Helium features are inconsistent with the spectral evolution of the kilonova AT2017gfo Albert Sneppen, Rasmus Damgaard, Darach Watson, Christine E. Collins, Luke Shingles and Stuart A. Sim A&A, 692 (2024) A134 Published online: 05 December 2024 DOI: 10.1051/0004-6361/202451450