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Main-sequence stars (stage I) Evolutionary Scenarios of Binary Evolutionary Scenarios of Binary

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 ( , ), time in million years ( yr), luminosities in units of erg s , wind velocities in units of cm s and accretion rates in units of M yr , 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).

I

a main-sequence (MS) star inside its Roche lobe  (RL);

II

a post-MS star inside its RL;

III

a MS or post-MS star filling its RL - the mass is transferred on to the companion;

IV

(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 ), or a non-degenerate helium star   (a Wolf-Rayet star if the initial MS mass > ).

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

• Main-sequence stars (stage I)
• Post main sequence stars (stage II)
• Roche lobe overflow (stage III)
• Wolf-Rayet and He stars (stage IV)