Context :

Aims : We measured the radial velocity of 139 stars in the region of NGC 6253 , discussing cluster ’ s membership and binarity in this sample , complementing our analysis with photometric , proper motion , and radial velocity data available from previous studies of this cluster , and analyzing three planetary transiting candidates we found in the field of NGC~6253 .

Methods : Spectra were obtained with the UVES and GIRAFFE spectrographs at the VLT , during three epochs in August 2008 .

Results : The mean radial velocity of the cluster is ( \overline { RV _ { cl } } \pm \overline { \sigma _ { cl } } ) = ( -29.11 \pm 0.85 ) km/s .
Using both radial velocities and proper motions we found 35 cluster ’ s members , among which 12 are likely cluster ’ s close binary systems .
One star may have a sub-stellar companion , requiring a more intensive follow-up .
Our results are in good agreement with past radial velocity and photometric measurements .
Furthermore , using our photometry , astrometry and spectroscopy we identified a new sub-giant branch eclipsing binary system , member of the cluster .
The cluster ’ s close binary frequency at ( 29 \pm 9 ) \% ( 34 \% \pm 10 \% once including long period binaries ) , appears higher than the field binary frequency equal to ( 22 \pm 5 ) \% , though these estimates are still consistent within the uncertainties .
Among the three transiting planetary candidates the brightest one ( V = 15.26 ) is worth to be more intensively investigated with higher percision spectroscopy .

Conclusions : We discussed the possibility to detect sub-stellar companions ( brown dwarfs and planets ) with the radial velocity technique ( both with UVES/GIRAFFE and HARPS ) around turn-off stars of old open clusters .
We isolated 5 stars that are optimal targets to search for planetary mass companions with HARPS .
Our optimized strategy minimizes the observing time requested to isolate and follow-up best planetary candidates in clusters with high precision spectrographs , an important aspect given the faintness of the target stars .