KOROTIN , S.

Context. Rubidium is one of the few elements produced by the neutron capture s - and r -processes in almost equal proportions. Recently, a Rb deficiency ([Rb/Fe] < 0.0), amounting to a factor of about two with respect to the Sun, has been found in M dwarfs of near-solar metallicity. This stands in contrast to the close-to-solar [Sr, Zr/Fe]...

In the framework of he ESO Large Program ``First Stars'', high resolution (R=45000) high S/N ratio spectra have been obtained for a sample of Extremely Metal Poor Stars (EMP stars), 35 giants and 18 turnoff stars. Among them 37 have a very low metallicity: [Fe/H]< -2.9.

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