that the SX Phe phenomenon is linked to metallicity, different formation efficiencies can be expected. We make two extreme assumptions to constrain the Galactic SX Phe population: 1) thick disk and halo have the same formation efficiency or 2) SX Phe stars are only formed from halo stars.

A total of 250 million SX Phe was simulated, making the statistical error of the Monte Carlo simulation negligible. We obtained a cumulative distribution of SX Phe stars as function of limiting magnitude. A catalogue of simulated stars in $1^\circ$ fields around the central coordinates of the RATS fields and brighter than the detection limit of SX Phe variables ($V=22$ \[for blue stars this implies $g$=22\]) was produced. Stars in this list were weighted with the effective field of view of the cameras (Barclay et al 2011). Simulated star numbers were scaled according to the predicted number of stars and the observed number of stars (11 in the low extinction fields). The result is that we predict 6.6$\times10^{4}$ SX Phe stars brighter than ($V=22$) in our Galaxy if a mix of halo and thick disk is assumed and 4.0$\times10^{4}$ if only the halo population contributes.

Recent determinations of the dynamical mass of 