Dodd, Emma and Baker, Harry and Child, Hamish and Harrison, Thomas and Hodge, Matthew and Hackett-Evans, Alexander and Sobral, David (2019) On the nature of Globular and Open Clusters (GOC): a study of M16, M67, M3 & M71. Notices of Lancaster Astrophysics (NLUAstro), 1. pp. 1-20.
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Abstract
A new study of two open clusters, M16 and M67, and two globular clusters, M3 and M71 is presented, exploring data taken with the WFC/INT and the Hubble Space Tele- scope (HST) in a variety of broad-band filters. A dedicated, fully functioning reduction pipeline was constructed to reduce the data used in this study. Employing SExtractor, photometry is conducted in both g and i band filters to obtain Hertzsprung-Russell (HR) diagrams which are fitted with isochrones to determine the average age, distance, metallicity and extinction of each cluster. We find that M16 is ≈ 2 kpc away, with a high dust extinction of E(B-V)≈ 0.5. For M67 the distance was found to be ≈ 0.7 kpc and the cluster is less affected by extinction, showing E(B-V)≈ 0.2. M3 is consistent with being 13 kpc away and it shows little to no extinction. For M71 the distance was found to be ∼ 3kpc and we estimate a moderate extinction of E(B-V)≈ 0.25. The re- sults of this study highlight the stark contrast between open and globular clusters. We find that M16 and M67 (open clusters) have average ages of < 10 Myrs and 3.5 Gyrs, respectively. Globular clusters are found to be much older with ages of 9.5Gyrs and 11 Gyrs for M3 and M71, respectively. It was found that open clusters contained stars that are on average more metal-poor, with lower metallicities of [Fe/H]≈ −0.8 to [Fe/H]≈ −0.5, compared to [Fe/H]≈ −0.5 and [Fe/H]≈ 0.05 for M16 and M67, re- spectively. Future work could be undertaken to correct for issues found in this study, and investigate/infer the metallicities of the birth clouds.