  We study the nucleosynthesis and the induced mixing during the merging of
massive stars inside a common envelope. The systems of interest are close
binaries, initially consisting of a massive red supergiant and a main-sequence
companion of a few solar masses. We apply parameterized results based on
hydrodynamical simulations to model the stream-core interaction and the
response of the star in a standard stellar-evolution code. Preliminary results
are presented illustrating the possibility of unusual nucleosynthesis and
post-merging dredge-up which can cause composition anomalies in the
supergiant's envelope.
