Spatial distributions of PN and PO in the shock region L1157-B1

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
e-mail: bertrand.le-floch@u-bordeaux.fr
² Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
³ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: claudio.codella@inaf.it
⁴ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
⁵ IRAP, Université de Toulouse, 9 avenue du colone Roche, 31028 Toulouse Cedex 4, France
⁶ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁷ Department of Physics and Astronomy, UCL, Gower St., London WC1E 6BT, UK
⁸ Centro de Astrobiologia (CSIC/INTA), Ctra de Torrejón a Ajalvir, km 4 Torrejón de Ardoz, 28850 Madrid, Spain

Received: 31 October 2022
Accepted: 2 April 2024

Abstract

Phosphorus plays an essential role in prebiotic chemistry. The origin of P-bearing molecules in the protostellar gas remains highly uncertain. Only PO and PN have been detected towards low-mass star-forming regions and their emission is mainly associated with outflow shocks. In order to make progress in the characterisation of P-chemistry, we present NOEMA observations of PO and PN at 3″−4″ resolution towards the outflow shock region L1157-B1. Our resolved observations confirm the association of both P species with the apex of the bow shock. High-velocity emission is detected in the compact region where the jet impacts the shock. Analysis of the spatial distributions of PO and PN indicates that these molecules are not sputtered from the icy mantles of dust grains; they are the gas-phase products of a P-mother species released in the shock. PO appears to form first in the gas phase, followed by PN, which remains longer in the shock, when PO is no longer detected. Variations of the PO/PN abundance ratio in the range 1–5 are detected over the apex and confirm the short time variability of P-chemistry, which typically lasts a few hundred years. These results are consistent with the previous modelling of P-chemistry in L1157-B1. Complementary observations of N-bearing species at high angular resolution are needed to better understand the formation pathways of PO and PN.