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.

Appendix

3.1.1 List of ‘sn’ stars

See Tables 3.2 and 3.3.

Table 3.2 A list of the ‘sn’ stars, assembled predominantly from Mermilliod (1983), which in turn was largely assembled from Abt (1979). Two stars (HD 5737&HD 79158) from Shore et al. (1987) were added, and supplemented with measurements from SIMBAD

Table 3.3 A list of the ‘sn’ star candidates, from Mermilliod (1983), identified as such because they are normal slow rotators