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SPIRou at IRAP (© S. Chastenet - CNRS/OMP)
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| Cassegrain Unit |
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The unit (to be) mounted at the Cassegrain bonnette of CFHT consists of two main modules: the mechanical interface to the telescope and the polarimeter. The upper part is responsible for the atmospheric dispersion correction, the guiding and the light injection into the fibers. The polarimeter is achromatic and splits the incoming light into two beams. The polarimeter can be configured to measure circular or linear polarization. Unpolarized light is always obtained in addition to the polarized light.
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| Fibers and Slicer |
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The light collected at the telescope is conveyed to the spectrograph through a set of optical fibers. The fiber routing follows the telescope and its mount and goes through the pier to the coudé room. A 35m circular fluoride fiber has been made with purified material to insure high throuput over the wide optical range. A segment of the fibers is made of octogonal fibers to homogeneize illumination. At the spectrograph entrance, a pupil slicer is used to minimize losses and maximize resolution.
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| Cryogenic spectrograph |
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SPIRou includes an echelle spectrograph (double pass cross-dispersed) which design has been based on ESPaDOnS and HARPS. The cryogenic vessel is under vacuum, cooled down to 80K and stabilized at a few milliK level. Such stability is required to insure the radial-velocity precision.
SPIRou optics sketch (© P. Rabou - CNRS/IPAG) and open cryogenic bench (© S. Chastenet - CNRS/OMP)
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| Detector |
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SPIRou will use an Hawaii 4RG detector, which is currently in the making at Teledyne Scientific and Imaging. It will have 4kx4k 15-micron pixels that will be read continuously in order to leave the cryostat temperature undisturbed. Since it is to be delivered after the lab tests in France, the SPIRou team is using an Hawaii H2RG 2kx2k detector with 18 microns pixels for alignments and performance tests. This detector covers a large fraction of the spectral range and gets most of the spectral resolution.
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| Calibration Unit |
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The calibration of SPIRou is done with lamps located in the coudé room. Flatfield lamps are used to locate the echelle orders; hollow-cathod lamps and a thermalized Fabry-Pérot etalon are used for the ultra-precise wavelength calibration. The light from calibration lamps will be injected through a fiber at the Cassegrain in order to follow the same path as the sky light.
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