Radioactive Clocks and Thermometer in S-type Stars

¹ I.A.A., Université libre de Bruxelles (ULB), CP 226, 1050 Bruxelles, Belgium
² LUPM, Université Montpellier, CNRS, 34095 Montpellier, France

Abstract

Direct probes of the temporal evolution of stars are rare. We derive the time spent by S-type stars since the onset of the first thermal pulse, from the ⁹⁹Tc – ⁹⁹Ru and ⁹³Zr – ⁹³Nb chronometers. Zirconium and niobium abundances constrain as well the nucleosynthesis temperature, supporting ¹³C(α,n)¹⁶O as the s-process neutron source. Niobium abundances are used, for the first time, to efficiently separate stars with active nucleosynthesis from binary stars with fossil overabundances resulting from a previous mass transfer. The abundances of Tc, Nb, and Zr thus give access to the nucleosynthesis chronology and temperature, and provide a diagnostic of possible external pollution from a companion star.