Gas structure inside dust cavities of transition disks: Ophiuchus IRS 48 observed by ALMA Simon Bruderer, Nienke van der Marel, Ewine F. van Dishoeck and Tim A. van Kempen A&A, 562 (2014) A26 Published online: 31 January 2014 DOI: 10.1051/0004-6361/201322857