Skip to content
DraconiticResearch
Search Sources API
203,203 studies31 sourcesUpdated 7 min ago
PreprintCC BY 4.0arXiv

The JWST Proto-PAH Project: Detection of the methyl radical CH3 in the highly evolved C-rich object SMP LMC 011

  • Jialu Li
  • D. A. García-Hernández
  • A. Manchado
  • Debayan Das
  • J. Cami
  • Els Peeters
  • G. C. Sloan
  • B. Aringer
  • J. Bernard-Salas
  • C. Bhatt
  • Nicholas Clark
  • Harriet L. Dinerstein
8 more authors
  • M. A. Gómez-Muñoz
  • Kathleen E. Kraemer
  • M. Matsuura
  • R. Sahai
  • N. C. Sterling
  • Kevin Volk
  • G. M. Wahlgren
  • A. A. Zijlstra
Open at sourcePDFDOICite

Abstract

We report the first detection of the neutral methyl radical CH3 in a highly evolved C-rich object, SMP LMC 011, using JWST MIRI/MRS. CH3 is well fitted by an excitation temperature of Tex ≃~190\,K and a column density of Ntot(CH3) ≃ 5.6×1017 cm−2. We also report the non-detection of ethane (C2H6), consistent with CH3 reacting preferentially with unsaturated radicals rather than self-recombination, which may be inefficient in SMP LMC 011. Combined with the exceptionally large benzene column density of SMP LMC 011, this supports a methyl-addition route from benzene towards alkyl-substituted aromatics. We propose that the high CH3 abundance is driven by the erosion of hydrogenated amorphous carbon (HAC) dust grains in the dense warm torus by UV photons from the central star and/or by shocks, which release CH3 directly into the gas phase. These results establish CH3 as a key reactive intermediate in the formation of complex hydrocarbons in C-rich circumstellar environments. Chemical models that incorporate methyl-addition reactions are needed for a better understanding of PAH formation pathways in evolved stars. The potential detection of alkyl-substituted aromatics such as toluene (C7H8) and ethylbenzene (C8H10) in C-rich evolved stars would provide direct confirmation of CH3-driven aromatic growth in circumstellar environments.

Related

  1. The JWST Proto-PAH Project: Detection of the Methyl Radical CH ₃ in the Highly Evolved C-rich Object SMP LMC 011
    Jialu Li, D. A. García-Hernández, A. Manchado +17
    The Astrophysical Journal LettersPeer-reviewedCC BY 4.0Full textSolar & stellar physicsCrossref
  2. Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS). VIII. First interstellar detection of fully deuterated methyl cyanide
    A. Belloche, J. K. Jorgensen, M. N. Drozdovskaya +12
    Astronomy & AstrophysicsPeer-reviewedPublisher termsSolar & stellar physicsCrossref
  3. Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VIII. First interstellar detection of fully deuterated methyl cyanide
    A. Belloche, J. K. Jørgensen, M. N. Drozdovskaya +12
    arXivPreprintarXiv licenceFull textGalaxiesarXiv
  4. Evolved stars, multiplicity and planets: Shaping and Being Shaped by Stellar Evolution
    Theo Khouri, Wouter Vlemmings, Elvire De Beck +21
    arXivPreprintCC BY-NC-SA 4.0Full textInstrumentation & methodsPlanetary science & exoplanetsarXiv
  5. Evolved stars: dust formation and mass loss
    Luis Velilla-Prieto, Wouter Vlemmings, Guillermo Quintana-Lacaci +18
    arXivPreprintCC BY 4.0Full textInstrumentation & methodsarXiv

Cite

BibTeXRIS
BibTeX
@misc{li2026jwst,
  title = {{The JWST Proto-PAH Project: Detection of the methyl radical CH$_3$ in the highly evolved C-rich object SMP LMC 011}},
  author = {Jialu Li and D. A. García-Hernández and A. Manchado and Debayan Das and J. Cami and Els Peeters and G. C. Sloan and B. Aringer and J. Bernard-Salas and C. Bhatt and Nicholas Clark and Harriet L. Dinerstein and M. A. Gómez-Muñoz and Kathleen E. Kraemer and M. Matsuura and R. Sahai and N. C. Sterling and Kevin Volk and G. M. Wahlgren and A. A. Zijlstra},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.15905},
  eprint = {2609.15905},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.15905},
  note = {CC BY 4.0},
}
RIS
TY  - UNPB
TI  - The JWST Proto-PAH Project: Detection of the methyl radical CH_3 in the highly evolved C-rich object SMP LMC 011
AU  - Jialu Li
AU  - D. A. García-Hernández
AU  - A. Manchado
AU  - Debayan Das
AU  - J. Cami
AU  - Els Peeters
AU  - G. C. Sloan
AU  - B. Aringer
AU  - J. Bernard-Salas
AU  - C. Bhatt
AU  - Nicholas Clark
AU  - Harriet L. Dinerstein
AU  - M. A. Gómez-Muñoz
AU  - Kathleen E. Kraemer
AU  - M. Matsuura
AU  - R. Sahai
AU  - N. C. Sterling
AU  - Kevin Volk
AU  - G. M. Wahlgren
AU  - A. A. Zijlstra
PY  - 2026
DA  - 2026/09/14
PB  - arXiv
DO  - 10.48550/arxiv.2609.15905
UR  - https://arxiv.org/abs/2609.15905
AB  - We report the first detection of the neutral methyl radical CH_3 in a highly evolved C-rich object, SMP LMC 011, using JWST MIRI/MRS. CH_3 is well fitted by an excitation temperature of T_ex ≃~190\,K and a column density of N_tot(CH_3) ≃ 5.6×10^17 cm^−2. We also report the non-detection of ethane (C_2H_6), consistent with CH_3 reacting preferentially with unsaturated radicals rather than self-recombination, which may be inefficient in SMP LMC 011. Combined with the exceptionally large benzene column density of SMP LMC 011, this supports a methyl-addition route from benzene towards alkyl-substituted aromatics. We propose that the high CH_3 abundance is driven by the erosion of hydrogenated amorphous carbon (HAC) dust grains in the dense warm torus by UV photons from the central star and/or by shocks, which release CH_3 directly into the gas phase. These results establish CH_3 as a key reactive intermediate in the formation of complex hydrocarbons in C-rich circumstellar environments. Chemical models that incorporate methyl-addition reactions are needed for a better understanding of PAH formation pathways in evolved stars. The potential detection of alkyl-substituted aromatics such as toluene (C_7H_8) and ethylbenzene (C_8H_10) in C-rich evolved stars would provide direct confirmation of CH_3-driven aromatic growth in circumstellar environments.
ER  -