New short period stellar pulsators at large Galactocentric distances
  We report the discovery of 31 blue, short period, pulsators made using data
taken as part of the Rapid Temporal Survey (RATS). We find they have periods
between 51-83 mins and full-amplitudes between 0.05-0.65 mag. Using the
period-luminosity relationship for short period pulsating stars we determine
their distance. Assuming they are pulsating in either the fundamental or first
over-tone radial mode the majority are located at a distance greater than 3kpc,
with several being more than 20 kpc distant. Most stars are at least 1 kpc from
the Galactic plane, with three being more than 10 kpc. One is located in the
direction of the Galactic anti-center and has Galactocentric distance of ~30
kpc and is ~20 kpc below the plane: they are therefore potential tracers of
Galactic structure. We have obtained low-resolution spectra for a small number
our targets and find they have temperatures between 7200--7900K and a metal
content less than Solar. The colours of the pulsators and the spectral fits to
those stars for which we have spectra indicate that they are either SX Phe or
delta Scuti stars. We estimate the number of SX Phe stars in our Galaxy and
find significantly fewer per unit mass than reported in massive globular
clusters or dwarf spheroidal galaxies.
