Abstract:
A large solar telescope is usually equipped with several postfocus
instruments deployed to study the dynamics of the solar features at
di erent wavelengths. Indian Institute of Astrophysics (IIA) has proposed
to build a 2-m class National Large Solar Telescope (NLST) to be located at
a site which is suitable for high resolution observations of the sun. The narrow
band imager (NBI) is proposed to be one of the back-end instrument
for NLST to provide a spectral resolution of 40 mÅ or better. The NBI
comprised of two Fabry-Perot interferometers kept in tandem. The instrument
will be capable of observing the solar atmosphere at various wavelength
positions of the spectral line with the expected temporal cadence of
about one spectral image per second. The instrument will also have the
additional capability of making Dopplergrams at very high cadence.The instrument
can be combined with a high precision polarimeter to obtain the
vector magnetic fields of the solar atmosphere (one or more levels) with
good temporal cadence. Several simulations and numerical studies have
been carried out to arrive at the optimal design of the instrument. In this
paper, we present the important design parameters of the instrument such
as wavelength coverage, optimum spacing ratio, parasitic light contribution,
field-of-view, spectral and spatial resolution, signal-to-noise ratio etc. The
theoretically estimated performance of the proposed NBI is also compared
with similar instruments used around the world.
