Comparison of stellar opacities at low temperatures

International audienceAn overview is presented of calculations of stellar opacities in the transition region below the photosphere corresponding to temperatures of 3,500-11,600 K. Available opacity calculations in the temperature range of interest are reviewed showing significant differences. The differences for specific classes of stellar opacities are attributed to changes in composition, temperature variations, and density variations. The influence of CO and CO(+) are examined in detail to demonstrate the affect of molecular composition on the determination of opacity. CO and CO(+) are expected to affect the opacities in the 70,000/cm and 10,000-20,000/cm regions, and it is concluded that other species can affect the opacity calculation, if not as markedly. The significance of the molecular processes for opacities in this range demonstrates that opacity calculations should incorporate these data for precise estimates