This study is about stellar populations of the Milky Way halo and is about to be submitted as my PhD thesis. We want to attack the problem of age-determination for halo field stars, where the distance is not known and classical age-dating techniques are not feasible. Our alternative is to use the turn-off stars, which can be found by looking at the hottest stars of a population with a given metallicity.
Metallicities and temperatures of halo field stars are determined from the spectra of the SEGUE stars. This is done with a novel and independent method, called MAX, which compresses the spectra allowing an extremely quick parameter determination.
We found finally ages for the halo of 12-13 Gyr, based on interesting similitudes between field and globular clusters stars.