Discovery of anomalous oxygen isotopic ratios in HR 4049

Abstract

We report the discovery in the ISO/SWS spectrum of the post-AGB star HR 4049 of emission bands due to ¹⁷O and ¹⁸O isotopes locked up in CO₂ molecules. It is the first time these isotopomers are detected outside the solar system. Isotopic ratios derived in the optically thin limit are as low as ¹⁶O/¹⁷O = 8.3+/- 2.3 and ¹⁶O/¹⁸O = 6.9 +/- 0.9. These values are at least one order of magnitude lower than any previously determined isotopic ratio in any type of evolved star. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the UK) with the participation of ISAS and NASA. The SWS is a joint project of SRON and MPE.