typically 7200–7900K (implying late A/early F spectral types), while the long period sdB stars have temperatures typically $\sim$25000–30000K (Green et al 2003). Our analysis of those sources for which we have spectra result in parameters which confirm a SX Phe/$\delta$ Scuti nature (§\[spectra\]). The observed colours are also consistent with this classification for all pulsators, although for fields with high extinction we cannot rule out some contamination from intrinsically redder sources. However, given that the amplitude of the long period sdB stars is very low (eg Fontaine et al 2003) we consider it highly unlikely that blue pulsators are sdB stars.

The light curves of our sources (Figure 2 and 3) appear to show regular pulsations periods, some displaying high ($\sim$60 percent) full-amplitude modulations, while others are much lower (a few percent). They are similar to the light curves of SX Phe and $\delta$ Sct stars which appear in the literature. We have low resolution spectra for a small number of our sources which were taken for identification purposes: they are consistent with A/F type stars. Although our spectra are not high resolution, our model fits indicate that all sources have metallicities which are less than Solar (for most sources 