Variations in H2O+/H2O ratios toward massive star-forming regions F. Wyrowski, F. van der Tak, F. Herpin, A. Baudry, S. Bontemps, L. Chavarria, W. Frieswijk, T. Jacq, M. Marseille, R. Shipman et al. (56 more) A&A, 521 (2010) L34 Published online: 01 October 2010 DOI: 10.1051/0004-6361/201015110