The binary landscape of massive stars at low $Z$: Insights from the BLOeM Campaign

Abstract

We present an overview of our recent results from the BLOeM campaign in the Small Magellanic Cloud ($Z=0.2{\mathrm{Z}}_{\odot }$). Using nine-epoch VLT/FLAMES spectroscopy, we investigated the multiplicity of 929 massive stars. Our findings reveal contrasting binary properties across evolutionary stages: O-type stars show an intrinsic close-binary fraction of $70\%$, and early B-type dwarfs/giants reach $\sim 80\%$, exceeding higher-metallicity samples. In contrast, B0-B3 supergiants drop to $\sim 40\%$, and A-F supergiants to $\sim 8\%$; intrinsic variability likely inflates the latter, so the true multiplicity may be lower. OBe stars display distinct binary properties consistent with a post-interaction origin. These results have profound implications for massive-star evolution at low metallicity, including the production of exotic transients, gravitational-wave progenitors, and ionising radiation in the early Universe.

5 pages, 5 figures, IAU Symposium 402 proceedings "Massive Stars Across Redshifts in the Era of JWST and Large-Scale Surveys"