The molecular environment of S106 IR

Millimetre and submillimetre images of the bipolar nebula S106 are presented which resolve the structure of the circumstellar material around the exciting star S106 IR. The previously unresolved ‘dust bar’ is seen to break up into a number of sources: there is no evidence for a smooth disc about the star. There is a bright, previously undetected far-infrared point source in the dust lane which is not detected at 20 μm, suggesting that it is an extremely embedded object of moderate luminosity (30–1000 Lʘ); this object maybe a very young protostellar companion to S106 IR. Maps of the C18O J = 1 → 0 and CS J = 3 → 2 emission are presented; these correlate well with the continuum maps. Consistent column densities can be derived from the dust and line emission using standard molecular abundances and modest dust temperatures (about 50 K), suggesting that most of the circumstellar dust and gas is warm and that no significant molecular depletion has occurred. We have also mapped the hot circumstellar gas as traced by the CO J = 6 → 5 line; we derive a lower limit to the temperature of this component of 165 K, and find that its mass is > 0.05 of the total molecular gas mass. This component is clumpy on 8-arcsec scales, has the same linewidth as the lower lying CO transitions, and is closely associated with the warm ( ≈ 50 K) molecular gas in the dust lane traced by the adjacent continuum radiation; these features are consistent with a model in which the hot and warm gases are approximately co-spatial and are heated from within the dust ring.