On the Heating Source of the Orion KL Hot Core

We present images of the J = 10-9 rotational lines of HC 3 N in the vibrationally excited levels 1 v 7, 1 v 6, and 1 v 5 of the hot core (HC) in Orion KL. The images show that the spatial distribution and the size emission from the 1 v 7 and 1 v 5 levels are different. While the J = 10-9 1 v 7 line has a size of 4'' × 6'' and peaks 1 1 northeast of the 3 mm continuum peak, the J = 10-9 1 v 5 line emission is unresolved (<3'') and peaks 1 3 south of the 3 mm peak. This is a clear indication that the HC is composed of condensations with very different temperatures (170 K for the 1 v 7 peak and >230 K for the 1 v 5 peak). The temperature derived from the 1 v 7 and 1 v 5 lines increases with the projected distance to the suspected main heating source I. Projection effects along the line of sight could explain the temperature gradient as being produced by source I. However, the large luminosity required for source I (>5 × 10 5 L ☉ ) to explain the 1 v 5 line suggests that external heating by this source may not dominate the heating of the HC. Simple model calculations of the vibrationally excited emission indicate that the HC can be internally heated by a source with a luminosity of 10 5 L ☉ , located 1 2 southwest of the 1 v 5 line peak (1 8 south of source I). We also report the first detection of high-velocity gas from vibrationally excited HC 3 N emission. Based on excitation arguments, we conclude that the main heating source is also driving the molecular outflow. We speculate that all the data presented in this Letter and the IR images are consistent with a young massive protostar embedded in an edge-on disk.