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We present atmospheric parameters for 51 nearby FG dwarfs uniformlydistributed over the -2.60 < [Fe/H] < +0.20 metallicity range that is suitablefor the Galactic chemical evolution research. Lines of iron, Fe I and Fe II,were used to derive a homogeneous set of effective temperatures, surfacegravities, iron abundances, and microturbulence velocities. We usedhigh-resolution (R>60000) Shane/Hamilton and CFHT/ESPaDOnS observed spectra andnon-local thermodynamic equilibrium (NLTE) line formation for Fe I and Fe II inthe classical 1D model atmospheres. The spectroscopic method was tested withthe 20 benchmark stars, for which there are multiple measurements of theinfrared flux method (IRFM) Teff and their Hipparcos parallax error is < 10%.We found NLTE abundances from lines of Fe I and Fe II to be consistent within0.06 dex for every benchmark star, when applying a scaling factor of S_H = 0.5to the Drawinian rates of inelastic Fe+H collisions. The obtained atmosphericparameters were checked for each program star by comparing its position in thelog g-Teff plane with the theoretical evolutionary track in the Yi et al.(2004) grid. Our final effective temperatures lie in between the T_IRFM scalesof Alonso et al. (1996) and Casagrande et al. (2011), with a mean difference of+46 K and -51 K, respectively. NLTE leads to higher surface gravity comparedwith that for LTE. The shift in log g is smaller than 0.1 dex for stars witheither [Fe/H] > -0.75, or Teff < 5750 K, or log g > 4.20. NLTE analysis iscrucial for the VMP turn-off and subgiant stars, for which the shift in log gbetween NLTE and LTE can be up to 0.5 dex. The obtained atmospheric parameterswill be used in the forthcoming papers to determine NLTE abundances ofimportant astrophysical elements from lithium to europium and to improveobservational constraints on the chemo-dynamical models of the Galaxyevolution.

Systematic NLTE study of the -2.6 < [Fe/H] < 0.2 F and G dwarfs in the solar neighbourhood. I. Stellar atmosphere parameters