JWST MIRI-MRS observations of the Red Rectangle: Aromatic infrared band class transformation in the outer nebula

We characterize the mid-infrared spectrum of the outer regions of the Red Rectangle nebula to probe the carbonaceous dust and molecular content beyond the circumbinary disk. We present JWST MIRI-MRS observations of the southwest whisker that were extracted from three distinct environments: the biconical outflow, the whisker itself, and the shadow region outside the outflow. We compare them with an archival ISO-SWS observation of the inner nebula. The JWST spectra display only classical aromatic infrared band (AIB) emission on a weak dust continuum, with no signatures of the oxygen-rich circumbinary disk mineralogy nor of the rich molecular emission seen at optical wavelengths. The AIBs are predominantly Class ļassA, which is in marked contrast to the exclusively Class ļassB profiles previously reported for the inner regions; there are systematic differences between the outflow and shadow regions that point to environmentally driven polycyclic aromatic hydrocarbon processing.