On-Sky Rotator Vector

ARCoIRIS hosts a J-band imaging detector, which contemporaneously acts as a slit viewer and a guider. Its on-sky orientation changes however as a function of instrument rotator angle, which can make the identification of fields difficult using the usual N-up, E-left norm for astronomical finding charts. The schematic below shows the on-sky cardinal directions for the slit viewer detector as a function of rotator angle.