Variation of the magnetic field of the Ap star HD 50169 over its 29-year rotation period G. Mathys, I. I. Romanyuk, S. Hubrig, D. O. Kudryavtsev, J. D. Landstreet, M. Schöller, E. A. Semenko and I. A. Yakunin A&A, 624 (2019) A32 Published online: 03 April 2019 DOI: 10.1051/0004-6361/201834706