We present the first detailed chemical abundances for three giant stars which are candidate members of the Canis Major overdensity , obtained by using FLAMES-UVES at VLT .
The stars , in the background of the open cluster NGC 2477 , have radial velocities compatible with a membership to this structure .
However , due to Galactic disc contamination , radial velocity by itself is unable to firmly establish membership .
The metallicities span the range -0.5 \la [ Fe / H ] \la + 0.1 .
Assuming that at least one of the three stars is indeed a member of CMa implies that this structure has undergone a high level of chemical processing , comparable to that of the Galactic disc .
The most metal-rich star of the sample , EIS 6631 , displays several abundance ratios which are remarkably different from those of Galactic stars : [ \alpha /Fe ] \sim - 0.2 , [ Cu/Fe ] \sim + 0.25 , [ La/Fe ] \sim + 0.6 , [ Ce/Fe ] \sim + 0.8 and [ Nd/Fe ] \sim + 0.6 .
These ratios make it likely that this star was formed in an external galaxy .