Transition disks: four candidates for ongoing giant planet formation in Ophiuchus M. Orellana, L. A. Cieza, M. R. Schreiber, B. Merín, J. M. Brown, L. J. Pellizza and G. A. Romero A&A, 539 (2012) A41 Published online: 22 February 2012 DOI: 10.1051/0004-6361/201117659