在CTIO 0.9米望远镜上测试LSST的光度校准策略
Testing of the LSST's photometric calibration strategy at the CTIO 0.9 meter telescope
摘要：
大型综合巡天望远镜（LSST）的定标硬件系统主要用于测量两个量：望远镜的仪器响应和大气透射，两者都是波长的函数。首先，设计了一个“准直光束投影仪”，通过将单色光通过掩模和准直光学系统投射到望远镜上来测量仪器的响应函数。在测量过程中，使用NIST可追踪光电二极管监测光水平。这种方法不会受到杂散光效应或使用平场屏幕照明时存在的反射（称为重影）的影响，而平场屏幕照明具有来自不受控制的反射的系统性不确定性来源。它允许独立测量望远镜的光学训练的吞吐量以及每个滤波器的传输作为主镜上的位置的函数。其次，CALSPEC恒星可以用作校准光源，照亮大气层并测量其透射率。为了测量大气的传递函数，我们使用望远镜的成像仪，用一个Ronchi光栅代替滤光片，将其配置为一个低分辨率的无狭缝光谱仪。在本文中，我们描述了这种校准策略，专注于从原型系统的Cerro Tololo美洲天文台（CTIO）0.9米望远镜的结果。我们比较仪器的吞吐量测量使用实验室分光光度计测量的标称值，我们描述了通过CALSPEC标准恒星在同一次运行中的大气测量。
英文摘要：
The calibration hardware system of the Large Synoptic Survey Telescope (LSST) is designed to measure two quantities: a telescope's instrumental response and atmospheric transmission, both as a function of wavelength. First of all, a "collimated beam projector" is designed to measure the instrumental response function by projecting monochromatic light through a mask and a collimating optic onto the telescope. During the measurement, the light level is monitored with a NIST-traceable photodiode. This method does not suffer from stray light effects or the reflections (known as ghosting) present when using a flat-field screen illumination, which has a systematic source of uncertainty from uncontrolled reflections. It allows for an independent measurement of the throughput of the telescope's optical train as well as each filter's transmission as a function of position on the primary mirror. Second, CALSPEC stars can be used as calibrated light sources to illuminate the atmosphere and measure its transmission. To measure the atmosphere's transfer function, we use the telescope's imager with a Ronchi grating in place of a filter to configure it as a low resolution slitless spectrograph. In this paper, we describe this calibration strategy, focusing on results from a prototype system at the Cerro Tololo Inter-American Observatory (CTIO) 0.9 meter telescope. We compare the instrumental throughput measurements to nominal values measured using a laboratory spectrophotometer, and we describe measurements of the atmosphere made via CALSPEC standard stars during the same run.
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