CO bands in V4334 Sgr (Sakurai's Object): the 12C/13C ratio
  We present the results of our analysis of a high resolution (R ~ 30000) infrared spectrum of V4334 Sgr (Sakurai's Object) around the first overtone CO bands, obtained in 1998 July. The 12CO and 13CO bands are well-resolved, and we compute synthetic hydrogen-deficient model atmosphere spectra to determine the 12C/13C ratio. We find 12C/13C ~ 4 +/-1, consistent with the interpretation of V4334 Sgr as an object that has undergone a very late thermal pulse. 
Ya. V. Pavlenko, T. R. Geballe, A. Evans, B. Smalley, S. P. S. Eyres,   V. H. Tyne, L.A. Yakovina