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 galaxy (dSph). We performed optical long-term monitoring observations for two red stars in the Sextans dSph. The light curves of both stars in the Ic band show large-amplitude (3.7 and 0.9 mag) and long-period (326 ± 15 and 122 ± 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 ± 10.0 kpc). These are the first Miras found in a stellar system with a metallicity as low as [Fe/H] ∼ -1.9 than any other known system with Miras.