A New Mid-Infrared Map of the BN/KL Region Using the Keck Telescope

Abstract

We present a new mid-infrared (12.5 m) map of the BN/KL high-mass star-forming complex in Orion using the LWS instrument on Keck I. Despite poor weather we achieved nearly diffraction-limited images (FWHM ¼ 0B38) over a roughly 25 00 ; 25 00 region centered on IRc2 down to a flux limit of %250 mJy. Many of the known IR sources in the region break up into smaller subcomponents. We have also detected six new mid-IR sources. Nearly all of the sources are resolved in our mosaic. The near-IR source ''n'' is slightly elongated in the mid-IR along a northwest-southeast axis and perfectly bisects the double-peaked radio source ''L.'' Source n has been identified as a candidate for powering the large IR luminosity of the BN/KL region (L ¼ 10 5 L). We postulate that the 12 m emission arises in a circumstellar disk surrounding source n. The morphology of the mid-IR emission and the Orion ''hot core'' (as seen in NH 3 emission), along with the location of water and OH masers, is very suggestive of a bipolar cavity centered on source n and aligned with the rotation axis of the hypothetical circumstellar disk. IRc2, once thought to be the dominant energy source for the BN/KL region, clearly breaks into four subsources in our mosaic, as seen previously at 3.8-5.0 m. The anticorrelation of mid-IR emission and NH 3 emission from the nearby hot core indicates that the IRc2 sources are roughly coincident (or behind) the dense hot core. The nature of IRc2 is not clear: neither self-luminous sources (embedded protostars) nor external heating by source ''I'' can be definitively ruled out. We also report the discovery of a new arclike feature southwest of the BN object and some curious morphology surrounding near-IR source ''t.''