Srinivasulu G.,Indian Institute of Astrophysics |
Raveendran A.V.,Shravanam |
Muneer S.,Indian Institute of Astrophysics |
Mekkaden M.V.,No 82 |
And 6 more authors.
Bulletin of the Astronomical Society of India | Year: 2014
We designed and built a new astronomical photo-polarimeter that can measure linear polarization simultaneously in three spectral bands. It has a Calcite beam-displacement prism as the analyzer. The ordinary and extra-ordinary emerging beams in each spectral bands are quasi-simultaneously detected by the same photomultiplier by using a high speed rotating chopper. A rotating superachromatic Pancharatnam halfwave plate is used to modulate the light incident on the analyzer. The spectral bands are isolated using appropriate dichroic and glass filters. We show that the reduction of 50% in the efficiency of the polarimeter because of the fact that the intensities of the two beams are measured alternately is partly compensated by the reduced time to be spent on the observation of the sky background. The use of a beam-displacement prism as the analyzer completely removes the polarization of background skylight, which is a major source of error during moonlit nights, especially, in the case of faint stars. The field trials that were carried out by observing several polarized and unpo-larized stars show the performance of the polarimeter to be satisfactory. © 2014 Astronomical Society of India, Indian Institute of Astrophysics. All rights reserved.