CN ABSORPTION IN COOL STARS
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Date
1970
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Ohio State University
Abstract
It has become clear in the last few years that the cyanogen molecule is one of the most important sources of opacity in the atmosphere of many types of cool stars and must be included in calculations of atmospheric models for these stars. The first step in this direction is the calculation of the absorption coefficient per molecule for a series of wavelengths and temperatures, and this has been done. We have represented the absorption due to the many close lines of CN by a straight mean absorption coefficient over wavenumber intervals of $100 cm^{-1}$ from 0 to $25,000 cm^{-1}$. Calculating the mean opacity over each interval is done simply by summing the integrated absorption due to each line in that interval and then dividing by the interval length. We have used all lines up to J=100 from a total of 198 bands in the sequences $\Delta v = \Delta_{lower}-\Delta_{upper}=- 3$ up to $\Delta v = 12$. Altogether this gives a total of nearly 100,000 strong and weak lines. Electronic f-values from Schadee (J.Q.S.R.T. 7, 1967) and Franck-Condon factors from Spindler (J.Q.S.R.T. 5, 1965) were used. Calculations were carried out at temperatures of 1000 K, 2000 K, 3500 K, and 5000 K. Results show that on the opacity due to bound-bound transistions of $C^{12} N^{14}$ form a quasicontinuous absorption extending over most of the visible and infrared. Over much of the wavelength region the opacity per molecule reaches values of $10^{-18}$ $cm^{2}$ per molecule, which is comparable to, or larger than, absorption coefficients due to CO and $H_{2}O$. Wherever the molecular abundance of CN approaches that of $H_{2} O$ and CO, CN will be the dominent source of opacity. The results can now be combined with calculations of molecular concentrations to produce the needed quantities for model atmosphere calculations.
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Author Institution: Astronomy Department, Indiana University