2024RNAAS...8..131W

Gamma Trianguli Australis is a nearby A-type star that was reported to be a 488 days astrometric binary in Gaia DR3. Here we report on a VLTI/GRAVITY observation of γ TrA in which we did not detect the companion down to a K band flux ratio of 0.5%. From the isochrone mass M_A = 3.04M_⊙ of the subgiant primary, this implies a semimajor axis a_orb = 1.8 au and that the companion is a M_B = 0.26M_⊙ M dwarf. The primary disk is partially resolved with an angular diameter θ₁ ≈ 1 mas ↔ 13.0R_⊙. The differential visibility phases across the Brγ absorption line allowed us to measure the longitude of the ascending node of the primary's rotational plane Ω_rot = 212° ± 3°. This implies a spin-orbit misalignment of at least 27° ± 3° based on the Gaia astrometric solution.