Testing the Atacama Compact Array Phase-Correction Scheme Using the Submillimeter Array

Abstract

Listen

Translate article

Abstract We conducted observational tests of a phase-correction scheme for the Atacama Compact Array (ACA) of the Atacama Large Millimeter and submillimeter Array (ALMA) using the Submillimeter Array (SMA) on Mauna Kea in Hawaii. Interferometers at millimeter and submillimeter waves are highly affected by refraction induced by water vapor in the troposphere, which results in phase fluctuations. The ACA is planning to compensate for the atmospheric phase fluctuation using phase information of the outermost antennas with interpolating into the inner antennas by creating a phase screen. The interpolation and extrapolation phase-correction schemes using phase screens have been tested by the SMA to study how effective they are. We produce a plane of wavefront (phase screen) from the phase information of three antennas for each integration, and this phase screen is used for interpolating the phase of the inner antenna and extrapolating that of the outer one. The interpolation scheme apparently obtains improved results, suggesting that the ACA phase-correction scheme works well. On the other hand, the extrapolation one often does not improve the results. After extrapolation, unexpectedly large phase fluctuations occur in the phases of the antennas at a distance of $\sim\ $140 m away from the center of the three reference antennas. The directions of these antennas are almost perpendicular to that of the wind, suggesting that the phase fluctuations can be well explained by the frozen phase screen in the atmosphere.