RVs of O-type stars in BLOeM survey

At high metallicity, a majority of massive stars have at least one close stellar companion, which dramatically impacts their evolution, feedback, and final fate. At low metallicity, constraints on the multiplicity of massive stars over the separation range leading to binary interaction have been crucially missing.

Here we show that the presence of massive stars in close binaries is ubiquitous, even at low metallicity. The Small Magellanic Cloud is a neighbouring low-metallicity dwarf galaxy with a metal content of about one fifth solar, hence similar to metallicity environments during and before the peak of star formation in the Universe. Using Very Large Telescope spectroscopy from the Binarity at LOw Metallicity large program, we obtained multi-epoch radial velocity measurements of a representative sample of 139 massive O-type stars across the Small Magellanic Cloud.