Detection of Na in WASP-21b’s lower and upper atmosphere G. Chen, N. Casasayas-Barris, E. Pallé, L. Welbanks, N. Madhusudhan, R. Luque and F. Murgas A&A, 642 (2020) A54 Published online: 02 October 2020 DOI: 10.1051/0004-6361/202038661