Am stars

Peculiar main-sequence stars (see peculiar stars) of spectral types from A0 to F0 in which there is an over-abundance of heavier elements and rare earths and (less so) of iron, and an apparent under-abundance of calcium. They rotate slower than normal A stars and are almost all short-period spectroscopic binaries. Current theory suggests that tidal effects slow the A star's rotation, leading to an unusually stable atmosphere where heavy elements can diffuse up from the interior. Compare Ap stars.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

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Ap 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.

Ordinary meeting, 2010 January 27: held at the Royal Astronomical Society, Burlington House, Piccadilly, London WI

Now Ireland AM stars Sinead Desmond and Mark Cagney are fronting a campaign to fund life-saving equipment for Temple Street Children's Hospital, to help children like Max.

MAXIMUM HELP; Brave three-year-old helps launch TV3 hospital appeal

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