At the star

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An Am star or metal line star is a type of chemically peculiar star of the spectral type  A, whose spectrum shows strong and often variable absorption lines of metals such as zinc , strontium , zirconium and barium as well as a deficit of others such as calcium or scandium . The strength of the potassium is too early compared to the hydrogen lines , while the metal lines are too late compared to the hydrogen lines. The fine classification of these stars would be e.g. B. AmkA8hA9mF3 (i.e. grouped accordingly Am-kA8-hA9-mF3), according to the spectral class derived from the potassium line k, the hydrogen lines h and metal lines m.

The Am stars represent up to 50% of all stars of the spectral type A8 and have frequency deviations of up to a factor of ten compared to normal A stars. These anomalies are caused by elements that absorb more electromagnetic radiation (e.g. light ) and rise up into the surface layers of stars due to the radiation pressure . Other elements are depleted because they sink into deeper layers due to the gravity of the star. These effects only come into play with slowly rotating stars, where no rapid rotation prevents the gravitational separation.

Typically, A-type stars have high rotational speeds . Most Am stars can therefore also be found in binary stars , where they give off part of their rotational energy to their partner via tidal forces .

Representative

The most famous of the metal line stars is Sirius (α Canis Majoris).

The following table contains some of the more well-known of these stars in decreasing apparent visual magnitude :

Surname Bayer or other name apparent visual brightness
Sirius A α Canis Majoris A −1.47
Castor Ba α Geminorum Ba 2.96
α Volantis 4.00
Acubens A α Cancri A 4.26
Kurhah ξ Cephei 4.29
θ 1 crucis 4.30
2 Ursae Majoris 5.46
Tau3 Gruis (τ 3 Gruis) 5.72
WW Aurigae 5.82

See also

Individual evidence

  1. ↑ Simon J. Murphy, A. Grigahcene, E. Niemczura, DW Kurtz, K. Uytterhoeven: Pulsational amplitude growth of the star KIC3429637 (HD178875) in the context of Am and ρ Pup stars . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1209.1493 .
  2. ↑ a b David Darling: Am star In: The Internet Encyclopedia of Science. Retrieved August 14, 2008.
  3. ↑ a b Name and apparent visual brightness from SIMBAD , unless from another source cited here.
  4. ↑ Acubens , Stars , Jim Kaler. Retrieved February 20, 2016.
  5. ↑ Kurhah , Stars , Jim Kaler. Retrieved February 20, 2016.
  6. ↑ WW Aurigae is a binary star system, both components of which are Am stars.

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