Nature of two massive protostellar candidates: IRAS 21307+5049 and IRAS 22172+5549 F. Fontani, R. Cesaroni, L. Testi, S. Molinari, Q. Zhang, J. Brand and C. M. Walmsley A&A, 424 1 (2004) 179-195 Published online: 17 August 2004 DOI: 10.1051/0004-6361:20035848