Astronomy

Enriched Old Stars

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Science  08 Nov 2013:
Vol. 342, Issue 6159, pp. 671
DOI: 10.1126/science.342.6159.671-a
CREDIT: NASA/JPL-CALTECH

Globular clusters, the oldest surviving stellar systems in galaxies, were for a long time thought to be composed of stars that formed simultaneously with the same initial chemical composition. However, multiple stellar populations with a range of chemical compositions have been observed over the last few years, hinting at a complex and prolonged history of star formation and chemical enrichment. To put constraints on models of globular cluster formation, Schiavon et al. studied the correlations between cluster mass and the mean stellar abundances of Fe, Mg, C, N, and Ca for 72 old globular clusters in the Andromeda galaxy—the nearest spiral galaxy to the Milky Way. They found a correlation between N abundance and cluster mass, implying that the chemical enrichment undergone by globular clusters is proportional to their masses. The absence of correlations between mass and Mg and Ca abundances rules out enrichment through explosive nucleosynthesis.

Astrophys. J. 776, L7 (2103).

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