Molecular astronomy using heterodyne detection at 691 GHz

Observations of the CO J=6→5 transition at 691 GHz (434 μm) in new interstellar and planetary sources have been made. The heterodyne receiver uses an optically pumped laser local oscillator and a quasi-optical Schottky diode mixer, with measured noise temperatures consistently under 4000 K (double sideband). Continued improvements in system performance and antenna coupling have made possible the mapping of 434 μm emission from W3, and the detection of CO J=5→6 absorption in the atmosphere of Venus. A detailed description of the instrumentation and recent observational data are provided.