Hot ammonia in Orion

Observations clearly indicating the presence of hot (greater than 220 K) ammonia associated with at least one of the infrared components of the Kleinman-Low (KL) nebula in Orion are presented. Ten nonmetastable rotational NH3 inversion lines with rest frequencies from 21.7 to 24.2 GHz, six of which were previously undetected, were studied with a 100-m radio telescope. The spike, plateau and hot core features common to all KL molecular emission are observed and an analysis of their characteristics indicates that the predominant hot core source, with an LSR radial velocity of approximately 5.2 km/sec, contains NH3 with an excitation temperature of 220 K, a mean density of approximately 5 x 10 to the 7th/cu cm, and a temperature greater than 220 K and is embedded in a substantial far-IR radiation field. The hot molecular core is identified with the shell source of H2O and SiO maser emission, and with an infrared object, believed to be a very young protostar in its initial stage of collapse.