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Chemical evolution ahead of Herbig--Haro objects
Serena Viti (UCL)
Compact regions of enhanced HCO+ and
NH3 emission have been detected
close to a number of HH objects. An interpretation of these detections is
the following: a transient clump within the molecular cloud has been
irradiated by the shock that generates the HH object. The irradiation
releases icy mantles from the grains within the transient clump and
initiates a photochemistry. On the basis of this picture, we have
developed an extensive chemical model which predicts that a wide range of
species, other than NH3 and HCO+,
should also be detectable. These
include CH3O,H2S, C3H4,
H2CO, SO, SO2, H2CS, and NS.
The chemical effects should last ca. 104 years.
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