We present a sample of \sim 5 , 000 RR Lyrae stars selected from the recalibrated LINEAR dataset and detected at heliocentric distances between 5 kpc and 30 kpc over \sim 8 , 000 deg ^ { 2 } of sky .
The coordinates and light curve properties , such as period and Oosterhoff type , are made publicly available .
We analyze in detail the light curve properties and Galactic distribution of the subset of \sim 4 , 000 type- ab RR Lyrae stars , including a search for new halo substructures and the number density distribution as a function of Oosterhoff type .
We find evidence for the Oosterhoff dichotomy among field RR Lyrae stars , with the ratio of the type II and I subsamples of about 1:4 , but with a weaker separation than for globular cluster stars .
The wide sky coverage and depth of this sample allows unique constraints for the number density distribution of halo RRab stars as a function of galactocentric distance : it can be described as an oblate ellipsoid with the axis ratio q = 0.63 and with either a single or a double power law with a power-law index in the range -2 to -3 .
Consistent with previous studies , we find that the Oosterhoff type II subsample has a steeper number density profile than the Oosterhoff type I subsample .
Using a group-finding algorithm EnLink , we detected seven candidate halo groups , only one of which is statistically spurious .
Three of these groups are near globular clusters ( M53/NGC 5053 , M3 , M13 ) , and one is near a known halo substructure ( Virgo Stellar Stream ) ; the remaining three groups do not seem to be near any known halo substructures or globular clusters , and seem to have a higher ratio of Oosterhoff type II to Oosterhoff type I RRab stars than what is found in the halo .
The extended morphology and the position ( outside the tidal radius ) of some of the groups near globular clusters is suggestive of tidal streams possibly originating from globular clusters .
Spectroscopic followup of detected halo groups is encouraged .