A study of carbon monoxide and neutral carbon in the SI 06 molecular core

Maps are presented of J=2–l and J=3–2 C18O emission from the molecular environment of the bipolar nebula SI06, together with complementary observations of the 3P1–3P0 CI emission. Line splitting observed extensively over the E molecular cloud suggests that it is best explained as the expanding remnant of a thick toroid surrounding the optical lobes. The poor correlation between the observed molecular line emission and dust continuum emission in the E cloud is probably due to a large temperature gradient. Strong CI emission from the protostellar candidate SI06 FIR suggests the nearby presence of a powerful source of far-UV radiation, whose energy supply is unlikely to arise from gravitational contraction of a protostar. It is probable that this source is the star SI06 IR, which also heats SI06 FIR. There is evidence, in both CI and C18O, for a predominantly blueshifted outflow from S106 IR, best interpreted as a stellar wind-driven shock into the toroidal remnant. C18O and 13CO appear to be depleted, relative to canonical values for their abundances, in SI06 FIR, despite its high optical extinction, which should discourage selective photodissociation. Elsewhere in the cloud the CI line profiles show a resemblance to those of C18O, with intensity equivalent to a few photodissociation regions (PDRs) along the line of sight.