Rotation and chemical abundances in the peculiar A stars - I.

The classifications and atmospheric structures displayed by early type peculiar stellar spectra are compared empirically with those of normal stars. It is concluded that the structures of the metal line forming regions of the atmospheres of the peculiar A and B stars are identical with those of the normal stars of the same hydrogen type. A consistent temperature sequence can be established for both types later than spectral type B . The differences in metal line strengths in stars of similar hydrogen type can be interpreted only as differences of abundance in the atmospheres.