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

A. Ebenbichler, P. Moraga Baez, A. Candian, E. Peeters, J. Cami, P. J. Sarre, A. N. Witt, I. Argyriou, B. Vandenbussche, H. Van Winckel, L. B. F. M. Waters

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.

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

Paper Structure

This paper contains 7 sections, 4 figures.

Table of Contents

  1. Introduction
  2. Observations
  3. Results
  4. Discussion
  5. Conclusions
  6. Diffraction effects from the central infrared source
  7. Spectra with continuum

Figures (4)

  • Figure 1: JWST-MIRI channel 2C apertures (summed from 10.01 to $11.7\,\mu$m) of the positions GO (north), P1P2 (south, mosaic of P1 and P2) and P3 (west) outlined in red on an HST WFPC2 F622W image. White contours represent a diffraction model of the central region at $10\,\mu$m, using the MIRI imaging point spread function (PSF).
  • Figure 2: JWST/MIRI spectra from Regions 1--3 compared with the ISO-SWS spectrum (black). All spectra are continuum-subtracted and normalized to the peak of the 6.2 $\mu$m AIB band. Apertures are defined in Fig. \ref{['fig:FOVs']}.
  • Figure 3: AIB profile comparison for the 6.2 $\mu$m (top); 7.7 $\mu$m and 8.6 $\mu$m (middle); 11.2 $\mu$m (bottom) AIB features. Spectra are normalized to the dominant AIB in each panel.
  • Figure 4: Comparison of JWST-MIRI spectra (from top to bottom: Region 1, 2, and 3) with the ISO-SWS spectrum (bottom). The MIRI apertures are defined in Fig. \ref{['fig:FOVs']}. The black dashed line indicates the continuum which was subtracted in Figs. \ref{['fig:Aps_full']} and \ref{['fig:Aps']}. Note that the JWST spectra are in surface brightness units (MJy/sr) while the ISO-SWS spectrum is in flux density (Jy).