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Wolf-Rayet Stars

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Manuel Wolff ; Johannes Zabl ; Jürgen Leschhorn
Leonard Storz
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Group 142

Classification

Generally the WR stars are divided in two main groups, the WN and the WC stars.

WN Stars are characterized by the presence of He and N, which is a product of the H-Burning (CN-Zyklus).
       

  • A subdivision into WNL (late = colder) and WNE (early = hotter) is necessary, because of differences in the nuclear synthesis and development.
    • The WNL are the youngest Wolf-Rayet stars with an incomplete H-burning. They are the heaviest and according to their size they are the most luminous. As a consequence of this great luminosity they are the most variable ones. They have a proportional high concentration of N while the concentration of O is low.
    • As a consequence of development the WNE have now a complete H-burning. Due to that there is not enough H left to keep the H-Fusion alive. N is still predominating. They are hotter and brighter than their predecessors.

    • ->  A possibility to decide between the WN subtypes could be made on the basis of the ratio N III / N V. Higher temperature causes higher ionisation, so if N V dominates it must be an earlier type.

 

  • In the class of the WC-stars the proportion of Carbon increases from wpe18.jpg (914 Byte)to 40 percent. 0xygen predominates and both Hydrogen and Nitrogen have disappeared completely. Despite being the hottest WR-types they represent the lower bound in luminosity. As they have ejected the main part of their atmosphere, they have shrinked and have lost a huge amount of their mass. They are the oldest and thus highest developed WR-stars.
    A subdivision is made between WC 5 till WC9 by decreasing number of C V in favour of C IV.
  • Some sources are reporting of another very rare third type, called WN+WC . It is assumed as a transition type between WN and WC for a very short period of time.

 

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Source: Group 142

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