H I bubbles surrounding southern optical ring nebulae: Anon (WR 23) and RCW 52 C. Cappa, V. S. Niemela, M. C. Martín and N. M. McClure-Griffiths A&A, 436 1 (2005) 155-163 Published online: 20 May 2005 DOI: 10.1051/0004-6361:20042344