¹² CO Rovibrational Spectroscopy of AB Aurigae—A Potential Point Source Is Present

Abstract The Herbig Ae star AB Aurigae hosts a vast, low-inclination protoplanetary disk that exhibits a plethora of substructures, including the protoplanet candidate AB Aur b. We present M -band spectroscopic data taken with the NASA Infrared Telescope Facility from 2024 February, covering multiple position angles that captured emission from an off-centered, low temperature, and compact source. Analysis of the 12 CO v = 1–0 low- J rovibrational emission line profiles and spectroastrometric signals localizes the source at around an orbital radius of 65 au and a position angle of 143°. These coordinates are distinctly different from those of AB Aur b, which was not detected. Although there is no obvious explanation for the detected source, if we assume it is a circumplanetary disk, then its maximum temperature would be about 550 K and its maximum radius would be about ∼5 au. Our results alludes to a previously unknown companion that may be residing in the AB Aurigae system.