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The iron dispersion of the globular cluster M 2, revised

Lardo, C, Mucciarelli, A and Bastian, N (2016) The iron dispersion of the globular cluster M 2, revised. Monthly Notices of the Royal Astronomical Society, 457 (1). pp. 51-63. ISSN 0035-8711

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M 2 has been claimed to posses three distinct stellar components that are enhanced in iron relative to each other. We use equivalent width measurements from 14 red giant branch stars from which Yong et al. detect a $\sim$0.8 dex wide, trimodal iron distribution to redetermine the metallicity of the cluster. In contrast to Yong et al., which derive atmospheric parameters following only the classical spectroscopic approach, we perform the chemical analysis using three different methods to constrain effective temperatures and surface gravities. When atmospheric parameters are derived spectroscopically, we measure a trimodal metallicity distribution, that well resembles that by Yong et al. We find that the metallicity distribution from Fe II lines strongly differs from the distribution obtained from Fe I features when photometric gravities are adopted. The Fe I distribution mimics the metallicity distribution obtained using spectroscopic parameters, while the Fe II shows the presence of only two stellar groups with metallicity [Fe/H]$\simeq$-1.5 and -1.1 dex, which are internally homogeneous in iron. This finding, when coupled with the high-resolution photometric evidence, demonstrates that M 2 is composed by a dominant population ($\sim$99%) homogeneous in iron and a minority component ($\sim$1%) enriched in iron with respect to the main cluster population.

Item Type: Article
Additional Information: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record MNRAS (2016) 457 (1): 51-63 is available online at:https://doi.org/10.1093/mnras/stv2802
Uncontrolled Keywords: astro-ph.SR; astro-ph.SR; astro-ph.GA
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
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Date Deposited: 19 Jan 2017 15:27
Last Modified: 02 Aug 2022 15:44
URI: https://researchonline.ljmu.ac.uk/id/eprint/2453
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