NLTE effects on oxygen lines

The NLTE effects affecting oxygen-abundance determinations of solar-type stars are discussed. LTE is perfectly safe for the forbidden lines. The permitted triplet at 777 nm is expected to show NLTE effects on the order of a few tenths of a dex (always in the sense that LTE overestimates the abundance), but the magnitude of the effects is dependent on the still very uncertain cross sections of collisional excitation by collisions with neutral hydrogen atoms. Little is known about the NLTE effects on molecular line formation. (C) 2001 Elsevier Science BY All rights reserved.