Optical nebular emission following the most luminous outburst of Aquila X-1 G. Panizo-Espinar, T. Muñoz-Darias, M. Armas Padilla, F. Jiménez-Ibarra, J. Casares and D. Mata Sánchez A&A, 650 (2021) A135 Published online: 21 June 2021 DOI: 10.1051/0004-6361/202140323