We report new statistical equilibrium calculations for Fe I and Fe II in the atmosphere of Late-Type stars .
We used atomic models for Fe I and Fe II having respectively 256 and 190 levels , as well as 2117 and 3443 radiative transitions .
Photoionization cross-sections are from the Iron Project .
These atomic models were used to investigate NLTE ( non local themodynamic equilibrium ) effects in iron abundances of Late-Type stars with different atmospheric parameters .
We found that most Fe I lines in metal-poor stars are formed in conditions far from LTE ( local thermodynamic equilibrium ) .
We derived metallicity corrections of about 0.3 dex with respect to LTE values , for the case of stars with [ Fe / H ] \sim - 3.0 .
Fe II is found not to be affected by significant NLTE effects .
The main NLTE effect invoked in the case of Fe I is overionization by ultraviolet radiation , thus classical ionization equilibrium is far to be satisfied .
An important consequence is that surface gravities derived by LTE analysis are in error and should be corrected before final abundances corrections .
This apparently solves the observed discrepancy between spectroscopic surface gravities derived by LTE analyses and those derived from Hipparcos parallaxes .
A table of NLTE [ Fe/H ] and log g values for a sample of metal-poor late-type stars is given .