Are there Normal Upper Main Sequence Stars: λ Bootis, …

Abstract

Our concept of normal A stars is severely influenced by the dearth of features in the low resolution spectra of these objects that have been used for classification. The relatively small number of lines visible at survey dispersion has also led us to greatly simplify the complexity of spectroscopic patterns that can occur. The λ Boo stars were noted as a class because of the prominence of the λ4481 line of Mg II. We call attention to lines of V II and Ni II that are strong in superficially normal stars, and surprisingly weak in strong-lined stars with obvious overabundances of chromium, manganese, and iron. It is also useful to note that iron itself can be both underabundant and overabundant in CP stars. We call attention to an important new work by Venn and Lambert that develops the earlier suggestion that λ Boo stars may have formed from gas that has been separated from interstellar grains.