Spectral modeling of type II supernovae - I. Dilution factors C. Vogl, S. A. Sim, U. M. Noebauer, W. E. Kerzendorf and W. Hillebrandt A&A, 621 (2019) A29 Published online: 03 January 2019 DOI: 10.1051/0004-6361/201833701