  We experimentally demonstrate optical trapping of 87Rb atoms using a
two-color evanescent field around an optical nanofiber. In our trapping
geometry, a blue-detuned traveling wave whose polarization is nearly parallel
to the polarization of a red-detuned standing wave produces significant vector
light shifts that lead to broadening of the absorption profile of a
near-resonant beam at the trapping site. A model that includes scalar, vector,
and tensor light shifts of the probe transition $5S_{1/2}$-$5P_{3/2}$ from the
trapping beams, weighted by the temperature-dependent position of the atoms in
the trap, qualitatively describes the observed asymmetric profile and explains
differences with previous experiments that used Cs atoms. The model provides a
consistent way to extract the number of atoms in the trap.
