A century of study has characterized Plaskett’s Star (HD 47129) as an evolved, massive, short-period, equal mass O+O binary system. The discovery of a magnetic field in the broad-line component by Grunhut et al. (2013) renewed interest in the study of this system and led to its establishment as the most rapidly rotating magnetic O-type star. Grunhut et al. (2021) observed the circular polarization signatures of the magnetic star to exhibit no radial velocity variations while the narrow-line star demonstrates radial velocity variations consistent with the established orbital period. This has raised fundamental questions about the architecture of this system and the nature of the magnetic star which have led to a major shift in our understanding of HD 47129.

We examine the role that stochastic fluctuations in the IMF and in the number of interacting binaries have on the spectro-photometric properties of sparse stellar populations as a function of age and metallicity.

Differences in the evolution of massive single stars and components of massive close binary systems are investigated. While for stars above the red supergiant luminosity limit, single star and case B primary evolution merge into a single scenario, large differences for less massive stars are demonstrated to occur at the example of MZAMS = 40M⊙, concerning the various WR subtypes, the nucleosynthesis yields, and the supernova stage.