Fabry-Perot based narrow band imager for solar filament observations

Abstract

We have recently developed a narrow band imager (NBI) using a n air gap based Fabry-P ́erot (FP) interferometer at the Indian Institute of Astrophysic s, Bangalore. Narrow band imaging is achieved by using an FP interferometer working in combination with an order sorting pre-filter. The NBI can be tuned to a different wavelength position on the line profile b y changing the plate separation of the FP. The interferometer has a 50 mm clear aperture with a bandpass of ∼ 247.8 m ̊ A and a free spectral range of ∼ 5.3 ̊ A at λ = 656.3 nm. The developed NBI is used to observe the solar filam ent in the H α wavelength. The instrument is being used to image the Sun at chromospheri c height and it is also able to scan the H α spectral line profile at different wavelength positions. We have also made Doppler velocity maps at chromospheric height by taking the blue and red wing images a t ± 176 m ̊ A wavelength positions separately away from the line center of the spectral line. In this paper, we present a description of the NBI including lab test results of individual components and some initial o bservations carried out with this instrument.