Dual channel imaging system in Hα and HeI 1083nm lines using a universal tunable filter

Hydrogen Hα (656.2nm) and HeI 1083nm are the spectral lines most commonly used for diagnosing the solar chromosphere. We aim to investigate the scientific advantage in combining these lines in imaging spectroscopic observation using a narrowband tunable filter. Simultaneous imaging in two wavelengths is possible by splitting the light with a polarizing beam splitter attached at the exit of the filter and using two cameras. We have constructed a setup that enables spectroscopic imaging in Hα and HeI 1083nm lines almost simultaneously, with a time required for switching the wavelength of about 0.1 second. The full width at half maximum of the transmission in Hα is 0.25A, while, with an additional stage of the Lyot filter, it is 0.367A in HeI 1083nm. In this paper, we describe the overview of the system and demonstrate its observing capability by presenting some examples of observations. We also discuss the advantage of combining these two lines in view of their responses to the physical condition as inferred from a non-LTE calculation.