A survey of molecular line emission towards ultracompact Hii regions J. Hatchell, M. A. Thompson, T. J. Millar and G. H. Macdonald Astron. Astrophys. Suppl. Ser., 133 1 (1998) 29-49 Published online: 15 November 1998 DOI: 10.1051/aas:1998309