HR4049: signature of nova nucleosynthesis?

The post-Asymptotic Giant Branch (AGB) star HR4049 is in an eccentric binary system with a relatively short period probably surrounded by a dusty circumbinary disk. Extremely anomalous oxygen isotopic ratios, O-16/O-17 similar or equal to O-16/O-18 similar or equal to 7, have been measured from CO2 molecules likely residing in the disk. Such a composition cannot be explained in the framework of AGB and post-AGB evolution while it can be qualitatively associated with the nucleosynthesis occurring during nova outbursts. We discuss nova models, the presence of a white dwarf companion to HR4049 and possible scenarios for the dynamical evolution of this binary system. Circumbinary disks in which mixing occurs between red-giant and nova material may also be invoked as the site of formation of some rare types of meteoritic presolar grains.