The Minimum Spanning Tree Problem in the Phase Calibration for the Spatial FFT Interferometer

Achieving a Nyquist-rate direct-imaging observation using a spatial FFT interferometer, instrumental phase errors in transmission lines must be calibrated before the observation. We improved the phase-calibrating system in the Waseda FFT interferometer by increasing the number of simultaneous obtainable fringe baselines from 84 to 128, and using the algorithm of the minimum spanning tree problem in graph theory. As a result, the main-beam intensity of the interferometer became 1.6 times on average.