Fabry-P\'erot based Narrow Band Imager for Solar Filament Observations

TL;DR

This paper introduces a newly developed Fabry-Pérot based narrow band imager designed for solar filament observations, capable of high-resolution imaging and spectral scanning at chromospheric heights.

Contribution

The paper presents the design, development, and initial testing of a Fabry-Pérot based narrow band imager for solar observations, including its ability to scan spectral lines and produce Doppler velocity maps.

Findings

Successful imaging of solar filaments in Hα line.

Capability to scan spectral line profiles at different wavelengths.

Initial Doppler velocity maps of the chromosphere.

Abstract

We have recently developed a narrow band imager (NBI) using an air gap based Fabry-P\'erot (FP) interferometer at the Indian Institute of Astrophysics, 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 by changing the plate separation of the FP. The interferometer has a 50 mm clear aperture with a bandpass of $\sim$247.8 m\AA and a free spectral range of $\sim$5.3\AA at $\lambda$ = 656.3 nm. The developed NBI is used to observe the solar filament in the H$\alpha$ wavelength. The instrument is being used to image the Sun at chromospheric height and it is also able to scan the H$\alpha$ 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 at $\pm$176 m\AA 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 observations carried out with this instrument.