Hidden Companions to Intermediate-mass Stars. XI. Uncovering a 0.7 M ⊙, 2.3 au Companion in the Astrometric Binary HIP 111200 = 58 Aquarii* *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

Abstract

We report on the direct VLTI/GRAVITY interferometric detection of a close companion in the nearby Hipparcos astrometric binary 58 Aquarii with a K band flux ratio of 5.0% at a projected separation 32 mas ↔ 2.3 au. Through isochrone fitting we find that the primary is a 1.4 Gyr old, 1.68 M ⊙ late A-type star and the companion is a 0.72 M ⊙ K-type star. The estimated cooling age of 900 Myr for the wide (9940 au), 0.70 M ⊙ white dwarf (WD) companion to the system is consistent with a progenitor star of 2.9 M ⊙ assuming single star evolution. The survival of the triple system at such large separation suggests a low kick in the formation of the WD or alternatively that it has since migrated outwards through three-body interaction.