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Title: Distances and ages of galactic globular clusters via infrared photometry
Author: Buckley, David R. V.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1994
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One of the most promising routes to the formation of a quantitative model of the processes and timescales involved in transforming primordial, pre-galactic material into the galaxy as we know it today is the study of the 'fossil record', one important component of which is the galactic globular-cluster system. It is therefore vital to have information of the basic parameters - reddening, chemical composition, distance, age and internal and orbital dynamics - of many globular clusters. This thesis is concerned with the derivation of the distances and ages of the four galactic globular clusters M13 (NGC6205), M30 (NGC7099), NGC6752 and 47 Tuc (NGC104). To this end we have obtained infrared photometry of respectively 21, 344, 123 and 688 stars in these clusters. We have matched this photometry with existing optical photometry to form the optical-infrared colour magnitude diagrams which are the basic tool for this study. These colour-magnitude diagrams are to the best of our knowledge the deepest of their kind in existence, and in NGC6752 and 47 Tuc reach to some five V magnitudes below the main-sequence turn-off. The distances are derived using a sample of six metal-poor field subdwarf stars with accurate trigonometric parallax measurements, and a discussion is given of the sensitivity of these distances to various sources of error. We find that distances derived using the optical-infrared colour-magnitude planes are less sensitive to some systematic errors in the photometry than purely optical colour-magnitude diagrams, while distances determined in K, (B-V) are least sensitive to errors in the adopted ratio of total-to-selective extinction. Other sources of error considered are small photometric errors and errors in the adopted values of E[B-V] and [Fe/H]. For M13, M30, NGC6752 and 47 Tuc we derive distances of 7.1, 8.1, 4.0 and 4.4 kpc without Lutz-Kelker corrections.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available