We present a detailed model-atmosphere analysis of ZNG 4 , a UV-bright star in the globular cluster M13 .
From the analysis of a high resolution ( R \approx 45 , 000 ) spectrum of the object , we derive the atmospheric parameters to be T _ { eff } = 8500 \pm 250 K , log g = 2.5 \pm 0.5 and [ Fe / H ] = -1.5 .
Except for magnesium , chromium and strontium , all other even Z elements are enhanced with titanium and calcium being overabundant by a factor of 0.8 dex .
Sodium is enhanced by a factor of 0.2 dex .
The luminosity of ZNG 4 and its position in the color-magnitude diagram of the cluster indicate that it is a Supra Horizontal Branch ( SHB ) ( post-HB ) star .
The underabundance of He and overabundances of Ca , Ti , Sc and Ba in the photosphere of ZNG 4 indicate that diffusion and radiative levitation of elements may be in operation in M 13 post-HB stars even at T _ { eff } of 8500K .
Detailed and more accurate abundance analysis of post-HB stars in several globular clusters is needed to further understand their abundance anomalies .