Planck polarization maps of the Rosette region: a) Q Stokes parameter; b) U Stokes parameter. The dashed circles, with radii 2° and 3°, define the region where we estimate the background level, the full circle centred on the star cluster represents the outer radius of the dust shell,  pc, and the rectangle encompasses the brightest part of the Mon OB2 cloud. c) Intensity map at 353 GHz with the plane-of-the-sky magnetic field orientation shown by headless vectors, obtained by rotating the polarization angle ψ by 90°. The vectors are plotted at every 6′, from the average of Q and U within the same distance from the central pixel. d) Polarization fraction p, with the same intensity contours as in Fig. 2.