Context :

Aims : In the framework of a project aiming at deriving in a homogeneous way the properties ( age , distance , reddening and detailed chemical abundances ) of a large sample of old open clusters , we present here the metal abundance and the abundance ratios of light ( C , N , O , Na , Mg , Al , Si , Ca , Ti ) and heavier ( Cr , Mn , Ni , Ba , Eu ) elements in the galactic open clusters NGCÂ 6253 and NGCÂ 6791 .

Methods : We performed spectrum synthesis of selected lines on high resolution spectra of four red clump stars in NGCÂ 6253 , taken with the UVES and FEROS spectrographs .
We also determined abundances of the same elements for four red clump stars in NGCÂ 6791 , observed with SARG , for which we had derived the atmospheric parameters and the iron , carbon and oxygen abundances in a previous paper ( Gratton et al .
2006 ) .

Results : The average metallicity of NGCÂ 6253 is [ Fe/H ] = +0.46 ( rms = 0.03 dex , systematic error = 0.08 dex ) , obtained by extensive spectral synthesis of Fe lines .
This intermediate age cluster closely resembles the old open cluster NGCÂ 6791 , as far as the chemical composition is concerned .
C , N , O do not show any significant abundance scatter ; they are underabundant with respect to the solar values both in NGCÂ 6253 and NGCÂ 6791 .
We also find no evident star-to-star scatter in any of the elements measured in both clusters , with the possible exception of Na in NGCÂ 6791 .
The two clusters show very similar abundances , except for Mg , overabundant in NGCÂ 6791 and not in NGCÂ 6253 .
Both have solar scaled \alpha -elements abundances .
We have compared our abundance ratios with literature values for disk giants and dwarfs and bulge giants , finding a general good agreement with the run of elemental ratios with [ Fe/H ] of disk objects .

Conclusions :