Hydrogen-free Wolf-Rayet stars: Helium stars with envelope-inflation structure and rotation Xizhen Lu, Chunhua Zhu, Helei Liu, Sufen Guo, Jinlong Yu and Guoliang Lü A&A, 674 (2023) A216 Published online: 23 June 2023 DOI: 10.1051/0004-6361/202243188