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تسجيل

Evolution of stellar populations

المؤلف:  James Binney and Michael Merrifield

المصدر:  GALACTIC ASTRONOMY

الجزء والصفحة:  P-314

2026-09-08

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Within a galaxy there are stars of every mass and frequently stars of widely differing ages. In this section we use the theory of stellar evolution to predict the observable properties of such stellar agglomerates. Even with the HST, colors and spectra can be obtained for individual stars only if they lie in the nearest galaxies; for most galaxies we can only analyze samples of radiation to which thousands or millions of stars make significant contributions. The question therefore arises, what can we learn from the colors or the spectrum of such integrated light about the nature of the stars in a galaxy? Presumably we will not be able to reconstruct the galaxy’s CM diagram from a single spectrum, but we might hope to estimate the mean metallicity of the system and perhaps constrain its age. Although a great deal of effort has gone into this problem over two decades, it is still not solved. Nevertheless, solid progress has been made, and several important results are available.

The simplest case is that in which all the system's stars formed at the same time. Not only can we derive some interesting analytical results for this case of coeval stars, but it describes rather accurately the status of globular clusters. Moreover, we can regard a population with any history of star formation as a superposition of coeval populations of different ages, so once we know how a coeval population evolves it is a straightforward matter to determine the evolution of any other population.