SIMBAD references

We report the detection of fully resolved absorption lines of A-X bands from interstellar ¹²C¹⁷O and ¹²C¹⁸O, through high-resolution spectroscopy of X Persei with the Space Telescope Imaging Spectrograph.(3) The first ultraviolet measurement of an interstellar ¹²C¹⁷O column density shows that its isotopomeric ratio is ¹²C¹⁶O/¹²C¹⁷O=8700±3600. Simultaneously, the second ultraviolet detection of interstellar ¹²C¹⁸O establishes its isotopomeric ratio at 3000±600. These ratios are about five times higher than local ambient oxygen isotopic ratios in the ISM. Such severe fractionation of rare species shows that both ¹²C¹⁷O and ¹²C¹⁸O are destroyed by photodissociation, whereas ¹²C¹⁶O avoids destruction through self-shielding. This is to be contrasted with our ratio of ¹²C¹⁶O/¹³C¹⁶O=73±12 toward X Per, which is indistinguishable from ¹²C/¹³C, the result of a balance between the photodissociation of ¹³C¹⁶O and its preferential formation via the isotope exchange reaction between CO and C⁺.