Mid-infrared spectral evidence for a luminous dust enshrouded source in Arp 220 H. W. W. Spoon, A. F. M. Moorwood, D. Lutz, A. G. G. M. Tielens, R. Siebenmorgen and J. V. Keane A&A, 414 3 (2004) 873-883 Published online: 27 January 2004 DOI: 10.1051/0004-6361:20031656