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An Ellipticity-Age Relation for Globular Clusters in the Large Magellanic Cloud

Published online by Cambridge University Press:  04 August 2017

S. Michael Fall
Affiliation:
Institute of Astronomy, Cambridge, England
Carlos S. Frenk
Affiliation:
Astronomy Department, Berkeley, California

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We have measured the ellipticities of 52 globular clusters in the LMC and 93 in the Galaxy by eye from polaroid enlargements of the sky surveys (Frenk & Fall 1982). In most cases, the measurements pertain to regions between (1–2)rh where rh is the median radius of a cluster; i.e. the radius containing half of the light in three dimensions. These were compared with determinations based on star counts for 12 members of the LMC sample and 19 members of the Galactic sample. We found no systematic difference between the ellipticities from the two methods and concluded that the eye-measurements are free of any major bias. They are also in reasonable agreement with the measurements by Geyer & Richtler (1981) and Geyer, Hopp & Nelles (1983), who used the Agfa contourfilm technique. The ellipticities measured by Geisler & Hodge (1980) from microdensitometer scans are systematically large in comparison with our results and those of Geyer and his associates. Since the scans cover only a small part of each cluster, a few bright stars can cause spurious elongations in the fitted contours.

Type
Magellanic Cloud Clusters
Copyright
Copyright © Reidel 1984 

References

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Geyer, E.H., Hopp, U. & Nelles, B. (1983) preprint.Google Scholar
Geyer, E.H. & Richtler, T. (1981) in “Astrophysical Parameters for Globular Clusters”, eds. Davis Philip, A.G. & Hayes, D.S. (L. Davis Press, Schenectady) p. 239.Google Scholar
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