Optical elemental abundance analyses of B and A stars - II. The hot AM stars omicron Pegasi and sigma Aquarii and the marginal peculiar A star nu Cancri.

Optical region data and fully line blanketed model atmospheres are used to perform abundance analyses for two sharp-lined hot Am stars, Omicron Pegasi and Sigma Aquarii, and for the sharp-lined marginally peculiar A star Nu Cancri. The abundances derived show definite anomalies compared with those of normal B-type stars and the sun. It is found that the values for both Omicron Peg and Sigma Aqr exhibit definite similarities and differences with those of both HgMn and Am stars, which are respectively hotter and cooler types of nonmagnetic chemically peculiar stars of the upper main sequence. However, the elemental abundances of Nu Cnc are similar to those of the HgMn stars. Since Nu Cnc is photometrically nonvariable, it is a member of this class. The conventional view that the hot Am stars merge smoothly into the HgMn stars is called into question by the abundance differences between Sigma Aqr and Nu Cnc, which have similar temperatures and surface gravities.