The spectral measurement of the solar atmosphere is another important task of NVST. The spectrometers of NVST include a multi-bands spectrometer (MBS) and a high dispersion spectrometer (HDS). They are placed on the vertical hanging bracket right below the rotating platform, which rotates along with the platform as a huge image de-rotator. A tunable slit of the spectrometers is installed at the center of the rotating platform. The width and the orientation of the slit can be changed for different spectrometers and various science cases. Before the slit, as described in previous section, about 10% of the photons are transferred into imaging system to display the image and the position of slit. The orientations of the two spectrometers are perpendicular to one another, and they share the same slit described above. Switching use of the spectrometer from MBS to HDS is realized by rotating the slit and moving the collimating mirror of MBS. This operation could not run during observations, and should be completed beforehand. Therefore, the two spectrometers cannot work simul-taneously. |