THE MOLECULAR SURROUNDINGS OF W3(OH)

We have observed the molecular cloud surrounding the ultra-compact HII region W3(OH) in (CO)-O-18(1-0), HCO+(l-0), and CH3CN(5-4) using the three element interferometer on the,Plateau de Bure. We also present H 41 alpha and H59 gamma measurements of the ionized gas. We find that o ur methyl cyanide image consists of two compact sources. Of these, one essentially coincides with the cluster of water masers to the east of the continuum source and shows evidence for an east-west velocity gra dient similar to that observed in water maser proper motions. The othe r compact methyl cyanide region appears to be identified with the high density molecular clump which harbors the OK masers. We estimate temp eratures of order 100 K from our methyl cyanide data for both compact regions. We also find a compact continuum source at 110 GHz towards th e CH3CN peak associated with the water maser cluster. Making the assum ption that the observed emission from this region is due to hot dust, we estimate that the source has a column density of 3 10(25) Cm-2 and a mass of 30 M circle dot but with considerable uncertainty. Interpret ing this as an outflow analogous to the low velocity ''plateau'' in Or ion, suggests that we may be observing mass loss at a rate of 0.005 so lar masses per year. The (CO)-O-18 and HCO+ maps towards W3(OH) show e vidence for much more extended structures and in fact, our maps ''miss '' a large fraction of the flux seen by single dish telescopes. We obs erve absorption in HCO+ towards the continuum source at a velocity of -45 km s(-1) which is similar to the value found for species such as N H3. Our (CO)-O-18 results show that, as well as the compact clump asso ciated with the water masers, there is a more extended region of rough ly 0.05 parsec in size and of mass 60 M circle dot surrounding the wat er maser complex. By contrast, we see no evidence in (CO)-O-18 emissio n or absorption for dense gas bordering the compact HII region and put an upper limit of 3 M circle dot on a hypothesised disk surrounding t he ionized gas. On larger size scales, we do see in (CO)-O-18 evidence for a structure with orientation NW-SE and with a velocity gradient o f 20 km s(-1)pc(-1).