HD 18078: A very slowly rotating Ap star with an unusual magnetic field structureG. Mathys, I. I. Romanyuk, D. O. Kudryavtsev, J. D. Landstreet, D. M. Pyper and S. J. AdelmanA&A, 586 (2016) A85DOI: https://doi.org/10.1051/0004-6361/201527476