PDRs4All: X. ALMA and JWST detection of neutral carbon in the externally irradiated disk d203-506: Undepleted gas-phase carbon
Journal article, 2024
The gas-phase abundance of carbon, xC = [C/H]gas = xC+ + xC0 + xCO + ¦, and its depletion factors are essential parameters for understanding the gas and solid compositions that are ultimately incorporated into (exo)planets. The majority of protoplanetary disks are born in clusters and, as a result, are exposed to external far-ultraviolet (FUV) radiation. These FUV photons potentially affect the disk's evolution, chemical composition, and line excitation. We present the first detection of the [C ¯I] 609 μm fine-structure (3P13P0) line of neutral carbon (C0), achieved with ALMA, toward one of these disks, d203-506, in the Orion Nebula Cluster. We also report the detection of [C ¯I] forbidden and C ¯I permitted lines (from electronically excited states up to ¼10 eV) observed with JWST in the near-infrared (NIR). These lines trace the irradiated outer disk and photo-evaporative wind. Contrary to the common belief that these NIR lines are C+ recombination lines, we find that they are dominated by FUV-pumping of C0 followed by fluorescence cascades. They trace the transition from atomic to molecular gas, and their intensities scale with G0. The lack of outstanding NIR O ¯I fluorescent emission, however, implies a sharper attenuation of external FUV radiation with E 12 eV (λ Lyman-β). This is related to a lower effective FUV dust absorption cross section compared to that of interstellar grains, implying a more prominent role for FUV shielding by the C0 photoionization continuum. The [C ¯I] 609 μm line intensity is proportional to N(C0) and can be used to infer xC. We derive xC 1.4- 104. This implies that there is no major depletion of volatile carbon compared to xC measured in the natal cloud, hinting at a young disk. We also show that external FUV radiation impacts the outer disk and wind by vertically shifting the water freeze-out depth, which likely results in less efficient grain growth and settling. This shift leads to nearly solar gas-phase C/O abundance ratios in these irradiated layers.
Protoplanetary disks
Photon-dominated region (PDR)
ISM: abundances
Author
J.R. Goicoechea
CSIC - Instituto de Fisica Fundamental (IFF)
Jacques Le Bourlot
Paris Descartes University
John H Black
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Felipe Alarcon
University of Michigan
E. A. Bergin
University of Michigan
O. Berné
Institut de Recherche en Astrophysique et Planétologie (IRAP)
E. Bron
Paris Observatory
Amelie Canin
Institut de Recherche en Astrophysique et Planétologie (IRAP)
E. Chapillon
Institut de Radioastronomie Millimétrique (IRAM)
Ryan Chown
Western University
Ohio State University
E. Dartois
University Paris-Saclay
M. Gerin
Paris Observatory
Emilie Habart
Institut d'Astrophysique Spatiale
Thomas J. Haworth
Queen Mary University of London
C. Joblin
Institut de Recherche en Astrophysique et Planétologie (IRAP)
Olga Kannavou
Institut d'Astrophysique Spatiale
Franck Le Petit
Paris Observatory
T. Onaka
University of Tokyo
Els Peeters
Western University
SETI Institute
J. Pety
Institut de Radioastronomie Millimétrique (IRAM)
Paris Observatory
Evelyne Roueff
Paris Observatory
Ameek Sidhu
Western University
Ilane Schroetter
Institut de Recherche en Astrophysique et Planétologie (IRAP)
Benoît Tabone
Institut d'Astrophysique Spatiale
A.G.G.M. Tielens
Leiden University
College of Computer, Mathematical, & Natural Sciences
Boris Trahin
Institut d'Astrophysique Spatiale
Dries Van De Putte
Western University
Space Telescope Science Institute (STScI)
S. Vicente
Instituto de Astrofísica e Ciências do Espaço
Marion Zannese
Institut d'Astrophysique Spatiale
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 689 L4Subject Categories
Astronomy, Astrophysics and Cosmology
Atom and Molecular Physics and Optics
DOI
10.1051/0004-6361/202450988