Near-infrared adaptive optics imaging- and spectro-polarimetry with the infrared camera and spectrograph of the Subaru Telescope

Makoto Watanabe, Tae-Soo Pyo, Hiroshi Terada, Takashi Hattori, Yutaka Hayano, Yosuke Minowa, Shin Oya, Masayuki Hattori, Tomoyuki Kudo, Mikio Morii, Jun Hashimoto, Motohide Tamura

We have developed the near-infrared high-spatial resolution imaging and spectro-polarimetric modes with the laser guide adaptive optics system (AO188) and the Infrared Camera and Spectrograph (IRCS) of the 8.2-m Subaru telescope. A LiNbO 3  Wollaston prism (as dual beam analyzer) and focal plane masks were installed into the camera section of the IRCS cryostat, enabling us to perform the low- and medium-resolution grism spectropolarimetry (λ/Δλ = 100-1960) as well as the imaging-polarimetry, in conjunction with a half-wave retarder, which had been introduced for the HiCIAO instrument originally, at the front of the AO188 system. The designed wavelength coverage of the Wollaston prism is 0.8-5 μm, although the polarimetry at the 0.95-2.5 μm region is presented in this paper because of the limitations on the current retarder and the dichroic beam splitter of AO188. The focal plane masks, which are reflecting mirror or slits made with tungsten carbide, provide two or four rectangular focal plane apertures with an individual field of view of 4.4 arcsec × 21 arcsec or 4.4 × 54 arcsec for the imaging-polarimetry, or two or four slits with a width of 0.10, 0.15, 0.225, and 0.60 arcsec and a length of 4.4 arcsec for the spectro-polarimetry. The Wollaston prism and polarimetry masks were installed on June and July 2013, and the polarimetric modes had the first light on October 2013. The polarization efficiency is 88-96% and 55-80% at maximum for the imaging- and spectro-polarimetry, respectively, and it depends heavily on the angle of image rotator of AO188. The measured instrumental polarization, which is introduced by the telescope tertiary mirror mainly, is 0.3-0.7%. We describe the design and current performance of the polarimetric function in the near-infrared region.

Proceedings of the SPIE

Society of Photo-Optical Instrumentation Engineers (SPIE)

10702

107023V

10.1117/12.2311969