The circumstellar shell of the post-AGB star HD 56126: the ${}^{12}$CN/${}^{13}$CN isotope ratio and fractionation

Eric J. Bakker, David L. Lambert

We have detected circumstellar absorption lines of the ${}^{12}$CN and ${}^{13}$CN Violet and Red System in the spectrum of the post-AGB star HD~56126. From a synthetic spectrum analys…