The location of the δ Scuti variables in the HR diagram is discussed on the basis of HIPPARCOS parallaxes and uvbyβ photometry together with the R00 catalogue (Rodríguez et al., 2000). In particular, the properties of the α Scuti-type pulsators with nonsolar surface abundances (SX Phe, λ Boo, ρ Pup, δ Del and classical Am stars subgroups) are examined.

The latter four classes of stars are spectroscopically defined subclasses with surface abundance anomalies. Although the stars ρ Pup and δ Del are also pulsators, the groups named after these stars should not be regarded as pulsation subclasses of δ Scuti stars. The abundance anomalies in these stars affect the pulsation properties, e.g., the classical Am stars are constant in light or show only small pulsation amplitudes (e.g., HD 1097). These four groups are only a small selection from the bewildering zoo of stars with unusual surface abundances in this temperature region and represent the groups with δ Scuti pulsation.