The observational datasets used in this study were obtained with the near-infrared polarimeter SIRPOL and the IRSF 1.4-m telescope (Left figure) located at Sutherland, South Africa (telescope site altitude = 1761 m).

SIRPOL consists of a wide-field infrared camera at Cassegrain and a (single-beam) polarimeter located upstream of the camera. Circularly polarized light passess through the polarimeter’s optical element units of 1) achromatic half waveplate with continuous rotation, 2) quater waveplate with step (90 degrees) rotation, and 3) high-efficiency wire grid polarizer, before detecting at the infrared camera.

The most important characteristics of IRSF/SIRPOL are summarized as follows.

1. 1.SIRPOL can measure circularly  polarized light as well as linearly polarized light can be measured at near-infrared wavelengths (1-2 micron).
   

2. 2.SIRPOL has an order of magnitude larger field-of-view (8 arcmin square) compared with other infrared polarimeters.
   

IRSF/SIRPOL has the outstanding performance in the ability to measure circular polarization distribution toward large field-of-view. These characteristics of the instrument enable our study based on wide-field circular polarization map of the Orion star-forming region.

Figure Credit: NAOJ, Nagoya University