A broad perspective on multiple abundance populations in the globular   cluster NGC 1851
  We present an analysis of the multiple stellar populations of the globular cluster NGC 1851. We used lower resolution spectra of giant stars to measure CN, CH, and calcium H & K spectral indices, and determine elemental abundances for carbon and nitrogen. The CN and CH indices were used to confirm that there are four populations of stars in the cluster. The primordial population of stars, with the lowest CN, was found to be generally chemically distinct in elemental abundances from the second generation populations. As expected, [N/Fe] increases with increasing CN strength, but the only other element that correlated with CN was barium. The two largest populations of stars were found to have the same rate of carbon astration as the stars ascend the giant branch. We were also able to confirm that four previously identified extratidal stars are chemically associated with the cluster. This work shows the benefit of considering the chemistry of globular clusters with both high- and low-resolution spectra. 
Jeffrey D. Simpson, Sarah L. Martell and Colin A. Navin
astro-ph.SR astro-ph.GA