Polarimetry at the coudé focus: instrumental effects.
Abstract
The coude focus is a poor focus to use for polarization observations because the intervening flat mirrors can considerably change the polarization properties of starlight. The present paper is intended to serve as a guide for the study of a coude system prior to its employment in polarization measurements and also for the later interpretation of the observations. Polarization characteristics of aluminized mirrors are studied experimentally, with consideration given to the uniformity of phase shifts on different parts of a mirror, the wavelength dependence of phase shifts, aging effects, and spurious linear polarization. Modifications of partially polarized starlight by a coude system are analyzed using a general procedure based on Mueller matrices and Stokes vectors; the method is then applied to investigate the phase shifts and instrumental polarization of a five-mirror coude system. It is concluded that very accurate absolute polarimetry is probably impossible with a complicated coude system, but relative measurements of the variation of polarization with wavelength can still be made with reasonable accuracy.
- Publication:
-
Publications of the Astronomical Society of the Pacific
- Pub Date:
- August 1976
- DOI:
- 10.1086/129983
- Bibcode:
- 1976PASP...88..548B
- Keywords:
-
- Aluminum Coatings;
- Mirrors;
- Phase Shift;
- Polarimetry;
- Polarization Characteristics;
- Reflecting Telescopes;
- Circular Polarization;
- Optical Polarization;
- Optical Reflection;
- Astronomy