MMA Memo #201

Hour Angle Ranges for Configuration Optimization

M.A. Holdaway

February 25, 1998

Keywords: array configuration, system temperature, atmospheric opacity

As a source is tracked to lower and lower elevations, the atmospheric opacity increases the system temperature rather dramatically, especially at submillimeter wavelengths. We find that configurations of 850~m or smaller can achieve excellent (u,v) coverage in under two hours of observations (the smallest arrays have complete (u,v) coverage in a snapshot), but the 3000~m configuration requires about eight hours to achieve excellent (u,v) coverage. We investigate reasonable hour angle ranges which result in minimal sensitivity loss for observations over the range of declinations accessible to Chajnantor at frequencies of 225, 345, and 875~GHz for each of the quartile opacity conditions. Typically, hour angle limits of 2-3 hours (ie, 4-6 hours total observing) are possible without increasing the system temperature too much. Since most configurations do not require long tracks to achieve good Fourier plane coverage, and the atmosphere discourages long tracks on sensitivity grounds, long sensitive integrations will require many short observations near transit spread out over many days.

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Last modified: 09 December, 1999