Blanco DECam Bulge Survey (BDBS) III: A new view of the double red clump
  in the Milky Way bulge through luminosity and color distribution
  Red clump (RC) stars are one of the best stellar tracers of the structure of
the Milky Way (MW) bulge. Here we report a new view of the double RC through
luminosity and color distributions of RC stars in nine bulge fields ($l$ =
0.0$^{\circ}$, $\pm$4.5$^{\circ}$; $b$ = -6.0$^{\circ}$, -7.5$^{\circ}$,
-9.0$^{\circ}$) from the Blanco DECam Bulge Survey (BDBS), which covers
near-ultraviolet to near-infrared bandpasses. The bright and faint RCs show
contrasting distributions in ($u-g$)$_{0}$ and ($u-i$)$_{0}$ colors but similar
distributions in ($J-K_{s}$)$_{0}$ with a variation depending on the Galactic
longitude, where the bright RC is typically redder than the faint RC. In
particular, the RC stars are clearly divided into the bluer and redder
populations when using the ($u-g$)$_{0}$ color (($u-g$)$_{0}$ $<$ 2.5 for the
bluer RC; ($u-g$)$_{0}$ $\ge$ 2.5 for the redder RC). The bluer stars show a
single clump on the faint RC regime, whereas the redder stars form double
clumps on both the bright and faint RCs. The bright clump of the redder stars
is dominant in the positive longitude fields, while the faint clump of those
red stars is significant at negative longitudes. We also confirm that the bluer
and redder stars have different peak metallicity through comparison with
spectroscopy ($\Delta$[Fe/H] $\sim$ 0.45 dex). Therefore, our results support a
scenario whereby the MW bulge is composed of a spheroid of metal-poor stars and
a boxy/peanut shape (X-shape) predominantly made up of metal-rich stars.
