Nitrogen abundance in the X-ray halos of clusters and groups of galaxies Junjie Mao, Jelle de Plaa, Jelle S. Kaastra, Ciro Pinto, Liyi Gu, François Mernier, Hong-Liang Yan, Yu-Ying Zhang and Hiroki Akamatsu A&A, 621 (2019) A9 Published online: 19 December 2018 DOI: 10.1051/0004-6361/201730931