FeI and FeII abundances with LOTUS

Non-local thermodynamic equilibrium (non-LTE; hereafter NLTE) models are often important for such high precision, however, can be computationally complex and expensive, which renders the models less utilized in spectroscopic analyses. To alleviate the computational burden of such models, we developed a robust 1D, NLTE fundamental atmospheric stellar parameter derivation tool, LOTUS, to determine the effective temperature Teff, surface gravity logg, metallicity [Fe/H], and microturbulent velocity v_mic_ for FGK-type stars, from equivalent width (EW) measurements of FeI and FeII lines.

We utilize a generalized curve of growth method to take into account the EW dependencies of each FeI and FeII line on the corresponding atmospheric stellar parameters. A global differential evolution optimization algorithm is then used to derive the fundamental parameters. Additionally, LOTUS can determine precise uncertainties for each stellar parameter using a Markov Chain Monte Carlo algorithm.