Shadow of a Schwarzschild black hole surrounded by a Bach–Weyl ring Mingzhi Wang, Songbai Chen, Jieci Wang and Jiliang Jing Eur. Phys. J. C, 80 2 (2020) 110 Published online: 10 February 2020 DOI: 10.1140/epjc/s10052-020-7641-3