Periodic variability of 6.7 GHz methanol masers in G22.357 + 0.066 M. Szymczak, P. Wolak, A. Bartkiewicz and H. J. van Langevelde A&A, 531 (2011) L3 Published online: 08 June 2011 DOI: 10.1051/0004-6361/201117145