Ap stars

Ap stars

(ay-pee ) Peculiar main-sequence stars (see peculiar stars) of spectral types from B5 to F5 in which the spectral lines of certain elements (mainly Mn, Si, Eu, Cr, and Sr) are selectively enhanced and are sometimes of varying intensity (see spectrum variables). The enhancement and its variation is apparently associated with strong and often variable magnetic fields. Like the Am stars, Ap stars are generally slow rotators, but they differ in being single stars rather than spectroscopic binaries. The relative enhancement may be due to diffusion in the stable atmosphere caused by slow rotation, modified by the effect of strong magnetism. The spectral peculiarities could also relate to stellar temperature, the manganese stars being hotter than the silicon stars, which in turn are hotter than the europium-chromium-strontium stars. See also magnetic stars.
References in periodicals archive ?
These are: Am stars, which show strong heavy metal lines, no magnetic field, and and are slow rotators; Ap stars, which show lines of strontium, chromium and rare earth elements, a strong magnetic field, and generally slow rotation; mercury-manganese stars, which show abundance of singly ionised Hg and Mn, but weak magnetic fields and very slow rotation rates; and finally, helium-weak stars, which have weaker helium lines than would be expected from their colour.
The speaker concentrated the rest of his talk on the Ap stars and the mercury-manganese stars.
He thought that his star was (1) nearly the same temperature as the Sun, (2) essentially free of iron, and (3) unique, rather than a member of the class of chemically peculiar Ap stars.
COWLEY, a professor of astronomy at the University of Michigan, chaired the International Astronomical Union's Working Group on Ap Stars.