We report the results of Faraday rotation measurements of 23 background radio sources whose lines of sight pass through or close to the Rosette Nebula .
We made linear polarization measurements with the Karl G. Jansky Very Large Array ( VLA ) at frequencies of 4.4 GHz , 4.9 GHz , and 7.6 GHz .
We find the background Galactic contribution to the rotation measure in this part of the sky to be + 147 rad m ^ { -2 } .
Sources whose lines of sight pass through the nebula have an excess rotation measure of 50-750 rad m ^ { -2 } , which we attribute to the plasma shell of the Rosette Nebula .
We consider two simple plasma shell models and how they reproduce the magnitude and sign of the rotation measure , and its dependence on distance from the center of the nebula .
These two models represent different modes of interaction of the Rosette Nebula star cluster with the surrounding interstellar medium .
Both can reproduce the magnitude and spatial extent of the rotation measure enhancement , given plausible free parameters .
We contend that the model based on a stellar bubble more closely reproduces the observed dependence of rotation measure on distance from the center of the nebula .