Blue Stragglers in the field of the Galactic halo

The field of the Galactic halo is dominated by a coeval stellar population which allows to find the turn-off stars 
at a given metallicity. By having the turn-off color as a function of metallicity in the halo-field, we can identify 
those stars that are bluer than the dominant population and look for the blue stragglers.  I will apply this idea 
in a sample of about 100,000 field stars from Sloan Digital Sky Survey.