Hidden Companions to Intermediate-mass Stars. IV. Uncovering a 1.1 M ⊙, 1.3 au Companion in the Astrometric Binary HIP 77541* *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

Abstract

There are many Hipparcos/Gaia astrometric binaries for which the nature of the companion is not known. Optical/near-infrared inteferometry is arguably the most efficient method to unambiguously identify such companions. Here we report on a VLTI/GRAVITY observation in which we detected a companion to the nearby astrometric binary HIP 77541 with a K band flux ratio of 20% at a projected separation ρ = 18 mas ↔ 1.3 au. The resulting isochrone masses 2.0 + 1.1M ⊙ imply that HIP 77541 is a potential progenitor for a close white dwarf binary within a Hubble time.