The effect of a strong external radiation field on protostellar envelopes in Orion J. K. Jørgensen, D. Johnstone, E. F. van Dishoeck and S. D. Doty A&A, 449 2 (2006) 609-619 Published online: 21 March 2006 DOI: 10.1051/0004-6361:20053011