species to disk stars shows that age, not metallicity, is the determining factor in the ratio of SN II/SN Ia nucleosynthesis. Galactic enrichment models show that these abundance ratios can be understood as being the result of these two clusters coming from an environment with multiple discontinuous star formation events.