| realistic stellar atmospheric models of two typical metal - poor giant stars in omega centauri that include a chromosphere ( chr ) influence the formation of optical lines of : the forbidden lines ( @xmath06300 , @xmath06363 ) and the infrared triplet ( @xmath0@xmath07771@xmath17775 ) . one - dimensional semi - empirical non - lte models are constructed based on observed balmer lines . a full non - lte formulation is applied in evaluating line strengths of o i including photoionization by the lyman continuum and photoexcitation by ly-@xmath2 and ly-@xmath3 . chromospheric models ( chr ) yield forbidden oxygen transitions that are stronger than in radiative / convective equilibrium ( rce ) models . the triplet oxygen lines from high levels also appear stronger than produced in an rce model . the inferred oxygen abundance from realistic chr models for these two stars is decreased by factors @xmath43 as compared to values derived from rce models . a lower oxygen abundance suggests that intermediate mass agb stars contribute to the observed abundance pattern in globular clusters . a change in the oxygen abundance of metal - poor field giants could affect models of deep mixing episodes on the red giant branch . changes in the oxygen abundance can impact other abundance determinations critical to astrophysics including chemical tagging techniques and galactic chemical evolution . |