Rotational mixing in close binaries

Understand

Rotational mixing is a very important but uncertain process in the evolution of massive stars.

• We propose to use close binaries to test its efficiency.
• Based on rotating single stellar models we predict nitrogen surface enhancements for tidally locked binaries.
• Furthermore we demonstrate the possibility of a new evolutionary scenario for very massive (M > 40 solar mass) close (P < 3 days) binaries: Case M, in which mixing is so efficient that the stars evolve quasi-chemically homogeneously, stay compact and avoid any Roche-lobe overflow, leading to very close (double) WR binaries.