Observations of forbidden Si II (35 microns) and Si I (25 microns) in Orion - Evidence of a wind shock near IRc2

Forbidden Si II and Si I line emission from Orion's BN-KL was measured using a cryogenic grating spectrometer aboard NASA's Kuiper Airborne Observatory. It is believed that the bulk of the forbidden Si II emission in Orion originates in photodissociated gas at the interface between the H II region and its parent molecular cloud. There is, however, a twofold enhancement in forbidden Si II emission near IRc2, which is attributed to fast dissociative J-shock where the wind from IRc2 impact slower moving material. Model fits suggest a silicon gas-phase depletion near ITc2 of 0.3-1.0 relative to solar. The spatial distribution of the forbidden Si II emission has a centralized peak.