Spectroastrometric Study of Ro-vibrational CO Emission from the Herbig Ae star HD~179218 with iSHELL on the NASA Infrared Telescope Facility

We present analysis of commissioning $M-$band data acquired with the infrared echelle spectrograph (iSHELL) on {\it NASA's Infrared Telescope Facility}. In this paper we describe the delivered performance of the instrument for these $M-$band observations and the data reduction process. The feasibility of using iSHELL for spectro-astrometry is tested on the Herbig Ae/Be star HD~179218 and we show that sub-milliarcsecond fidelity is achievable.