The Atacama Compact Array (ACA)

For realizing high fidelity of imaging with mosaicing observations, the Atacama Large Millimeter/submillimeter Array (ALMA) consists of a homogeneous array of 12 m antennas (12 m Array) and the Atacama Compact Array (ACA) in order to cover all spatial frequency Fourier components of the brightness distribution of observed sources. The array is located at an altitude site of about 5000 m with an operating wavelength range of 0.3 to 3 mm. ACA is an array composed of four 12 m dishes [TP (Total Power) Array] and twelve 7 m dishes (7 m Array). The 7 m Array has a very compact configuration to take short-baseline data corresponding to the low spatial frequency Fourier components. The 7 m Array has two configurations extended over 30-50 m to avoid shadowing at low elevation. The scientific importances and operation concepts of ACA, and the system design of ACA and its performance are presented in this paper.