The old and metal rich open cluster NGC 6253 was observed with the FLAMES multi-object spectrograph during an extensive radial velocity campaign monitoring 317 stars with a median of 15 epochs per object .
All the targeted stars are located along the upper main sequence of the cluster between 14.8 < V < 16.5 .
Fifty nine stars are confirmed cluster members both by radial velocities and proper motions and do not show evidence of variability .
We detected 45 variable stars among which 25 belong to NGC 6253 .
We were able to derive an orbital solution for 4 cluster members ( and for 2 field stars ) yielding minimum masses in between \sim 90 M _ { J } and \sim 460 M _ { J } and periods between 3 and 220 days .
Simulations demonstrated that this survey was sensitive to objects down to 30 M _ { J } at 10 days orbital periods with a detection efficiency equal to 50 % .
On the basis of these results we concluded that the observed frequency of binaries down to the hydrogen burning limit and up to 20 days orbital period is around ( 1.5 \pm 1.3 ) % in NGC 6253 .
The overall observed frequency of binaries around the sample of cluster stars is ( 13 \pm 3 ) % .
The median radial velocity precision achieved by the GIRAFFE spectrograph in this magnitude range was around \sim 240m s ^ { -1 } ( \sim 180 m s ^ { -1 } for UVES ) .
Based on a limited follow-up analysis of 7 stars in our sample with the HARPS spectrograph we determined that a precision of 35 m s ^ { -1 } can be reached in this magnitude range , offering the possibility to further extend the variability analysis into the substellar domain .
Prospects are even more favourable once considering the upcoming ESPRESSO spectrograph at VLT .