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William E. Harris |
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"Ages of the Halo Stars in E
Galaxies" |
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The halo stars in large galaxies contain the direct record of their earliest chemical evolution history and age distribution. Metallicity-sensitive features of the color-magnitude diagram such as the temperatures of the red-giant stars, and age-sensitive features such as the luminosity function and helium-burning phases, can be combined to gauge both the age distribution function and the heavy-element distribution function of the halo. I will describe our recent work using synthesis of CMDs for old stellar population mixtures, along with high precision photometry of the halo stars, to derive these distributions for nearby E galaxies, especially NGC 5128 (Cen A). |