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Structure and Evolution of Star Clusters in the Vicinity of the Magellanic Clouds

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posted on 08.11.2021, 00:29 by Banks, Timothy Stuart

This thesis describes the collection, reduction, and analysis of Charge Coupled Detector (CCD) images of star clusters. The objects studied are primarily in the Large Magellanic Cloud (LMC), a nearby galaxy. The study of these groupings can provide information such as the initial dynamic state of Globular Clusters, the heavy-clement enrichment rate of the LMC, the distribution of masses that stars form with, and the validity of given stellar evolution models. The majority of the observations were collected at Mount John University Observatory (NZ). Procedures for the collection and transfer of the data are described, along with an overview of the analysis facility and CCDs. Statistical moment-based ellipse fitting was applied to the observations, confirming that trends are evident in the position angles and ellipticities of the clusters, as had been reported in the literature. Artificial images of clusters with known parameters were generated and subjected to the same analysis techniques, revealing apparent trends caused by stochastic processes. Caution should therefore be exercised in the interpretation of observational trends in the structure of young LMC clusters. Isochrones were used to date the 19 clusters. The resulting ages are in good agreement with the literature, as are results from profile modeling. There is no evidence for tidal truncation of the young clusters. Observations were made of two LMC and two Galactic star clusters in a test of imaging clusters with the Vilnius photometric system and a CCD. The colour-magnitude diagrams, distances and interstellar reddenings of the clusters were derived and found to be in agreement with the literature. This is the first time that the standard Vilnius filter set has been used with a CCD. Use of the system for direct imaging of star clusters appears promising. Johnson BV CCD observations were made of the young LMC cluster NGC 2214 and a nearby field using the Anglo-Australian Telescope. It has been suggested in the literature that this elliptical cluster is actually two clusters in the process of merging. No evidence was found from profile fitting or the colour-magnitude diagrams to support this contention. Completeness factors were estimated for the CCD frames. These values were used in conjunction with luminosity functions to estimate the Initial Mass Function (IMF) for NGC 2214. A power-law M-(1+x) was assumed for the IMF (where M is stellar mass relative to that of the Sun Mo), with a good fit being found for x = 1.01 plus-minus 0.09. There is some indication that the low mass end (less than or equal to 3oMo) has a smaller gradient than the high mass end of the derived IMF. The value of x is in reasonable agreement with literature values for other Magellanic IMFs, and not substantially different from the poorly determined Galactic IMFs, suggesting the possibility of a 'universal' IMF over the Magellanic Clouds and our Galaxy in the mass range tilde 1 to tilde 10 Mo.


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Date of Award



Te Herenga Waka—Victoria University of Wellington

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Author Retains Copyright

Degree Discipline


Degree Grantor

Te Herenga Waka—Victoria University of Wellington

Degree Level


Degree Name

Doctor of Philosophy

Victoria University of Wellington Item Type

Awarded Doctoral Thesis



Victoria University of Wellington School

School of Chemical and Physical Sciences


Dodd, Richard; Sullivan, Denis