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American Astronomical Society, Research Notes of the American Astronomical Society, 5(8), p. 131, 2024

DOI: 10.3847/2515-5172/ad4a7b

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Hidden Companions to Intermediate-mass Stars. XIX. Spin–Orbit Misalignment and a 0.26M <sub>⊙</sub>, 1.8 au Companion in the Astrometric Binary Gamma Trianguli Australis*

Journal article published in 2024 by Idel Waisberg ORCID, Ygal Klein ORCID, Boaz Katz ORCID
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Red circle
Preprint: archiving forbidden
Red circle
Postprint: archiving forbidden
Green circle
Published version: archiving allowed
Data provided by SHERPA/RoMEO

Abstract

Abstract 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 θ 1 ≈ 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 Ωrot = 212° ± 3°. This implies a spin–orbit misalignment of at least 27° ± 3° based on the Gaia astrometric solution.