The chemical composition of the lambda Bootis stars.

Abstract

Measurements of the equivalent widhts of 24 UV lines from IUE spectra of 10 λ Bootis or suspected λ Bootis stars and 19 normal standard stars of spectral types B8-A7 are compared with line strengths calculated from model atmospheres. The light elements (C, N, and O) in the λ Boo stars are in the range slightly overabundant relative to the standard (solar composition) stars. On the other hand, the heavier elements (Mg, Al, Si, S, Mn, Fe, and Ni) are moderately deficient (≅0.5 dex) in the λ Boo stars compared to the standard stars. The results are difficult to understand in terms of nucleosynthesis, nor is an explanation based on a possible low-abundance fluctuation in the interstellar medium at the time of star formation very satisfactory. A model based on the diffusion hypothesis has attractive features, but the rapid rotation of the λ Boo stars may present difficulties.