Rubidium-Rich Asymptotic Giant Branch Stars
D. A. García-Hernández,1*
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(
,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.
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.
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
