抚仙湖一米红外太阳望远镜Hα窄带滤光器扫描轮廓的检测与修正

An Investigation of Spectral-Line Profiles from the Wavelength-Scanning with a Narrow-Band Hα Lyot Filter on the YNAO New Vacuum Solar Telescope

抚仙湖1m红外太阳望远镜的重要终端之一是多通道高分辨成像系统，主要由两路宽带和一路窄带成像系统组成。目前窄带成像系统的工作谱线为Ha。主要介绍了窄带成像系统扫描轮廓的检测和修正。主要检测内容包括扫描轮廓的中心波长位置、扫描轮廓对称性、前置滤光片对扫描轮廓的影响、滤光器工作温度稳定性等问题。检测结果显示：扫描轮廓在656．281—0．15nm到656．281＋0．4nm的范围内与理论轮廓较好地吻合，而在656．281-0．15nm到656．281—0．4nm的范围内明显衰减。同时轮廓中心波长位置（即强度最低点的波长位置）相对于滤光器显示的“0nm”偏带点蓝移了0．013nm。针对上述检测结果，将滤光器的工作温度提高了约0．3cI=。在温度调整之后，扫描轮廓的整体特征不变，轮廓中心波长位置与“0nm”偏带点偏差小于0．004nm，同时红蓝翼对称偏带点的强度差异小于10％（对应1．8km／s的多普勒速度测量误差）。目前可以明确，扫描轮廓的蓝翼衰减是由前置滤光片造成，对于常用工作范围（656．281±0．1nm），可以忽略前置滤光片的影响。滤光器工作温度比较稳定，1个月内温度变化幅度的标准方差约0．0017℃。目前，该滤光器仍存在的问题是扫描轮廓在“0nm”偏带点略有突起，幅度在6％～8％。建议在以后的使用过程中，需要定期定量地对滤光器的扫描轮廓以及前置滤光片的透过率曲线进行检测。

The lm New Vacuum Solar Telescope （NVST） at the Fuxian-Lake Solar Observation Station of the YNAO is a new-generation ground-based solar research facility of China. One instrument on the NVST is a multi-channel high-resolution imaging system, which has been in operation since October 2010. The observation wavelength range of the system includes the Hot, TiO band, G band, Ca II 854. 2nm, and He I 1083nm. Although only the channels of the Hot, TiO band, and G band have been used, the observations impressively demonstrate the high-resolution capability of the NVST. The channels for the TiO band and G band both use broad-band filters with full widths of 1 nm. In contrast, the Hot channel uses a narrow-band filter with a full width of 0. 025nm （ corresponding to a spectral FWHM of ~ 1 lkm/s）. The wavelength center of the channel can be adjusted within the range 656. 281 ± 0.4nm. Since profiles observed with narrow-band filters are severely blurred by Doppler broadening, some spectral-line information is needed to extract useful physical results from these. Profiles from wavelength scanning can provide the needed line information, which makes it important to achieve accurate wavelength scanning. A new Hot Lyot filter was installed on the NVST in April 2013. In this paper, we investigate the performances of this filter system by examining spectral-line profiles from the wavelength-scanning with it. We use the observations of the central parts of the solar disk with the multi-channel imaging system to derive Hot line profiles. Our investigation focuses on the following aspects： deviations between the filter central band and the centers （ e. g. absorption peaks） of the line profiles from the scanning , the symmetries of the profiles from the scanning, influences of a front broad-band filter, and the stability of the temperature of the system. We have found the following results. （ 1 ） The center of a line profile from the scanning is 0. 013nm away from the filter central band （＂0nm＂）. The deviation can be corrected through increasing the working temperature of the system by about O. 3℃. （2） After the correction, the deviation is reduced to less than 0. 004nm by keeping the asymmetry of a profile below 10%. （3） The profile intensities at ＂Onm＂ are higher than the expected values by 6% to 8%. （4） The front broad-band filter has appreciable influences on the shapes of the profiles from the scanning only in the wavelength range 656. 281- 0. 15nm to 656. 281-0. 4nm. （5） The working temperature of the filter system is stable, with the monthly standard deviation at about 0. 0017℃.