Differential rotation near the Orion-Kleinmann-Low region : aperture synthesis observations of HCN emission.

The 88.6 GHz J = 1-0 transition of HCN toward the Orion-Kleinmann-Low nebula has been mapped with an angular resolution of 6 arcsec using the Hat Creek interferometer. Systematic gradients have been detected in the velocity of the molecular 'ridge' gas across a 1 arcmin region centered near the BN and TRc2 infrared cluster. Approaching IRc2 from the south, the ridge velocity decreases from roughly 8 to 6 km/s, but from the north it increases from roughly 10 to 11 km/s. The velocity gradient is interpreted as rotation of the cloud complex. The rotation curve is consistent with a density distribution in which the cloud mass increases linearly with distance from IRc2.