Detection of PO in Orion-KL: Phosphorus Chemistry in the Plateau Outflow
Abstract
The PO molecule (X2Πr) 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2021
- DOI:
- 10.3847/1538-4357/abc87b
- Bibcode:
- 2021ApJ...906...55B
- Keywords:
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- Astrochemistry;
- Star formation;
- Interstellar abundances;
- Interstellar molecules;
- Molecular clouds;
- Astrobiology;
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- 1569;
- 832;
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