The IACOB project: XVI. Surface helium abundances in Galactic O-type stars: indications for identifying binary interaction products

S. Simón-Díaz, G. Holgado, C. Martínez-Sebastián +13

The presence of massive O-type stars with surfaces enriched by CNO-cycle products has been known since the early 1980s. For many years, internal rotational mixing was assumed to be…