  We report a measurement of the dimensionless enhancement factor $\kappa_0$
for the Rb-$^{129}$Xe pair commonly used in spin exchange optical pumping
(SEOP) to produce hyperpolarized $^{129}$Xe. $\kappa_0$ characterizes the
amplification of the $^{129}$Xe magnetization contribution to the Rb electronic
effective field, compared to the case of a uniform continuous medium in
classical magnetostatics. The measurement is carried out in Rb vapor cells
containing both $^3$He and $^{129}$Xe and relies on the previously measured
value of $\kappa_0$ for the Rb-$^3$He pair. The measurement is based on (1) the
optically detected (Faraday rotation) frequency shift of the $^{87}$Rb EPR
hyperfine spectrum caused by the SEOP nuclear polarization and subsequent
sudden destruction of nuclear polarization of both species and (2) a comparison
of NMR signals for the two species acquired just prior to the EPR frequency
shift measurements. We find $(\kappa_0)_{\rm RbXe} = 518\pm 8$, in good
agreement with previous measurements and theoretical estimates but with
improved precision.
