4 research outputs found
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Elusive Iron: Detection of the FeC Radical (X 3Δi ) in the Envelope of IRC+10216
A new interstellar molecule, FeC (X 3Δi ), 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. The J = 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 near V LSR ≈ −26 km s−1 and linewidths of ΔV 1/2 ≈ 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 300 R * (∼6″) extending out to ∼500 R * (∼10″) and a fractional abundance, relative to H2, of f ∼ 6 × 10−11. The previous FeCN spectra were also modeled, yielding an abundance of f ∼ 8 × 10−11 in a larger shell situated near 800 R *. 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. © 2023. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
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Phosphorus-bearing molecules PO and PN at the edge of the Galaxy
Despite its importance in planet formation and biology 1, phosphorus has been identified only in the inner 12 kpc of the Galaxy 2–19. The study of this element has been hindered in part by unfavourable atomic transitions 2,4,20. Phosphorus is thought to be created by neutron capture on 29Si and 30Si in massive stars 20,21, and released into the interstellar medium by Type II supernova explosions 2,22. However, models of galactic chemical evolution must arbitrarily increase the supernovae production 23 to match observed abundances. Here we present the detection of gas-phase phosphorus in the Outer Galaxy through millimetre spectra of PO and PN. Rotational lines of these molecules were observed in the dense cloud WB89-621, located 22.6 kpc from the Galactic Centre 24. The abundances of PO and PN in WB89-621 are comparable to values near the Solar System 25. Supernovae are not present in the Outer Galaxy 26, suggesting another source of phosphorus, such as ‘Galactic Fountains’, where supernova material is redistributed through the halo and circumgalactic medium 27. However, fountain-enriched clouds are not found at such large distances. Any extragalactic source, such as the Magellanic Clouds, is unlikely to be metal rich 28. Phosphorus instead may be produced by neutron-capture processes in lower mass asymptotic giant branch stars 29 which are present in the Outer Galaxy. Asymptotic giant branch stars also produce carbon 21, flattening the extrapolated metallicity gradient and accounting for the high abundances of C-containing molecules in WB89-621. © 2023, The Author(s).Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
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Detection of po in orion-kl: Phosphorus chemistry in the plateau outflow
The PO molecule (X2r) has been detected toward Orion-KL via its J = 2.5 → 1.5 transition near 109 GHz using the 12 m telescope of the Arizona Radio Observatory. This transition consists of a quartet of lines, generated by lambda-doubling and phosphorus hyperfine interactions, creating a distinct pattern of doublets of doublets. All four features (F = 3 → 2, e, f and 2 → 1, e, f ) were detected. The line profiles measured were relatively broad, with ΔV1/2 ∼ 21-25 km s-1, and VLSR ∼ 10 km s-1, clearly identifying the molecule as arising from the Orion "plateau"region. The J = 2 → 1 transition of PN (X1Σ) at 94 GHz was also measured, and its line profile indicates a plateau origin in Orion, as found previously by Ziurys. Therefore, PO and PN arise from the same gas. There was no evidence of a "hot core"or "ridge"component in either molecule. The column densities determined for PO and PN in the Orion plateau are Ntot ≈ 5.4(0.2) × 1013 and 2.0(0.4) × 1013 cm-2, respectively, with corresponding abundances, relative to H2, of f ∼ 1.6(0.1) × 10-10 and 6.1(0.6) × 10-11, resulting in PO/ PN ∼ 3. The PO and PN line profiles also resemble those of SiO and SiS, suggesting that the phosphorus molecules are produced by shocks in the plateau outflow. The observed PO/PN ratio in Orion-KL is very close in value to that measured in other warm molecular clouds, indicating a common synthesis pathway for these two molecules in outflows caused by star formation. © 2021. The American Astronomical Society.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
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Laboratory and Astronomical Detection of the SiP Radical (X2Πi): More Circumstellar Phosphorus
The millimeter-wave spectrum of the SiP radical (X2Πi) has been measured in the laboratory for the first time using direct-absorption methods. SiP was created by the reaction of phosphorus vapor and SiH4 in argon in an AC discharge. Fifteen rotational transitions (J + 1 ← J) were measured for SiP in the Ω = 3/2 ladder in the frequency range 151-533 GHz, and rotational, lambda doubling, and phosphorus hyperfine constants determined. Based on the laboratory measurements, SiP was detected in the circumstellar shell of IRC+10216, using the Submillimeter Telescope and the 12 m antenna of the Arizona Radio Observatory at 1 mm and 2 mm, respectively. Eight transitions of SiP were searched: four were completely obscured by stronger features, two were uncontaminated (J = 13.5 → 12.5 and 16.5 → 15.5), and two were partially blended with other lines (J = 8.5 → 7.5 and 17.5 → 16.5). The SiP line profiles were broader than expected for IRC+10216, consistent with the hyperfine splitting. From non-LTE radiative transfer modeling, SiP was found to have a shell distribution with a radius ∼300 R *, and an abundance, relative to H2, of f ∼ 2 × 10−9. From additional modeling, abundances of 7 × 10−9 and 9 × 10−10 were determined for CP and PN, respectively, both located in shells at 550-650 R *. SiP may be formed from grain destruction, which liberates both phosphorus and silicon into the gas phase, and then is channeled into other P-bearing molecules such as PN and CP. © 2022. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]