南极5 m太赫兹望远镜指向与调焦校准精度分析

Accuracy Analysis of the Pointing and Focusing Calibration of the 5 m Terahertz Telescope for Dome A in Antarctica

指向校准与副面调焦是天线测量的重要组成部分,对射电望远镜实际的观测性能有重要影响.根据南极5 m太赫兹望远镜(DATE5)指向精度和离焦增益损失的指标要求,计算得到了指向校准与副面调焦观测过程中对信噪比的要求,并以此为依据选取了若干可行的候选校准源,包括太阳系行星和超致密电离氢区.分析了大气吸收和校准源角直径对测量精度的影响.仿真分析结果表明:望远镜在南极工作时,这些校准源在一定的高度角范围内可以提供足够强的流量密度,用来验证预先建立的太赫兹和光学望远镜两光轴指向偏差模型以及副面调焦模型.

Pointing calibration and sub-reflector focusing are important task of an- tenna measurements, which significantly contribute to the observational performance of radio telescopes. According to the pointing accuracy and defocusing gain loss require- ments of the 5 m Dome A Terahertz Explorer （DATE5）, this paper has derived the requirements of signal-to-noise ratio for pointing and sub-reflector focusing calibration observations, and selected several astronomical radio sources suitable in terahertz band for pointing and focusing calibrations in Antarctica, which include planets and ultra- compact HII regions. The effects of the atmospheric absorption and the source angular diameter on the calibration-measurement errors are analyzed. Simulations show that, when the telescope operates in Antarctica, these sources could provide sufficient flux density for verifying the pre-established pointing model and the focusing model.