Am star
Wiley Book of Astronomy:
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Am star
Also known as a metallic-line star, a type of A star whose spectrum has strong and often variable absorption lines of some metals (hence the “m”), such as zinc, strontium, zirconium, and barium, more typical of an F star, and deficiencies of others, such as calcium and/or scandium. These abundance anomalies are due to some elements being pushed to the surface because they are better light absorbers, while other elements sink to lower levels under gravity—an effect that requires slow stellar rotation. Normal A stars spin quickly, but most Am stars are known to be members of close binary systems in which the two stars slow each other down by tidal action. Familiar examples include Sirius and Acubens. See also Ap star and mercury-manganese star.
Oxford Dictionary of Astronomy:
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Am Star
A star of spectral type A whose spectrum additionally contains very strong metallic lines (hence the suffix ‘m’) more typical of type F. Am stars are usually members of close binary systems. They rotate more slowly than normal A stars, thereby allowing some elements to sink and some to rise in their atmospheres, and this produces the observed abundance anomalies. Sirius is an Am star.
Wikipedia on Answers.com:
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Am star
An Am star or metallic-line star is a type of chemically peculiar star of spectral type A whose spectrum has strong and often variable absorption lines of metals such as zinc, strontium, zirconium, and barium, and deficiencies of others, such as calcium and scandium. These abnormalities are due to some elements which absorb more light being pushed towards the surface, while others sink under the force of gravity. This effect takes place only if the star has low rotational velocity.[1]
Normally, A-type stars rotate quickly. Most Am stars form part of a binary system in which the rotation of the stars has been slowed by tidal braking.[1]
The best-known metallic-line star is Sirius (α Canis Majoris.) The following table lists some metallic-line stars in order of descending apparent visual magnitude.
| Name[2] | Bayer or other designation | Apparent visual magnitude[2] |
|---|---|---|
| Sirius A | α Canis Majoris A | −1.47 |
| Castor Ba | α Geminorum Ba | 2.96 |
| α Volantis | 4.00 | |
| Acubens A[3] | α Cancri A | 4.26 |
| Kurhah[4] | ξ Cephei | 4.29 |
| θ1 Crucis | 4.30 | |
| 2 Ursae Majoris | 5.46 | |
| τ3 Gruis | 5.72 | |
| WW Aurigae[5] | 5.82 |
Notes and references
- ^ a b Am star, The Internet Encyclopedia of Science, David Darling. Accessed on line August 14, 2008.
- ^ a b Names and apparent visual magnitudes taken from SIMBAD, unless otherwise noted.
- ^ Acubens, Stars, Jim Kaler. Accessed on line August 14, 2008.
- ^ Kurhah, Stars, Jim Kaler. Accessed on line August 14, 2008.
- ^ WW Aurigae is a binary star both of whose components are Am stars.
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Wiley Book of Astronomy
Copyright © 2004 by Wiley-Blackwell. Wiley and the Wiley logo are registered trademarks of John Wiley & Sons, Inc. and/or its affiliates in the United States and other countries. Used here by license. Read more
Oxford Dictionary of Astronomy
A Dictionary of Astronomy. © 1997
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