Abstract. We have used the JCMT to survey molecular line emission towards 14 ultracompact Hii regions (G5. 89, G9.62, G10.30, G10.47, G12.21, G13.87, G29.96, G31.41, G34.26, G43.89, G45.12, G45.45, G45.47, and G75.78). For each source, we observed up to ten 1 GHz bands between 200 and 350 GHz, covering lines of more than 30 species including multiple transitions of CO isotopes, CH 3 OH, CH 3 CCH, CH 3 CN and HCOOCH 3 , and sulphuretted molecules. The number of transitions detected varied by a factor of 20 between sources, which were chosen following observations of high-excitation ammonia (Cesaroni et al. 1994a) and methyl cyanide (Olmi et al. 1993). In half our sample (the line-poor sources), only C 17 O, C 18 O, SO, C 34 S and CH 3 OH were detected. In the line-rich sources, we detected over 150 lines, including high excitation lines of CH 3 CN, HCOOCH 3 , C 2 H 5 CN, CH 3 OH, and CH 3 CCH. We have calculated the physical conditions of the molecular gas. To reproduce the emission from the line-rich sources requires both a hot, dense compact core and an ambient cloud consisting of less dense, cooler gas. The hot cores, which are less than 0.1 pc in size, reach densities of at least 10 8 cm −3 and temperatures of more than 80 K. The line-poor sources can be modelled without a hot core by a 20−30 K, 10 5 cm −3 cloud. We find no correlation between the size of the Hii region and the current physical conditions in the molecular environment. A comparison with chemical models (Millar et al. 1997) confirms that grain surface chemistry is important in hot cores.

Abstract. Continuum emission at 450 and 850 µm from warm dust has been mapped in the fields of 71 methanol masers. Within these fields lie 30 centimetre-wave radio continuum sources and an additional 13 methanol maser sites. Sub-mm emission is detected at all but one of the maser sites, confirming the association of methanol maser emission with deeply embedded objects. Measured bolometric luminosities confirm that methanol maser emission is an excellent signpost of high-mass star formation. Examples of nearby isolated maserless dust cores may be harbouring massive protostars at an earlier evolutionary stage.

We present a SCUBA submillimetre (450 and 850 µm) survey of the environment of 105 IRAS point sources, selected from the Wood & Churchwell (1989a) and Kurtz et al. (1994) radio ultracompact (UC) Hii region surveys. We detected a total of 155 sub-mm clumps associated with the IRAS point sources and identified three distinct types of object: ultracompact cm-wave sources that are not associated with any sub-mm emission (sub-mm quiet objects), sub-mm clumps that are associated with ultracompact cm-wave sources (radio-loud clumps); and sub-mm clumps that are not associated with any known ultracompact cm-wave sources (radio-quiet clumps). 90% of the sample of IRAS point sources were found to be associated with strong sub-mm emission. We consider the sub-mm colours, morphologies and distance-scaled fluxes of the sample of sub-mm clumps and show that the sub-mm quiet objects are unlikely to represent embedded UC Hii regions unless they are located at large heliocentric distances. Many of the 2. 5 SCUBA fields contain more than one sub-mm clump, with an average number of companions (the companion clump fraction) of 0.90. The clumps are more strongly clustered than other candidate HMPOs and the mean clump surface density exhibits a broken power-law distribution with a break at 3 pc. We demonstrate that the sub-mm and cm-wave fluxes of the majority of radio-loud clumps are in excellent agreement with the standard model of ultracompact Hii regions. We speculate on the nature of the radio-quiet sub-mm clumps and, whilst we do not yet have sufficient data to conclude that they are in a pre-UC Hii region phase, we argue that their characteristics are suggestive of such a stage.

Abstract. -A 330−360 GHz spectral survey of the hot molecular core associated with the 'cometary' ultracompact HII region G 34.3+0.15 observed with the James Clerk Maxwell Telescope has detected 338 spectral lines from at least 35 distinct chemical species plus 19 isotopomers. 70 lines remain unidentified. Chemical abundance and rotation temperature have been determined by rotation diagram analysis for 12 species, and lower limits to abundance found for 38 others.

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