Hidden Companions to Intermediate-mass Stars. XXV. Uncovering a 2.6 M_⊙, 0.36 au Companion to m Carinae (Plus Evidence for a M ∼ 0.5M_⊙ Outer Companion)*

Abstract m Carinae is a B9V star and the most massive member of the nearby and young (13 Myr) Carina association containing about 25 stars. It has been reported as SB2 in the past but the nature of the companion was only vaguely assessed. Here we report on a VLTI/GRAVITY interferometric observation which revealed that the companion has a K band flux ratio of 92% at a projected separation ρ = 5.20 mas ↔ 0.36 au. Isochrones based on the photometry imply masses M Aa = 2.75 M ⊙ and M Ab = 2.63 M ⊙ . This companion, however, cannot explain either the Gaia-Hipparcos acceleration of m Car or its X-ray emission. We suggest that both are most likely caused by an additional M ∼ 0.5 M ⊙ companion at a separation of about 20 au and which could be easily detected with modern Adaptive Optics observations.