Atmospheric dynamics and shock waves in RR Lyr - I. The three Hα emissions D. Gillet, F. L. Sefyani, A. Benhida, B. Mauclaire, D. El Youssoufi, T. de France, Z. Benkhaldoun and P. Lailly A&A, 680 (2023) A97 Published online: 15 December 2023 DOI: 10.1051/0004-6361/202347355