We present an improved analysis of halo substructure traced by RR Lyrae stars in the SDSS stripe 82 region .
With the addition of SDSS-II data , a revised selection method based on new ugriz light curve templates results in a sample of 483 RR Lyrae stars that is essentially free of contamination .
The main result from our first study persists : the spatial distribution of halo stars at galactocentric distances 5–100 kpc is highly inhomogeneous .
At least 20 % of halo stars within 30 kpc from the Galactic center can be statistically associated with substructure .
We present strong direct evidence , based on both RR Lyrae stars and main sequence stars , that the halo stellar number density profile significantly steepens beyond a Galactocentric distance of \sim 30 kpc , and a larger fraction of the stars are associated with substructure .
By using a novel method that simultaneously combines data for RR Lyrae and main sequence stars , and using photometric metallicity estimates for main sequence stars derived from deep co-added u -band data , we measure the metallicity of the Sagittarius dSph tidal stream ( trailing arm ) towards R.A . \sim 2 ^ { h } -3 ^ { h } and Dec \sim 0 ^ { \circ } to be 0.3 dex higher ( [ Fe / H ] = -1.2 ) than that of surrounding halo field stars .
Together with a similar result for another major halo substructure , the Monoceros stream , these results support theoretical predictions that an early forming , smooth inner halo , is metal poor compared to high surface brightness material that have been accreted onto a later-forming outer halo .
The mean metallicity of stars in the outer halo that are not associated with detectable clumps may still be more metal-poor than the bulk of inner-halo stars , as has been argued from other data sets .