2025RNAAS...9..107W

Beta2 Tucanae (β² Tuc) is a nearby a = 22 au visual binary (C+D) and one of the brighter members of the young Tucana-Horologium association. Here we report on a VLTI/GRAVITY interferometric observation which revealed that β² Tuc is actually a rather compact triple system: the primary is itself a close binary (Ca+Cb) with a projected separation ρ = 13.56 mas ↔ 0.59 au and a K band flux ratio of 56.65%. We estimate isochrone masses M_Ca ≃ 2.0M_⊙, M_Cb ≃ 1.45M_⊙ and M_D ≃ 1.45M_⊙. Together with its wide (∼1200 au) companion β¹ Tuc (itself a binary) and very wide (∼23,000 au) companion β³ Tuc, this makes the β Tuc system a sextuple. The compactness and rather low effective hierarchy of β² Tuc $\frac{{a}_{{\rm{out}}}(1-{e}_{{\rm{out}}})}{{a}_{{\rm{in}}}}\lesssim 7$ make it a particularly interesting system for triple dynamics and stability studies.