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.

List

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
	θ^1 Crucis	4.30
	π Virginis[5]	4.64
	2 Ursae Majoris	5.46
	τ^3 Gruis	5.72
	WW Aurigae[6]	5.82

Notes and references

1. Am star, The Internet Encyclopedia of Science, David Darling. Accessed on line August 14, 2008.
2. Names and apparent visual magnitudes taken from SIMBAD, unless otherwise noted.
3. Acubens, Stars, Jim Kaler. Accessed on line August 14, 2008.
4. Kurhah, Stars, Jim Kaler. Accessed on line August 14, 2008.
5. Paunzen, E.; et al. (February 2013), "A photometric study of chemically peculiar stars with the STEREO satellites - II. Non-magnetic chemically peculiar stars", Monthly Notices of the Royal Astronomical Society, 429 (1): 119−125, arXiv:1211.1535, Bibcode:2013MNRAS.429..119P, doi:10.1093/mnras/sts318.
6. WW Aurigae is a binary star both of whose components are Am stars.