Advanced evolution of massive stars. VI. Oxygen burning.

Evolutionary sequences of massive helium stars (M = 4, 8, 16, and 32 M0) are continued through oxygen burning and up to ignition of silicon burning in the center. During these stages the time scale becomes too short for convection to be regarded as beginning instantaneously or to cause mixing at infinite velocity. For M = 4 and 8 M0, a complex neon-oxygen flash occurs after ignition of 160 + 160 in the center. Strong shell flashes occur until the cores are large enough to ignite silicon burning. Subject headings: interiors, stellar - massive stars - nucleosynthesis - stellar evolution - instabilities