中国科学院云南天文台机构知识库

观测目标的亮度越小,杂散光对其的影响越大。在光谱观测中,由于谱线线心的剩余能量较小,所以杂散光对光谱观测的影响显著。在用抚仙湖1 m太阳望远镜多波段光谱仪进行光谱观测时发现,CaⅡ光谱图像在855.6 nm吸收线右侧的亮度有肉眼可见的明显下降,针对此现象分析产生光谱图像色散方向上亮度左右差异的原因,结合杂散光的理论用实验的方法找出杂散光的来源及传输路径。分析结果表明,产生此种现象是由于狭缝的次极大衍射光照亮成像镜后反射到CCD,形成一个弧形的杂散光亮斑,强度约为光谱图像平均光子数的20.9%,对CaⅡ通道的光谱图像产生了严重的影响。对分析的结果进行了理论验证。利用遮挡杂散光传输路径与图像处理两种抑制杂散光的方法对其进行消除,使CaⅡ通道杂散光恢复到正常水平。

Stray-light can affect the astronomical observations, especially for those faint observational objects. Because the residual energy in the spectral line center is very low, the stray-light has significant effect on spectral observations. From the high-resolution spectral observations with the New Vacuum Solar Telescope in Fuxian Solar Observatory, we found that the left side of 855.6nm absorption line in the Ca ]I spectral images has lower brightness. To study the intrinsic reason of the differences in the left-right dispersion directions of the spectral images, the stray-light theory and the experimental method are combined to analyze the origin and the transmission path of the stray-fight. Analysis results indicate that the secondary maximum of the diffraction light in the spectrometer slit can beacon the imaging mirror and then reflect to the surface of the CCD target. This will produce a stray-light bright spot with an arc shape, and its brightness is about 20. 9% of the average intensity of spectral image, bringing out a serious impact for the Ca II channel in spectral observations. At last, analysis results are verified by experiments. Two methods--blocking the stray-light transmission path and signal image processing--are utilized to eliminate the stray-light. The final result shows that the stray-light in the Ca 1I channel can be reduced to normal levels.