The PA averages of the emission line profiles (bottom) and spectroastrometric signals (top) from AB Aur’s high-J (left) and low-J (right) ¹²CO rovibrational v = 1–0 transitions (Section 3.1). Variable emission between PAs was captured in the low-J line profiles as well as a spatial offset in the spectroastrometric signals. This behavior is not mirrored in the high-J equivalent, and that can be an indication of a low-temperature substructure being present in the protoplanetary disk (Sections 3.3.2 and 3.3.3). Also, the high-J line profiles are used for determining the thermophysical environment of the protoplanetary disk’s emitting surface layer (Section 3.3.1).