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 Towertunnel Telescope to study the active regions at Chromospheric level, in Ca ii 8542Å 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 × 10 −2 and 3 × 10 −3 respectively.
A better understanding of the processes involved in the energy transport across the solar atmosphere (e.g., jets, waves) demands more effort towards the observations. Hence, existing instruments may need to be upgraded to gain additional capabilities. To this effect, we conceive an upgrade for the HELioseismic Large Regions Interferometric DEvice (HELLRIDE) instrument at Vacuum Tower Telescope (VTT) to enable the recording of the magnetograms. We present the instrumentation aspects of this development consisting of integrating a liquid crystal-based dual-beam polarimeter with the existing instrument, compatible new hardware and software with the improved operating scheme, and the first observations to verify its functionality. The new HELLRIDE now observes a field of view of $90^{\prime \prime } \times 90^{\prime \prime }$
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in four spectral lines, two chromospheric spectral lines in spectroscopy mode and two photospheric spectral lines in spectropolarimetry mode, with a cadence of 40 seconds. The increased complexity of the system, as well as the data, calls for the creation of a rigorous data processing pipeline, which is currently under development.
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