Opacity effects and the classification of carbon stars.

The dependence of the stratification of easily ionized metals on the CN opacity in cool carbon stars is examined. The larger electron pressure in stars with small (C-O)/H ratios strengthens the lines of neutral metals, simulating a temperature decrease. Synthetic spectra computed for modified diffusion-approximation carbon-star atmospheres are used to show that many of the temperature criteria in the C classification scheme are dependent on this opacity effect. This effect also is capable of explaining the discrepancy between color temperatures and spectral temperatures, the correlation of C2 strength with Na D strength, and the tendency for strong lithium lines and CaCl bands to occur in stars with very weak C2 bands. Subject headings: atmospheres, stellar - carbon stars - opacities - spectral classification