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Title: Elusive Iron: Detection of the FeC Radical (X 3 Δ i) in the Envelope of IRC+10216
Abstract A new interstellar molecule, FeC (X3Δi), has been identified in the circumstellar envelope of the carbon-rich asymptotic giant branch star IRC+10216. FeC is the second iron-bearing species conclusively observed in the interstellar medium, in addition to FeCN, also found in IRC+10216. TheJ= 4 → 3, 5 → 4, and 6 → 5 rotational transitions of this free radical near 160, 201, and 241 GHz, respectively, were detected in the lowest spin–orbit ladder, Ω = 3, using the Submillimeter Telescope of the Arizona Radio Observatory (ARO) for the 1 mm lines and the ARO 12 m at 2 mm. Because the ground state of FeC is inverted, these transitions are the lowest energy lines. The detected features exhibit slight U shapes with LSR velocities nearVLSR≈ −26 km s−1and linewidths of ΔV1/2≈ 30 km s−1, line parameters characteristic of IRC+10216. Radiative transfer modeling of FeC suggests that the molecule has a shell distribution with peak radius near 300R*(∼6″) extending out to ∼500R*(∼10″) and a fractional abundance, relative to H2, off∼ 6 × 10−11. The previous FeCN spectra were also modeled, yielding an abundance off∼ 8 × 10−11in a larger shell situated near 800R*. These distributions suggest that FeC may be the precursor species for FeCN. Unlike cyanides and carbon-chain molecules, diatomic carbides with a metallic element are rare in IRC+10216, with FeC being the first such detection.  more » « less
Award ID(s):
1907910 2307305
PAR ID:
10484828
Author(s) / Creator(s):
;
Publisher / Repository:
IOP
Date Published:
Journal Name:
The Astrophysical Journal Letters
Volume:
958
Issue:
1
ISSN:
2041-8205
Page Range / eLocation ID:
L6
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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