The halo stars on highly radial orbits should inevitably pass the center regions of the Milky Way, although they are hard to be detected from the crowded bulge/bar. Under the assumption that the stellar halo is in ``dynamical equilibrium", and axisymmetric, we integrate the orbits of ~11,000 halo K-giants at 5 r 50 kpc cross-matched from LAMOST DR5 and Gaia DR2. By carefully considering the selection function, we construct the stellar halo density distribution at r 50 kpc. It keeps q~ 0.6 toward the Galactic center, and its density is lower than the inward extrapolation of a power-law profile fitted from outer regions. The stellar halo shows a negative metallicity gradient along the radius, the gradient is steep at the inner 10 kpc and becomes shallower in outer regions. We find ~ 8% of the halo stars are trapped in the bar resonant orbits. They construct a clear peanut-shaped structure, with a mass of 1.0 * 10^8 M_sun and metallicity of -1.5+-0.4 dex. The mass and metallicity distribution of halo stars in the Galactic center suggest that they contribute only partially to the metal-poor stars in the bulge/bar regions.
Host: Dandan Xu
