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Originally published in Science Express on 9 November 2006
Science 15 December 2006:
Vol. 314. no. 5806, pp. 1751 - 1754
DOI: 10.1126/science.1133706
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Reports

Rubidium-Rich Asymptotic Giant Branch Stars

D. A. García-Hernández,1*{dagger} P. García-Lario,1,2 B. Plez,3 F. D'Antona,4 A. Manchado,5 J. M. Trigo-Rodríguez6,7

A long-debated issue concerning the nucleosynthesis of neutron-rich elements in asymptotic giant branch (AGB) stars is the identification of the neutron source. We report intermediate-mass (4 to 8 solar masses) AGB stars in our Galaxy that are rubidium-rich as a result of overproduction of the long-lived radioactive isotope 87Rb, as predicted theoretically 40 years ago. This finding represents direct observational evidence that the 22Ne({alpha},n)25Mg reaction must be the dominant neutron source in these stars. These stars challenge our understanding of the late stages of the evolution of intermediate-mass stars and would have promoted a highly variable Rb/Sr environment in the early solar nebula.

1 ISO Data Centre, European Space Astronomy Centre, Research and Scientific Support Department, European Space Agency, Villafranca del Castillo, Apdo. 50727, E-28080 Madrid, Spain.
2 Herschel Science Centre, European Space Astronomy Centre, Research and Scientific Support Department, European Space Agency, Villafranca del Castillo, Apdo. 50727, E-28080 Madrid, Spain.
3 Groupe de Recherches en Astronomie et Astrophysique du Languedoc, UMR 5024, Université de Montpellier 2, F-34095 Montpellier Cedex 5, France.
4 INAF–Osservatorio Astronomico di Roma, via Frascati 33, I-00040 MontePorzio Catone, Italy.
5 Instituto de Astrofísica de Canarias and Consejo Superior de Investigaciones Científicas, La Laguna, E-38200 Tenerife, Spain.
6 Institute of Space Sciences and Consejo Superior de Investigaciones Científicas, Campus UAB, Facultat de Ciències, Torre C-5, parells, 2a planta, 08193 Bellaterra, Barcelona, Spain.
7 Institut d'Estudis Espacials de Catalunya, Ed. Nexus, Gran Capità 2-4, 08034 Barcelona, Spain.

{dagger} Present address: W. J. McDonald Observatory, University of Texas, Austin, TX 78712, USA.

* To whom correspondence should be addressed. E-mail: agarcia{at}astro.as.utexas.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)