Pop III i-process and the most iron-poor stars: data and plotting scripts for Figure 4 of Clarkson, Herwig & Pignatari (2018)

Observational data, NuGrid single-zone post-processing (PPN) nucleosynthesis model data, and the plotting code needed to reproduce Figure 4 of Clarkson, Herwig & Pignatari (2018, MNRAS Letters 474, L37) and its 2019 erratum (MNRAS 488, 222). Figure 4 compares the observed elemental abundances of the three most iron-poor stars known — SMSS J0313-6708, HE 1327-2326 and HE 0107-5240 — with single-zone i-process (hydrogen-ingestion) nucleosynthesis models of a 45 solar-mass Population III star. The plotted quantity is [X/H] versus proton number Z. Contents: observed [X/H] tables for the three stars; the NuGrid USEEPP solar/initial-abundance reference; the raw decayed PPN abundance snapshots (iso_massf files) for the five model runs OZ.c-H, OZ.s-He and OZ.i-p:t1/t2/t3; a derived [X/H]-vs-Z CSV; a simple, self-contained Jupyter notebook (plot_abundances.ipynb) that reproduces the figure with only numpy + matplotlib and documents how to add your own observations or models; and a script (reproduce_fig4.py) that regenerates the published figure from the raw PPN output using NuGridPy. See README.md for full details.