Oral Presentation
The Correction of the Scattered Light of An Inner-occulted Coronagraph
Presenter: Xuefei Zhang (中国科学院云南天文台)
The Lijiang Coronagraph Station of Yunnan Observatories, established in 2013, was the first optical coronal observation station in China. A 10 cm Lyot coronagraph was shipped from Norikura Station of NAOJ and installed at Lijiang Station during the summer of 2013. The first coronal image was successfully taken on 2013 October 25. For the ground-based Inner-occulted coronagraph with regular observations, scattering from dust on the objective surface can be slowed down by frequent cleaning of the objective surface and the level of such stray light can be suppressed, the objective surface unable to maintain cleanliness at all times due to weather, atmospheric particle pollution and other factors. Frequent cleaning and multiple disassembly of the objective lens can to some extent cause secondary pollution on the surface of the objective lens. The scattering light of the Coronagraph changes with time, resulting in different amounts of background scattering in the coronal image, which brings great inconvenience to the analysis of the coronal structure and the calibration of the coronal intensity. Based on the Lijiang Coronagraph, we discussed the influence of the surface cleanliness of the objective lens on the coronal intensity through experiments, and corrected the coronal intensity. We created different scattering backgrounds with different objective cleanliness and corrected the coronal intensity through fitting methods. Our method not only effectively improves the quality of coronal images, but also makes weak coronal structures more prominent and clear, which helps us obtain more accurate results when analyzing the decay trend of internal coronal intensity and changes in coronal structure. More importantly, it will help us to analyze the scattered light of the Coronagraph and discuss the influence of other scattered light inside the Coronagraph on the coronal image.
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