Hidden Companions to Intermediate-mass Stars. XII. Discovery of a 1.8 M ⊙, 1.3 au Companion to Delta Serpentis A*

Abstract

Abstract Delta Serpentis is a nearby 4″ visual binary (A+B) that has accrued a number of astrometric anomalies. Here we show that the primary component is actually a close binary based on a VLTI/GRAVITY archival interferometric observation. The newly discovered companion has a K band flux ratio of 33% at a projected separation ρ = 23.9 mas ↔ 1.3 au. Through isochrone fitting we find somewhat evolved 1.2 Gyr old M Aa = 1.98 M ⊙, M Ab = 1.80 M ⊙ and M B = 1.88 M ⊙ stars. Delta Ser joins a growing list of intermediate mass hierarchical multiples and may be a progenitor of a rather rare system of three white dwarfs.