We present oxygen abundances derived from both the permitted and forbidden oxygen lines for 55 subgiants and giants with { [ Fe / H ] } values between -2.7 and solar with the goal of understanding the discrepancy in the derived abundances .
A first attempt , using T _ { eff } values from photometric calibrations and surface gravities from luminosities , obtained agreement between the indicators for turn-off stars , but the disagreement was large for evolved stars .
We find that the difference in the oxygen abundances derived from the permitted and forbidden lines is most strongly affected by T _ { eff } , and we derive a new T _ { eff } scale based on forcing the two sets of lines to give the same oxygen abundances .
These new parameters , however , do not agree with other observables , such as theoretical isochrones or Balmer-line profile based T _ { eff } determinations .
Our analysis finds that one-dimensional , LTE analyses ( with published NLTE corrections for the permitted lines ) can not fully resolve the disagreement in the two indicators without adopting a temperature scale incompatible with other temperature indicators .
We also find no evidence of circumstellar emission in the forbidden lines , removing such emission as a possible cause for the discrepancy .