The JWST Proto-PAH project: Infrared spectroscopy of highly evolved carbon-rich objects

G.C. Sloan (STScI, UNC Chapel Hill), K. Volk (STScI), J. Cami (Univ. Western Ontario), D. Das (Univ. Western Ontario), C. Bhatt (Univ. Western Ontario), N. Clark (Univ. Western Ontario), K.E. Kraemer (Boston College), B. Aringer (Uppsala Univ., Univ. Vienna), J. Bernard-Salas (ACRI-ST), H.L. Dinerstein (Univ. Texas Austin), D.A. Garcia-Hernandez (Inst. Astrof. Canarias, Univ. La Laguna), M.A. Gomez-Munoz (Univ. Barcelona, IEEC), J. Li (Inst. Astrof. Canarias, Univ. La Laguna), A. Manchado (Inst. Astrof. Canarias, Univ. La Laguna, CSIC), M. Matsuura (Cardiff Univ.), E. Peeters (Univ. Western Ontario), A. Ricca (NASA Ames, SETI), R. Sahai (JPL), N.C. Sterling (Univ. West Georgia), G.M. Wahlgren (STScI), A.A. Zijlstra (Univ. Manchester)

2026, ApJ, submitted

Full manuscript available locally (PDF)

IMPORTANT DISCLAIMER: we have posted the submitted manuscript as a courtesy, but bear in mind that it may change, perhaps significantly, during the review process. The same is true of the abstract below.

Spectra from JWST reveal the rich chemistry of gas and dust around seven carbon-rich objects in the Magellanic Clouds as they evolve from the asymptotic giant branch (AGB) to planetary nebulae. As the hot central star is increasingly exposed, polycyclic aromatic hydrocarbons (PAHs) replace the amorphous carbon dust. The JWST spectra reveal strong emission and absorption at 3.4--3.5, 6.9, and 7.3 µm from aliphatic hydrocarbons bonded to aromatic skeletons. The spectra show emission and absorption bands from many gas-phase molecules, including H₂, CO, CN, CH₃, CH₄, C₂H₂, C₄H₂, C₆H₂, C₂H₄, C₆H₆, HCN, and HC₃N. Atomic lines include hydrogen in emission and absorption and forbidden lines in emission. Several molecules can exhibit P Cygni profiles from molecular outflows, including CO centered at 4.7 µm, C₄H₂ at 15.94 µm and C₆H₂ at 16.11 µm. This wealth of chemical clues adds to the information needed to understand how PAHs and related carbonaceous material form in the outflows of stars evolving away from the AGB.

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Last modified 24 August, 2026. © Gregory C. Sloan and others.