Observing the changing surface structures of the active K giant σ Geminorum with SONG H. Korhonen, R. M. Roettenbacher, S. Gu, F. Grundahl, M. F. Andersen, G. W. Henry, J. Jessen-Hansen, V. Antoci and P. L. Pallé A&A, 646 (2021) A6 Published online: 01 February 2021 DOI: 10.1051/0004-6361/202038799