Hot ammonia in Orion

Ten inversion lines from nonmetastable rotational levels of NH3 have been detected in the Kleinmann-Low (KL) nebula in Orion. Six of these lines were previoulsy undetected. The emission arises from levels which have energies up to 1150 K above the ground state, indicating that the NH3 is immersed in a hot, dense medium. Three well-defined kinematical components within KL are evident in emission from NH3 and other molecules. The emission from hot NH3 is dominated by the component having V/sub LSR/=5.2 km s-1 and ΔV =10--12 km s-1. A non-LTE analysis of NH3 emission from this ''hot core'' component reveals that the minimum particle density in this source is approx.5 x 10 cm-3, and that the kinetic temperature is > or approx. =220 K. The diameter of the hot core source is probably within a factor of 2 to 6'' (5 x 1016 cm). The hot core is undoubtedly associated with one of the compact infrared sources in KL, and we suggest on the basis of position and velocity coincidences that it is IRc2. The hot core appears to contain about one Jeans mass at the inferred temperature and density. We therefore suggest that this object is a very young protostar which is still in the throes of its initial collapse