A Selective Review of Spectral Peculiarities in the A Stars

Abstract

The literature on Am stars is extensively reviewed, paying particular attention to abundance anomalies and the state of Am-star models in light of pulsations found in many of these objects. A new study into the non-\(\delta \) Sct A stars using Kepler data, and the spectroscopic classification of two thirds of them as chemically peculiar stars is also performed with complementary abundance analyses. Although there are chemically normal \(\gamma \) Dor stars in the \(\delta \) Sct instability strip without \(\delta \) Sct pulsation, the least variable stars (without \(\gamma \) Dor pulsation either) are chemically peculiar, and some strongly so. The \(\rho \) Pup stars of spectral type A/F are reviewed. For this group there is a consensus that they are the evolved Am stars. This chapter also reviews a class of B stars—it offers one of the few reviews of the ‘sn’ stars, whose spectra display both sharp and nebulous lines, and proposes a link between these and the Ap stars. Additionally, the two main theories for the origin of abundance anomalies in \(\lambda \) Boo stars are discussed and it is suggested that both of them imply the \(\lambda \) Boo stars contain a high fraction of pulsators—a suggestion that is backed up by observations in the literature.