Quantitative technetium abundances in the long-period variables Chi Cygni and Omicron Ceti

Abstract

We have analyzed spectra of 2.4 A mm-1 dispersion to derive abundances of V, Zr, Nb, and Tc in χ Gygni, o Ceti, and R Lyrae. For χ Cyg an excess of Zr by 0.4 dex and a Tc/Zr ratio of -1.3 dex were found. For Mira Tc/Zr is -2.0 dex. In χ Cyg Nb is not enhanced, while it is depleted in o Cet. The spectrum of R Lyr shows no Tc lines and we derive Tc/Zr < -2.6 dex. We interpret the presence of Tc, and the small enhancement of Zr, in χ Cyg as evidence for a recent conventional s-process event. The time since the event is sufficiently short (≲ 1.5 × 105 yr) that neither has the 99Tc had a chance to decay nor has any 93Zr that may have been produced had a chance to decay to 93Nb. For о Cet the excess of Tc is accompanied by a deficiency of Nb, and no other abundance anomalies. We can understand this by a very small pulse of neutrons in which no more than one neutron is absorbed by any isotope.