High Amplitude δ Sct-type variables

Historically, the high amplitude δ Sct-type variables (δ Sct pulsators with full amplitudes larger than 0.m3) have been considered as a separated group from the “normal” low amplitude δ Sct variables on the basis, mainly, of their pulsation amplitudes. This has been a subject of controversy by a number of authors. After the review papers by Breger (1979, 1980), the commonly accepted idea is that, independently of the amplitude, the δ Sct variables are normal Population I stars in, or evolving off, the main sequence according to standard stellar evolution theory. This excludes the recently discovered pre-main sequence δ Sct pulsators. Nevertheless, some differences remain and some interesting aspects make these high amplitude objects very useful.