Lithium and S-Type Stars

A survey of 188 S- and 188 C-type stars has revealed two new S-type lithium stars, TT9 and RZ Sgr with lithium equivalent widths of about |1·5| Å. The radial velocity of TT9 indicates its membership in NGC 3372 (the eta Carinae complex). It is thus a young object evolved from a massive star. The galactic latitude and radial velocity of RZ Sgr suggest that it is a low mass object. Radial velocities are given for three other lithium stars. An abundance analysis of RZ Sgr yields log |Li/Ca)\,=\,-3·59\,| and log |(Zr/Tr)\,=\,-\,1·01| unusually high values for S-type stars. There is no evidence for stratification effects. The low mass suggested for RZ Sgr places restrictions on both the ‘ hotbottom ’ and the ‘ plume-mixing ’ theories of lithium production. The high Zr/Ti in lithium-rich S stars does not appear to follow immediately from the ‘ hot-bottom ’ theory. Contrary to recent conclusions we find that the Zr: Ti ratios for the C stars studied by Kilston are substantially greater than for the S stars of Boesgaard when these investigations are reduced to a common system of oscillator strengths.