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Science 15 December 2006:
Vol. 314. no. 5806, p. 1653
DOI: 10.1126/science.314.5806.1653b
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This Week in Science
When stars get old, they swell into giants. At the bottom of their convecting zones, heavy elements, such as rubidium and strontium, are produced through the s process by slow nuclear reactions involving the capture of neutrons. In hot stars that are several times more massive than the Sun, theory predicts that the neutrons generated by conversion of 22Ne to 25Mg should produce large amounts of the long-lived isotope 87Ru, but little of this material has been observed. García-Hernández et al. (p. 1751, published online 9 November; see the Perspective by Boothroyd) have found the missing Rb in 60 asymptotic giant branch stars in our Galaxy. These stars have levels of 87Ru that are 10 to 100 times greater than that of the Sun but are only three to eight times more massive. The discovery points to metallicity differences in nucleosynthesis reactions in the late stages of the evolution of intermediate-mass stars, and also has implications for isotopic anomalies observed in some presolar grains found in meteorites.
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Science. ISSN 0036-8075 (print), 1095-9203 (online)
