Shapes of stellar activity cycles T. Willamo, T. Hackman, J. J. Lehtinen, M. J. Käpylä, N. Olspert, M. Viviani and J. Warnecke A&A, 638 (2020) A69 Published online: 12 June 2020 DOI: 10.1051/0004-6361/202037666