Chemical abundance spots

Early-type stars often posses inhomogeneous distribution of chemical elements across their surfaces. Spectral lines belonging to non-uniformly distributed elements show large variations of both line strength and shape as a function of rotational phase. These variations are diverse and typically differ for different elements in the same star. Some chemical elements may have an enhanced concentration inside localised spots and a lower abundance outside. The resulting spectral line variation (left) is seen as dips in the line profile, propagating from blue to red. Other chemical elements concentrated in arc-like structures or rings, leading to another pattern of spectral variation (right).