The enigmatic magnetic field of the planet hosting Herbig Ae/Be star HD 169142

Context. Recent observations of the accretion disk around the Herbig Ae/Be star HD 169142 have revealed its complex and asymmetric morphology that indicates the presence of planets. The knowledge of the magnetic field structure in host stars is indispensable for our understanding of the magnetospheric interaction between the central stars, the circumstellar (CS) environment, and the planetary companions. Aims. We want to study the geometry of the magnetic field of HD 169142. Methods. We measured the mean longitudinal magnetic field from high-resolution ESPaDOnS and HARPSpol spectra of HD 169142 using the least-squares deconvolution technique. Additionally, the spectral variability of hydrogen lines is studied using dynamical spectra. Results. Our analysis of the Stokes V spectra reveals the presence of definitely detected narrow Zeeman features observed using line masks with neutral iron lines. On two observing epochs, we also obtain marginally detected broad Zeeman features. To explain the simultaneous appearance of narrow and broad Zeeman features, we discuss different scenarios, including one scenario related to a non-photospheric origin of the narrow Zeeman features due to magnetospheric interaction with warm CS matter. In an environment such as a wind or an accretion disk, spectral lines may form over a relatively large volume, and the field topology may therefore be complex not only in latitude and azimuth, but in radius as well. Dynamical plots of the Hβ line show an intriguing very complex structure with appearing and disappearing absorption features, which can be related to the complex morphology of the CS matter with asymmetric dust clump structures. The profiles of spectral lines belonging to different elements are variable, indicating the presence of chemical spots.