Stellar variability on time-scales of minutes: results from the first 5
  years of the Rapid Temporal Survey (RATS)
  The Rapid Temporal Survey (RATS) explores the faint, variable sky. Our
observations search a parameter space which, until now, has never been
exploited from the ground. Our strategy involves observing the sky close to the
Galactic plane with wide-field CCD cameras. An exposure is obtained
approximately every minute with the total observation of each field lasting
around 2 hours. In this paper we present the first 6 epochs of observations
which were taken over 5 years from 2003--2008 and cover over 31 square degrees
of which 16.2 is within 10{\deg} of the Galactic plane. The number of stars
contained in these data is over 3.0 x10^6. We have developed a method of
combining the output of two variability tests in order to detect variability on
time-scales ranging from a few minutes to a few hours. Using this technique we
find 1.2 x 10^5 variables -- equal to 4.1 per cent of stars in our data.
Follow-up spectroscopic observations have allowed us to identify the nature of
a fraction of these sources. These include a pulsating white dwarf which
appears to have a hot companion, a number of stars with A-type spectra that
vary on a period in the range 20--35 min. Our primary goal is the discovery of
new AM CVn systems: we find 66 sources which appear to show periodic modulation
on a time-scales less than 40 min and a colour consistent with the known AM CVn
systems. Of those sources for which we have spectra of, none appears to be an
AM CVn system, although we have 12 candidate AM CVn systems with periods less
than 25 min for which spectra are still required. Although our numbers are not
strongly constraining, they are consistent with the predictions of Nelemans et
al.
