Mapping the Milky Way with LAMOST II: the stellar halo
  The radial number density and flattening of the Milky Way's stellar halo is
measured with $\mathrm{5351}$ metal-poor ([Fe/H]$<-1$) K giants from LAMOST
DR3, using a nonparametric method which is model independent and largely avoids
the influence of halo substucture. The number density profile is well described
by a single power law with index $5.03^{+0.64}_{-0.64}$, and flattening that
varies with radius. The stellar halo traced by LAMOST K giants is more
flattened at smaller radii, and becomes nearly spherical at larger radii. The
flattening, $q$, is about 0.64, 0.8, 0.96 at $r=15$, 20 and 30 kpc (where
$r=\sqrt{R^2+\left[Z/q\left(r\right)\right]^2}$), respectively. Moreover, the
leading arm of the Sagittarius dwarf galaxy tidal stream in the north, and the
trailing arm in the south, are significant in the residual map of density
distribution. In addition, an unknown overdensity is identified in the residual
map at (R,Z)=(30,15) kpc.
