Collision strengths for FIR and UV transtions in PIII and the phosphorus abundance

TL;DR

This paper provides the first detailed calculations of collision strengths for specific FIR and UV spectral lines of PIII, aiding accurate phosphorus abundance measurements in astrophysical objects, with implications for understanding nucleosynthesis and planetary nebulae.

Contribution

It introduces the first calculations of collision strengths for PIII FIR and UV transitions using the Breit-Pauli R-Matrix method, including auto-ionizing resonances.

Findings

Collision strengths exhibit extensive auto-ionizing resonance structures.

The FIR 17.9 μm transition's effective collision strength varies with temperature, peaking at nebular temperatures.

Theoretical emissivities suggest previous phosphorus abundance estimates are 3-5 times sub-solar.

Abstract

Phosphorus abundance is crucial for DNA-based extraterrestrial life in exoplanets. Atomic data for observed spectral lines of P-ions are needed for its accurate determination. We present the first calculations for collision strengths for the forbidden PIII fine structure transition $3s^23p (^2P^o_{1/2-3/2})$ within the ground state at 17.9 $\mu$m, as well as allowed UV transitions in the $3s^23p (^2P^o_{1/2,3/2}) \rightarrow 3s3p^2 (^2D_{3/2,5/2}, ^2S_{1/2}, ^2P_{1/2,3/2})$ multiplets between 915-1345 $\AA$. Collision strengths are computed using the Breit-Pauli R-Matrix method including the first 18 levels, and they exhibit extensive auto-ionizing resonance structures. In particular, the Maxwellian averaged effective collision strength for the FIR 17.9 $\mu$m transition shows a factor 3 temperature variation broadly peaking at typical nebular temperatures. Its theoretical emissivity with solar phosphorus abundance is computed relative to H$\beta$ and found to be similar to observed intensties from planetary nebulae; the abundances derived in earlier works are 3-5 times sub-solar. The results pertain to the reported paucity of phosphorus from preferred production sites in supernovae, and abundances in planetary nebulae and supernova remnants.