Fr.: étoile Ap/Bp
A class of → intermediate-mass stars which possess anomalously strong → magnetic fields (about 100-10000 G). Ap/Bp stars typically show → overabundances of → iron peak elements, → rare earths, and → silicon, ranging up to ~2 dex above solar. These magnetic → chemically peculiar stars make up about 5% of the → main sequence A and B population (→ A star, → B star). Ap/Bp stars have predominantly → dipolar magnetic fields. The presence of strong, ordered magnetic fields in some main sequence A and B stars has been known for nearly one-half of a century (Babcock 1947). However the cause of the magnetic field is still a matter of debate. There are two competing theories: the contemporaneous → dynamo effect, and the → fossil magnetic field theory. Contemporaneous dynamo effect suggests that there is a dynamo effect currently working in the → convective core of the star. The fossil field theory assumes that the magnetic field is a remnant, produced by a dynamo effect operating at an earlier evolutionary phase, or swept up from the → interstellar medium during → star formation (Power et al., 2006, astro-ph/0612557).
A and B represent spectral types and p stands for → peculiar.