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 repository@u.library.arizona.edu