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Title: An efficient modulation scheme for dual beam polarimetry
Authors: Nagaraju, K
Ramesh, K. B
Sankarasubramanian, K
Rangarajan, K. E
Keywords: Instrumentation: Polarimeter;Technique: Polarimetric
Issue Date: Sep-2007
Publisher: Astronomical Society of India
Citation: Bulletin of the Astronomical Society of India, Vol. 35, No. 3, pp. 307 - 318
Abstract: An eight stage balanced modulation scheme for dual beam polarimetry is presented in this paper. The four Stokes parameters are weighted equally in all the eight stages of modulation resulting in total polarimetric efficiency of unity. The gain table error inherent in dual beam system is reduced by using the well known beam swapping technique. The wavelength dependent polarimetric efficiencies of Stokes parameters due to the chromatic nature of the waveplates are presented. The proposed modulation scheme produces better Stokes Q and V efficiencies for wavelengths larger than the design wavelength whereas Stokes U has better efficiency in the shorter wavelength region. Calibration of the polarimeter installed as a backend instrument of the Kodaikanal Tower Telescope is presented. It is found through computer simulation that a 14% sky transparency variation during calibration of the polarimeter can introduce 1.8% uncertainty in the determination of its response matrix.
ISSN: 0304-9523
???metadata.dc.rights???: © Astronomical Society of India
Appears in Collections:IIAP Publications

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