Additional late-type stars with technetium

Abstract

The authors present the results of a survey of 279 late-type giants and supergiants for the spectral lines of the radioactive element technetium (Tc I) at 4297, 4262, and 4238 Å. They reach the following conclusions: (1) the presence of Tc correlates very strongly with the existence of light variability; (2) evolutionary MS stars show Tc and spectroscopic MS stars do not show Tc; (3) single S stars show Tc; (4) SC stars show Tc; (5) about 75% of the C stars show Tc; (6) Ba II stars do not show Tc. The findings are compatible with the predictions from stellar evolution theory that Tc, along with other s-process elements and carbon, is mixed with the surface materials after helium shell flashing episodes. The presence of Tc is a very sensitive indicator of the third dredge-up and can be detected in the spectrum before enhancements of other s-process elements are measurable.