ULTIMATE-Subaru: Conceptual design of WFI, a near-infrared wide field imager

摘要

Results of a conceptual design study of ULTAIMTE-Wide Field Imager (WFI) is presented. ULTIMATE-WFI is a near-infrared wide-field imager for the ground-layer adaptive optics system of the Subaru telescope (ULTIMATE-Subaru) which realizes a 0".2 seeing size over 20'diameter at the Cassegrain focus utilizing a deformable 2ndry mirror. WFI has a 15'.7× 15'.7 FoV with a wavelength coverage of 0.9 -2.5μm. The FoV is covered by four identical optics, each having a square field lens with 226mm on a side. Its effective FoV is 7'.2 on a side, and is covered by a HAWAII-4RG array detector with a pixel scale of 0".11/pix. Effective FoV will be 14'.×14'.4 or 207□' in total. Spot sizes at a detector plane are less than 0".l over the wavelength coverage. Due to the large FoV, vignetting by the telescope structure occurs and an additional cold stop is necessary to block their thermal emission, which causes ~80% vignetting at the edge of the FoV. All the optics are contained in a cylindrical structure to be installed on the Cassegrain focus of the telescope, and kept under cryogenic temperature except for the field lenses. Gravitational deformation will be smaller than lmm, and may have negligible impact on the final image quality.