Limits on the spatial variations of the electron-to-proton mass ratio in the Galactic plane S. A. Levshakov, D. Reimers, C. Henkel, B. Winkel, A. Mignano, M. Centurión and P. Molaro A&A, 559 (2013) A91 Published online: 20 November 2013 DOI: 10.1051/0004-6361/201322535