Subaru Prime Focus Camera — Suprime-Cam

Abstract

We have built an 80-mega pixels ($10240 \times 8192$) mosaic CCD camera, called Suprime-Cam, for the wide-field prime focus of the 8.2 m Subaru telescope. Suprime-Cam covers a field of view $34' \times 27'$, a unique facility among the 8–10 m class telescopes, with a resolution of ${0\rlap {.}{}^{\mathrm {\prime \prime }}202}$ per pixel. The focal plane consists of ten high-resistivity $2\mathrm{k} \times 4\mathrm{k}$ CCDs developed by MIT Lincoln Laboratory, which are cooled by a large Stirling-cycle cooler. The CCD readout electronics was designed to be scalable, which allows the multiple read-out of tens of CCDs. It takes 50 seconds to readout entire arrays. We designed a filter-exchange mechanism of the jukebox type that can hold up to ten large filters ($205\times 170 \times 15 \,\mathrm{mm}^3$). The wide-field corrector is basically a three-lens Wynne-type, but has a new type of atmospheric dispersion corrector. The corrector provides a flat focal plane and an un-vignetted field of view of $30'$ in diameter. The achieved co-planarity of the focal array mosaic is smaller than 30$\,{\mu \mathrm {m}}$ peak-to-peak, which realizes mostly the seeing limited image over the entire field. The median seeing in the $I_\mathrm{c}$-band, measured over one year and a half, is ${0\rlap {.}{}^{\mathrm {\prime \prime }}61}$ . The PSF anisotropy in Suprime-Cam images, estimated by stellar ellipticities, is about 2% under this median seeing condition. At the time of commissioning, Suprime-Cam had the largest survey speed, which is defined as the field of view multiplied by the primary mirror area of the telescope, among those cameras built for sub-arcsecond imaging.