5
Minimum Number of Antennas

Millimeter and submillimeter observations are very important to contemporary astronomy. No better defense of this proposition is needed than the list of advances in the 15 years that have elapsed since the 1991 astronomy and astrophysics decadal survey was written. Nonetheless it is legitimate to ask at what point a descoped telescope would fail to sustain support in the highly competitive environment for new facilities today. This committee’s answer, inevitably somewhat subjective, is based on the performance measures presented in Table 1. Table 1 shows, for example, that a 30-antenna array has only 3 to 4 times the sensitivity of Plateau de Beure at wavelengths longer than 1 millimeter and would not have ALMA’s potential enormous mosaicing speed advantage at high frequency over that of the Submillimeter Array (SMA), which is the one other high-altitude facility capable of observing at 900 GHz.

The committee concludes that a 40-antenna array would retain ALMA’s strong support within the general astronomical community. However, the rapid decline in imaging capability that would result with a further reduction below 40 antennas would erode this support.



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The Atacama Large Millimeter Array: Implications of a Potential Descope 5 Minimum Number of Antennas Millimeter and submillimeter observations are very important to contemporary astronomy. No better defense of this proposition is needed than the list of advances in the 15 years that have elapsed since the 1991 astronomy and astrophysics decadal survey was written. Nonetheless it is legitimate to ask at what point a descoped telescope would fail to sustain support in the highly competitive environment for new facilities today. This committee’s answer, inevitably somewhat subjective, is based on the performance measures presented in Table 1. Table 1 shows, for example, that a 30-antenna array has only 3 to 4 times the sensitivity of Plateau de Beure at wavelengths longer than 1 millimeter and would not have ALMA’s potential enormous mosaicing speed advantage at high frequency over that of the Submillimeter Array (SMA), which is the one other high-altitude facility capable of observing at 900 GHz. The committee concludes that a 40-antenna array would retain ALMA’s strong support within the general astronomical community. However, the rapid decline in imaging capability that would result with a further reduction below 40 antennas would erode this support.

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