Sampling molecular gas in the Helix planetary nebula: Variation in HNC/HCN with UV flux J. Bublitz, J. H. Kastner, P. Hily-Blant, T. Forveille, M. Santander-García, J. Alcolea and V. Bujarrabal A&A, 659 (2022) A197 Published online: 29 March 2022 DOI: 10.1051/0004-6361/202141778