AGB Variables in Local Group Dwarf Irregular Galaxies
  The near and mid-infrared characteristics of large amplitude, Mira, variables
in Local Group dwarf irregular galaxies (LMC, NGC 6822, IC 1613, Sgr dIG) are
described. Two aspects of these variables are discussed. First, the short
period (P < 420 days) Miras are potentially powerful distance indicators,
provided that they have low circumstellar extinction, or can be corrected for
extinction. These are the descendants of relatively low mass stars. Secondly,
the longer period stars, many of which undergo hot bottom burning, are poorly
understood. These provide new insight into the evolution of intermediate mass
stars during the high mass-loss phases, but their use as distance indicators
depends on a much firmer understanding of their evolution.
  The change in slope of the K period luminosity relation for O-rich stars that
is seen around 400 to 420 days in the LMC is due to the onset of hot bottom
burning. It will be sensitive to metallicity and should therefore be expected
at different periods in populations with significant differences from the LMC.
  The [4.5] period-luminosity relation splits into two approximately parallel
sequences. The fainter one fits stars where the mid-infrared flux originates
from the stellar photosphere, while the brighter one fits observations
dominated by the circumstellar shell.
