Total intensity (I, bottom panel) and circular polarisation (V, top panel) CN spectra. The 1σ and 3σ limits are indicated by the short and long dashed lines, respectively. Left panel: spectra stacking the nine strongest CN N = 2−1 hyperfine components that we extracted at the position of the strongest emission peak. The 1σ limit corresponds to a magnetic field strength |Bz| = 2.7 mG, for which the V-spectrum is indicated in red. The effective line width is 0.45 km s−1. The apparent non-zero baseline in the Stokes I spectrum is due to the contribution to the stacked spectrum of hyperfine components that occur within 1.5 km s−1 of each other. Middle panel: azimuthally averaged spectra obtained by stacking the two strongest CN hyperfine components in our data that are not significantly blended. The rms limit corresponds to a magnetic field strength |Bz| = 0.8 mG, for which the V-spectrum is indicated in red. The effective line width is 0.45 km s−1. Beyond +0.5 km s−1, the spectrum is affected by a blend with a neighbouring hyperfine component. Right panel: similar to the middle panel, but only for emission along the line of nodes (see text). Here the signature of a toroidal field would be strongest. The fractional rms reached on the V-spectrum is 0.33%. The rms limit corresponds to a magnetic field strength |B| = 2.6 mG, for which the V-spectrum is indicated in red. This corresponds to a toroidal field strength limit of |Bϕ| < 30 mG. The effective line width is 0.5 km s−1.
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