Discovery of Mira variable stars in the metal-poor Sextans dwarf
  spheroidal galaxy
  We report the discovery of two Mira variable stars (Miras) toward the Sextans
dwarf spheroidal (dSph) galaxy. We performed optical long-term monitoring
observations for two red stars in the Sextans dSph. The light curves of both
stars in the $I_{\rm c}$ band show large-amplitude (3.7 and 0.9 mag) and
long-period ($326\pm 15$ and $122\pm 5$ days) variations, suggesting that they
are Miras. We combine our own infrared data with previously published data to
estimate the mean infrared magnitudes. The distances obtained from the
period-luminosity relation of the Miras ($75.3^{+12.8}_{-10.9}$ and
$79.8^{+11.5}_{-9.9}$ kpc, respectively), together with the radial velocities
available, support memberships of the Sextans dSph ($90.0\pm 10.0$ kpc). These
are the first Miras found in a stellar system with a metallicity as low as
${\rm [Fe/H]\sim -1.9}$, than any other known system with Miras.
