are given in Table 3 of Robin et al. (2003). No self-consistant modelling of the evolution of main sequence stars and possible binary channels, which might lead to the formation of SX Phe stars, is performed. We assume that the absolute brightness of SX Phe is randomly distributed within the observed interval $M_V=2.1-3.2$ (which is the implied absolute magnitude for SX Phe stars with periods of 2–1 hr respectively, McNamara 1997) and that the space density of SX Phe is simply proportional to the density of the parent population. This should be a good approximation for the field population in which dynamical interaction plays a very small role.

SX Phe stars are observed in globular clusters and are known to be metal poor. Thus it is clear that the thin disk can be ruled out as the parent population, but both the thick disk and halo populations, are feasible. The thick disk population is almost as old as the Galactic halo and some stars of this population have quite low metallicities. However, some thick disk stars have overall abundances comparable to thin disk stars (Bensby, Feltzing & Lundström 2003, Fuhrmann 2004). Depending on the degree of this fraction and noting 