study of the photometric variability of individual systems can give insight to the physical conditions deep inside the star (eg Kurtz 2004).

In recent years many photometric surveys have been undertaken, leading to a corresponding increase in the number of known stellar pulsators. Factors such as cadence, depth, sky coverage and duration makes any individual survey more (or less) likely to discover specific types of stellar pulsator. The Rapid Temporal Survey (RATS) is a deep, high-cadence photometric survey covering nearly 40 square degrees which took place between 2003 and 2010 (Ramsay & Hakala 2005, Barclay et al 2011). This strategy allows us to detect sources which vary in their intensity on a timescale of a few minutes to several hours.

In our first set of wide-field camera data taken in 2003, we identified a small number of blue stars which pulsate on a period between 40–70 mins. An analysis of their optical spectra indicated they were SX Phe stars or $\delta$ Sct stars (Ramsay et al 2006). SX Phe stars are old, metal-poor stars which are likely to be halo objects (see Nemec & Mateo 1990 for a review). The $\delta$ Sct stars show similar characteristics to the SX Phe 