An interferometric study of B star multiplicity^⋆

¹ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
² Institute of Astronomy, KU Leuven, Celestijnlaan 200D, 3001 Leuven, Belgium
³ Leuven Gravity Institute, KU Leuven, Celestijnenlaan 200D, box 2415 3001 Leuven, Belgium
⁴ Univ. Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France
⁵ Physics Department, Technion – Israel Institute of Technology, Haifa 3200002, Israel
⁶ Anton Pannekoek Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
⁷ School of Mathematics, Statistics and Physics, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
⁸ Royal Observatory of Belgium, Avenue Circulaire/Ringlaan 3, 1180 Brussels, Belgium
⁹ ESO Headquarters, Karl-Schwarzchild-Str 2, 85748 Garching, Germany
¹⁰ German Aerospace Center (DLR), Institute for AI Safety and Security, Rathausallee 12, St. Augustin 53757, Germany

^⋆⋆ Corresponding author: abigail.frost@eso.org

Received: 1 March 2025
Accepted: 5 June 2025

Abstract

Context. Massive stars can have extreme effects on their environments from local to galactic scales. Their multiplicity can affect this influence by altering how they evolve over time by causing dynamical interactions, common-envelope evolution, mergers and more. While O star multiplicity has been studied over a broad separation range (to the point where absolute masses of these systems have been determined and investigations into multiple system formation and interactions have been performed), studies of B star multiplicity are lacking, even though they dominate the production of core-collapse supernovae and neutron stars.

Aims. Using interferometry, we investigated the multiplicity of a statistically significant sample of B stars over a range of separations (∼0.5–35 au, given that the average distance to our sample is 412 pc).

Methods. We analysed high angular resolution interferometric taken with the PIONIER (Precision Integrated-Optics Near-infrared Imaging ExpeRiment) instrument at the Very Large Telescope Interferometer (VLTI) for a sample of 32 B stars. Using parametric modelling of the closure phases and visibilities, we determined best-fitting models to each of the systems and investigated whether each source was best represented by a single star or a higher-order system. The detection limits were calculated for companions to determine whether they were significant. We then combined our findings from the interferometric data with results from a literature search to determine whether other companions were reported at different separation ranges.

Results. Within the interferometric range 72 ± 8% of the B stars are resolved as multiple systems. The most common type of system are binary systems, followed by single stars, triple systems, and quadruple systems. The interferometric companion fraction derived for the sample is 1.88 ± 0.24. When we accounted for spectroscopic companions that have been confirmed in the literature and wide companions inferred from Gaia data in addition to the companions we found with interferometry, we obtain multiplicity and companion fractions of 0.88 ± 0.06 and 2.31 ± 0.27, respectively, for our sample. The number of triple systems increases significantly to the second-most populous system when we account for spectroscopic companions. This suggests that binarity and higher-order multiplicity are as integral to the evolution of B stars as they are for O stars.