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Durham University

Department of Physics

Staff profile

Publication details for Prof Carlos Frenk

Frenk, C.S. & Fall, S.M. (1982). An ellipticity-age relation for globular clusters in the Large Magellanic Cloud. - I. Measurements. Monthly Notices of The Royal Astronomical Society 199(2): 565-580.

Author(s) from Durham

Abstract

We have estimated the ellipticities of 52 globular clusters in the LMC and 93 in the Galaxy by the eye-measurement of their images on Sky Survey enlargements. These were checked against star counts in 12 clusters of the LMC sample, using a procedure developed for this purpose, and against star counts in 19 clusters of the galactic sample, using determinations reported by Kholopov. The results from the eye and count methods are in excellent agreement and a comparison of the two samples shows that the globular clusters in the LMC are significantly flatter than those in the Galaxy. As a means of investigating evolutionary effects, we have used UBV photometry to arrange the LMC clusters in a sequence of relative ages that is equivalent to the one devised by Searle, Wilkinson & Bagnuolo. Our results show that young clusters are flatter on average than old clusters and that the shapes of the oldest clusters in the LMC are similar to those of galactic globular clusters. The dependence of ellipticity on age may be due to changes in the shapes of the clusters, changes in the condition of their formation or some combination of both effects. For the clusters in our sample, there is no significant correlation between ellipticity and distance from the centre of the LMC. This restricts the degree to which changes in the conditions of formation might be responsible for the ellipticity-age relation and suggests that changes in the shapes of the clusters might play an important role.