2018MNRAS.479L..60N

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 [P III] fine structure transition 3s²3p⁽2Po_1/2–3/2^) within the ground state at 17.9 µm , as well as allowed UV transitions in the 3s²3p⁽2Po_1/2,3/2^) →3s3p²(²D_3/2,5/2, ²S_1/2, ²P_1/2,3/2) multiplets between 915 and 1345 Å. 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 µm 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 β and found to be similar to observed intensities 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.