Exoplanet atmospheres

Abstract:

We present the optical and mechanical design of the KMOS spectrograph module together with a detailed analysis of its performance. KMOS is a cryogenic near-infrared multi-object spectrograph being developed as a second-generation instrument for the VLT by a consortium of UK and German institutes. Three identical spectrograph modules provide Nyquist sampled spectra in the wavelength range covering the atmospheric bands z, J, H, and K with a resolving power exceeding 3200. The spectrographs are fully achromatic over the bands and the single mirror collimator and six-element camera, together with six high efficiency gratings provide high throughput. The optical performance analysis includes amongst others the spectral resolving power and variation of the PSF as a function of the pupil illumination.

Abstract:

We present the SWIFT image slicer and its novel de-magnifying design. It is based on the MPE-3D and SPIFFI image slicers, uses plane mirrors to slice the input field, but achieves a considerable de-magnification through the use of a mosaic of spherical lenses. As only plane and spherical surfaces are used in the design, classical polishing techniques can be applied to achieve very high surface accuracy and quality. This reduces aberrations and scattered light, mandatory for an image slicer working at optical wavelengths and behind an adaptive optics system. Except for the lens mosaic, the SWIFT slicer is built entirely from Zerodur and is assembled using optical contacting. We present a detailed description of the design as well as results of the early stages of its fabrication.

Abstract:

We present the design of the Oxford SWIFT integral field spectrograph, a dedicated I and z band instrument (0.65 mu m - 1.0 mu m at R similar to 4000), designed to be used in conjunction with the Palomar laser guide star adaptive optics system (PALAO, and its planned upgrade PALM-3000). It builds on two recent developments (i) the improved ability of second generation adaptive optics systems to correct for atmospheric turbulence at wavelengths <= 1 mu m, and (ii) the availability of CCD array detectors with high quantum efficiency at very red wavelengths (close to the silicon band edge). Combining these with a state-of-the-art integral field unit design using an all-glass image slicer, SWIFT's design provides very high throughput and low scattered light.SWIFT simultaneously provides spectra of similar to 4000 spatial elements, arranged in a rectangular field-of-view of 44 x 89 pixels. It has three on-the-fly selectable pixel scales of 0."24, 0."16 and 0."08. First light is expected in spring 2008.