Resolved gas cavities in transitional disks inferred from CO isotopologs with ALMA N. van der Marel, E. F. van Dishoeck, S. Bruderer, S. M. Andrews, K. M. Pontoppidan, G. J. Herczeg, T. van Kempen and A. Miotello A&A, 585 (2016) A58 Published online: 16 December 2015 DOI: 10.1051/0004-6361/201526988