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First Detection of Rubidium in Asymptotic Giant Branch Stars

WHT+UES

A long debated issue concerning the nucleosynthesis of neutron-rich elements in Asymptotic Giant Branch (AGB) stars is the identification of the neutron source. Recently, a team of astronomers using the Utrecht Echelle Spectrograph (UES) on the William Herschel Telescope has detected rubidium from the overproduction of the long-lived radioactive isotope 87Rb in intermediate-mass AGB stars in our Galaxy. This represents a direct observational evidence, predicted theoretically 40 years ago, of the slow-neutron capture process following the 22Ne(α,n)25Mg reaction.

Because huge amounts of rubidium-rich processed material can be transferred to the interestellar medium by massive AGB stars, this result has also relevant implications for the rubidium primeval solar nebula abundance. Radioactive dating studies of primitive chondrites assume that the initial conditions are known and that the oldest components of chondrites evolved without external exchange of rubidium but this research suggests that the initial abundance may has been altered by a nearby population of massive AGB stars during the early evolution of our Solar System, and consequently, the rubidium abundance measured in primitive meteorites should be considered only as a qualitative measure of antiquity.

Rubidium in BW Cam
Figure 1. Rubidium line at 7800 angstroms as detected by UES spectrograph on the William Herschel Telescope in BW Cam, one of observed AGB stars in this study. Credit: IAC/ESA. [ JPEG | TIFF ].

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Last modified: 22 December 2010