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Principal Evolutionary States of Normal Stars

We begin with a description of normal star evolution. The evolutionary states of normal stars will be written using roman figures (I-IV), whereas those of compact stars will be denoted by capital letters (E, P, A, SA ...) (see Section 4).  We will implicitly express the mass and radius of the star in solar units ( tex2html_wrap_inline9152, tex2html_wrap_inline9154 ), time in million years ( tex2html_wrap_inline9156 yr), luminosities in units of tex2html_wrap_inline9158 erg s tex2html_wrap_inline8853 , wind velocities in units of tex2html_wrap_inline9162 cm s tex2html_wrap_inline8853 and accretion rates tex2html_wrap_inline9166 in units of tex2html_wrap_inline9168 M tex2html_wrap_inline9170 yr tex2html_wrap_inline8853 , unless other units are clearly indicated.

The evolution of normal star is subdivided into four basic stages, which are significant for binary system evolution and have clear physical meaning (see Figure 2).

a main-sequence (MS) star inside its Roche lobe  (RL);
a post-MS star inside its RL;
a MS or post-MS star filling its RL - the mass is transferred on to the companion;
(or WR) a helium star   remaining after the mass transfer in cases B and C of binary evolution; may be in the form of a hot white dwarf  (for tex2html_wrap_inline9174 ), or a non-degenerate helium star   (a Wolf-Rayet star if the initial MS mass > tex2html_wrap_inline9178 ).

Typically, the evolution of a single star proceeds like I tex2html_wrap_inline9180 II tex2html_wrap_inline9180 compact remnant, whereas when in binary, the star evolves as I tex2html_wrap_inline9180 II tex2html_wrap_inline9180 III tex2html_wrap_inline9180 IV tex2html_wrap_inline9180 compact remnant.

Mike E. Prokhorov
Sat Feb 22 18:38:13 MSK 1997