  Observations from the Heliospheric Imagers (HI-1) on both the STEREO
spacecraft have been analysed to search for very long period large amplitude
stellar variability, finding 6 new candidates. A total of 85 objects, mostly
previously known Mira variables, were found to show convincing variability on
time scales of over a hundred days. These objects range in peak brightness from
about 4th magnitude to 10th magnitude in R and have periods between about 170
days and 490 days. There is a period gap between 200 and 300 days where no
objects were found and this is discussed. 15 of the Miras in the sample are
previously recorded as having variable periods and the possibility for these
and 2 other stars to have undergone a period change or to be irregular is
discussed. In addition to the 6 stars in the sample not previously recorded as
variable, another 7 are recorded as variable but with no classification. Our
period determination is the first to be made for 19 of these 85 stars. The
sample represents a set of very long period variables that would be challenging
to monitor from the Earth, or even from Earth orbit, owing to their position on
the Ecliptic Plane and that their periods are often close to a year or an
integer fraction thereof. The possibility for the new candidates to possess
circumstellar shells is discussed.
