次毫米波干涉陣列影像相位修正策略

Abstract

毫米(millimeter)與次毫米波(Submillimeter)提供了宇宙中低溫塵埃輻射與許多分子光譜資訊，是地面天文觀測最後的波段。建造當中的新一代地表最大次毫米波干涉儀（the Atacama Large Millimeter and submillimeter Array，簡稱ALMA）是有史以來最大的地面望遠鏡興建計畫。毫米和次毫米波的干涉影像相位起伏擾動主要都是受到對流層水汽分布的影響。為了減低觀測影像相位擾動，我們使用夏威夷白山(Mauna Kea)上的次毫米波干涉陣列（Submillimeter Array，簡稱SMA）的觀測數據來發展相位補償修正策略，以作為最大次毫米波干涉儀ALMA當中的短基線密集陣列（the Atacama Compact Array，簡稱ACA）影像修正用。運用內插和外插的演算技巧來比較與了解影像相位補償修正的有效程度。

Millimeter and submillimeter astronomers pursue science and technology development with ground-based millimeter/submillimeter interferometers through the opaque atmosphere. This waveband provides a unique window on cold dust emission and highly excited lines from molecules and ions. The next generation interferometer at this waveband is the Atacama Large Millimeter and submillimeter Array (ALMA) with the Atacama Compact Array (ACA). The interferometers at this waveband are, however, highly affected by the water vapor induced refraction, which results as phase fluctuations. To reduce the phase fluctuation, we conducted a phase correction scheme using the observing data of the Submillimeter Array (SMA) for the ACA. The phase correction schemes, interpolation and extrapolation, are studied to know how effective these scheme are. Three simultaneously detected antenna phases form a plane of a wave front, and this phase screen are used for the interpolation and extrapolation. The interpolation scheme can apparently obtain improved results, while the extrapolation scheme often does not. There are unexpectedly large phase fluctuations showed up only around the 60 meters away from the reference antennas. This can be explained with considering the frozen phase screen. It may be explained more clearly after more careful investigation of the wind aloft and the temporal and spatial turbulent structure on the summit of Mauna Kea.