Chemically peculiar star

A star whose surface elemental abundances differ markedly from those of comparable stars. The anomalies often arise through diffusion, magnetic fields, or nuclear processing.

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Stellar abundance: The relative amounts of chemical elements in a star, inferred chiefly from its spectrum. Chemical peculiarity is defined by abundance departures from comparable stars.
Gravitational settling: The downward diffusion of particles under gravity in a fluid or plasma. It can deplete heavy elements from a star’s observable surface.
Ap star: A chemically peculiar A-type main-sequence star, often with a strong, organized magnetic field. Ap stars are the classic magnetic examples, with unusual abundances of elements such as silicon and rare earths.
Normal star: A star whose observed properties fall within the usual range for its stellar type and evolutionary state. Comparable normal stars provide the abundance baseline against which peculiarity is judged.
Stellar magnetic field measurement: The inference of a star’s magnetic-field strength and geometry from its observable effects. Field measurements test whether magnetic structure tracks particular abundance patterns.
Stellar spectroscopy: The study of stars through the wavelengths and strengths of their emitted or absorbed light. Spectral lines reveal the surface elements that appear unusually abundant or scarce.
Stellar magnetic field: A magnetic field generated within a star and extending through its atmosphere and surroundings. Strong, structured fields can shape abundance patterns and stabilize peculiar atmospheres.
Bp star: A chemically peculiar B-type main-sequence star with anomalous surface abundances. Bp stars extend magnetic chemical peculiarity to hotter, more massive stars.
Population II star: An old, generally metal-poor star formed from gas enriched by earlier generations of stars. Its low metal content reflects birth composition, not necessarily atmospheric separation.
Zeeman effect: The splitting or polarization of spectral lines caused by a magnetic field. It provides a direct spectroscopic probe of fields in magnetic chemically peculiar stars.