Are there tangled magnetic fields on HgMn stars
Context. Several recent spectrophotometric studies failed to detec t significant global magnetic fields in late-B HgMn chemicall y peculiar stars, but some investigations have suggested the pr esence of strong unstructured or tangled fields in these obje cts. Aims. We used detailed spectrum synthesis analysis to search for evidence of tangled magnetic fields in high-quality observed spectra of 8 slowly rotating HgMn stars and one normal late-B star. We also evaluated recent sporadic detections of weak longitudinal magnetic fields in HgMn stars based on the moment technique. Methods. Our spectrum synthesis code calculated the Zeeman broadening of metal lines in HARPS spectra, assuming an unstructured, turbulent magnetic field. A simple line formation mod el with a homogeneous radial field distribution was applied t o assess compatibility between previous longitudinal field measure ments and the observed mean circular polarization signatures. Results. Our analysis of the Zeeman broadening of magnetically sensitive spectral lines reveals no evidence of tangled magnetic fields in any of the studied HgMn or normal stars. We infer upper limits of 200‐700 G for the mean magnetic field modulus ‐ much small er than the field strengths implied by studies based on di fferential magnetic line intensification and quadratic field d iagnostics. The new HARPSpol longitudinal field measurements for the extreme Hg Mn star HD 65949 and the normal late-B star 21 Peg are consistent with zero at a precision of 3‐6 G. Re-analysis of our Stokes V spectra of the spotted HgMn star HD 11753 shows that the recent moment technique measurements retrieved from the same data are incompatible with the lack of circular polarization sig natures in the spectrum of this star. Conclusions. We conclude that there is no evidence for substantial tangled magnetic fields on the surfaces of studied HgMn stars. We cannot independently confirm the presence of very strong qua dratic or marginal longitudinal fields for these stars, so re sults from the moment technique are likely to be spurious.