Ap and Bp stars

Ap and Bp stars are peculiar stars (hence the “p”) of types A and B which show overabundances of some rare earth metals (e.g., europium) or others (e.g., strontium). These stars have a much slower rotation than normal for A and B type stars , although some have up to ≈ 100 km s${\displaystyle ^{-1}}$. They also have stronger magnetic fields, in some cases reaching ≈ 40kG (4T). The spatial locations of the chemical overabundances have been shown to be connected with the geometry of the magnetic field. Some of these stars have shown radial velocity variations arising from pulsations of a few minutes. For studying these stars high-resolution spectroscopy is used, together withDoppler imaging which uses the rotation to deduce a map of the stellar surface.