Ultraviolet and extreme-ultraviolet line ratio diagnostics for O IV F. P. Keenan, P. J. Crockett, K. M. Aggarwal, D. B. Jess and M. Mathioudakis A&A, 495 1 (2009) 359-362 Published online: 14 January 2009 DOI: 10.1051/0004-6361:200811222