RR Lyrae Variable Stars in the Crater II Dwarf Galaxy
  We report the detection of RR Lyrae variable stars in Crater II, a recently
discovered large and diffuse satellite dwarf galaxy of the Milky Way (MW).
Based on B, V time-series photometry obtained with the Korea Microlensing
Telescope Network (KMTNet) 1.6-m telescope at CTIO, we identified 83 ab-type
and 13 c-type pulsators by fitting template light curves. The detected RR Lyrae
stars are centrally concentrated, which ensures that most of them are members
of Crater II. In terms of the distribution of RRab stars in the
period-amplitude diagram, Crater II is clearly different from ultra-faint dwarf
(UFD) galaxies, but very similar to the two classical MW dwarf spheroidal
(dSph) galaxies Draco and Carina with Oosterhoff-intermediate (Oo-int)
properties. Combined with the mean period of ab-type variables (<Pab> =
0.631+-0.004 d) and the c-type fraction (~0.14) in Crater II, this suggests an
Oo-int classification for Crater II and implies that its nature is more like a
dSph rather than a UFD. We also estimated the mean metallicity, reddening, and
distance of Crater II, from the photometric and pulsation properties of the RR
Lyrae stars. The stellar population model we have constructed indicates that
Crater II is dominated by an old population, but is relatively younger than the
oldest globular clusters in the MW. With a lack of high-amplitude short-period
RRab stars, Crater II, like most of the other less massive dSphs, is probably
not a surviving counterpart of the major building blocks of the MW halo.
