Further evidence for carbon isotopic structure in the lambda lambda 5797 and 6614 diffuse interstellar bands

Profiles of the lambda lambda 5797 and 6614 diffuse interstellar bands (DIB s) in our high-resolution spectra (R = 120,000-60,000) of five stars provid e strong support for the model proposed by Webster, in which C-13 atoms are randomly substituted for C-12 in highly symmetric molecules. These stars h ave narrow interstellar Na D lines, and the DIB profiles can be reproduced, as predicted, by a band of equally spaced, equally wide Gaussians with a P oisson intensity distribution. Other good fits are possible with components of unequal FWHM, but the widths, positions, and relative amplitudes of the components then differ from star to star, which is less credible for a com mon absorber. The average numbers of C-13 atoms per molecule derived from t he model are about 0.95 and 1.41 for the lambda lambda 5797 and 6614 DIBs, respectively, which correspond to between 40 and 100 carbon atoms per molec ule. Sharp features in the cores of the lambda 5797 DIB are not exactly mat ched by the Gaussians, which implies a more complex intrinsic structure. Fo r HD 37061 in Orion, both DIBs are weak and have a component on the short-w avelength side of the normal profile, possibly indicating higher rotational temperatures.