An Analysis of Spectrum Curvatures for the Multi-Wavelength Spectrometer of the New Vaccum Solar Telescope of the Yunnan Observatories

In observation of long-slit solar spectra, the slit direction and dispersion direction of a spectrum should ideally be parallel to two sides of the CCD, respectively. In practice this is difficult to be achieved because of errors of the relative positions of the slit, grating grooves, and the detector as introduced in installation of the mechanisms. Observed solar spectra are then always curved (or inclined). The purpose of this paper is to measure and analyze the curvatures of Hα solar spectra obtained by the Multi-Wavelength Spectrometer of the new vaccum solar telescope of the Yunnan Observatories. We also discuss influences of spectral curvatures on evaluation of flatfields.