Magnetic field strength as a function of the distance (Vlemmings 2012). The different boxes show the range of observed magnetic field strengths derived from observations of SiO masers (Kemball et al. 2009; Herpin et al. 2006), H₂O masers (Vlemmings et al. 2002 and Vlemmings et al. 2005), OH masers (e.g Rudnitski et al. 2010) and CN (this work, triangles indicate Zeeman detection and arrows indicate the upper values). The dashed and solid lines indicate r^-2 solar-type and r^-1 toroidal magnetic field configurations, respectively. The vertical dashed line indicates the stellar surface for the Miras, and the star corresponds to the magnetic field measured at the surface of χ Cyg by Lèbre et al. (2014) for this object.