Hidden Companions to Intermediate-mass Stars. Upgraded Multiplicity 1 → 2. XXXI. Discovery of a 0.64<i>M</i> _⊙, 3.4 au Companion to Psi Scorpii*

Abstract Stars with both a significant astrometric acceleration and no detected companion are candidates for having a compact object companion but they must first pass through the sieve of near-infrared interferometry. Psi Scorpii ( ψ Sco) is a nearby A-type star that has amassed a number of astrometric anomalies while previous observations did not detect any companion. Here we report on a VLTI/GRAVITY observation in which we detected a companion to ψ Sco with a K band flux ratio of 3.5% ± 0.1% at a projected separation ρ = 78 mas ↔ 3.4 au. Isochrone fitting implies masses M A ≃ 1.95 M ⊙ and M B ≃ 0.64 M ⊙ and a system age of 630 Myr. The orbital motion with a period of about 10 yr can explain the astrometric anomalies of ψ Sco.