Star Clusters in M 31. IV. A Comparative Analysis of Absorption Line Indices in Old M 31 and Milky Way Clusters

• Published in: arXiv.org 2011-12
• Main Authors: Schiavon, Ricardo P, Caldwell, Nelson, Morrison, Heather, Harding, Paul, Courteau, Stephane, MacArthur, Lauren A, Graves, Genevieve J
• Format: Article
• Language: English
• Subjects: Absorption; Chemical composition; Globular clusters; Milky Way Galaxy; Organic chemistry; Spectra; Star clusters; Uncertainty
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1112.2737

We present absorption line indices measured in the integrated spectra of globular clusters both from the Galaxy and from M 31. Our samples include 41 Galactic globular clusters, and more than 300 clusters in M 31. The conversion of instrumental equivalent widths into the Lick system is described, and zero-point uncertainties are provided. Comparison of line indices of old M 31 clusters and Galactic globular clusters suggests an absence of important differences in chemical composition between the two cluster systems. In particular, CN indices in the spectra of M 31 and Galactic clusters are essentially consistent with each other, in disagreement with several previous works. We reanalyze some of the previous data, and conclude that reported CN differences between M 31 and Galactic clusters were mostly due to data calibration uncertainties. Our data support the conclusion that the chemical compositions of Milky Way and M 31 globular clusters are not substantially different, and that there is no need to resort to enhanced nitrogen abundances to account for the optical spectra of M 31 globular clusters.