The CN-CH positive correlation in the globular cluster NGC 5286
  We performed low-resolution spectroscopy for the red giant stars in the
Galactic globular cluster (GC) NGC 5286, which is known to show intrinsic heavy
element abundance variations. We found that the observed stars in this GC are
clearly divided into three subpopulations by CN index (CN-weak,
CN-intermediate, and CN-strong). The CN-strong stars are also enhanced in the
calcium HK' (7.4{\sigma}) and CH (5.1{\sigma}) indices, while the
CN-intermediate stars show no significant difference in the strength of HK'
index with CN-weak stars. From the comparison with high-resolution
spectroscopic data, we found that the CN- and HK'-strong stars are also
enhanced in the abundances of Fe and s-process elements. It appears, therefore,
that these stars are later generation stars affected by some supernovae
enrichment in addition to the asymptotic giant branch ejecta. In addition,
unlike normal GCs, sample stars in NGC 5286 show the CN-CH positive
correlation, strengthening our previous suggestion that this positive
correlation is only discovered in GCs with heavy element abundance variations
such as M22 and NGC 6273.
