Integral field unit for the existing imaging and spectroscopy instrument, FOCAS

• DOI: 10.1093/pasj/psaa092
• Publication Date: 2020-09-11T19:11:14Z
• Authors: Shinobu Ozaki; Mitsuhiro Fukushima; Hikaru Iwashita; Kenji Mitsui; Takashi Hattori; Chien-Hsiu Lee; Yoko Tanaka; Toshihiro Tsuzuki; Satoshi Miyazaki; Takuya Yamashita; Norio Okada; Yoshiyuki Obuchi
• Keywords: Subaru Telescope; Vignetting; Cassegrain reflector; Field of view

Abstract The Faint Object Camera and Spectrograph (FOCAS) is an optical imaging spectroscopy instrument for the Subaru Telescope. It has been a workhorse since first-light phase of telescope. We describe integral field unit (IFU) that recently installed in FOCAS. IFU utilizes image slicer divides ${13{^{\prime \prime }_{.}}5}$ × ${10{^{\prime }_{.}}0}$ view into 23 stripes, with width ${0{^{\prime }_{.}}435}$. A sky spectrum separated from object by approximately ${5{^{\prime }_{.}}2}$ can be obtained at same time as spectrum. Test observations confirmed quality does not degrade }_{.}}435}$ sampling, slice length are consistent design. Highly reflective multilayer dielectric coatings were coated on all mirrors IFU, thereby offering high mean throughput ∼85% over field. However, outer part showed degradation, which was mainly caused vignetting result misalignment. flat-fielding accuracy degraded vignetting, variation depending direction