F turnoff stars are important tools for studying Galactic halo substructure because they are plentiful , luminous , and can be easily selected by their photometric colors from large surveys such as the Sloan Digital Sky Survey ( SDSS ) .
We describe the absolute magnitude distribution of color-selected F turnoff stars , as measured from SDSS data , for eleven globular clusters in the Milky Way halo .
We find that the M _ { g } distribution of turnoff stars is intrinsically the same for all clusters studied , and is well fit by two half Gaussian functions , centered at \mu = 4.18 , with a bright-side \sigma = 0.36 , and with a faint-side \sigma = 0.76 .
However , the color errors and detection efficiencies cause the observed \sigma of the faint-side Gaussian to change with magnitude due to contamination from redder main sequence stars ( 40 % at 21st magnitude ) .
We present a function that will correct for this magnitude-dependent change in selected stellar populations , when calculating stellar density from color-selected turnoff stars .
We also present a consistent set of distances , ages and metallicities for eleven clusters in the SDSS Data Release 7 .
We calculate a linear correction function to Padova isochrones so that they are consistent with SDSS globular cluster data from previous papers .
We show that our cluster population falls along the Milky Way Age-Metallicity Relationship ( AMR ) , and further find that isochrones for stellar populations on the AMR have very similar turnoffs ; increasing metallicity and decreasing age conspire to produce similar turnoff magnitudes and colors for all old clusters that lie on the AMR .