K. Nagaraju, K.
Sankarasubramanian†, K. E.
Rangarajan, K. B. Ramesh, Jagdev Singh, P. Devendran and
Hariharan
Abstract.
Calibration and characterization of a dual-beam polarimeter installed at
Kodaikanal Tower Telescope (KTT) for spectropolarimetric observations
are presented in this paper.
It was found that a slit width of 48 μ is optimum
for the spectrograph setup at KTT and corresponding spectral resolution
is 32.47 m\AA.
It was demonstrated that the precision in polarization measurement can be
achieved better than 0.1 % by increasing the exposure time.
However, the polarimetric calibration accuracy is limited to 0.35% for
Stokes Q and U parameters and 0.2% for Stokes V parameter, mainly
due to the uncertainty in the retardance of the calibration retarder.
A comparison of the magnetic field measurement between the
Solar Optical Telescope (SOT) onboard Hinode and KTT for an active region
was made and a good match was found
after spatial smearing of Hinode/SOT measurements by 5.12''.
Keywords:
Instrumentation : polarimeter
Indian Institute of Astrophysics, Bangalore 560 034,
India
†Space Astronomy and Instrumentation Division,
ISRO Satellite center, Bangalore 560094, India