Density diagnostics derived from the O iv and S iv intercombination lines observed by IRIS V. Polito, G. Del Zanna, J. Dudík, H. E. Mason, A. Giunta and K. K. Reeves A&A, 594 (2016) A64 Published online: 13 October 2016 DOI: 10.1051/0004-6361/201628965