A detailed abundance analysis of the hot post-AGB star ZNG-1 in M10

We present a model-atmosphere analysis for the bright (V similar to 13) sta r ZNG-1, in the globular cluster M10. From high-resolution (R similar to 40 000) optical spectra we confirm ZNG-1 to be a post-asymptotic giant branch (post-AGB) star. The derived atmospheric parameters are T-eff = 26 500 +/- 1000 K and log g = 3.6 +/- 0.2 dex. A differential abundance analysis reve als a chemical composition typical of hot post-AGB objects, with ZNG-1 bein g generally metal poor, although helium is approximately solar. The most in teresting feature is the large carbon underabundance of more than 1.3 dex. This carbon deficiency, along with an observed nitrogen enhancement relativ e to other elements, may suggest that ZNG-1 evolved off the AGB before the third dredge-up occurred. Also, iron depletions observed in other similar s tars suggest that gas-dust fractionation in the AGB progenitor could be res ponsible for the observed composition of these objects. However, we need no t invoke either scenario since the chemical composition of ZNG-1 is in good agreement with abundances found for a Population II star of the same metal licity.