Abstract: Massive stars are chemical factories producing key elements, they are progenitors of supernovae, neutron stars and black holes, and they play a crucial role in the formation and evolution of galaxies. Given their prevalence in binary systems, at the end of their lives they may produce double-compact objects, which are potential gravitational-wave sources. During their life cycles, interactions with their companion stars can drastically alter the evolution of both stars. Yet, the complex interaction physics as well as the outcome of the interactions remain poorly understood, especially at low metallicity.

In my talk, I will introduce the Binarity at LOw Metallicity (BLOeM) Survey that obtains multi-epoch spectroscopy of almost 1000 massive stars in the Small Magellanic Cloud. I will present recent results of the multiplicity properties of different types of massive stars, including OB main-sequence stars as well as blue and yellow supergiants. In particular, I will focus on the so-called classical OeBe stars, which are rapidly rotating OB-type stars with emission lines indicative of a circumstellar disk. I will discuss the multiplicity fractions obtained in the upper HRD, report observational evidence that massive OeBe stars are predominantly binary interaction products, and discuss how our findings can be used to constrain binary interaction physics, especially at low metallicity.