A spatial study of the mid-IR emission features in four Herbig Ae/Be stars C. Boersma, E. Peeters, N. L. Martín-Hernández, G. van der Wolk, A. P. Verhoeff, A. G. G. M. Tielens, L. B. F. M. Waters and J. W. Pel A&A, 502 1 (2009) 175-187 Published online: 27 May 2009 DOI: 10.1051/0004-6361/200911820