A double image chopping polarimeter.
Abstract
Summary. A new single channel polarimeter using a plane parallel calcite slab to produce two orthogonally polarized images of a star in the focal plane of the telescope and chopping techniques to measure the intensities of the two images with a single photo multiplier, has been constructed and tested. The most important advantages of the polarimeter are: simplicity, fully achromatic square wave modulation and direct elimination of position angle and time dependent instrumental errors. Also sky background polarization is directly eliminated. For stars brighter than the magnitude 6.5, with a 60 cm telescope and 20 seconds integration time in each of eight position angles, the internal mean error of a single observation has been found to be of the order of .01%. A drawback is that some astigmatism and dispersion is introduced by the polarizer. However the aberrations are usually negligible compared with atmospheric disturbances. Key words: polarimetry - instruments
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- September 1973
- Bibcode:
- 1973A&A....27..383P