选址与日冕观测组知识库

埃文斯目视日晕光度计(Evans Visual Sky Photometer,EVSP)是应用于日冕仪选址的重要仪器,从20世纪40年代一直使用至今,它为现代日晕光度计的定标提供了参考标准。通过使用云南天文台现存的一架EVSP研究了它的工作原理,并重点介绍了所利用的简易定标方法。给出了国际现有的多台EVSP日晕亮度定标曲线。由于EVSP内部光学元件反射率和透过率,以及中性渐变光楔的光学密度等存在未知的时间缓变特点,因此利用这种新定标手段可以高效经济地获得各自的定标曲线。

An Evans Visual Sky Photometer (EVSP) is important for a site survey for coronagraph(s) . It has been applied since 1940s to judge and estimate sky brightness levels for observatories. Long-term site data have been obtained and recorded for some observatories. These data provide the calibration references for sky brightness monitors (SBMs) currently developed for site survey projects for large-aperture solar instruments, especially high-sensitivity coronagraphs. New SBMs have been developed in 2010 for the solar site survey in the west China.  Like other observatories in the world, we need to use an EVSP for the calibration in the next measurement stage of work. In this paper, we study the theoretical basis and calibration method of an EVSP in the Yunnan Observatory. We compare the calibration curves for a few EVSPs. Because of the well known parameter variance of the optical elements inside an EVSP, including that of the density of wedge, it is efficient to make the Isky-Scalewedge calibration with our method introduced to obtain the calibration curve. With good maintenance of the optical system this EVSP can function properly.