Detection of Na in WASP-21b’s lower and upper atmosphereG. Chen, N. Casasayas-Barris, E. Pallé, L. Welbanks, N. Madhusudhan, R. Luque and F. MurgasA&A, 642 (2020) A54DOI: https://doi.org/10.1051/0004-6361/202038661