RR Lyrae in XSTPS: The halo density profile in the North Galactic Cap
  We present a catalog of RR Lyrae stars (RRLs) observed by the Xuyi Schmidt
Telescope Photometric Survey (XDSS). The area we consider is located in the
North Galactic Cap, covering 376.75 sq deg at RA $\approx$ 150 deg and Dec
$\approx$ 27 deg down to a magnitude limit of i $\approx$ 19. Using the
variability information afforded by the multi-epoch nature of our XDSS data,
combined with colors from the Sloan Digital Sky Survey, we are able to identify
candidate RRLs. We find 318 candidates, derive distances to them and estimate
the detection efficiency. The majority of our candidates have more than 12
observations and for these we are able to calculate periods. These also allows
us to estimate our contamination level, which we predict is between 30% to 40%.
Finally we use the sample to probe the halo density profile in the 9-49 kpc
range and find that it can be well fitted by a double power law. We find good
agreement between this model and the models derived for the South Galactic Cap
using the Watkins et al. (2009) and Sesar et al. (2010) RRL data-sets, after
accounting for possible contamination in our data-set from Sagittarius stream
members. We consider non-spherical double power law models of the halo density
profile and again find agreement with literature data-sets, although we have
limited power to constrain the flattening due to our small survey area. Much
tighter constraints will be placed by current and future wide-area surveys,
most notably ESA's astrometric Gaia mission. Our analysis demonstrates that
surveys with a limited number of epochs can effectively be mined for RRLs. Our
complete sample is provided as accompanying online material.
