Molecular Column Densities Near the Center of the Milky Way

The observations were performed during the austral winter seasons of 2001 and 2002 at the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO), located at 2847m at the Amundsen-Scott South Pole Station. This site has very low water vapor, high atmospheric stability and a thin troposphere making it exceptionally good for submillimeter observations. AST/RO is a 1.7m diameter, offset Gregorian telescope capable of observing at wavelengths between 200 μm and 1.3 mm (Stark et al. 2001). A dual-channel SIS waveguide receiver (Walker et al. 1992; Honingh et al. 1997) was used for simultaneous 461–492 GHz and 807 GHz observations, with double-sideband noise temperatures of 320–390 K and 1050–1190 K, respectively. Telescope efficiency, η, estimated using moon scans, skydips, and measurements of the beam edge taper, was 81% at 461–492 GHz and 71% at 807 GHz. Atmosphere-corrected system temperatures ranged from 700 to 4000 K at 461–492 GHz and 9000 to 75,000 K at 807 GHz.