# Imaging Spectropolarimeter for Multi-application Solar Telescope at Udaipur Solar Observatory: Characterization of polarimeter and preliminary observations

## TL;DR

This paper describes the development and characterization of an imaging spectropolarimeter for the MAST at USO, including preliminary solar observations and comparison with SDO/HMI data, to study solar magnetic fields.

## Contribution

It introduces a new spectropolarimeter for MAST, details its polarization calibration, and presents initial solar observations and validation against SDO data.

## Key findings

- Good agreement between MAST and SDO/HMI observations.
- Successful characterization of Liquid Crystal Variable Retarders.
- Preliminary active region observations demonstrate instrument capability.

## Abstract

Multi-Application Solar Telescope (MAST) is a 50 cm off-axis Gregorian telescope and started operational recently at Udaipur Solar Observatory (USO). For understanding the evolution and dynamics of solar magnetic and velocity fields, an imaging spectropolarimeter is being developed as one of the back-end instruments of MAST. This system consists of a narrow-band filter and a polarimeter. Polarimeter includes a linear polarizer and two sets of Liquid Crystal Variable Retarders (LCVRs). The instrument is intended for the simultaneous observations in the spectral lines 617.3 nm and 854.2 nm, which are formed in photosphere and chromosphere, respectively. In this paper, we present results from the characterization of the LCVRs for the spectral lines of interest and response matrix of the polarimeter. We also present preliminary observations of an active region obtained using the spectropolarimeter. For verification, we compare the Stokes observations of the active region obtained from Helioseismic Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO) with that of MAST observations in the spectral line 617.3 nm. We found good agreement between both the observations, considering the fact that MAST observations are seeing limited.