The JWST Proto-PAH Project. Computational Modeling of the Emission Carriers
11 affiliations
- 1NASA Ames Research Center
- 2SETI Institute
- 3Space Telescope Science Institute
- 4University of North Carolina
- 5The University of Western Ontario
- 6Cardiff University
- 7California Institute of Technology
- 8ACRI-ST
- 9INCLASS Common Laboratory
- 10Instituto de Astrofísica de Canarias
- 11Universidad de La Laguna (ULL)
Abstract
The infrared spectra of many carbon-rich postasymptotic giant branch stars are dominated by emission features from aromatic and aliphatic hydrocarbons, but the chemical structure of the carriers remains unidentified. Class D sources show unusual emission profiles with strong aliphatic emission, providing a stringent test of carrier candidates. Here we investigate whether hydrogenated carbonaceous molecular particles can be the carriers of these features. Rather than assuming candidate geometries we generate the initial structures using ab initio molecular dynamics simulations and optimize them using density functional theory. We then compare the computed emission spectra to JWST NIRSpec and MIRI/MRS observations of Class D sources. The structures providing the best agreements contain sizeable domains with defect-bearing aromatics and hydrogenated aromatics connected by aliphatic bridges, in contrast to the “arophatic” cluster model of isolated two- to three-ring aromatics connected by aliphatic and olefinic bridges. As a representative example, we discuss in detail the molecular particle C ₁₃₀ H ₉₆ (radius of 5.5 Å) and compare its computed spectrum to the JWST spectra of IRAS 05110-6616, a Class D2 source with apparent shifts of the aromatic C–H out-of-plane bands. The calculated spectra are in qualitative agreement with the observed 3 μ m profile, the aliphatic C–H bending bands, the broad 8 μ m feature, the 11–14 μ m C–H out-of-plane region, and the bands at 16 and 21 μ m. We hypothesize that UV photodriven fragmentation of such molecular particles releases aromatics linked by aliphatics, followed by the formation of polycyclic aromatic hydrocarbons and fullerenes as these objects evolve into planetary nebulae.
Related
- The JWST Proto-PAH project: Aromatic backbones with extensive aliphatic substitution account for both the aromatic and aliphatic emission
- The JWST Proto-PAH project: Aromatic backbones with extensive aliphatic substitution account for both the aromatic and aliphatic emission
- An updated model of neutrino emission from proto-neutron stars
- The JWST Proto-PAH Project: Detection of the methyl radical CH3 in the highly evolved C-rich object SMP LMC 011
- The JWST Proto-PAH Project: Detection of the Methyl Radical CH ₃ in the Highly Evolved C-rich Object SMP LMC 011
BibTeX
@article{ricca2026jwst,
title = {{The JWST Proto-PAH Project. Computational Modeling of the Emission Carriers}},
author = {A. Ricca and G. C. Sloan and E. Peeters and J. Cami and N. Clark and M. Matsuura and R. Sahai and J. Bernard-Salas and D. A. García-Hernández and J. Li and C. Bhatt},
journal = {The Astrophysical Journal},
year = {2026},
month = nov,
doi = {10.3847/1538-4357/aeacd8},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aeacd8},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - The JWST Proto-PAH Project. Computational Modeling of the Emission Carriers
AU - A. Ricca
AU - G. C. Sloan
AU - E. Peeters
AU - J. Cami
AU - N. Clark
AU - M. Matsuura
AU - R. Sahai
AU - J. Bernard-Salas
AU - D. A. García-Hernández
AU - J. Li
AU - C. Bhatt
PY - 2026
DA - 2026/11/03
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aeacd8
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aeacd8
AB - The infrared spectra of many carbon-rich postasymptotic giant branch stars are dominated by emission features from aromatic and aliphatic hydrocarbons, but the chemical structure of the carriers remains unidentified. Class D sources show unusual emission profiles with strong aliphatic emission, providing a stringent test of carrier candidates. Here we investigate whether hydrogenated carbonaceous molecular particles can be the carriers of these features. Rather than assuming candidate geometries we generate the initial structures using ab initio molecular dynamics simulations and optimize them using density functional theory. We then compare the computed emission spectra to JWST NIRSpec and MIRI/MRS observations of Class D sources. The structures providing the best agreements contain sizeable domains with defect-bearing aromatics and hydrogenated aromatics connected by aliphatic bridges, in contrast to the “arophatic” cluster model of isolated two- to three-ring aromatics connected by aliphatic and olefinic bridges. As a representative example, we discuss in detail the molecular particle C ₁₃₀ H ₉₆ (radius of 5.5 Å) and compare its computed spectrum to the JWST spectra of IRAS 05110-6616, a Class D2 source with apparent shifts of the aromatic C–H out-of-plane bands. The calculated spectra are in qualitative agreement with the observed 3 μ m profile, the aliphatic C–H bending bands, the broad 8 μ m feature, the 11–14 μ m C–H out-of-plane region, and the bands at 16 and 21 μ m. We hypothesize that UV photodriven fragmentation of such molecular particles releases aromatics linked by aliphatics, followed by the formation of polycyclic aromatic hydrocarbons and fullerenes as these objects evolve into planetary nebulae.
SN - 1538-4357
SN - 0004-637X
ER -