Signatures of carbon-13 and nitrogen-15 in the spectrum of comet LINEAR (C/2000 WM1)

Enlarged view of a small section of the high-resolution UVES spectrum of Comet LINEAR (C/2000 WM1) with emission lines from CN-molecules (blue line), compared to the "synthetic" spectrum based on theoretical calculations and laboratory measurements (black line; some of the lines are labeled with quantum numbers). In the upper panel, the synthetic spectrum has been produced on the basis of the most abundant isotopic species (12 C 14 N). The lower panel shows that the observed spectrum is in nearly perfect agreement with a synthetic spectrum which includes contributions from two other isotopic species, 13 C 14 N (emission lines at wavelengths indicated by red ticks) and 12 C 15 N (blue ticks); they are added in proportions of 1/115 and 1/140, respectively. The isotopic abundances of carbon-13 and nitrogen-15 are measured accordingly. Introducing instead the terrestrial ratio for nitrogen-15 (1/272) significantly degrades the fit and thus that ratio can clearly be ruled out in Comet LINEAR.