  We report a combined theoretical and experimental study of the spectral and
polarization dependence of near resonant radiation coherently backscattered
from an ultracold gas of 85Rb atoms. Measurements in an approximately 6 MHz
range about the 5s^{2}S_{1/2}- 5p^{2}P_{3/2}, F=3 - F'=4 hyperfine transition
are compared with simulations based on a realistic model of the experimental
atomic density distribution. In the simulations, the influence of heating of
the atoms in the vapor, magnetization of the vapor, finite spectral bandwidth,
and other nonresonant hyperfine transitions are considered. Good agreement is
found between the simulations and measurements.
