The Period-Luminosity Relation of RR Lyrae Stars in the SDSS Photometric   System
  We provide the first detailed study of the RR Lyrae period-luminosity (PL) relation in the ugriz bandpasses of the Sloan Digital Sky Survey (SDSS) filter system. We argue that tight, simple PL relations are not present in the SDSS filters, except for the redder bandpasses i and (especially) z. However, for all bandpasses, we show that, by incorporating terms involving a (fairly reddening-independent) "pseudo-color" C_0 = (u-g)_0 - (g-r)_0, tight (non-linear) relations do obtain. We provide theoretically calibrated such relations in the present paper, which should be useful to derive precise absolute magnitudes (hence distances) and intrinsic colors (hence reddening values) to even {\em individual} field RR Lyrae stars. For applications to cases where photometry in all five passbands may not be available, we also provide simple (though less precise) average PL relations for the i and z bandpasses, which read as follows:   M_z = 0.839 - 1.295 log P + 0.211 log Z,   M_i = 0.908 - 1.035 log P + 0.220 log Z.   Similarly, simple period-color relations for (r-i)_0, (g-r)_0, and (u-z)_0 are also provided. 
C. C\'aceres and M. Catelan