Schonberg-Chandrasekhar limit

Fig. 5.7. Evolutionary tracks for Z = 0.02 (near solar metallicity) stars with different masses in the HR diagram. (Luminosities are in solar units.) Points labelled 1 define the ZAMS and points labelled 2 the terminal main sequence (TAMS), the point where central hydrogen is exhausted. The Schonberg-Chandrasekhar limit may be reached either before or after this (for M > 1.4 Af0). Points marked 3 show the onset of shell hydrogen-burning. Few stars are found in the Hertzsprung gap between point 4 and point 5 , where the surface convection zone has grown deep enough to bring nuclear processed material to the surface in the first dredge-up. Adapted from Iben (1967).

The Schonberg-Chandrasekhar limit [30] represents a limit above which an isothermal non-degenerate core can support the remainder of the star. Its value is ss 0.1 — 0.15M and is valid for stars with total mass between 2 and 6 Mq. Less massive stars develop an electron-degenerate core and more massive stars ignite helium before this value is reached. 

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