The ARAUCARIA project: Grid-based quantitative spectroscopic study of massive blue stars in NGC 55 N. Castro, M. A. Urbaneja, A. Herrero, M. Garcia, S. Simón-Díaz, F. Bresolin, G. Pietrzyński, R.-P. Kudritzki and W. Gieren A&A, 542 (2012) A79 Published online: 12 June 2012 DOI: 10.1051/0004-6361/201118253