JWST MIRI-MRS observations of the Red Rectangle: AIB class transformation in the outer nebula

TL;DR

This study uses JWST MIRI-MRS observations to analyze the outer Red Rectangle nebula, revealing environment-dependent PAH processing and AIB class variations, contrasting inner and outer regions.

Contribution

First detailed mid-infrared spectral analysis of the Red Rectangle's outer nebula, highlighting environmental effects on PAH features and dust composition.

Findings

Outer nebula shows classical AIB emission with a weak dust continuum.

AIBs are predominantly Class A, differing from the Class B profiles of the inner nebula.

Environmental differences influence PAH processing in the nebula.

Abstract

Aims: 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. Methods: We present JWST MIRI-MRS observations of the SW whisker, extracted from three distinct environments: the biconical outflow, the whisker itself, and the shadow region outside the outflow. We compare these with an archival ISO-SWS observation of the inner nebula. Results: The JWST spectra display only classical 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 A - in marked contrast to the exclusively Class B profiles previously reported for the inner regions - with systematic differences between the outflow and shadow regions pointing to environmentally driven PAH processing.