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A Method for Determining the Chemical Composition Parameters (X, Y, Z) of Galactic Clusters

Published online by Cambridge University Press:  14 August 2015

Wayne Osborn  and
Juan J. Clariá
Wayne Osborn
Affiliation:
Instituto Venezolano de Astronomía, Mérida, Venezuela
Juan J. Clariá
Affiliation:
Instituto Venezolano de Astronomía, Mérida, Venezuela

Abstract

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A method is described by means of which the chemical composition parameters (X, Y, Z) may be derived for galactic clusters that contain evolved red giant members and for which the cluster reddening and distance moduli are known. The method is based on observations of the evolved stars utilizing the DDO intermediate-band system. First, the DDO photometry by itself allows one to separate with a high degree of certainty the physical members of the clusters from the field stars. In cases where membership in the cluster can be confirmed, the unreddened DDO colours can be used to obtain the effective temperatures, surface gravities and metal abundances (Z) of the stars. These data combined with the absolute magnitudes available from the distance modulus permit the masses to be calculated. Finally, if some of the observed red giants form part of a clump on the giant brach in the HR diagram, the helium abundance (Y) of the clusters can be estimated by comparing the derived physical parameters of these stars with theoretical models. An example of the application of the method to the galactic cluster NGC 2420 is given.

Type
Part III/Derivation of Abundances Through Photometric and Spectroscopic Methods
Information
Symposium - International Astronomical Union , Volume 72: Abundance Effects in Classification , 1976 , pp. 101 - 109
Copyright
Copyright © Reidel 1976 

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