On the Absence of Young White Dwarf Companions to Five Technetium Stars

Abstract

A search for hot companions to five stars of type MS and S has been carried out using the International Ultraviolet Explorer (IUE) satellite. No hot companions were detected for the MS stars HR 85, 4647, 6702, and 8062, and the S star HR 8714. Limits on the luminosities of possible white dwarf companions provide lower limits of 2 - 5×10⁸yr to the ages of any degenerate companions. All five stars exhibit strong Tc I lines, and the presence of technetium, with a half-life of 2.1×10⁵yr, signifies recent nucleosynthesis. The limits on the ages of possible white dwarf companions that are ≥1000 half-lives of Tc exclude the possibility that the s-process elemental enhancements seen in these MS and S stars resulted from mass transfer from a more highly evolved companion (as is probably the mechanism by which barium stars are created). These MS and S stars represent a sample of true thermally pulsing asymptotic giant-branch stars.