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PyNeb (previously PyNebular) is an update and expansion of the IRAF package NEBULAR; rewritten in Python, it is designed to be more user-friendly and powerful, increasing the speed, easiness of use, and graphic visualization of emission lines analysis. In PyNeb, the atom is represented as an n-level atom. For given density and temperature, PyNeb solves the equilibrium equations and determines the level populations. PyNeb can compute physical conditions from suitable diagnostic line ratios and level populations, critical densities and line emissivities, and can compute and display emissivity grids as a function of Te and Ne. It can also deredden line intensities, read and manage observational data, and plot and compare atomic data from different publications, and compute ionic abundances from line intensities and physical conditions and elemental abundances from ionic abundances and icfs.
BOND infers oxygen and nitrogen abundances in giant H II regions by comparison with a large grid of photoionization models using strong and semi-strong emission line ratios. Our grid spans a wide range in O/H, N/O and ionization parameter U, and covers different starburst ages and nebular geometries. The first novelty, in comparison to other statistical methods, is that BOND relies on the [Ar III]/[Ne III] emission line ratio to break the oxygen abundance bimodality. In doing so, we can measure oxygen and nitrogen abundances without assuming any a priori relation between N/O and O/H. The second novelty is that BOND takes into account changes in the hardness of the ionizing radiation field, which can come about due to the ageing of H II regions or the stochastically sampling of the IMF. We use the emission line ratio He I/Hβ, in addition to commonly used strong lines, to constrain the hardness of the ionizing radiation field. In a nutshell, our Bayesian inference code relies on the emission line ratios [O III]/Hβ, [O II]/Hβ and [N II]/Hβ, [Ar III]/Hβ, [Ne III]/Hβ, He I/Hβ as its input parameters, while its output values are the measurements and uncertainties for O/H and N/O.