Optical properties of Y dwarfs observed with the Gran Telescopio Canarias E. L. Martín, J.-Y. Zhang, H. Lanchas, N. Lodieu, T. Shahbaz and Ya. V. Pavlenko A&A, 686 (2024) A73 Published online: 31 May 2024 DOI: 10.1051/0004-6361/202347581