Outflow of Matter in the KL Nebula - the Role of IRC2
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Abstract
New observations have been made of the Orion-KL Nebula with the Infrared Telescope Facility on Mauna Kea at 8.7 μm and 20 μm with 2" resolution. The maps show many new infrared peaks, with good correlation with H2O masers, as well as 20 μm emission reaching to the outermost peaks of the 2 μm molecular hydrogen emission. New spectrophotometric measurements of the stronger peaks in the range 4.8-20 μm show that the compact source IRc2 has a very deep silicate feature with τ9.7μm ≳ 5, and hence that its luminosity has been hitherto seriously underestimated. The other infrared peaks have silicate absorption comparable with that of the BN object (τ9.7μm ≈ 0.5-1). IRc2 and BN are "hot" sources with color temperatures ≳ 350 K over 8-20 μm, while the other features of the KL Nebula have Tc ∼ 120-150 K. The infrared observations suggest that IRc2 is a star of 104 - 105 Lsun and is the primary source of energy for all of the outflow phenomena seen in molecular-line spectra. The rate of mass loss in the outflow from IRc2 is ∼ 10-4 - l0-3 Msun yr-1, continuous over the past l03 to 104 years; the mass contained in the flow is ∼1-10 Msun. IRc2 may be a young, massive star in the last stages of its formation rather than an evolved star. The high rate of mass loss prevents the formation of a compact H II region and the clearing out of a large, ionized cavity in KL. The mass loss from IRc2 and BN could account for their dust envelopes, their strong infrared emission, and their high visual extinction. Heating by the radiation and outflow from IRc2 may be responsible for the infrared appearance of the KL nebula.
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