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We attempt to produce low temperature opacity data incorporating the effectsof varied abundances of the elements carbon and nitrogen. For our temperaturerange of interest, molecules represent the dominant opacity source. Our datasetcovers a wide metallicity range and is meant to provide important input datafor stellar evolution models and other applications. We conduct chemicalequilibrium calculations to evaluate the partial pressures of neutral atoms,ions, and molecules. Based on a large dataset containing atomic line andcontinuum data and, most importantly, a plethora of molecular lines, wecalculate Rosseland mean opacity coefficients not only for a number ofdifferent metallicities, but also for varied abundances of the isotopes ^{12}Cand ^{14}N at each metallicity. The molecular data comprise the main opacitysources for either an oxygen-rich or carbon-rich chemistry. We tabulate theopacity coefficients as a function of temperature and, basically, density. Dueto the special role of the CO molecule, within a certain chemistry regime analteration to the carbon abundance causes considerable changes in the Rosselandopacity. The transition from a scaled solar (i. e. oxygen-rich) mixture to acarbon-rich regime results in opacities that can, at low temperatures, differby orders of magnitude from to the initial situation. The reason is that themean opacity in either case is due to different molecular absorbers. Variationsin the abundance of nitrogen have less pronounced effects but, nevertheless,cannot be neglected. [abridged]

Low temperature Rosseland opacities with varied abundances of carbon and nitrogen