# Solar Spectropolarimetry of Ca II $8542~\AA$ Line: Polarimeter Development,Calibration and Preliminary Observations

## TL;DR

This paper presents the development, calibration, and preliminary observations of a new polarimeter at Kodaikanal Solar Observatory for studying chromospheric magnetic fields using the Ca II 8542 Å line, enhancing solar magnetic field measurements.

## Contribution

The paper introduces a novel polarimeter design and calibration strategy for chromospheric magnetic field observations at Kodaikanal, including instrumental polarization modeling and software control.

## Key findings

- Polarimetric accuracy better than 0.03
- Sensitivity of 0.003 achieved in measurements
- Instrument successfully captures Stokes profiles in Ca II line

## Abstract

Chromospheric magnetic fields are of paramount importance in understanding the dynamics of energetic events in the solar atmosphere. At the Kodaikanal Solar Observatory, several polarimeters were developed in the past to study the active region magnetic fields. A new polarimeter has been developed and installed at Kodaikanal Tower-tunnel Telescope to study the active regions at Chromospheric level, in Ca II $8542~\AA$ spectral line. Design aspects of the instrument and polarimetry strategy are discussed. Telescope instrumental polarization has been revisited and possible ways to reduce it have been proposed. Telescope polarization model developed in Zemax to examine the analytical instrumental polarization model is discussed. The polarimeter control unit, and the software developed to operate the polarimeter are briefly described. Polarimetric calibration of the instrument, observations, corrections for instrumental polarization and the sample Stokes profiles are presented. Polarimetric accuracy and sensitivity are estimated to be better than $3\times10^{-2}$ and $3\times 10^{-3}$ respectively.