NGC 6791 is a unique stellar cluster , key to our understanding of both the multiple stellar population phenomenon and the evolution and assembly of the Galaxy .
However , despite many investigations , its nature is still very controversial . \citet Gei12 found evidence suggesting it was the first open cluster to possess multiple populations but several subsequent studies did not corroborate this .
It has also been considered a member of the thin or thick disk or even the bulge , and both as an open or globular cluster or even the remnant of a dwarf galaxy .

Here , we present and discuss detailed abundances derived from high resolution spectra obtained with UVES at VLT and HIRES at Keck of 17 evolved stars of this cluster .
We obtained a mean [ Fe/H ] = +0.313 \pm 0.005 , in good agreement with recent estimates , and with no indication of star-to-star metallicity variation , as expected .
We also did not find any variation in Na , in spite of having selected the very same stars as in \citet Gei12 , where a Na variation was claimed .
This points to the presence of probable systematics in the lower resolution spectra of this very high metallicity cluster analysed in that work .
In fact , we find no evidence for an intrinsic spread in any element , corroborating recent independent APOGEE data .
The derived abundances indicate that NGC 6791 very likely formed in the Galactic Bulge and that the proposed association with the Thick Disk is unlikely , despite its present Galactic location .
We confirm the most recent hypothesis suggesting that the cluster could have formed in the Bulge and radially migrated to its current location , which appears the best explanation for this intriguing object .